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The Specialist Group in Tectonics and Structural Geology Field Guide No. 16.

Contrasting styles of deformation in the Melbourne, Tabberabbera and -Omeo zones, Victoria

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SGTSG Field Guide No. 16, Geological Society of Australia ISBN 978-0-9806264-8-3

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The Specialist Group in Tectonics and Structural Geology Field Guide No. 16. Contrasting styles of deformation in the Melbourne, Tabberabbera and Omeo zones, Victoria

Vince Morand and Ross Cayley GeoScience Victoria, GPO Box 4440, Melbourne, Victoria 3001

Field Trip Guide for

Waratah Bay SGTSG Conference, January-February 2012

Bibliographic reference: Morand V.J. & Cayley R.A. 2012. Contrasting styles of deformation in the Melbourne, Tabberabbera and Omeo zones, Victoria. Specialist Group in Tectonics and Structural Geology Field Trip Guide No. 16, Geological Society of Australia. ISBN 978-0-9806264-8-3

Purchase requests should be addressed to: Sue Fletcher Business Manager Geological Society of Australia Suite 61 , 104 Bathurst Street, Sydney NSW 2000. © Geological Society of Australia, Specialist Group in Tectonics and Structural Geology

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TABLE OF CONTENTS Acknowledgements.............................................. ... ..................... ............... ................... ................. 2 Part 1: Overview of the geology of the central and eastern Lachlan Fold Belt... ............................ 3 Regional tectonic setting ..................... .. ................................................................................3 Melbourne Zone .................................................................................................................... 8 Rock units ............................................................ ..................................................... 8 Structures...................................................................................................... .......... 10 Tabberabbera Zone ............................................................................................................. 12 Rock units ............................................................................................................... 13 Structures............... ................................................. ................................................ 13 Omeo Zone ......................................................................................................................... 14 Rock units.............. ................................................................................................. 15 Structures................. ........................... .................................................................... 16 Part 2: Field trip itinerary ...................................... ...................................... .. .. .... .. ........................ 18

References............................................................................................................................... ....... 71 Appendix 1: Legends for Figs 2-1, 2-2, 2-7, 2-8 and 2-17 ............................................................ 75

ACKNOWLEDGEMENTS We acknowledge the contributions made to the mapping and interpretation of Palaeozoic rocks in eastern Victoria by numerous geologists, in particular David Gray, Chris Fergusson, Fons VandenBerg, Clive Willman, David Taylor, Cameron Quinn, Christopher Osborne, Bruce Simons, Suzanne Haydon, Tony Crawford. This publication draws on many reports and maps produced by GeoScience Victoria (and Geological Survey of Victoria) over the past 20 years.

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PARTl OVERVIEW OF THE GEOLOGY OF THE CENTRAL AND EASTERN LACHLAN FOLD BELT REGIONAL TECTONIC SETTING The rocks we will examine in this field trip are the central parts of deformed Early Palaeozoic successions that form part of the Tasman orogenic system, or Tasmanides, an accretionary orogen formed along the Pacific margin of Gondwanaland from the late Proterozoic to Early Cretaceous (Coney et al. 1990; VandenBerg et al. 2000; Birch 2003; Cawood 2005; Turner et al. 2009). Its long history is reflected in its complex structure and stratigraphy. It contains fragments of Neoproterozoic continental crust, incorporated into Palaeozoic subduction- accretionary systems that young eastwards and include Cambrian-Ordovician oceanic boninitic and MORB-type tholeiitic volcanic rocks, deep-ocean sedimentary rocks and arc-related volcanic rocks (Coney 1992; VandenBerg et al. 2000; Gray & Foster 2004; Percival & Glen 2007).

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Subdivisions within the Tasman orogenic system include the (now) inboard Cambrian Delamerian Orogen, which is widely exposed in South Australia and westernmost Victoria, and the adjacent and extensive Cambrian-Devonian Lachlan Orogen that is widely exposed across Victoria, Tasmania and New South Wales. The geological histories of the Delamerian and

4 Lachlan Orogens overlap in time, but development of the Lachlan Orogen is younger and more protracted, with several cycles of deposition and deformation continuing from the Cambrian, in the west, into the Early Carboniferous eastwards (VandenBerg et al. 2000, Miller et al. 2005). The New England Orogen lies along the eastern edge of the system. The Victorian part of the Lachlan Orogen comprises, from west to east, the Stawell, Bendigo, Melbourne, Tabberabbera, Omeo, Deddick, Kuark and Mallacoota structural zones (Figure 1-1 ). This excursion is a transect across the eastern Melbourne Zone into the Tabberabbera and Omeo zones. Victoria is unique in that outcrop of Early Palaeozoic rocks is virtually continuous across its width. Early Paleozoic rocks form the spine of the southern end of the Great Dividing Range. This fortuitous circumstance has allowed relationships between all the various subdivisions of the Delamerian and Lachlan orogens to be directly investigated. In its present strongly shortened condition the Lachlan Fold Belt is still about 700 km wide. Its total strike length, including the New South Wales and Tasmanian portions, is about 1200 km. It is a short and fat orogen. The Lachlan Fold Belt preserves a history of volcanism, sedimentation, magmatism and metamorphism spanning the whole of the Palaeozoic, but the period between the Cambrian and Middle Devonian is the most important part of this history. This interval essentially defines the main period of cratonisation and accretion to the Australian craton. The lithotectonic environment of the Lachlan Fold Belt during its main depositional stage (Cambrian - Early Silurian) was overwhelmingly one of an oceanic setting. Most of the Lachlan Orogen apparently originated as Cambrian to Ordovician oceanic boninitic, MORB-type tholeiitic and island arc crust (Crawford et al. 1984) and conformably overlying deep-ocean sedimentary rocks (Figure 1-2). Abundant Ordovician arc-related volcanic rocks-the Macquarie Arc-are exposed northeast of the Omeo Zone, but these rock are confined, almost exclusively, to New South Wales (Coney 1992; Percival & Glen 2007; Glen et al. 2007b). In Victoria the sedimentary rocks deposited into the deep water oceanic setting all have a provenance (detrital zircon, mica geochronology) suggesting the Delamerian Fold Belt and the greater Ross Orogen of Gondwanaland to the west and south are the source terrains. Therefore the belt as a whole remains close to its original position with respect to this older craton. Most of the rocks we will see on this excursion are part of a vast Ordovician-Early Silurian metasedimentary succession. In Eastern Victoria, the dominant Early Ordovician unit across several zones is the Pinnak Sandstone. You would have to be a real aficionado to discriminate this siliciclastic turbidite package from the coeval Castlemaine Group that dominates outcrop of the Bendigo Zone much farther west (hint: the Pinnak has more thin chert beds, and less black graptolitic shale). The Omeo Zone is dominated by high-grade metamorphic rocks, migmatite, and syn-tectonic granite, but examination of provenance demonstrates that these rocks represent... .. melted Pinnak Sandstone. Sediments in the intervening Melbourne Zone are different; this region was starved of sediment in the Early to Late Ordovician accumulating shale and chert. Subsequent Silurian and Devonian elastic successions contain detritus reworked from the adjacent zones, initially from the Bendigo Zone (Foster et al., 1999) and, beginning in the Early Devonian, from the Tabberabbera Zone (VandenBerg et al., 2000). The main structural zones are all dominated by meridionally folded and faulted, metamorphosed Palaeozoic deep marine sedimentary rocks, with occasional outcrops of underlying Cambrian mafic oceanic volcanic rocks in major fault slice , or in windows eroded through the metasedimentary veneer. The contacts between all structural zones are seen, in outcrop, to be major faults. In most cases these are large thrust faults of either west or east dip, with significant

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5 vertical throws. In at least one instance-between the Tabberabbera and Omeo zones-the zonebounding fault is strike-slip (Morand & Gray, 1991). The various structural zones recognised in the Lachlan Fold Belt in Victoria can be grouped together into two or three major terranes on the basis of obviously-linked depositional relationships, or similarities in structural history. Such grouping is useful for considering the large-scale evolution of the orogen. A major terrane boundary occurs in the position of the Governor Fault, the faulted boundary between the Melbourne and Tabberabbera zones (VandenBerg et al., 2000). To the west, the Western Lachlan Fold Belt (Gray, 1997) includes the Melbourne Zone along its eastern margin, while to the east the Central and Eastern parts of the Lachlan Fold Belt (Gray, 1997) includes the Tabberabbera and Omeo Zones. There are marked breaks in depositional and structural history across the Governor Fault that are a continuing challenge to explain (see VandenBerg et al., 2000). The main structural difference is that the Governor Fault marks the position of major structural vergence-reversal. To the west, most thrust faults in the Bendigo and Melbourne zones dip west and verge east. To the east, most thrust faults in the Tabberabbera Zone dip northeast and verge southwest. Orogen-parallel movements also played a much more significant role in shaping the parts of the central and eastern Lachlan Fold Belt east of the Governor Fault. Structural zones within a single terrane can show major differences, but these are outweighed by basic shared traits. For example, in the Western Lachlan Fold Belt the Bendigo and Melbourne zones are regarded as part of a single terrane (VandenBerg et al. 2000), despite the fact that they experienced different ages of regional deformation with consequent differences in depositional history. This is because there is ample sedimentological evidence that the Bendigo and Melbourne zones were neighbours prior to Lachlan orogenesis and have remained so, with a linked sedimentological and structural history since that time. The differences are explained by interpreting some parts of the region as underlain by older structural basement, the Selwyn Block-rocks overlying this behaved differently during subsequent deformation events (Cayley et al., 2011). The Selwyn Block is exposed in occasional windows eroded through the eastern part of the Melbourne Zone (V andenBerg et al. 1995, 2006), but none of the inland outcrops are of the quality we have already seen at Waratah Bay. Deformation across the Lachlan Orogen has traditionally has been ascribed to pulses, named the Benambran (~455-440 Ma), Bindian, (~420 Ma), Tabberabberan (~390 Ma), and Kanimblan (~350-320 Ma) orogenies. The effects of these orogenies are complexely distributed. In the eastern Lachlan Fold Belt, the Benambran orogenic cycle certainly involved subduction-accretion processes, as the event is associated with the culmination of magmatism in the Ordovician intraoceanic Macquarie Arc. The Wagga-Omeo Metamorphic Complex lies just to the west of the Macquarie Arc, was also deformed at this time, and high-grade metamorphism seen here is likely to be related to the Macquarie Arc somehow (Collins & Vernon, 1992). In the western Lachlan orogen the Benambran Orogeny also deformed the Bendigo Zone, but here there is no associated magmatism, suggesting a setting remote to active plate margins. The significance and origin of other deformation events in the Lachlan Fold Belt is less well understood, although the Late Silurian-Early Devonian Bindian Orogeny clearly involved a change from the east-west directed shortening seen in both the Delamerian and Benambran orogenies to one of southerly-directed tectonic transport, especially in the central and eastern subprovinces (VandenBerg et al., 2000).

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7 Another significant feature of the Lachlan Fold Belt is the voluminous 'post-tectonic' granite magmatism. These intrusive systems occur over widespread areas in discrete time pulses, include both S and I-types, and do not appear to be related to arc systems. There is a spatial and temporal link between volcanics related to these intrusive phases and episodes of rifting in the eastern and western Lachlan Fold Belt. Decompression melting during periods of crustal extension may therefore be an explanation for their origin (Cayley et al., 2011). If so, these are not 'posttectonic' granites at all. Pulses of granite intrusion occur across the western, central and eastern Lachlan Fold Belt in the Early and Late Devonian. There is little spatial overlap between these pulses. Although there is general agreement that much of the western Lach Ian Orogen (Gray 1997, after Glen 1992) was formed in an oceanic environment (e.g. Crawford & Keays 1978; Crawford et al. 1984) and that plate tectonic processes drove orogenesis, the composition of the lower crust and the location and number of subduction zones have remained controversial topics. Dating of the western Stawell Zone by Miller et al. (2005) has shown that part of the Stawell Zone was clearly involved in Cambrian orogenesis, most likely related to west-dipping subduction, but the role of subduction in deforming the Bendigo and Melbourne Zones remains controversial. The complete lack of any magmatism associated with the Benambran orogenic cycle in the western Lachlan Orogen suggests that this region, including the Melbourne Zone, remained distal to major plate margins throughout this period (Taylor & Cayley 2000), for example, in a backarc setting. The recent seep seismic data has reaffirmed this view (Cayley et al., 2011). The central and eastern parts of the Lachlan Fold Belt are a different proposition. Deformation in the southern parts of the Tabberabbera Zone is early and of a style reminiscent of the upper parts of accretionary complexes, suggesting the influence of underlying or nearby subduction systems (Fergusson, 1998). The syn-tectonic granitic magmatism seen in the Omeo Zone suggests a very high heat flow, consistent with an arc-origin and proximity to a convergent plate margin system (Collins & Vernon, 1992). Father east again, the structural style and rock relationships in the Mallacoota Zone and strongly suggestive of a subduction accretion origin (Miller & Gray, 1997). Recent tectonic models for the Lachlan Fold Belt have either attributed geometry (structural vergence changes between west, central and eastern portions), sedimentary relationships, width and magmatic history to several coeval subduction zones of opposing polarity (eg. Gray & Foster, 1998), or to large-scale horizontal movements along structures such as the mid- to Late Silurian Baragwanath Transform, a strike-slip structure that was inferred to lie near the position now occupied by the Governor Fault (Willman et al., 2002). Aeromagnetic data now shows that the Baragwanath Transform does not occur in southwestern New South Wales (Hallett et al., 2005). Multiple subduction models, with subduction beneath the western Lachlan Fold Belt in particular, are not supported by new seismic data (Cayley et al., 2011). Compelling sedimentological evidence that the Tabberabbera Zone was not contiguous with the Melbourne Zone until the Early Devonian remains (Fergusson et al., 1986). A new tectonic model under development (Cayley, 2010; Cayley et al, 2012) proposes a solution that involves mid- to Late Silurian clockwise oroclinal folding within the Lachlan Fold Belt adjacent to large dextral strike-slip faults in central-west NSW and eastern Victoria, the key structure being the Kiewa-Kancoona Fault that separates the Tabberabbera and Omeo zones, and continues north beneath Murray Basin cover to link into the Bootheragandra Fault in central NSW (Musgrave & Rawlinson, 2010). A fault-segmented, orogen-scale Z-shaped fold in Victoria and southern NSW can explain the vergence reversal seen across the Governor Fault. It can explain the different structural traits observed in the different Lachlan Fold Belt terranes, while affirming their common depositional

8 ongm. Oroclinal folding explains the apparent great width of the Lachlan Fold Belt. Undoing the oroclinal fold greatly simplifies its Late Cambrian-Early Silurian configuration. The oroclinal fold couple hypothesis potentially adds a great number of additional geological constraints, because some western Lachlan Fold Belt geology that is now well understood and imaged by deep seismic data can be extrapolated directly into the central and eastern Lachlan Fold Belt where there are less constraints. This model also greatly simplifies the Lachlan Fold Belt during the early stages of its accretion. It can be interpreted as a 'long and skinny' continentfringing accretionary system developed above a simple, continent-dipping subduction zone in the Late Ordovician. It's the subsequent Late Silurian oroclinal folding that's made it short and fat.

Melbourne Zone The Melbourne Zone occupies a large area of central Victoria totalling about 40 000 km 2 . The northern and eastern boundaries are clearly defined by the Governor Fault. The western boundary is mostly defined by the Mount William Fault (a reactivated part of the larger Heathcote Fault Zone). The Melbourne Zone has been subdivided into two provinces, the Darraweit Guim Province in the west, and the Mount Easton Province in the east. The subdivision is made on sedimentological grounds (the stratigraphy is thicker in the west), but as it happens the subdivision is also convenient for describing structural character. We will examine outcrops in the Mount Easton Province.

Rock Units: The Melbourne Zone is characterised by a thick, unbroken sedimentary sequence of Lower Silurian to Middle Devonian rocks, the Murrindindi Supergroup. Where not faulted, the Murrindindi Supergroup lies conformably on Lower and Upper Ordovician sedimentary rocks. In the Darraweit Guim Province, these are condensed Castlemaine Group turbidites, black shale, and the Sunbury Group. In the Mount Easton Province they are the black and relatively thin Early Ordovician Phosphate Hill Formation (VandenBerg et al., 2006) and Late Ordovician Mount Easton Shale. The Murrindindi Supergroup and underlying Ordovician rocks are largely nonmagnetic. Magnetic highs do occur within the Melbourne Zone are these are attributed to magnetic rocks that underlie the Murrindindi Supergroup. Mode!Iing of the depth, susceptibility, and likely geometry of these rocks has provided important constraints on the likely thickness of the Melbourne Zone, and likely composition of the underlying Selwyn Block (McLean et al, 2010). Sedimentary features such as westward-shoaling and eastward-thinning indicate that the Melbourne Zone overlying the Selwyn Block may have formed as a foreland basin to the uplifted Bendigo Zone from the Late Ordovician to Devonian (Cayley et al. 2002). Although laterally thinning overall, the Murrindindi Supergroup layer-cake shows remarkable lateral persistence within the Mount Easton Province. Even thin units within the succession, such as the Mount Eildon Sandstone and Wilson Creek Shale, are able to be traced around regionalscale folds on scales of lO's to over 100 km (VandenBerg et al., 2006; Figures 2-1, 2-2). Prior to regional deformation in the Tabberabberan Orogeny, the proto-Melbourne Zone basin must have been one with a very low relief depositional surface, and little internal sediment reworking.

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Figure 1-3. Time-event plot for the eastern Melbourne Zone, showing relationships between various stratigraphic units and events.

Unlike the regular trains of structures in the flanking Bendigo and Tabberabbera zones, regional folds in the Melbourne Zone first developed in the Tabberabbran Orogeny. These vary widely in profile, wavelength and trend, and cleavage is generally weak except in the east. The zone also has the lowest metamorphic grade in the Lachlan Fold Belt in Victoria. Grade varies from unmetamorphosed (diagenetic zone) in the west (Offler et al., 1998a), to low greenschist in the easternmost outcrops. This increase is accompanied by an increase in cleavage development.

Fig f.4: Oblique ~iewnorth attire southea;tern Mel~urne Zone. The Baw Baw Granite intrudes folded Murrindindi Group stratigraphy. Compound image draped on DTM: Scott Welch, GSV.

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10 The deformed Murrindindi Supergroup is intruded by Middle and Late Devonian granites and unconformably overlain by Upper Devonian rocks of the Howitt Province and caldera volcanics of the Central Victorian Magmatic Province. The Howitt Province are fluvial sedimentary rocks and are preserved in synclines straddling the faul ted boundary between the Melbourne and Tabberabbera zones.

Structures:

,--------------------------- ---, Melbourne Modelling Zone

Location Map

Figure 1-5 - Map showing extent of the Melbourne Zone and major structural elements draped over a TM/ greyscale, with post-Carboniferous rocks omitted. Dark purple rocks 13re windows of Selwyn Block crust poking up through the overlying Melbourne Zone cover. Pink rocks are granite.

The Melbourne Zone was deformed during the Middle Devonian Tabberabberan Orogeny, dominantly by approximately east-west shortening, with a lesser component of north-south shortening confined to the north. The major structures are northerly-trending folds, culminating as major anticlinoria and synclinoria in places. The largest of these probably mark the position of underlying thrust-fault splays. The major faults are the bounding faults- the east-dipping Governor Fault which bounds the western side of the Tabberabbera Zone, and the west-dipping Mt William Fault that bounds the

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11 east side of the Bendigo Zone. Deformation of the intervening Melbourne Zone was probably driven by convergence of these faults as they overthrust the margins of the underlying Selwyn Block basement. The Thomas Fault is the decollement surface inferred to separate the underlying Selwyn Block from the overlying folded marine turbidites of the Melbourne Zone. In most places, any such structure lies deeply buried, especially in the western parts of the zone. Approaching the eastern margin of the Melbourne Zone the folds tighten, metamorphic grade climbs, and cleavage intensifies into the broad Mount Useful Fault Zone that occupies the eastern 15 km or so of the zone (VandenBerg et al., 1995, 2006; Gray, 1995). The Thomas Fault detachment is exposed in several 'windows' eroded through the Mount Useful Fault Zone, where it is seen to be the faulted contact between overlying Melbourne Zone rocks and underlying deformed Cambrian metavolcanics of the Selwyn Block.

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Figure 1-6 - 3-0 model of the Melbourne Zone constructed by Mark McLean, GSV. A: Plan view of the Melbourne Zone. B: Oblique view looking north-west of the fault network. C: Oblique view looking north-west at major faults, stratigraphy, intrusions and Late Devonian sedimentary basins. The light blue surface represents the top of the Ordovician turbidites and the pink surface represents the top of the Silurian turbidites. D: Oblique view of the southeastern region of the Melbourne Zone model showing the fault network and top of Ordovician surface (light blue). This image also has cross-sections from the Matlock and Walhalla map sheets displayed and registered in 30 space.

I I 12 A period of synsedimentary folding, and perhaps reverse faulting, affected the western margin of the Howitt Province during the Late Devonian (O.Halloran & Cas, 1995). Its main effect was the production of the Jamieson Syncline. The Kanimblan Orogeny in the Carboniferous caused mostly mild deformation of Late Devonian rocks but had limited effects on earlier rocks-minor sinistral offsets along the eastern margin of the Melbourne Zone, involving minor thrusting of parts of the Selwyn Block over the western margin of the Macalister Synclinorium along the Barkly Thrust.

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Eastern Victorian Structural Zones Location Map

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Zone Bo,.,,da,y

A '"' :::::==========:::::...-. Figure 1-7- Major faults and rock units of Eastern Victoria . Note the position of the Tabberabbera and Omeo zones east of the Melbourne Zone and west of the Deddick, Kuark and Mallacoota structural zones.

Tabberabbera Zone The Tabberabbera Zone is a northwest-trending belt with an outcrop distance of about 240 km and an average width of 70 km. It lies between the Melbourne and Omeo zones and has a total area of about 24 000 km 2 . The Tabberabbera Zone extends southeast to the Buchan Rift (VandenBerg et al., 2000; bright green rocks in Fig. 1-7). The boundary between the Tabberabbera and Kuark Zones lies hidden under the Buchan Rift. Their relationship is unclear-they might once have been continuous (Hendrickx, 1999; Cayley, 2010) but today are most likely somewhat separated by the rift structure. Only a small area of the Tabberabbera Zone is exposed in southern New South Wales. This may be because the Tabberabbera Zone represents an oroclinally folded portion of the Bendigo Zone (Cayley, 20 I0), and therefore does not extend north of the southern margin of the Hay-Booligal Zone in southern NSW (Hallett et al., 2005). Like the Bendigo Zone in the Western Lachlan Fold Belt, the bedrock of the Tabberabbera Zone is dominated by thick, deep marine siliciclastic turbidites of Lower to Middle Ordovician age-

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13 the Pinnak Sandstone, part of the Adaminaby Group. Unlike the Bendigo Zone, the Ordovician stratigraphy persists into the Upper Ordovician and Early Silurian as the Bendoc and Cobbannah Groups respectively (see Fig.1-2). All these units are deep marine. The Bendoc Group is dominated by black shale, and represents a period of protracted sediment starvation within the Tabberabbera Zone and adjacent parts of the Eastern Lachlan Fold Belt. Compared to adjacent zones, the Tabberabbera Zone shows a relative dearth of granite(< 10% in area). The granites that are present are Early Devonian, and mostly I-type. Metamorphic grade is generally low greenschist, in marked contrast to the adjacent Omeo Zone.

Rock units: The Early Ordovician Pinnak Sandstone is the dominant outcropping rock unit. It conformably overlies Late Cambrian shale (Howqua Shale) and Middle to Early Cambrian mafic oceanic volcanics that are only exposed along the Governor Fault at the western margin of the Tabberabbera Zone. Cambrian rocks along the western margin are the Dookie Igneous Complex, and Lickhole volcanics, tholeiites and boninites which suggest that, like the Bendigo Zone farther west, the Tabberabbera Zone developed over oceanic basement (Fergusson, 1998). Talcose schists in the hanging wall of the Wonnangatta Fault may also be Cambrian. If so, they would represent the most easterly known volcanic-derived Cambrian rocks in Victoria. The Upper Ordovician Bendoc Group, dominated by deep marine black shale, crops out in long, narrow fault slices and the Lower Silurian Cobbannah Group, also deep marine, occurs in broad outcrop belts along the western margin of the Tabberabbera Zone. Upper Devonian fluvial rocks of the Howitt Province occur in basins straddling the western margin of the zone.

Structures: Like the Bendigo and Omeo Zones, the main structures in the Tabberabbera Zone were generated in the Benambran Orogeny. The zone is characterised by tight north to northwest-trending folds with a strong axial plane cleavage, and sub-parallel faults with an overall south to southwest vergence. The structural style of the zone varies across its width. In the west, the zone is characterised by large thrust faults, separating regions that are strongly cleaved, and tightly folded by upright, chevron-style F 1 folds with wavelengths of lO's to hundreds of metres. In the middle of the zone, the structural style begins to change to that of large tracts of consistently eastdipping and facing Pinnak Sandstone with few folds. The high apparent stratigraphic thicknesses in the east of the Tabberabbera Zone suggest the presence of several bedding-parallel faults along which the succession has been imbricated, but insufficient biostratigraphic control exists at present to accurately locate these (Willman et al., 2005). Approaching the eastern edge of the zone, F 1 folding begins to become significant once more (Morand et al., 2005), perhaps bracketing the margins of this structural system. The largest structures are the zone-bounding faults, the Governor and Kiewa-Kancoona faults . The largest internal fault is the Wonnangatta Fault Zone. The northeast-dipping Governor Fault dips north to northeast and has thrust Cambrian to Silurian rocks of the Tabberabbera Zone over younger rocks of the Melbourne Zone. It appears to have formed as a result of amalgamation of the Central and Western terranes of the Lachlan Fold Belt during the Tabberabberan Orogeny. Field relationships in the Jamieson-Licola region clearly show that the Governor Fault overthrusts the Mount Useful Fault Zone of the eastern Melbourne

14 Zone. It forms the western boundary of outcrops of Cambrian Lickhole Volcanics, and in places occurs as a sub-horizontal structure that emplaces these directly over Ordovician and Silurian metasediments of the Melbourne Zone. Small outliers of Lickhole Volcanics occur west of the main fault trace, and appear to be klippes of the Governer Fault hangingwall resting upon the Melbourne Zone footwall rocks (R. Cayley, unpublished data). Magnetic and radiometric data show that the faulted edge of the Lickhole Volcanics and Dookie Igneous Complex is strongly sinuous, suggesting that the Governor Fault is a low-angle thrust, a geometry confirmed in the one place where the fault has been imaged by seismic data (Cayley et al., 2011 ). The Wonnangatta Fault Zone is a very large, northeast-dipping set of anastomosing thrust faults in the western Tabberabbera Zone. Near Darga, it is a 1.2 km wide fault zone with abundant broken formation and with a very large dip-slip displacement; at least several kilometres is likely (Willman et al. 2005). Here it is a major northeast-dipping fault zone that separates lowermost Pinnak Sandstone, and in places the Howqua Chert, to the east, from Bendoc and Cobbannah groups. Farther north, the continuation of the fault zone appears to branch into a number of faults with smaller displacements juxtaposing Bendoc Group against Pinnak Sandstone and Cobbannah Group. Splays include the Bread and Butter Fault, and the Nug Nug Shear Zone, both of which we visit on the excursion. The subvertical Kiewa-Kancoona Fault is described in more detail in the description of the Omeo Zone. Strike-slip faults that splay from this structure into the interior of the southern Tabberabbera Zone include the Kalk Kalk Fault, over which the Lower Devonian fluvial Mitchell Syncline succession was deposited, and the Shanahan and Barmouth faults. These are all subvertical structures that preserve evidence of dextral strike-slip displacement. These structures cut across regional folding and are therefore younger than the large thrust faults. They were apparently active in the Bindian Orogeny. Although the zone was possibly subjected to wholesale rotation and southward transport in the Bindian Orogeny (Cayley 2010), the internal effects of the Bindian Orogeny are relatively weak, confined to minor warps and crenulation cleavage generations. The effects of the Tabberabberan Orogeny, while widespread, were also generally mild. The contents of the Mitchell Syncline were tightly folded in the Tabberabberan Orogeny. The Kanimblan Orogeny can only be identified where it deforms the Upper Devonian rocks of the Howitt Province.

Omeo Zone: The Omeo Zone lies between the Tabberabbera and Deddick zones and covers an area of about 12,400 krn 2 in Victoria. It has a much larger extent in New South Wales where it is known as the Wagga-Omeo Zone (Glen, 1992; Scheibner & Basden, 1998). The Omeo Zone is a complex amalgam of a variety of Late Silurian - Early Devonian units over a basement of Ordovician sedimentary and Early Silurian metamorphic rocks. It includes a Late Silurian rift basin, (Wombat Creek Graben), and three Early Devonian cauldrons. Synclines with Late Silurian or Early Devonian fill occur along the southern zone margin. The Omeo Zone is characterised by north to northwest structural trends and a number of large strike-slip faults. It is also characterised by the presence of the Omeo Metamorphic Complex, part of the Wagga-Omeo Metamorphic Belt whose northern extent remains largely unmapped.

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LOCATION MAP

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14G

1 pale areas are covered by !_ _ - - -' Gainozoic and younger rocks

Devonian riff volcanic L. Silurian Cobba'lnah Group ii. &L sediment.-y rocks Silurian riff volcanic Ii. Triassic igneous rocks Ii. u. Ordovician Bendoc Group ii. &L sediment.-y rocks r - , L. to M. OrdOvician L Silurian to L Devonian nes ii. u. Devonian sedimentary rocks ii. gran L__J Pinnak Sandstone Hign Tilow P metamorphic rocks 1111 Cambrian volcanic & + U. Devonian grannes Ill derived from Pinnak Sandstone sedimentary rocks Ii. U. Devonian volcanic rocks ~ Major faults and snear zones • '·:.r -... Orogenic gold deposits 1

, , ... It,

~ - Bedding trends in low-grade rocks ~ ' Metamorpnic foliation in metamorpllic rocks

50km

Figure 1-8 Geological Map showing major Palaeozoic geological units in northeast Victoria. Note the Kiewa Shear Zone at the boundary between the Tabberabbera and Omeo Zones, and the horsetail splay it breaks down into at its southern end (near Darga)

A prominent intra-zone fault, the Tallangatta Creek Fault Zone, divides the Omeo Zone into two portions, the High Plains and Corryong subzones (Figure 1-8). Both subzones consist mostly of the Omeo Metamorphic Complex. The Omeo Metamorphic Complex comprises Pinnak Sandstone regionally metamorphosed to high grades and, in places, partially melted to migmatite and syn-tectonic granite. Other early granites within the complex have tonalitic compositions that do not reflect melting of Pinnak Sandstone. These may have been generated a greater depths, and it is possible that their intrusion could have carried sufficient heat into the mid-crust to generate the in-situ partial melting.

Rock units: The High Plains Subzone is largely composed of low-pressure regional and contact metamorphic rocks produced in two events. The first and most important metamorphic event occurred in the

16 Early Silurian, associated with the Benambran Orogeny (Beavis, 1962). Fagan (1979) referred to this as Ml and the rocks are collectively named the Omeo Metamorphic Complex (Morand, 1990). They are entirely derived from Pinnak Sandstone and consist of phyllite, schist, gneiss, migmatite and S-type granite. Bendoc Group roe were not involved, probably due to their position higher in the crust. The second metamorphic event occurred at about the Silurian-Devonian boundary, associated with the Bindian Orogeny. This resulted in schistose aureoles around some granites, and greenschist facies assemblages in mylonites and mafic to intermediate dykes. This was referred to as M2 by Fagan (1979) and was broadly coeval with a period of widespread granite intrusion and local metamorphism. Metamorphic grade decreases from west to east across the subzone. The high-grade rocks along the western margin are sharply truncated by the Kancoona-Kiewa-Cassilis-Ensay Shear Zone where they are juxtaposed against low-grade Pinnak Sandstone of the Tabberabbera Zone. Low grade Pinnak Sandstone also makes up around 20% of the Omeo Zone. Upper Ordovician Bendoc Group occurs throughout the Corryong Subzone but is only preserved in a few fault zones in the High Plains Subzone. Palaeozoic granites include S, I and A-types; no gabbros have been identified. They occupy nearly a third of the area of the Omeo Zone. Magmatism occurred in two episodes, the first associated with M 1 metamorphism in the Benambran Orogeny and the second during and just after the Bindian Orogeny. Many of these granites are foliated and have intruded active fault zones, particularly those formed during the Bindian Orogeny. An unusual feature of the Omeo Zone is the occurrence of a small area (150 krn 2) of Triassic Atype granites (Mount Leinster Igneous Complex) in the southwestem comer of the Corryong Subzone (VandenBerg et al., 1998).

Structures: The main structural event in the Omeo Zone is the Benambran Orogeny, which deformed all Ordovician and Lower Silurian rocks with a generation of tight folds and cleavage, and generated the Omeo Metamorphic Complex. Apart from local domal patterns (south of the Tawonga Fault; Beavis, 1962), regional trends show a dominant WNW strike that swings north westerly along the western margin of the High Plains subzone. Structures generaJiy show increased complexity with increasing metamorphic grade due to the more ductile behaviour of high-grade rocks. It is common to find an extra generation of structures in the higher metamorphic grade rocks; structural trends in the Omeo Metamorphic Complex are mostly defined by second-generation fabrics such as S2 schistosity and gneissosity. S-t:ype granites were formed in a sociation with metamorphism. Most large faults in the zone originated in the Bindian Orogeny, and most are strike-slip structures. As in the other zones, the largest structure is zone-bounding. The Kancoona-KiewaCassilis-Ensay shear zone juxtaposes the Omeo Zone against the Tabberabbera Zone. This fault network is subvertical, and records evidence of major dextral and later minor sinistral strike-slip movements, and occasional lesser dip-slip movement components. The Kancoona Fault is a major northwest-trending strike-slip fault with a mylonite zone up to 600 m wide separating highgrade metamorphics from low-grade Pinnak Sandstone (Morand & Gray, 1991 ). Early dextral strike-slip movement is constrained to the Bindian Orogeny by Ar/Ar data and the age of granites. Sinistral strike-slip movement occurred in the Tabberabberan Orogeny. The Kiewa Fault is a major NNW-trending fault, prominent in the magnetic data because of magnetic granites in

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17 the fault zone. it to be a steep west-dipping strike-slip fault with dextral movement (Scott, 1985; Morand & Gray, 1991). South of Mount Beauty the Kiewa Fault has a mylonite zone up to 2 km wide separating highgrade metamorphics from low-grade Pinnak Sandstone. Mylonitic granite in the fault has a welldeveloped S-C fabric indicating initial dextral strike-slip movement during the Bindian Orogeny, with sinistral reactivation during the Tabberabberan Orogeny (Morand & Gray, 1991). Based on offset of the boundary of the Omeo Metamorphic Complex and structural trends within it, Morand and Gray (1991) estimated a dextral displacement along the fault of about 50 km. The Cassilis Shear Zone forms part of the southwestern boundary of the High Plains Subzone over a distance of about 50 km. It probably links with the Kiewa Fault and is known to link with the Ensay Shear Zone. Within internal parts of the zone, the Bindian Orogeny was characterised internal fragmentation that began along large strike-slip faults that apparently splayed out from the major bounding Kiewa-Kancoona fault system. The splay faults formed linked systems with strike-slip faults along the margins of crustal fragments such as the Talgarno and Jarvis Creek faults, and the Nelse Shear Zone and Tallangatta Creek Fault Zone, with contractional faults at their leading edges, such as the Indi Fault. The Indi Fault is a northwest dipping thrust fault, also of Bindian age, that has em placed the Omeo Zone over the adjacent Deddick Zone (Morand & Gray, 1991 ). Some larger fragments, such as the Corryong Subzone, appear to have behaved like thrust sheets. An episode of crustal extension in the Early Devonian opened several large north-trending basins. They received significant thicknesses of marine sediment, and one, the Buchan Rift, began with bimodal volcanism. Felsic volcanism also occurred in several cauldrons. The Tabberabberan Orogeny was a weak event in the Omeo Zone. Regional east-west compression caused reactivation of some faults and generated some northeast-trending dextral strike-slip faults.

PART2 FIELD TRIP ITINERARY The field trip starts in the eastern part of the Melbourne Zone, then moves into the Tabberabbera Zone and then the Omeo Zone. Each of these tectonic zones has a distinct tectonic history and style of deformation. The Melbourne Zone has had only one major folding event, for the most part, whereas the Tabberabbera and Omeo Zones have been through several orogenies and have numerous generations of structures.

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Most of the information on the various sites visited comes from work carried out by GeoScience Victoria in the course of mapping at 1:50 000 scale, including the Omeo 1: 100 000 sheet (Willman et al. 1999), Bo gong 1: 100 000 sheet (Morand et al. 2005), Buffalo 1: 100 000 sheet (VandenBerg et al. 2003) and the Walhalla-Woods Point-Tallangallook area (Vandenberg et al. 2006). Each site has its location given as a Map Grid of Australia (MGA) grid reference, with an easting and northing in metres, based on the GDA 94 datum, Zone 55.

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Figure 2-1. Geological map of the route from Rawson to Woods Point, showing stops 1-1 to 1-6. Grid lines are spaced 5 km apart. Legend in Appendix 1.

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Figure 2-2. Geological map of the route from Woods Point to Mansfield, showing stops 1-7 to 1-9. Grid lines are spaced 5 km . Legend in Appendix 1.

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Saturday February 4: Rawson to Mansfield Examines the structural style of the eastern Melbourne Zone - deep marine sedimentary rocks deformed in the Mid-Devonian Tabberabberan Orogeny.

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Drive north from Rawson along the Thompson Valley Road.

Stop 1-1. MGA 447120-5802750. A large road cutting on the Thomson Valley Road, 5.7 km north of Parkers Corner. This cutting is in the Early Devonian Boola Formation of the Jordan River Group. It shows the range of rock types found in this unit: interbedded siltstone, lithic sandstone and lithic conglomerate. There are shelly fossils in the conglomerate at the southern end of the cutting, including crinoids, bryozoans, gastropods and brachiopods. Amongst the lithic components in the Boola Formation are mafic volcanic clasts thought to have been derived from Cambrian volcanics exposed to the south. These volcanics were at or near the surface in the Early Devonian in the Cape Liptrap area to the south, where Early Devonian shallow marine limestone rests unconformably on thin Ordovician limestone overlying the Cambrian volcanic sequence. The Cambrian volcanic sequence is part of the Selwyn Block, basement to the Melbourne Zone that is contiguous with Cambrian and older rocks in Tasmania (Cayley et al. 2002). The simple structure in this cutting is typical of the Melbourne Zone, with only a weak slaty cleavage developed in the siltstone. Folds in the Jordan River Group tend to be larger than the average road cutting, so outcrop-scale folds are rarely observed. Drive north along the Thompson Valley Road which becomes the Thompson Dam Access Road.

Stop 1-2. MGA 447000-5809870. Road cutting on the Thomson Dam Access Road, just past a tight bend with a turnoff to the right.

An angular anticline in the Early Devonian Norton Gully Sandstone (Walhalla Group) is exposed here (Fig. 2-3). Close folds with angular profiles are common in this thin-bedded turbidite unit, and several more folds can be seen as you walk 200 m to the west. There are also several faults in these cuttings ; some are accommodation structures within folds, and others are steep reverse faults, usually marked by eroded zones of red weathered broken rock. A steeply-dipping slaty cleavage is locally developed, but is not a prominent feature.

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Figure 2-3. Stop 1-2. Angular anticline in Norton Gully Sandstone.

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Figu re 2-4. Simplified geology of the area covered by the Walhalla-Woods Point-Tallangallook maps in the eastern Melbourne Zone (VandenBerg et al. 2006). The first day covers this area.

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23 A mudstone unit with plant stem fossils can be seen here, although the best samples are found as loose blocks at the base of the cutting. These plant remains were presumably washed out to sea from flooding rivers.

Turn around and drive back along the Thompson Dam Access Road. Turn sharp right into the Thompson Valley Road and drive north.

Stop 1-3. MGA 437010-5819000. A road cutting on the Thomson Valley Road, about 1.5 km past the bridge over Bell Clear Creek.

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The Late Devonian Baw Baw Granodiorite is exposed in the cutting on the west side of the road, with fresh boulders lying around the east side. The Baw Baw Granodiorite makes up Mt Baw Baw, a large granite dome. It is a post-tectonic intrusion, like all granites in the Melbourne Zone, and is a grey, medium-grained equigranular I-type biotite granodiorite with minor hornblende and containing some small dark grey microgranitoid enclaves. Accessory zircon, apatite and opaques are present in a thin section from here. Some hornblende grains have cores of pale green cummingtonite. As with other I-type plutons in the Melbourne Zone, the Baw Baw Granodiorite is non-magnetic, in contrast to non-fractionated I-types in the rest of the Lachlan Fold Belt. The route from here runs along the side of the Baw Baw plateau, across the northern end of the Baw Baw Granite, along a screen of hornfels within the granite, then north along the Gregory Plateau to join the Warburton-Woods Point Road at The Triangle. Most of the route is in Norton Gully Sandstone. Turn right at a T-intersection into Nine Mile Road and follow this to the Warburton-Woods Point Road at The Triangle. Turn right at The Triangle and drive toward Matlock. The route here runs across the Mount Easton Anticlinorium.

Stop 1-4. MGA 426720-5838820. Road cuttings on the Warburton-Woods Point Road. Strata of the lower part of the Melbourne Zone sequence are seen here. Rock units exposed are the Late Ordovician Mount Easton Shale (black graptolite-bearing shale with conspicuous detrital muscovite), McAdam Sandstone (quartz-lithic sandy turbidite, with some small pyrite cubes) and a weathered diorite dyke of the Late Devonian Woods Point Dyke Swarm. The dyke is about 10 m wide, coarse-grained and equigranular. A fault is recognized as a zone of no outcrop between the Mount Easton Shale and the McAdam Sandstone. It is also indicated by the absence of the Lazarini Siltstone, a unit that lies between the Mount Easton Shale and the McAdam Sandstone. This site is in the core of the Mount Easton Anticlinorium (Figs 2-4, 2-6), a large structure that brings up the older units of the Melbourne Zone. Continue east towards Matlock.

Stop 1-5. MGA 427360-5839840. Road cuttings on Warburton-Woods Point Road. A section along the road here exposes the lower units of the Jordan River Group faulted against the Walhalla Group along the Enochs Point Fault. Starting in the west are cuttings in the Early Silurian McAdam Sandstone, then Early Silurian Lazarini Siltstone (grey-green massive siltstone with splotches of dark grey bioturbation), followed by patchy outcrop of the Late Ordovician Mount Easton Shale (full of graptolites), then a gap in outcrop marking the Enochs Point Fault,

I I 24 followed to the east by cuttings in the Early Devonian Norton Gully Sandstone (feldspar-lithic sandy turbidites).

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Figure 2-5. Map of geology around Matlock, showing stops 1-4, 1-5 and 1-6. Bedding dips and strikes are shown for upright and overturned bedding. Oxe - Mount Easton Shale Sjl- Lazarini Siltstone Sjm - McAdam Sandstone Sjb - Bullung Siltstone Sjs - Sinclair Valley Sandstone Sjw - Whitelaw Siltstone Sji - Wilson Creek Shale Dnn - Norton Gully Sandstone Dnm - Montys Hut Formation Ywp - Woods Point Dyke Swarm

The three Ordovician-Silurian units are all NE-dipping and apparently NE-younging, but have the youngest unit (McAdam Sandstone) at the bottom and the oldest (Mount Easton Shale) at the top, indicating the boundaries between them are thrust faults. Younging was determined from grading in the McAdam Sandstone, from the cleavage-bedding relationship in the Lazarini Siltstone, and undetermined in the Mount Easton Shale. The faults are probably back-thrusts splaying of the Enochs Point Fault (Fig. 2-5). The Enochs Point Fault marks the eastern edge of the Mount Easton Anticlinorium. The anticlinorium has been thrust eastwards over the adjacent Walhalla Synclinorium along the Enochs Point Fault. This fault is a deeply cutting structure, as it appears to cut magnetic units in the basement. A throw of at least 4 km is indicated by the juxtaposition of the lowest stratigraphic unit in the area (Mount Easton Shale) against one of the highest stratigraphic units (Fig. 2-6). Continue east to Matlock. At Matlock veer left and take the road to Woods Point.

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Stop 1-6. MGA 433450-5840200. Cutting on Warburton-Woods Point Road. This site is the hinge of the Bald Hill Syncline (Fig. 2-5), a structure within the Walhalla Synclinorium that exposes the youngest unit in the eastern Melbourne Zone folded sequence, the Early Devonian Montys Hut Formation. This unit consists of laminated siltstone with a few thin interbeds of fine-grained sandstone. Being the hinge of an upright syncline, beds are horizontal and the slaty cleavage is vertical. A horizontal bedding/cleavage intersection is visible on cleavage planes, indicating a horizontal fold axis.

Stop 1-6

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E -MATLOCK--F ABERFELDY A--,BERFELDY----BC--MATLOCK--0

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Norton Gully Sandstone

Figure 2-6. Cross-section through the eastern Melbourne Zone in the Matlock area, from VandenBerg et al. (2004), showing approximate location of stops 1-4, 1-5 and 1-6, projected along strike. HCF = Howes Creek Fault, FGF = Fiddlers Green Fault, TF = Thomas Fault, EPF = Enochs Point Fault. The inclusion of basement slivers along the Enochs Point Fault is based on the magnetic basement feature having a sharp cut-off parallel to the surface trace of the fault, implying the magnetic feature is cut by the fault.

Based on well constrained cross-sections there are potentiaJly 10-12 km of deformed Melbourne Zone strata below this site (Fig. 2-6), and below the folded strata is basement to the Melbourne Zone, the Selwyn Block. Forward models based on gravity and magnetics have been applied to three cross-sections through the central and eastern Melbourne Zone (McLean et al. 2010). A section to the south of here showed basement at a depth of 10 km below the Walhalla Synclinorium near WalhaJla, while a section to the north indicated basement at 14 km below the Walhalla Synclinorium. Continue to Woods Point. Lunch at Woods Point. Drive north along Mansfield-Woods Point Road.

Stop 1-7. MGA 429430-5849340. Road cutting and river outcrops at Al Mine Settlement. Park on the left at intersection of Gaffneys Creek Jeep Track. Rocks here are steeply dipping quartz-lithic turbidites of the Norton Gully Sandstone. The beds are younging east here, but there are numerous close folds in this unit. The rocks are deep marine and Early Devonian in age. When the Norton Gully Sandstone was being deposited (410-400 Ma), eastern Victoria was mostly above sea level, and had experienced two major deformation events. Explosive silicic volcanics were abundant in the Omeo Zone in this interval, while the Tabberabbera Zone was intruded by numerous granites. In the Melbourne Zone, deepwater sedimentation continued uninterrupted from Early Ordovician through to the end of the Early Devonian. The disparate geological histories of the Melbourne Zone and eastern Victoria indicate that they were separated by a large distance. The two regions were brought together in the collision event known as the Tabberabberan Orogeny, about 390 Ma. Continue north along the Mansfield-Woods Point Road.

Stop 1-8. MGA 432020-5857220. Road cutting on Mansfield-Woods Point Road just south of the Knockwood Bridge, Knockwood, on the junction with the Lazarini Spur Track. A low cutting shows thinly-bedded grey-brown shaly siltstone with occasional thin sandstone beds that are typical of the Montys Hut Formation, the youngest stratigraphic unit of the eastern Melbourne Zone sequence. Small-scale folds are present. They are tight with steep plunges and wavelengths of about 40 cm. Folds in the larger cutting just south of the intersection are truncated by a fault with a moderate easterly dip. The folds and the fault are at the western limit of complex deformation related to the Fiddlers Green Fault System (Fig. 2-2), a complex structure with both easterly reverse movement and sinistral strike-slip movement. Continue north along Mansfield-Woods Point Road.

Stop 1-9. MGA 424050-5883640. Road cutting on Mansfield-Woods Point Road 900 m south of Martins Gap, 4 km south of the tumoff to Goughs Bay. The cutting exposes red mudstone and interbedded gritty sandstone of the Late Devonian Kevington Creek Formation. This is part of the Avon Supergroup, the overlap sequence of red beds deposited unconformably on the boundary between the Melbourne and Tabberabbera zones after the Tabberabberan Orogeny. The Avon Supergroup and the underlying Tolmie Igneous Complex (subaerial felsic cauldron volcanics) together constitute the Howitt Province. Rocks of the Howitt Province were deformed in the Early Carboniferous Kanimblan Orogeny, the last orogenic event in Victoria. The site is close to the Mansfield Fault (Fig. 2-2), which separates the Avon Supergroup from the older Walhalla Group to the west. A notable feature is the numerous faults in the sandstone, probably small splays off the Mansfield Fault. Bedding is steep and overturned, as it is along much of the western margin of the Jamieson Syncline. The small faults dip steeply, both northeast and southwest, with generally steeply pitching slickenlines on fault surfaces that indicate largely dip-slip movements. Also observed in the mudstone is a slaty cleavage, a product of the Kanimblan Orogeny. Drive on to Mansfield.

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Figure 2-7. Map of Mansfield Mt Buffalo area, with stops 2-1 to 2-4 marked. Grid spacing is 10 km . Legend in Appendix 1. 460000

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Figure 2-8. Map of Mt Buffalo -Bright area, showing locations of stops 2-3 to 2-10. Grid spacing is 10 km. Legend in Appendix 1.

Sunday February 5: Mansfield to Bright Examines the Tabberabbera Zone and Omeo Zone: deep marine turbidites deformed in the Early Silurian, the Siluro-Devonian and the Mid-Devonian; broken formation and tectonic melange; Kancoona Shear Zone (dextral strike-slip). The route from Mansfield to Stop 2-1 traverses the Mansfield Basin, with the main rocks being red siltstone and sandstone of the Late Devonian Mansfield Group, part of the Avon Supergroup. From Mansfield take the Mansfield-Whitfield Road. Tum right at the sign to Powers Lookout.

Stop 2-1. MGA 443800-5922050. Powers Lookout. Park in the car park and walk 200 m to Powers Lookout Number I. Powers Lookout is not named after the power lines here, but after the bushranger Harry Powers, who had his hideout in this locality. He was captured here by police in 1870. Rocks here are reddish conglomerate of the Snowy Plains Formation (Mansfield Group), part of a Late Devonian overlap sequence. deposited unconformably on the boundary between the Melbourne and Tabberabbera zones. These fluvi al-lacustrine deposits lie on top of a thick ignimbrite sequence which is exposed in cuttings a few kilometres back, marked by prominent vertical joints. Both the ignimbrites and the sedimentary rocks constitute the Howitt Province, deposited immediately after the Tabberabberan Orogeny. This was the main deformation in the Melbourne Zone, caused by its collision with the Tabberabbera Zone in the Middle Devonian. A further deformation in the Early Carboniferous, the Kanimblan Orogeny, folded the Howitt Province into broad synclines and anticlines, with limb dips rarely greater than 30°, although vertical to overturned beds occur on the western, faulted side of the synclines. From the lookout one can see across the full width of the Tabberabbera Zone, to Mt Feathertop on the eastern horizon. Almost nothing was known about the rocks of the Tabberabbera Zone in view here until about 10 years ago. Drive back to Mansfield-Whitfield Road and tum right. Driving down off the Wabonga Plateau one passes road cuttings in the Late Devonian Ryans Creek Rhyolite and Toombullup Jgnimbrite of the Tolmie Igneous Complex, welded ignimbrite units with prominent vertical joints. At Whitfield tum right onto the King Valley Road, and at Cheshunt continue straight ahead onto the Rose River Road.

Stop 2-2. MGA 455500-5922360. Big cutting on the Rose River Road where road gravel has been extracted. Park on the left. This site is in the Tabberabbera Zone, which is dominated by Early Ordovician quartz turbidites and Late Ordovician to Early Silurian black shale and siltstone. This cutting is in black slate of the Late Ordovician Warbisco Shale (Bendoc Group). Bedding is difficult to discern. The main structure is a steep slaty cleavage, in places folded into irregular mesoscale folds and cut by shear zones dipping NE with southwesterly transport. Zones of

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29 shearing, faulting and melange are common in the western half of the Tabberabbera Zone (Fig. 29) and have been documented by Fergusson (1987), Watson & Gray (2001), VandenBerg et al. (2003) and Willman et al. (2005). Some have features indicating they formed before lithification, while others formed well after the rocks were lithified. The shear zones at this site fall into the latter category. They are a manifestation of a fault separating Warbisco Shale from New Country Sandstone that was mapped on the Dandongadale I :50 000 sheet (Willman et al. 2003) and is part of Markovs Fault Zone (Fig. 2-9). Timing of different cleavages in the Tabberabbera Zone is not well established, but the dominant upright folds are probably Early Silurian (Benambran Orogeny), while later crenulation cleavages probably range from Late Silurian to Middle Devonian. Continue along Rose River Road to the Rose River.

Stop 2-3. MGA 460120-5919540. Park just after the bridge over the Rose River. Outcrops are on the river bank. This site has outcrops of black graphitic slate and quartz-mica sandstone of the Late Ordovician New Country Sandstone (Bendoc Group). The slate has one steep cleavage axial planar to a few tight horizontal folds in bedding. There are narrow zones of shearing and veining, suggesting sinistral shear. Quartz sandstone at the upstream end of the outcrop shows little deformation. The black shale units in the Tabberabbera Zone commonly act as weak zones along which most of the faulting and shearing occurs . Continue along the Rose River Road.

Stop 2-4. MGA 467130-5926650. Rose and Dandongadale rivers confluence. Park near the bridge on Rose River Road across Dandongadale River and walk down to the river bank. The outcrops here are of Late Ordovician Warbisco Shale, consisting mostly of black slate with a few poorly preserved graptolites. Bedding is visible, as is a strong slaty cleavage S, which is parallel to bedding. The cleavage is folded about steeply plunging open F2 chevron folds. A few hundred metres west of here the Warbisco Shale is faulted against the Early Silurian Dandongadale Siltstone along the Bread and Butter Fault. This fault is the western margin of the Wonnangatta Fault Zone, a complex zone of faulting and strata! disruption running through the Tabberabbera Zone (Fig. 2-9). Structures within the Wonnangatta Fault Zone include very early, possible syn-sedimentary, structures such as broken formation and melange, as well as later structures such as crenulation cleavage. The Bread and Butter fault is steep and has a complex movement history. It has features indicating sinistral displacement (Fig. 2-10), although the main displacement is probably east over west reverse movement, based on regional mapping (VandenBerg et al. 2003). Continue along the Rose River Road and turn left at Dandongadale onto the Buffalo River Road. Cross the Buffalo Dam and continue north. Driving from here to the next stop you will notice Mt Buffalo looming up on the east. This mountain is formed by the Mount Buffalo Granite, one of many Early Devonian intrusions emplaced into the Tabberabbera 'Zone after the main Benambran Orogeny, and therefore largely undeformed.

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Figure 2-9. Structural map of the Buffalo 1:100 000 sheet (from VandenBerg et al. 2003) , covering much of the routei of Day 2.

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Figure 2-10. Bread and Butter Fault Zone. A. Winged pale sandstone clast in matrix of strongly sheared Warbisco Shale, from near Stop 2-4. The clast symmetry indicates sinistral displacement. B. Thin section from 2.5 km NNW of Stop 2-4, showing sandstone completely disaggregated into spindle-shaped blocks which, together with the anastomosing foliation in the mudstone matrix, indicate a sinistral sense of shear. Scan of thin section 32 mm long.

Stop 2-5. MGA 471230-5940480. Osbornes Bridge over Buffalo River. Park on side road to the left on the north side of the bridge and walk back across bridge, and find a track on the southeast side of the bridge leading down to the river. Outcrops are mostly on the upstream side of the bridge. River bank outcrops expose tectonic melange in the Nug Nug Shear Zone - disrupted and lenticular bedding, broken formation and crenulation cleavage are all well displayed. Deformation began soon after sedimentation, but continued well after lithification. The rock unit here is the Pinnak Sandstone, an Early-Middle Ordovician quartzose turbidite unit that crops out in much of the eastern Lachlan Fold Belt. Because of the strong deformation here, this is not a typical exposure of the Pinnak Sandstone. Early structures are dismembered bedding (Fig. 2-11 ), boudinaged sandstone beds with pinch and swell structures and anastomosing cleavage that wraps around sandstone clasts. These suggest deformation while the rocks were still water-saturated. Later structures such as crenulation cleavage (Fig. 2-11) and shear bands indicate deformation in well lithified rocks, suggesting that deformation continued for an extended period of time. A gentle west-dipping foliation (S 1A) is pervasive and in thin section is seen to overprint an early, very fine fabrics •. In places S 1A forms shear bands indicating west over east thrusting movement. The main foliation is overprinted by open crenulations with near vertical axial planes. Some outcrops show well preserved thin bedding, but generally bedding has been destroyed, with small Ienticles of sandstone forming the only remnants of original sandstone beds. Overall the Nug Nug Shear Zone has a moderate westerly dip and folds in the adjacent rocks become more inclined as the shear zone is approached (Fig. 2-12). This is consistent with it being

Figure 2-11. Stop 2-5. Nug Nug Shear Zone , showing disrupted and lenticular pale sandy beds overprinted by crenulation folds.

a reverse fault with easterly transport. As it is entirely within Pinnak Sandstone, there is no way to tell if the hanging wall rocks are older or younger than the footwall rocks.

cross section F l kM

Mount Buffalo Gran~e

AOAMINABY GROUP Lower Ordovician

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cross section E

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Figure 2-12. Cross-sections E and F from Fig. 2-9, crossing the Nug Nug Shear Zone (from VandenBerg et al. 2003). The lower section runs through Stop 2-5.

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I 33 Continue north to Myrtleford.

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Lunch in Myrtleford. The next two stops are in the eastern Tabberabbera Zone, which Jacks the early deformation features and broad fault zones seen in the western half of the zone. The main structures are close to tight upright folds, small brittle faults and several generations of crenulation cleavage. From Myrtleford drive east to Bright. The bare granite face of Mt Buffalo is obvious on the south side of the valley. From Bright drive east and tum left onto the Bright-Tawonga Road.

Stop 2-6. MGA 503000-5935350. Cutting on Bright-Tawonga Road. Park on left. This cutting exposes Pinnak Sandstone (quartz sandstone and slate) showing upright beds dipping steeply west, steep S 1 slaty cleavage in slate and well developed disjunctive cleavage (or stripy cleavage) in sandstone (Fig. 2-13). There are also upright open, N-trending Tabberabberan folds with a weak axial planar crenulation cleavage. This locality is on the western limb of an F 1 anticlinori um.

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Figure 2-13. Pinnak Sandstone from just east of Stop 2-6, showing overturned bedding parallel to the pen , younging to the left, with a well developed stripy S1 cleavage in the sandstone layers.

The deformation responsible for the dominant F 1 folds and S 1 slaty cleavage is thought to be the Early Silurian Benambran Orogeny, although Ar39/Ar40 dating of rocks in the Tabberabbera Zone has not produced definitive metamorphic ages. The Tabberabberan cleavage is common throughout the Tabberabbera Zone. The type locality for the Tabberabberan Orogeny is in the southern Tabberabbera Zone in the Mitchell Syncline. There Early Devonian strata have been folded into a large tight NNE-trending syncline that is unconformably overlain by Late Devonian strata, thus bracketing the folding as Middle Devonian. Continue eastwards.

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Stop 2-7. MGA 506810-5936010. Cutting on Bright-Tawonga Road. Park on N side of road 130 m before the site.

This site shows Pinnak Sandstone with steeply SW-dipping overturned bedding. It is cut by a 30 cm wide zone of fault breccia. The fault dips moderately SE, at a high angle to bedding and S 1 cleavage. This site is in a well-exposed package of eastward-younging beds, some overturned, about 3 km thick (Fig. 2-14). It is the east limb of an F 1 anticlinorium. No F 1folds have been seen in this package, nor any large faults. Unless there are significant reverse faults in the few zones of no outcrop, this implies the Pinnak Sandstone is at least 3 km thick. So far no marker units have been found in the Pinnak Sandstone in the Tabberabbera Zone that would enable its thickness to be measured, and the close folding and faulting make it difficult to gauge the thickness except in small well-exposed sections. There are also small open folds formed in the mid-Devonian Tabberabberan Orogeny. Their axial plane is almost vertical and strikes north. In thin section there is a well developed crenulation cleavage axial planar to these folds. Continue eastwards.

Stop 2-8. MGA 510100-5936420. Cutting on Bright-Tawonga Road. Park on left. This weathered cutting exposes schistose mylonite of the Kancoona Shear Zone, showing dextral S-C fabrics and a low-plunging stretching lineation. The angle between S and C is about 20°. The original rock was probably a mica schist of the Omeo Metamorphic Complex. A weathered mafic dyke intrudes the mylonite, parallel to the C surfaces. It is undeformed and therefore postdates the shearing. Here the Kancoona Shear Zone forms the boundary between the Tabberabbera and Omeo Zones, with low-grade Pinnak Sandstone on the west and high-grade Omeo Metamorphic Complex on the east (Fig. 2-14). This boundary is a system of large dextral strike-slip mylonite zones (Kancoona, Kiewa, Cassilis and Ensay shear zones) that were active in the Early Devonian. A similar m~lonitic rock from about 5 km along strike to the NW gave an age of 402±2 Ma, dated by the Ar 9/ Ar40 method (Foster et al. 1999). Further along strike to the NW, the Kancoona Shear Zone shows mainly sinistral shearing resulting from reactivation in the mid-Devonian Tabberabberan Orogeny. Continue eastwards.

Stop 2-9. MGA 511510-5935690. Cutting on Bright-Tawonga Road. Parking on left of road. This cutting displays layered migmatite of the Omeo Metamorphic Complex. Layering (S 1) is folded into isoclinal rootless F2 folds (Fig. 2-15). The axial plane structure S2 is the predominant foliation in the high grade rocks of the complex, and is commonly the earliest fabric visible at outcrop scale. Thin sections often reveal an earlier folded S I fabric defined by aligned sillimanite and biotite grains, or by aligned inclusions within porphyroblasts. Fresh rock is exposed about 50 m up the road. Here the rock is mostly psammitic gneiss with a well developed S1/S2 lamination.

36 The protolith for the migmatite is the Early Ordovician Pinnak Sandstone. On the eastern side of the Omeo Metamorphic Complex a smooth gradation can be observed from chlorite zone Pinnak Sandstone through biotite, cordierite, andalusite-K-feldspar and sillimanite-K-feldspar zones into migmatite. Metamorphism occurred in the Early Silurian Benambran Orogeny, with later retrogressive metamorphism in the Late Silurian to Early Devonian.

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Figure 2-1 5. Stop 2-9. Layered migmatite with light coloured granitic layers within darker biotite-rich layers. Width of photo about 60 cm .

Continue downhill.

Stop 2-10. MGA 511860-5935820. Cutting on Bright-Tawonga Road. Park on left side of road. There is also parking space on the right side of the road further downhill. A high cutting exposes sillimanite-K-feldspar zone gneiss with a horizontal shear zone. The main gneissic layering dips steeply NE and curves into the shear zone (Fig. 2-16), which is about one metre wide and shows top to south movement. It appears to be a high temperature shear zone formed in the late stages of the Benambran Orogeny.

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Figure 2-16. Horizontal shear zone, about 1 metre thick, cutting a steep gneissic foliation . Hammer for scale.

Return to Bright.

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Monday February 6: Bright to Omeo Structural style and rock types of the eastern Tabberabbera Zone (low-grade turbidites) and the Omeo Zone (high grade metamorphics and various granites), Ensay Shear Zone (dextral strike-slip).

From Bright, take the Great Alpine Road to Harrietville, with views of Mt Feathertop and Mt Hotham on the left. From Harrietville the road winds up toward Mt Hotham, passing cuttings in the Pinnak Sandstone. These are mostly quite weathered. Fresh rocks are exposed in cuttings close to Mt Hotham.

Stop 3-1. MGA 510770-5907430. Cutting on Great Alpine Road. Park at the right side of the road on the saddle at the southern end of a long cutting, and walk up the road to examine the structures exposed for the next 300 m. Near the southern end of this long cutting in Pinnak Sandstone is a well exposed close F 1 syncline with a rounded hinge (Fig. 2-18). The rock is fresh quartzose sandstone and slate, with sandstone beds up to 1 or 2 metres thick. Grading establishes the folds as upward facing. More folds of the same style are exposed about 50 m up the road, as well as some minor steep faults. This structural style is typical of the eastern half of the Tabberabbera Zone, with the predominant structures being tight to close, upright folds with an axial planar slaty cleavage and common steep reverse faults on the fold limbs.

Figure 2-18. Stop 3-1. Close syncline in Pinnak Sandstone.

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About I00 m north of the start is the beginning of a wide fault zone with complex brittle and ductile structures (Fig. 2-19). Some parts of the fault zone are tectonic melange with strongly sheared slate and siltstone displaying scaly fabric and in places surrounding large blocks of sandstone (Fig. 2-20). Other parts have intensely fractured sandstone beds and discrete faults, and beds that pinch out over short distances. These structures appear to have formed in lithified rock, in contrast to the large fault zones in the western part of the Tabberabbera Zone.

Figure 2-20. Fault zone at Stop 3-1. Variably oriented blocks of bedded sandstone are surrounded by strongly cleaved mudstone. At the top right are coherent beds. Hammer for scale.

The orientation of the fault zone is difficult to establish because individual faults and fault fabrics have a range of orientations, some striking NE, others striking NW, all with steep to moderate dips. It is likely that fault zone strikes NW, parallel to the predominant F 1 folds and cleavage here. Such a strike would mean the fault zone runs into steep thickly forested country either side of the road, and no attempt has been made to trace it. Continue through Mt Hotham (Hotham Heights) along the Great Alpine Road.

Stop 3-2. MGA 515290-5905700. Slaty Cutting on Great Alpine Road. Park in the large car park on the right side of the road. This cutting exposes east younging and dipping turbidites of the Pinnak Sandstone. Walking eastward along the cutting several metadiorite dykes are encountered. They are dark grey, roughly parallel to bedding, and up to a few metres wide with chilled margins. The first dyke encountered is massive, about 5 m thick and may have intruded up a fault as the hanging wall is disrupted and quartz-veined. The next dyke, about 20 m farther east, has a strong cleavage parallel to that in the host rock, suggesting the possibility that it may have been an early sill intruded along bedding before deformation. A thin section of this dyke (Fig. 2-21) shows an originally fine-grained quartz diorite with a few plagioclase phenocrysts, probable biotite and possible hornblende. The rock is

42 largely composed of metamorphic chlorite, sericite, albite, quartz and leucoxene , with a strong tectonic foliation defined by aligned chlorite, sericite and trails of leucoxene. Foliated mafic to intermediate dykes are extremely rare in the Tabberabbera and Omeo zones, as most dykes of this composition have intruded after the main Early Silurian Benambran deformation. This dyke appears to predate the main Early Silurian cleavage-forming event.

Figure 2-21 . Thin section of foliated metabasic dyke at Stop 3-2. Aligned metamorphic chlorite, sericite and leucoxene define a tectonic foliation. Plane polars. Photo is 4 mm wide.

On the second, higher bench of this cutting the dyke has a very irregular pod-like shape, and to the east much of the cutting consists of irregular masses of dyke which lack a fabric, although there are faults parallel to bedding that cut the dyke. Some of the fault surfaces have lineated quartz fibre growths indicating dip-slip movement.

Continue east along Great Alpine Road toward Omeo. This road passes into the Omeo Zone, which has the Kiewa Shear Zone as its western boundary structure. The road runs over the Eocene Mount Jim Volcanic Group (formerly Older Volcanics) consisting of basalt flows, so the shear zone is not encountered on this route. It crops out in rugged valleys to the north and south. The next three sites examine the Ensay Shear Zone, one of several large dextral shear zones in the Omeo Zone that were active in the latest Silurian to Early Devonian.

After passing the town of Dinner Plain drive for about 40 km towards Omeo and take a left tum into Dry Gully Road. Drive about 3.5 km along this road.

Stop 3-3. MGA 548530-5893560. Cutting on Dry Gully Road. Park on the roadside beyond the bend. Foliated biotite granodiorite within the Ensay Shear Zone is exposed here. Bodies of this medium-grained equigranular granite occur throughout the highest grade parts of the Omeo Zone (Fig. 2-23). They are distinct from the widespread Cobungra Granite, the end result of partial melting of metasedimentary rocks in the Omeo Metamorphic Complex, in that they have fewer enclaves of metasedimentary rock, and no K-feldspar phenocrysts (Willman et al. 1999). They appear to be the same age as the Cobungra Granite, having gradational and interlayered contacts with it, and range from massive to foliated. A 3 m wide dyke of medium-grained equigranular biotite-hornblende diorite intrudes the granite. Also here is a rhyolite dyke several metres wide, intruded along the steeply dipping shear zone foliation. It has flow banding (Fig. 2-24) and a horizontal flow lineation. The flow banding is

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Unfoliated plutons Weakly to moderately foliated plutons Early Devonian strata Late Silurian strata Ordovician to Ea~ Silurian rocks including Omeo etamorphic Complex

Strongly deformed to myfonitic granite Broad fault zones and shear zones

-==---- -

MHF TCFZ

Mount Hopeless Fault Tallangatta Creek Fault Zone

------

MRF

Mc Enzies Road Fault Scrubby Creek Syncline

scs

..---

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Figure 2-22. Structural trends in the Omeo 1:100 000 sheet (Willman et al. 1999). S1 is the prominent cleavage in non-metamorphic rocks , S2 is the dominant schistosity and gneissosity in the metamorphic rocks, and Sr is crenulation cleavage formed in the mid-Devonian Tabberabberan Orogeny.

Figure 2-23. Geological map of the area around Omeo, showing stops 3-3 to 3-10. The shaded zone is the Ensay Shear Zone, a dextral strike-slip fault of Siluro-Devonian age. Faults shown as bold lines. Stippling = contact aureole. Grid lines are spaced 5 km . Qa1 - alluvium Qc1 , Nc1 , Nc4 - colluvium Nxo - Oriental Claims Gravel Trlt - Teapot Creek Formation G559 - Day Hill Syenite (Triassic) G558 - Sisters Granite (Triassic) G114 -Anglers Rest Granite G467 - Bundara Munjie Quartz Diorite G468 - Dry Gully Granodiorite G81 - Bingo Munjie Quartz Diorite G143 - Mungobabba Tonalite G145 - Livingstone Creek Tonalite G146 - Polar Star Tonalite G147 - Dry Hill Granodiorite G148 - Halletts Road Tonalite G548- Jim and Jack Tonalite G119Mountain Maid Granite G 117 - Connleys Track Granodiorite G549 - Cobungra Granite Sop - phyllite Sos - schist Sog - gneiss Som - migmatite Sol -- leucogranite Sor - biotite granodiorite Oap Pinnak Sandstone

Figure 2-24. Stop 3-3. Flow banded rhyolite dyke intruding foliated biotite granodiorite. The flow banding is deflected around a protrusion of granodiorite.

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Figure 2-25. Total magnetic intensity image overlain by greyscale first vertical derivative of the same area as figure 2-23 (red = highly magnetic, blue = non-magnetic). The Polar Star Suite plutons in the Ensay Shear Zone show up as elongate magnetic features in the Ensay Shear Zone. The abundant linear magnetic features elsewhere are mafic to intermediate dykes.

that splits into several thinner dykes. It is undeformed and therefore post-dates the shearing in the Ensay Shear Zone.

Continue along Dry Gully Road.

Stop 3-4. MGA 547880-5893960. Gambetta Mine, Dry Gully Road. This site is about 4.5 km from the start of Dry Gully Road at a mullock heap just after a small creek. Gambetta Mine is a disused gold mine site on the edge of the Ensay Shear Zone, within the Polar Star Tonalite. It was the richest mine in the Dry Gully gold field, and was worked on and off from 1882 to 1912. It exploited a reef up to 0.9 m wide following a fault striking 015° and dipping 75° E. This quartz reef locally had visible gold. In common with other reefs in the OmeoCassilis area, the Gambetta reef strikes at a high angle to the main Early Silurian metamorphic foliations and to the Early Devonian Ensay Shear Zone, indicating the mineralisation is Early Devonian or younger. The brittle nature of the mineralisation also indicates it post-dates the largely ductile shearing of the Ensay Shear Zone here. The Polar Star Tonalite (Willman et al. 1999) is a magnetic biotite tonalite forming a small elongate pluton running along the Ensay Shear Zone (Figs 2-23, 2-25). A grain-alignment foliation is developed throughout the pluton, oriented parallel to the shear zone (vertical, striking NW). The pluton was emplaced during dextral strike-slip movement of the mylonitic shear zone. A SHRIMP zircon date from this site gave an age of 418±4 Ma (Fanning & Morand 2002), which straddles the Silurian-Devonian boundary.

46 No outcrops of the tonalite are exposed at the mine, and the shaft is overgrown with vegetation. However, the mullock heap has plenty of fresh tonalite, both pristine and altered. Here it is medium-grained, equigranular and moderately foliated. Ore samples are mainly brecciated tonalite with much silicification and quartz deposition as well as epidote-sericite alteration. This gives a pale green colour to the rock. Sulphides are very finegrained and tend to rim fragments of altered tonalite that are surrounded by quartz. Ore minerals include pyrite, arsenopyrite, galena, sphalerite, minor chalcopyrite and a sulphosalt. Rare hand samples consisting almost entirely of sulphides, dominantly arsenopyrite and sphalerite, can be found here. Observant people will have noticed samples of Gambetta ore embedded in the road surface in some places along Dry Gully Road. Perhaps the streets here are indeed paved with gold!

Tum around and drive back to Great Alpine Road, and tum left there.

Stop 3-5. MGA 549900-5892260. Cuttings on Great Alpine Road. Park on left side of road. Walk down the road to a big bend, examining the cuttings on the way. Cuttings here expose a section through the Ensay Shear Zone. Rocks present are mylonitic Early Silurian Cobungra Granite and foliated Early Devonian Dry Hill Granodiorite.

Figure 2-26. Outcrop of Dry Hill Granodiorite at Stop 3-5. At the top is a fine-grained plagioclase-phyric phase, and at the bottom is a medium-grained equigranular phase.

Figure 2-27. Thin section of porphyritic phase of Dry Hill Granodiorite from Stop 3-5, showing moderately developed foliation defined by aligned small grains of plagioclase and biotite and polygonal quartz aggregates, anastomosing around zoned plagioclase phenocrysts. Crossed polars . Photo is 4 mm wide.

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47 The first rock unit is the Dry Hill Granodiorite, a small pluton that was emplaced during shearing, hence its elongate shape and its confinement to the shear zone (Willman et al. 1999). Dextral S-C fabrics in various rocks can be seen in places in outcrop, but are best seen in oriented thin sections. There are two phases here: a medium-grained equigranular phase and a fine-grained porphyritic phase (Fig. 2-26). They are interlayered parallel to the shear zone foliation. Thin sections show a ductile deformation style (Fig. 2-27), ranging from moderately foliated to mylonitic with dextral S-C fabrics . Towards the bend in the road are cuttings in mylonitised Cobungra Granite. It shows S-C fabrics defined by aligned metamorphic biotite and muscovite. Feldspar porphyroclasts show dextral tails, and a horizontal stretching lineation is present on S surfaces (Fig. 2-28).

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Figure 2-28. Stereonets of structural measurements from the Ensay Shear Zone in the Omeo area. Poles to S, C and Sm (mylonitic layering) are shown , and also the stretching lineation Lm. The foliations are subvertical and the lineation is horizontal. C is clockwise divergent from S, indicating dextral shear sense.

Several post-tectonic dykes intrude along the mylonitic fabric, including diorite and rhyolite (both probably Devonian) and olivine- and augite-bearing microgabbro (probably Cainozoic). Continue downhill and drive into Omeo. Lunch in Omeo. The next four stops are a traverse through the Omeo Metamorphic Complex from the cordierite zone upgrade to the sillimanite-K-feldspar zone and into Cobungra Granite. The traverse is along the Omeo-Benambra Road, northeast of Omeo. Drive north out of Omeo along the Omeo Highway, and turn left after 4 km onto the BenambraCorryong Road. Drive along this road for about7 km.

Stop 3-6. MGA 557750-5901610. Cutting on Omeo-Benambra Road. Cordierite schist of the cordierite zone is exposed here. The metamorphic assemblage is cordierite-biotite-muscovite-quartz. Bedding is visible at this grade, and here the beds are upright and dipping steeply NE, with a subvertical axial planar S2 schistosity. The intersection of bedding and schistosity plunges at a low angle to the NW, parallel to the mesoscale F2 folds in this area.

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49 The main metamorphic fabric S2 tends to be steep in the cordierite zone schist, but moderate to low dips are common at higher grades within gneiss and migmatite (Fig. 2-29). Tum around and drive back toward Omeo.

Stop 3-7. MGA 557060-5900430. Big cutting on left (south) side of road. Park on the right (north) side of road. This cutting is in cordierite schist. Pelitic layers have small cordierite porphyroblasts altered to fine-grained muscovite and biotite. Bedding is apparent, and younging can be determined from graded bedding in several places. A few close to tight upward facing F2folds here have subvertical S2 axial plane schistosity. Fold limbs tend to be faulted, and syncline hinges have been faulted out. Continue toward Omeo.

Stop 3-8. MGA 555170-5899520. Large cutting on left (south) side of road. Park on the right side. With increasing metamorphic grade the cordierite zone gives way to the andalusite-K-feldspar zone, then the sillimanite-K-feldspar zone. The rock here is layered metasedimentary gneiss of the sillimanite-K-feldspar zone intruded by thin pegmatite sills. Pelite layers have abundant cordierite, along with sillimanite and K-feldspar, while psammitic layers are mainly quartz and biotite. Bedding is still apparent here (Fig. 2-30), and graded bedding can be seen as an increase in abundance of biotite and cordierite going from psammite to pelite. Beds here are upright, dipping moderately NE, but the dominant S2 foliation dips less steeply than bedding, indicating a downward facing F 2 relationship. This is caused by the presence of tight F1 folds on the limb of a larger F2 fold.

Figure 2-30. Stop 3-8. Relic bedding in sillimanite-K-feldspar gneiss. Pegmatite sills have intruded parallel to bedding.

50 Several pale yellow to white lenses of calc-silicate gneiss lie parallel to bedding. When fresh they are dark grey, fine grained, granular rocks. Minerals present are quartz, calcic plagioclase, diopside, hornblende and sphene. These calc-silicate lenses are widespread, although uncommon, at all grades of metamorphism, and also in the Pinnak Sandstone, where they are most obvious in contact aureoles. A weak east-west striking foliation, defined by aligned cordierite grains, occurs sporadically here. It is best seen on the roadside on the west side of the road, and is axial planar to small, open F3 folds plunging moderately ENE. Cutting bedding at a high angle are several mafic dykes (Fig. 2-31 ). Although weathered they are still moderately magnetic. Many of the weak, linear magnetic anomalies in this area are probably similar mafic dykes. They are probably Cainozoic, but none have been dated.

Figure 2-31. Stop 3-8 . Gneiss with layering dipping moderately to the left (NE), and on the left two weathered mafic dykes dipping to the right (SW).

Continue toward Omeo.

Stop 3-9. MGA 554140-5897800. Cutting on both sides of the road. Park on the right (north) side of the road just before the cutting. We have passed through a narrow zone of migmatite and are now in the Cobungra Granite, the end product of melting in the migmatite zone (Willman et al. 1990). Its boundaries with migmatite are gradational and irregular, but the granite has been mobile enough to escape its envelope of migmatite and intrude into gneiss and schist in places. A steep east-striking tectonic foliation is present here. Several enclaves of migmatite are aligned the foliation. Typical of thi s granite are small dark enclaves of biotite and sillimanite, interpreted as restite, and enclaves of pegmatite and vein quartz. Drive back to Omeo Highway. Tum left and drive to Omeo. Just before Omeo veer left and continue along the Omeo Highway. After 1.4 km tum left onto the Great Alpine Road.

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Stop 3-10. MGA 554420-5892120. Cutting on Great Alpine Road. Park at SE end of cutting. Foliated Cobungra Granite with a 2 m wide sinistral shear zone showing S-C fabric locally. Toward the NW end of the cutting the granite becomes streaky and migmatitic. Several trachyte dykes intrude the granite. At the SE end of the cutting is a vertical breccia dyke about 3 m wide, with margins 50 cm thick of normal trachyte. The breccia has angular clasts up to 20 cm across of trachyte and Cobungra Granite, with very little matrix (Fig. 2-32). Voids several cm across are filled with yellow chalcedony, identified in thin section (Willman et al. 1999). Another dyke of normal trachyte is about 10 m wide, strikes E-W and is fine-grained and equigranular. These dykes are Triassic, and related to the nearby Days Hill Syenite and Tea Pot Creek Formation consisting of trachyte flows. Two other trachytic breccia dykes have been found in the Omeo area. Figure 2-32. Trachyte breccia at Stop 3-10. The trachyte fragments are closely packed together.

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Turn around and drive back to Omeo.

I I 52

Tuesday February 7: Omeo to Mt Beauty

Omeo Metamorphic Complex migmatite, gneiss and granites, Nelse Shear Zone (dextral strike-slip), various undeformed dykes.

From Omeo drive north along the Omeo Highway. This route runs along the foot of a scarp formed by the Livingstone Creek Fault, a late Cainozoic fault with about 200 m west-side up displacement. It is not known if it is reverse or normal, but a reverse sense would be consistent with the current state of stress in southeastem Australia, namely compressive stress acting in a NW-SE direction. The highway crosses the fault then winds its way up the fault scarp.

Stop 4-1. MGA 552400-5901900. Cutting on Omeo Highway. Park on the left at an abandoned tight curve on the highway and walk along the old dirt road to the gully at the bend in the road. Rocks in the gully are migmatite with prominent large K-feldspar crystals, as well as cordierite and sillimanite, and the ever-present quartz and biotite. No bedding is visible, but a weak irregular layering can be seen, partly defined by granitic streaks and pegmatite lenses. A few thin basalt dykes (presumably Cainozoic) intrude the migmatite and have controlled the course of the creek here. The dykes contain some small xenoliths, both light and dark coloured (Fig. 2-33). A thin section of a light-coloured xenolith shows it is a partially melted quartzofeldspathic rock, consisting mainly of quartz and devitrified glass. These xenoliths are probably fragments of leucosome that were incorporated into the basalt and then were partially melted and subsequently quenched as the dyke cooled. Figure 2-33. Stop 4-1 . Migmatite with large Kfeldspar crystals, intruded by a basalt dyke with both light and dark xenoliths. Lens cap for scale.

From here follow the old road along the north side of the gully, back to the highway. As the highway is approached the migmatite grades into Cobungra Granite over a distance of about 100 m, with increase in the granitic component. The Cobungra Granite exposed in the big cutting on the highway is largely unfoliated, and is characterised by small dark clots of biotite+sillimanite and white phenocrysts of perthitic K-feldspar, as well as nebulous metasedimentary enclaves. It is a grey, medium-grained biotite-muscovite-cordierite granite, although the cordierite is typically altered to pinite or muscovite+chlorite. On close inspection some apparent feldspar phenocrysts turn out to be chunks of pegmatite (K-feldspar and quartz).

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MAIN STRUCTURAL FEATURES BOGONG 1:100 000 SHEET

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TABBERABBERA ZONE

Low-grade Ordovician rocks OMEOZONE

D D

Devonian plutons Silurian plutons Large shear zone

Low-grade Ordovician rocks Omeo Metamorphic Complex including Cobungra Granite

Slaty cleavage in low-grade rocks; sch istosity & gneissosity in metamorphic rocks Crenulation cleavage in low-grade rocks

Figure 2-34. Structural trends in the Bogong 1: 100 000 sheet (Morand et al. 2005 , with Cainozoic cover rocks not shown . Several stops from day 2, day 3, day 4 and day 5 are on this map sheet , as indicated. The boxes indicate detailed maps or cross sections shown in other figures.

I I 54 Continue north along the Omeo Highway. After a few kilometres abundant outcrops of pink granite make their presence felt. This is the Early Devonian Anglers Rest Granite, an undeformed leucogranite belonging to the Boggy Plain Supersuite. The combination of endless sharp bends and seemingly endless expanse of undeformed granite may engender a sense of ennui in structural geologists.

Stop 4-2. MGA 542430-5908840. Creek next to Omeo Highway, near road cutting. Mylonitic granite, probably a fine-grained variant of the Cobungra Granite, showing dextral strike-slip, adjacent to the Anglers Rest Granite. The rock in the creek has an S-C fabric indicating dextral strike-slip movement, but overprinted by contact metamorphism against the nearby Anglers Rest Granite. This is possibly a splay off the Nelse Shear Zone, a wide zone of mylonite trending NW through the Omeo Metamorphic Complex (Fig. 2-34) with dextral strikeslip movement. The road cutting has an irregularly shaped mafic dyke or plug intruding the Cobungra Granite. It is non-magnetic, fine-grained and dark brown. Continue north along the Omeo Highway.

Stop 4-3. MGA 542180-5911400. Jokers Flat. Outcrops along Big River. May need to park on main road and walk a few hundred metres along a dirt road to the picnic area -- depends on the state of the road. The river bank here has outcrops of various phases of sheared and mylonitic granite and migmatite within the Nelse Shear Zone. The migmatite is a lens within the Wollonaby Granite, and locally preserves folds pre-dating the shearing in the Nelse Shear Zone. The only structures in the Wollonaby Granite are mylonitic fabrics , including dextral S-C fabrics, formed during displacement on the shear zone. In places the migmatite is relatively undeformed by the shearing, preserving complex mesoscale folds, but elsewhere it shows a strong NNW-striking vertical fabric with dextral shear sense indicators (Fig. 2-35).

Figure 2-35. Stop 4-3. Strongly sheared migmatite or granite with K-feldspar phenocrysts. Much of layering has been dragged into shear zones with dextral shear sense.

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55 Several kinds of undeformed dykes are present, including flow banded rhyolite, pink quartzfeldspar porphyry (related to the Anglers Rest Granite) and diorite. Dykes of various ages and compositions are abundant in the Omeo Metamorphic Complex (Fig. 2-36). Many are magnetic and visible in the aeromagnetic image - these include Devonian diorite and Cainozoic basalt and dolerite. Most dykes post-date the Early Silurian regional metamorphism and deformation, but some, although undeformed, are metamorphosed to low greenschist facies grade, probably during the Siluro-Devonian Bindian Orogeny.

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Figure 2-36. Geological map (with Cainozoic cover removed) of the southern part of the Nelse Shear Zone and the Wollonaby Granite (Morand et al. 2005) , showing various dyke types, and location of Stops 4-3 and 4-4. Dyke symbols with no tails have no strike direction determined.

Continue north along the Omeo Highway.

Stop 4-4. MGA 542210-5912370. Park at the intersection with a dirt track leading to the right (east). Walk down the track to the Big River. This site on the bank of the Big River has magnificent outcrops of Wollonaby Granite, deformed into mylonite with S-C fabrics (Fig. 2-37). The granite is an equigranular, medium grained biotite granite with no enclaves. It is contained completely within the Nelse Shear Zone and is mylonitic in every outcrop so far seen, and is interpreted as being emplaced syntectonically into the shear zone. The S-C fabrics are vertical, strike NW and contain a horizontal stretching lineation indicating strike-slip movement. The relationship between S and C indicates dextral shearing.

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In thin section the granite shows strong alteration/metamorphism, with igneous biotite replaced by chlorite + rutile + muscovite, and plagioclase partly replaced by sericite. Other igneous minerals are quartz, orthoclase, muscovite, zircon, apatite and opaques. Metamorphic minerals defining the S and C fabrics are quartz, muscovite, chlorite, rutile and albite, suggesting low greenschist facies conditions. In addition to the S-C fabric, there are mica fish and rounded feldspar porphyroblasts with 8 shapes indicating dextral shear.

Figure 2-37. Stop 4-4. Mylonitic Wollonaby Granite displaying dextral S-C foliations.

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I A SHRIMP zircon date of the Wollonaby Granite from here gave an age of 427±8 Ma (Morand & Fanning 2009), which is slightly older than other syntectonic plutons emplaced into shear zones in the Omeo Metamorphic Complex. This raises the possibility that the Wollonaby Granite is pre-shearing rather than syn-shearing. However, the age overlaps with that of the Polar Star Tonalite (418±4 Ma) which was intruded syntectonically into the Ensay Shear Zone, a probable extension of the Nelse Shear Zone. Metamorphic mica dates on mylonites from major shear zones in the Omeo Zone tend to be in the range 403-413 Ma (Foster et al. 1999), suggesting cooling to about 300° C over about l O Ma. A prominent pink dyke about 5 m wide crops out here, striking NW. It is a granophyric quartzfeldspar porphyry, the feldspars being orthoclase and albite, with minor altered biotite. Running along the NE side of this dyke is a dyke of fine-grained microgabbro about 80 cm wide. It is mostly equigranular but contains a few dark phenocrysts about 2 m across. The granophyre dyke can be followed NW for a short distance through riparian vegetation to where it cross the river again. Here it forms a spectacular pink outcrop about 15 m high (Fig. 2-38). This dyke is probably the same magma that formed the pink Anglers Rest Granite which crops out 2 km to the east. Similar pink porphyry dykes crop out elsewhere within 2 or 3 km of the Anglers Rest Granite. Both the porphyry and the microgabbro are undeformed and therefore post-date movement in the Nelse Shear Zone.

Go back to the Omeo Highway and drive north past cuttings in mylonite of the Nelse Shear 'Zone. Take the tumoff to the left onto the Bogong High Plains Road and continue towards Falls Creek. Near Falls Creek the road runs around Basalt Hill, a basalt cap of Eocene Mount Jim Volcanic Group. At the eastern end of Rocky Valley Reservoir numerous tors of granite crop out. These are

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57 the East Kiewa Granodiorite, an unfoliated Early Devonian pluton that post-dates the high-grade metamorphism and deformation of the Omeo Metamorphic Complex.

Figure 2-38. Large dyke of pink granophyric porphyry at Stop 4-4. This undeformed dyke intrudes mylonite of the Nelse Shear Zone, running parallel to the mylonitic foliation.

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Stop 4 -5. MGA 527100-5919230. Lake shore outcrops of Rocky Valley Reservoir. Park on the left and walk down to prominent outcrops on the lake shore. This site has good exposures of the Cobungra Granite and small intrusions of the East Kiewa Granodiorite. Here the Cobungra Granite ranges from massive to moderately foliated, with a schlieric foliation defined by aligned enclaves and biotite grains (Fig. 2-39). The characteristic large K-feldspar crystals are not all phenocrysts: some are chunks of pegmatite that include quartz. Small biotite-sillimanite enclaves are also common - these are restite. In a few places patches of pale fine-grained equigranular East Kiewa Granodiorite can be seen intruding the Cobungra Granite (Fig. 2-40). The East Kiewa Granodiorite is a non-foliated, variably magnetic, equigranular, biotite granodiorite and in the Falls Creek area forms numerous small intrusions I0 m to 500 m across (Fig. 2-43). It is an early Devonian I-type granite according to Morand et al. (2005), although Rossiter (2003) claimed it to be an S-type

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Figure 2-39. Stop 4-5. Schlieric fo liation in Cobungra Granite.

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Figure 2-40. Stop 4-5. Pale East Kiewa Granodiorite intruding Cobungra Granite containing white fragments of feldspar and a banded gneiss enclave above the pen .

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59 Continue east along the road.

Stop 4-6. MGA 526820-5918890. Lake shore outcrops of Rocky Valley Reservoir. Park at the picnic area just before the boat ramp access road and walk straight down to the lake shore. Here there are good exposures of the Cobungra Granite. It has numerous enclaves of metasedimentary rock and vein quartz (Fig. 2-47). The metasedimentary enclaves include large migmatite blocks and small biotite-sillimanite enclaves that are refractory restite fragments . Abundant K-feldspar phenocrysts and pegmatite chunks are present. The rock ranges from unfoliated to weakly foliated.

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Figure 2-41. Stop 4-6. Cobungra Granite featuring an enclave of layered migmatite and an irregular chunk of vein quartz. Note also the numerous small dark biotite-sillimanite enclaves.

Drive across the Rocky Valley Dam towards Falls Creek and take a sharp left turn about 200m past the end of the dam wall. This leads to a car park with a view over the lake.

Stop 4-7. MGA 525950-5919050. Car park at lookout over Rocky Valley Reservoir. A large diameter piece of drill core is embedded in the ground here, drilled from near here as part of the Kiewa Hydro-electric scheme. It is in foliated tonalite identical to the Pretty Valley Tonalite, a small pluton that crops out 4 km west of here. This distinctive I-type tonalite is biotite-rich and also contains hornblende, but is non-magnetic. Several small plutons of similar

I I 60 tonalite occur in the western part of the Omeo Metamorphic Complex, forming the Pretty Valley Suite (Morand et al. 2005). The foliation is caused by aligned biotite and plagioclase and schlieric streaks of lighter and darker material, with leucocratic segregations parallel to it. It is probably a largely magmatic foliation, as there is little solid state deformation of foliation-defining minerals (Fig. 2-42). A SHRIMP U/Pb zircon date of 422±3 Ma for the Pretty Valley Tonalite (Morand & Fanning 2009) places it as mid- to Late Silurian (Wenlock to Ludlow), slightly younger than the Benarnbran Orogeny which was thought by Morand et al. (2005) to be responsible for the steep foliation and NW trend of the Pretty Valley Suite plutons. It is possible that the NW-striking foliation was formed in the Siluro-Devonian Bindian Orogeny, at the same time as NW-striking shear zones were active.

Figure 2-42. Thin section of Pretty Valley Tonalite , crossed polars. Minerals are quartz, twinned plagioclase and biotite. The alignment of largely undeformed biotite and plagioclase indicates a magmatic flow origin for the foliation. Thin section width 4 mm.

Go back to the Bogong High Plains Road, head toward Falls Creek and take the first left tum onto the Mt McKay/Pretty Valley Road.

Stop 4-8. MGA 524360-5919600. Big cutting on Mt McKay/Pretty Valley Road. Park on right (north) side of road. This cutting is in migmatite transitional to Cobungra Granite. The rock is quartzofeldspathic gneiss with small dark lenses of refractory material, rich in biotite and sillirnanite, and lenses of granite that have segregated parallel to the layering. Augen of feldspar and quartz are also present. Minerals in the gneiss are quartz, K-feldspar, plagioclase, biotite, sillimanite and cordierite. The main gneissic fabric S2 dips about 30° south. It is axial planar to intrafolial recumbent folds of S1 layering. The biotite-sillimanite lenses commonly have a steep S 1 schistosity that curves into the main S2 gneissosity. S2 is commonly dragged into shear zones that are almost parallel to it, suggesting that shearing was a major process during the D2 deformation. Structures are quite irregular, as is typical of high temperature deformation. Moderate to low dips of the gneissic layering are common in the Falls Creek area (Fig. 2-43), having been folded into several open dome and basin structures several kilometres across (Fig. 2-34).

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Drive west, skirting around the basalt outcrop of Ruined Castle. This is part of the Mount Jim Volcanic Group.

Stop 4-9. MGA 522960-5918860. Cutting on Pretty Valley Road. This cutting exposes folded migmatitic gneiss of the sillimanite-K-feldspar zone. The rocks are biotite-rich and well layered. 522000

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Figure 2-43. Geological map of Falls Creek area showing stops 4-5 to 4-9. Geology under Rocky Valley Reservoir is shown. Structural measurements of metamorphic foliations (double ticks where known to be S2 , single ticks for dominant gneissic fabric) . Grid spacing 1 km. Qc1 , Qc7 - colluvium -Puj - Mount Jim Volcanic Group -Po2 - basaltic plugs G151 - East Kiewa Granodiorite G154- Pretty Valley Tonalite G549 - Cobungra Granite Som - migmatite Sog - gneiss

The main layering is an S2 gneissosity, and this is folded into upright, mesoscale F3 folds. These are close, rounded to chevron in profile, plunging at a low angle to the NW and verging SW. F3 folds are the latest folds developed in the high-grade metamorphics. In the Falls Creek area F3 folds appear to have interfered with NE trending folds to produce the domes and basins.

Drive back to Falls Creek, either by turning around here, or driving on to a T-intersection and turning right to follow the McKay Road back to Falls Creek. Then continue north towards Mt Beauty. Most of the reasonably fresh road cuttings on this route are in East Kiewa Granodiorite.

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Stop 4-10. MGA 519490-5929560. Kiewa River East Branch below Clover Dam. Park on the right just before Big River Track tumoff, next to a pile of boulders and walk down the Big River Track to the Kiewa River East Branch. The outcrops are upstream, between here and the dam wall. Good fresh creek exposures of migmatite and gneiss, cut by dykes of diorite and leucogranite, can be seen here. The migmatite is well layered (Fig. 2-44), with melanosomes rich in biotite and sillimanite, and leucosomes mainly of quartz and feldspar. In situ partial melting is indicated by biotite-rich selvedges around leucosomes, formed by the differentiation of the melt component from the more refractory biotite+sillimanite component. Some boulders of laminated psammitic gneiss in the creek have contorted polyclinal folds indicative of high temperature deformation (Fig. 2-45). Also, several sinistral shear zones striking SE cut the gneissic layering. One of these has a fine-grained , weakly layered leucogranite dyke intruding along it.

Figure 2-44. Stop 4-10. Boulder of well-layered migmatite cut by a dyke of Cobungra Granite at the bottom. The granite merges with the S2 layering and also cuts across it, suggesting it was present as melt during and after the D2 deformation. Pen for scale.

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I I A non-foliated biotite diorite dyke about 5 m wide cuts the migmatite with sharp chilled margins, indicating it post-dates the regional metamorphism and deformation. The unusual chilled margins are fine-grained, flow-banded and have sharp contacts with the coarse-grained interior of the dyke.

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63 These outcrops demonstrate the presence of melt at various stages of the deformation history of these mid-crustal rocks, with locally generated magma forming during and after the earliest deformations (Dl and D2) in the Early Silurian, and more exotic intermediate magma probably in the Early Devonian.

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Figure 2-45. Stop 4-10. A block of psammitic gneiss showing the lamination (probably S2 ) that is typical of this rock type. The lamination is folded into disharmonic polyclinal folds, and there are nebulous bands of fine-grained granite ramifying through the rock.

Walk back to the road and drive north to Mt Beauty.

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Wednesday February 8: Mt Beauty to M·elbourne Kiewa Shear Zone (dextral strike-slip), Kancoona Shear Zone (dextral strike-slip overprinted by sinistral strike-slip and contact metamorphism). The first 4 stops examine the Kiewa Shear Zone, a broad zone of mylonite and foliated granite that extends about 150 km in Victoria and continues north into NSW. It is one of the largest shear zones in the Lachlan Fold Belt, typically 1.5 - 2 km wide. It is a dextral strike-slip structure that was active in the Siluro-Devonian, with localised sinistral reactivation in the Middle Devonian (Morand & Gray 1991). Drive north from Mt Beauty along the Kie wa Valley Highway.

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Stop 5-1. MGA 512800-5937410. Cutting on Kiewa Valley Highway. Opposite Mt Bogong lookout. Park at the lookout car park on the right (east) side of the road. The cutting is in weathered ultramylonite of the Kiewa Shear Zone. One main fabric is present, subvertical and striking north. The rock appears to be a fine-grained schist, but a thin section from here shows it is ultramylonite consisting of quartz, mica and feldspar. The oriented thin section shows evidence of early dextral shearing followed by sinistral shearing (Fig. 2-46). Mica fish have dextral shapes, but feldspar porphyroclasts have sinistral shapes, while the matrix shows both dextral and sinistral fabrics. The protolith was probably gneiss and migmatite.

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Figure 2-46. Stop 5-2. Oriented thin section of ultrarnylonite from Kiewa Shear Zone at Stop 5-1, looking down. On the left a feldspar porphyroclast (F) shows sinistral shear. On the right a muscovite fish (M) shows dextral shear, but is deformed by kinks generated by sinistral reactivation. Photo is 4 mm wide. Plane polars.

Drive north along the Kiewa Valley Highway and tum off to the right onto Redbank-Mongans Road.

Stop 5-2. MGA 510550-5946230. Cutting on Redbank-Mongans Road. Park on the left (west) side at the first opportunity after the cutting. These road cuttings are in mylonitic granite within the Kiewa Shear Zone. The cuttings along here show various granitic phases, including leucocratic layers and more biotite-rich layers with

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65 feldspar porphyroclasts. One strong fabric/layering is present, but dextral shear is evident in places where C surfaces are developed. On the hill just to the north are outcrops of foliated Dederang Granite, but the road cuttings may include bands of mylonitic gneiss that have been caught up in the shear zone. Outcrops in the adjacent Kiewa River are reasonably homogeneous mylonitic Dederang Granite with dextral S-C fabrics. The Kiewa Shear Zone in this area follows the Kiewa River valley in a northerly direction. It has high-grade gneiss and migmatite on both sides, and is over one kilometre wide. The Dederang Granite lies along the shear zone for 30 km (Fig. 2-48), and appears to have intruded before shearing, being stretched out in a dextral manner along the shear zone, but extending out of the shear zone in the NW and SE. There are no radiometric dates on the granite. Continue north along Redbank-Mongans Road, which becomes Mullagong Road after Mongans Bridge.

Stop 5-3. MGA 508240-5952100. Cutting on Mullagong Road. Cutting in mylonitic Dederang Granite in the Kiewa Shear Zone, showing dextral shear. The main mylonitic fabric Sm strikes 155° and dips steeply east. C surfaces strike 175° and also dip steeply east. The hills on the east side of the road have outcrops of foliated Dederang Granite (Fig. 2-47) and schistose mylonite (possibly derived from gneiss adjacent to the granite). Much of the Kiewa Shear Zone in the lower Kiewa Valley is covered by alluvium and colluvium, and most of the outcrops are in the more resistant Dederang Granite.

Figure 2-47. Oriented thin section, looking down, of mylonitic Dederang Granite from 2 km north of Stop 53. S-C foliations indicate dextral shearing. Quartz is recrystallised, fine-grained metamorphic micas have grown along the foliations, and feldspar porphyroclasts have rounded asymmetric shapes. Crossed polars. Width of photo is 4 mm.

Continue north along Mullagong Road, which becomes Gundowring Road after Keegans Lane.

Stop 5-4. MGA 506200-5967050. Cutting on Gundowring Road. Park on left (west) side of road at a long cutting 7.3 km north of Keegans Lane, but don't park on exposed rock here. The road cutting is in mylonite of the Kiewa Shear Zone. There are good pavement exposures on the ground on the left side of the road, where fine-grained mylonite shows dextral S-C fabrics, mylonitic layering and cr porphyroclasts indicating dextral shearing (Fig. 2-50). This mylonite was probably derived from migmatite and gneiss.

I I 66 480000

490000

485000

495000

500000

505000

510000

032 Nc1 c1

i.,,"'

i.,,

G172

Qa2 0c1Nc1 Oc1 Oap

I.,,...

Nc4

Oc1

Nc1 N~

Oa1

g ~ .,,

Qa1 0c, Oc1

Nc1

G183

Oc1 Nc1 Nc1

I.,, :I:

oap

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Nc1 Nc1

i.,,

c1 C1

Sos Nc4

oap • Barwidgu Creek

i.,,

Nc4

Nc1 0

.,,"'~

oap

ac,

Gt77a G'77a Nc4 G177a

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01 1

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• G

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ac,

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485000

490000

495000

500000

505000

510000

Figure 2-48. Geological map of part of the Kancoona and Kiewa shear zones, showing stops 5-2 to 5-6. The Yackandandah Granite (G177) is offset sinistrally by the Kancoona Shear Zone. The outer phase (G 177a) is coarse-grained and porphyritic, the inner phase (G 177b) is fine-grained and equigranular. Bold lines are faults, cross-hatch patterns are shear zones. Grid spacing is 5 km. Qa1, Qa2 , Na - alluvium Qc1 , Qc4, Nc1, Nc4 - colluvium Nws - Shepparton Formation Pxo - Boorhaman Conglomerate G194 - Morilla Granite G195 - Beechworth Granite G176 - Baranduda Granite G177 - Yackandandah Granite G180 - Kergunyah Granite G 183 - Mount Stanley Granite G 169 - Dederang Granite G 172 - Yabba Granite G161 - Mount Buffalo Granite G549 - Cobungra Granite Soc - unnamed cordierite granite Som - migmatite Sog - gneiss Sos - schist Oap - Pinnak Sandstone Blue stipple - contact aureole

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67 480000

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490000

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500000

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..,,I

..,..,,_._

.,,

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.,,"'

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....__-=-.,.___,,......,"'-'~,._.a;a.........LL~....-,,;:...mii:.IB:::JJ!:..!.au...a......,1i.aJ~~"2'1~c..:JLmi..lll"2~ 480000

485000

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500000

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510000

Figure 2-49. Total magnetic intensity image overlain by grey scale first vertical derivative image of the same area as Fig. 2-48 (red and white= highly magnetic, purple= non-magnetic). The inner part of the Yackandandah Granite has concentric magnetic zones, while the outer part is non-magnetic. Note that the inner magnetic zone is much larger than the inner fine-grained zone. The inner magnetic zones show less offset than the outer ones, indicating emplacement during sinistral shearing. Also note the elongate strongly magnetic bodies along the Kiewa Shear Zone: these are probably dykes or thin plutons of diorite, although no outcrops of strongly magnetic material have been found.

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Figure 2-50. Stop 5-4. S-C mylonite of the Kiewa Shear Zone, showing dextral shearing and o porphyroclasts of feldspar. C surfaces strike approximately north.

Several NE-striking sinistral kink bands cut the north-striking mylonitic fabric at a high angle (Fig. 2-51). They are consistent with N-S shortening, possibly coeval with the E-W S20 cleavage in the Tabberabbera Zone.

Figure 2-51. Stop 5-4. Sinistral kink bands cutting the mylonitic layering.

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69 Turn around and drive back to Keegans Lane, turn right there and cross the Kiewa River. Turn left at the Kiewa Valley Highway. After 4.6 km take a right turn onto Running Creek Road. This becomes Happy Valley Road at Kancoona, where Kancoona South Road goes off to the left. Continue along Happy Valley Road up to Kancoona Gap. The next two stops are in the Kancoona Shear Zone, a Siluro-Devonian dextral shear zone that was reactivated sinistrally in the Middle Devonian Tabberabberan Orogeny (Morand & Gray 1991 ). It forms the boundary between the Tabberabbera Zone and the Omeo Zone.

Stop 5-5. MGA 497260-5954200. Kancoona Gap on Happy Valley Road. Parking area on left. This weathered cutting in the Kancoona Shear Zone exposes mylonitised schist that was contact metamorphosed during sinistral reactivation in the Middle Devonian. It is also in the Yackandandah Granite contact aureole. This granite sits astride the Kancoona Shear Zone, and was emplaced during sinistral shearing in the Middle Devonian. K-Ar biotite ages from undeformed parts of the pluton are 391±7 Ma and 392±7 Ma (McKenzie et al. 1984). Foster et al. (1999) recorded an Ar 39 -Ar40 age of 383±3 Ma on biotite from mylonitic granite within the Kancoona Shear Zone. The igneous biotite in this sample is marginally altered to metamorphic biotite, sphene and opaques, so the Ar-Ar date is probably the age of shearing. This date overlaps with the igneous dates of McKenzie et al. (1984), indicating syn-shearing emplacement of the Yackandandah Granite. Continue along Happy Valley Road for about 1 km.

Stop 5-6. MGA 496820-5954950. Cutting on Happy Valley Road. Room for parking on the left (west) . Here we can see a contact metamorphosed mylonite of the Kancoona Shear Zone; it is schistose with retrogressed cordierite. In thin section the rock is very messy, with a relic poorly defined schistosity and retrogressed cordierite porphyroblasts, as well as much muscovite overgrowing the schistosity. This rock is interpreted as being deformed and contact metamorphosed by syntectonic emplacement of the Yackandandah Granite during sinistral reactivation of the Kancoona Shear Zone in the Middle Devonian. The granite is only a few metres away (unexposed) to the west. A small sinistral shear zone cuts the main schistosity, and may be part of the sinistral deformation. From here the concentrically zoned Yackandandah Granite and its aureole can be appreciated. The granite forms the cleared flat areas to the west (mostly covered by older colluvium - Nc4 on Fig. 2-48) and the forested hills to the northwest, while the aureole forms the ring of forested hills to the south and southwest. Magnetic images reveal concentric zones of alternating magnetic and non-magnetic granite within the pluton (Fig. 2-49). The inner (and presumably younger) zones show less offset along the Kancoona Shear Zone than the outer zones of the granite, suggesting emplacement during shearing, with the older parts of the granite accumulating more offset than the younger parts. Where the Kancoona Shear Zone cuts the granite, the deformation is mainly ductile with mylonite and ultramylonite developed, showing sinistral strike-slip shearing (Fig. 2-52), although cataclasite is also locally developed (VandenBerg et al. 2003).

Figure 2-52. Oriented thin section , looking down, of mylonitic Yackandandah Granite from about 4 km NW of Stop 5-6. Feldspars show bookshelf gliding consist,ent with sinistral shearing, with individual fragments showing dextral displacement relative to each other. Ouartz forms ribbons defining the mylonitic foliation along with tiny aligned metamorphic micas, and igneous biotite is deformed into elongate brown grains. Crossed polars. Photo width 4 mm.

Continue along Happy Valley Road into Myrtleford, thence back to Melbourne via the Hume Freeway.

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REFERENCES Beavis, F.C., 1962. The geology of the Kiewa area. Proceedings of the Royal Society of Victoria. 75, 349-410.

Birch W. D. ed. 2003. Geology of Victoria. Geological Society of Australia Special Publication 23. Geological Society of Australia (Victoria Division).

Cawood, P.A., 2005. Terra Australia Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic. Earth Science Reviews 69 (~). 249-279. Cayley R. A., 2011. Exotic crustal block accretion to the eastern Gondwanaland margin in the Late Cambrian-Tasmania, the Selwyn Block, and implications for the Cambrian-Silurian evolution of the Ross, Delamerian, and Lachlan orogens. Gondwana Research, 19, 628 - 649. Cayley, R. A., Korsch, R.J. , Moore, D.H. , Costelloe, R.D., Nakamura, A., Willman, C.E., Rawling, T.J., Morand, V.J., Skladzien, P.B. & O' Shea, P.B., 2011. Crustal architecture of central Victoria: Results from the 2006 deep crustal reflection seismic survey. Australian Journal of Earth Sciences, 58, 113 - 156. Cayley, R. A., Musgrave, R, & Preiss, W., 2012. see 2012 SGTSG Abstracts Volume. Cayley RA., Taylor D.H., VandenBerg A. H. M. & Moore D. H. 2002. Proterozoic-Early Palaeozoic rocks and the Tyennan Orogeny in central Victoria: the Selwyn Block and its tectonic implications. Australian Journal of Earth Sciences 49, 225-254. Collins, W.J. & Vernon, R.H., 1992. Palaeozoic arc growth, deformation and migration across the Lachlan Fold Belt, southeastern Australia. Tectonophysics 214, 381 - 400. Coney, P. J. 1992. The Lachlan belt of eastern Australia and Circum-Pacific tectonic evolution. In: Fergusson C. L. & Glen R. A. eds. The Palaeozoic Eastern Margin of Gondwanaland: Tectonics of the Lach/an Fold Belt, Southeastern Australia and Related Orogens, Tectonophysics 214, 1 - 25. Coney, P.J., Edwards, A., Hine, R., Morrison, F., Windrim, D., 1990. The regional tectonics of the Tasman orogenic system, eastern Australia. Journal of Structural Geology 12, 519-543. Crawford, A. J., Cameron, W. E. & Keays, R. R. 1984. The association boninite-low-Ti andesite-tholeiite in the Heathcote Greenstone Belt, Victoria: ensimatic setting for the Early Lachlan Fold belt. Australian Journal of Earth Sciences 31, 161-177. Crawford A. J. & Keays R.R. 1978. Cambrian greenstone belts in Victoria: Marginal seacrust slices in the Lachlan Fold Belt of southeastern Australia. Earth and Planetary Science Letters 41, 197-208. Fagan, R.K., 1979. Deformation, metamorphism and anatexis of an Early Palaeozoic flysch sequence in northeastern Victoria. Ph.D. Thesis, University of New England, Armidale (unpubl.). Fanning C.M. & Morand V.J. 2002. Results of some SHRIMP U/Pb zircon dating of rocks from Victoria. Geological Survey of Victoria, Technical Record 2002/1.

I I 72 Fergusson C.L. 1987. Early Palaeozoic back-arc deformation in the Lachlan Fold Belt, southeastern Australia: implications for terrane translations in eastern Gondwanaland. In Leitch, E.C. & Scheibner E. (eds), Terrane Accretion and Orogenic belts. American Geophysical Union, Geodynamics Series 19, 39-56.

Foster D. A., Gray D.R. & Bucher M. 1999. Chronology of deformation within the turbiditedominated Lachlan Orogen: implications for the tectonic evolution of eastern Australia and Gondwana. Tectonics 18, 452-485.

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Glen R. A. 1992. Thrust, extensional and strike-slip tectonics in an evol_ving Palaeozoic orogena structural synthesis of the Lachlan Orogen of southeastern Australia. Tectonophysics 214, 341380.

Fergusson, C. L. 1998. Cambrian-Silurian oceanic rocks, upper Howqua River, eastern Victoria: tectonic implications. Australian Journal of Earth Sciences 45, 633-644. Fergusson C. L., Gray D. R. & Cas R. A. F. 1986. Overthrust terranes in the Lachlan Fold Belt, southeastern Australia. Geology 14, 519-522.

Glen R. A., Crawford A. J., Percival I. G. & Barron L. M. 2007. Early Ordovician development of the Macquarie Arc, Lachlan Orogen. New South Wales. Australian Journal of Earth Sciences 54, 167-179. Gray, D. R. 1997. Tectonics of the southeastern Australian Lachlan fold belt: Structural and thermal aspects. In: Burg J.P. & Ford M. eds. Orogeny through Time. Geological Society of London Special Publication 121, 149-177. Gray D. R. & Foster D. A. 2004. Tectonic evolution of the Lachlan Orogen, southeast Australia: historical review, data synthesis and modem perspectives. Australian Journal of Earth Sciences 51 , 773-817. Gray, D.R. & Foster, D. A. 1998. Character and kinematics of faults within the turbiditedominated Lachlan Orogen: implications for tectonic evolution of eastern Australia. Journal of Structural Geology 20, 1691-1720. Hallett M., Vassallo J., Glen R. & Webster S. 2005. Murray- Riverina region: an interpretation of bedrock Palaeozoic geology based on geophysical data. Quarterly Notes of the Geological Survey of New South Wales 118, 1-16. Hendrickx, M. A., I 999. The 1-S line: a thrust sheet boundary in eastern Victoria. Geological Society of Australia Abstracts 53, I 0 1-102. McKenzie D.A. , Nott R.J. & Bolger P.F. 1984. Radiometric age determinations. Geological Survey of Victoria Report 74. Department of Minerals & Energy, Victoria.

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McLean M.A., Morand V.J. & Cayley R.A. 2010. Gravity and magnetic modelling of crustal structure in central Victoria: what lies under the Melbourne Zone? Australian Journal of Earth Sciences 57, 153-173.

Miller J.McL. & Gray D.R. 1997. Subduction related deformation and the Narooma anticlinorium, eastern Lachlan fold belt. Australian Journal of Earth Sciences 44, 237-251.

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73 Miller, J.McL., Phillips, D., Wilson, C.J.L. & Dugdale, L.J., 2005. Evolution of a reworked orogenic zone: the boundary between the Delarnerian and Lachlan Fold Belts, southeastern Australia. Australian Journal of Earth Sciences, 52(6), 921-940. Morand V.J. 1990. Low-pressure regional metamorphism in the Omeo Metamorphic Complex, Victoria, Australia. Journal of Metamorphic Geology 8, 1-12. Morand V.J. & Fanning C.M. 2009. SHRIMP zircon dating results for various rocks from Victoria, 2009. GeoScience Victoria Technical Record 2009/2. Morand V.J. & Gray D.R. 1991. Major fault zones related to the Omeo Metamorphic Complex, northeast Victoria. Australian Journal of Earth Sciences 38, 203-221. Morand V.J., Simons B.A., Taylor D.H., Cayley R.A., Maher S., Wohlt K.E. & Radojkovic AM. 2005. Bogong I: I 00 000 map area geological report. Geological Survey of Victoria Report 125. Offler R., McKnight S. & Morand V. 1998. Tectono-thermal history of the western Lachlan Fold Belt, Australia-insights from white mica studies. Journal of Metamorphic Geology 16, 531540. O'Halloran, G.J. & Cas, R.A.F, 1995. Sedimentary responses to deformation from the Late Devonian of the Mansfield Basin, east-central Victoria. Australian Journal of Earth Sciences 42, 581-596. Percival I. G. & Glen R. A. 2007. Ordovician to earliest Silurian history of the Macquarie Arc, Lachlan Orogen, New South Wales. Australian Journal of Earth Sciences 54, 143-165. Rossiter A.G. 2003. Granitic rocks of the Lachlan Fold Belt in Victoria. In W.D. Birch (ed.) Geology of Victoria, pp. 217-237, Geological Society of Australia Special Publication 23. Geological Society of Australia (Victoria Division).

Scheibner, E. & Basden, H. (ed.), 1996. Geology of New South Wales - Synthesis. Volume 1, Structural Framework, Geological Survey of new South Wales Memoir Geology 13(1)

Scott, R., 1985. The Kiewa Fault, and its role in the evolution of the western margin of the Omeo Metamorphic Belt. B.Sc. (Hons) thesis, Monash University, Melbourne (unpubl.).

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Taylor, D. H. & Cayley, R. A. 2000. Character and kinematics of faults within the turbiditedominated Lachlan Orogen: implications for tectonic evolution of eastern Australia. Discussion. Journal of Structural Geology 22, 523-528.

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Turner S., Haines P., Foster D. A., Powell R. , Sandiford M. & Offler R. 2009. Did the Delarnerian Orogeny start in the Neoproterozoic? Journal of Geology 117, 575-583. VandenBerg A.H.M., Cayley, R.A., Willman C.E., Morand V.J., Seymon AR., Osborne C.R., Taylor D.H., Haydon S.J., McLean M., Quinn C., Jackson P. & Sandford AC. 2006. WalhallaWoods Point-Tallangallook special map area geological report. Geological Survey of Victoria Report 127. VandenBerg, A.H.M., Hendrickx, M.A., Willman, C.E., Magart, A.P.M., Simons, B.A. & Ryan, S.M., I 998. Benambra I: 100 000 map area geological report. Geological Survey Report 114.

74 VandenBERG, A. H. M. , Willman, C. E., Hendrickx, M.A., Bush, M. D. & Sands, B. 1995. The geology and prospectivity of the 1993 Mount Wellington Airborne Survey area. Victorian Initiative for Minerals and Petroleum Report 2. Department of Agriculture, Energy and Minerals . VandenBerg, A. H. M., Willman, C. E., Maher, S., Simons, B. A., Cayley, R. A., Taylor, D. H., Morand, V. J., Moore, D. H. & Radojkovic, A. 2000. The Tasman Fold Belt System in Victoria. Geological Survey of Victoria Special Publication. VandenBerg A.H.M., Willman C.E., Morand V.J., McHaffie I.W. , Simons B.A., Quinn C. & Westcott A.L. 2003. Buffalo 1:100 000 Geological Report. Geological Survey of Victoria Report 124. Watson J.M. & Gray D.R. 2001. Character, extent and significance of broken formation for the Tabberabbera Zone, central Lachlan Orogen. Australian Journal of Earth Sciences 48, 943-954. Willman C.E., Cayley R. A., VandenBerg A.H.M., Haydon S.J., Osborne C.R., Seymon A.R. & Thom J.L. 2005. Dargo l: l 00 000 map area report. Geological Survey of Victoria Report 126. Willman C.E., Morand V.J., Hendrickx M.A., VandenBerg A.H.M., Haydon S.U. & Carney C. 1999. Omeo 1:100 000 map geological report. Geological Survey of Victoria Report 118. Willman C.E., Quinn C., VandenBerg A.H.M., Morand V.J., Simons B.A. & Edwards J. 2003. Dandongadale 1:50 000 geological map. Geological Survey of Victoria. Willman C. E., VandenBerg A. H. M. & Morand V. J. 2002. Evolution of the southeastern Lachlan Fold Belt in Victoria. Australian Journal of Earth Sciences 49, 271-289.

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Appendix 1: Legends for Figs 2-1, 2-2, 2-7, 2-8 and 2-17.

The colours in this table are a guide only to the units shown on the geological maps, and a visual aid in grouping the units into either stratigraphic or time divisions. The tables are divided into Mesozoic and Cainozoic cover rocks, Howitt Province consisting of Avon Supergroup and Tolmie Igneous Complex (overlap sequence deposited on top of the boundary between the Melbourne and Tabberabbera zones), Melbourne Zone strata, Tabberabbera and Omeo zones strata, Omeo Metamorphic Complex, and intrusions.

Mesozoic and Cainozoic cover rocks Ma code Qa1 , Qa2 , Qb, 011 , 012, Nws, Nx·, Nxo Qc1 , Qc4, Qc5, Qc7, Nc1 , Nc4 Nlh

Nur Nuf Nun Nul Nuc -Pu , -Puw, -Pu· -Pa

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Unit alluvium and lake deposits

A e Pliocene - Quaternary

colluvium

Pliocene - Quaternary

Haunted Hill Formation fluvial elastics

basalt flows

Howitt Province: Middle Devonian-Carboniferous overlap sequence Dam

Dab

Daw

Dad

Group Mansfield Group (fluvial and lacustrine elastics)

Formation

Age Late Devonian-Early Carboniferous Late Devonian-Early Carboniferous Late Devonian Late Devonian Late Devonian

Dams

Snowy Plains Formation

Damk

Mount Kent Conglomerate

Dawb Dawh Dawo Dawr

Bindaree Formation Highton Volcanics Howitt Spur Formation Refrigerator Gap Dacite late Middle Devonian

Late Devonian Late Devonian Late Devonian Late Devonian Dad

Dadk Dadm Dade

Kevington Creek Formation Moroka Glen Formation Callemondah Conglomerate

late Middle Devonian late Middle Devonian late Middle Devonian Late Devon ian

Ott Dtr Dth Dtw Dtc Dtb

Toombullup IQnimbrite Ryans Creek IQnimbrite Hollands Creek Rhyolite Mount Warrick Rhyolite Cobbler Rhyol ite Bennies Formation

Late Devonian Late Devonian Late Devonian Late Devonian Late Devonian Late Devonian

Y-F

felsic dykes

Late Devonian

Basalt flows and sills Wellington Volcanic Group (subaerial silicic volcanics)

Delatite Group (fluvial elastics)

Tolmie Igneous Complex (silicic cauldron volcanics)

Group Walhalla Group (deep marine elastics)

Formation

Dnm Dnn One Dnw

Age Early Devonian

Montys Hut Siltstone Norton Gully Sandstone Easts Lookout Formation Wh ite Star Formation

Early Devonian Early Devonian Early Devonian Early Devonian

Jordan River Group (deep marine

~ I

Oxe

Mount Easton Shale (black shale)

: D

n m :

-Cl

..i

...

Group

Wilson Creek Shale

Boola Formation Wurutwun Fonnation Whitelaw Slllltone Srnclair VIIIIIIV Sandstone Bulluna Sillslone Murderers HUI . McAdam Sandstone Creak--·n Creek Lazarini SIIIBtone

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Early Silurian ar r, Devonian lll'YDevonian BI '/ Devonian

clastlc8)

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Melbourne Zone Palaeozoic strata Dn

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81 I/Devonian :81 ~ tavnnian

Late Late

,..i....

,...,

II Y SIiurian 81 "Silurian

mvSllurian Ear YSilUrian Ear vSilurlan

Late Ordovician "

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Tabberabbera and Omeo zones Palaeozoic strata Group St

Dfb

Formation Besford lanimbrite

Stl

Blackfellows Flat Conglomerate

Sxt

Mitta Mitta Rhyolite

Mount Tambo Group (fluvial elastics and silicic volcanics)

Devonian Sw

Wombat Creek Group (shallow marine to fluvial elastics and limestone) Yalmy Group (deep marine elastics)

Svn

Tonaaro Formation

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Earlv Silurian Early Silurian

Cobbannah Group (deep marine elastics)

Bendoc Group (deep marine black shale and elastics)

Late Ordovician

Adaminaby Group (deep marine turbidites and chert)

Late Cambrian Middle Ordovician Early - Middle Ordovician Late Cambrian Early Ordivician

-Ci

-cxv

Oap

Pinnak Sandstone

Oah

Howqua Shale

Lickhole Volcanic Group (tholeiitic basalt, boninite and seroentinitel lllltmlOrphoNd maflc

Cambrian

-· --·

Omeo Metamorphic Complex

Late Silurian Late Silurian

Early Silurian

Unit

Aae Earlv Devonian Late Silurian-Early Devonian Late Silurian-Early

and sillimanite-K-telds

e Soe G549

Granite

Intrusive rocks Mao code Ywp G236 G237 G239 G224 G216

Unit Woods Point Dyke Swarm Baw Baw Granodiorite Taniil Granodiorite Tynona Granite Buxton Granodiorite Bariara Granite

Late Devonian Late Devonian Late Devonian Late Devonian Late Devonian Late Devonian

G184 G186

Mount Stirling Granodiorite Mirimbah Granodiorite Yackandandah Granite oorohvritic chase Y ckandndah G it ; h •

Middle Devonian Middle Devonian Middle Devonian Middl D a

G1na

G1nb

Aae

Dfs Y-ov-af G106 G113 G114 G116 G150 G151 G152a

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G168 G166

Sloan Knob Microoranite Quartz-feldsoar oorohvrv dvke Charlestown Tonalite Post Office Granite Analers Rest Granite Lower Tableland Granite Simmonds Gao Granite East Kiewa Granodiorite Big Hill Quartz Diorite - quartz diorite phase Bia Hill Quartz Diorite - tonalite oahse Niaaerheads Granodiorite Mount Anaus Granodiorite Mount Buffalo Granite Mount Emu Granodiorite Carruno Tonalite Dinner Plain Tonalite High Tops Tonalite Jim and Jack Tonalite Bingo Munjie Quartz Diorite Munaobabba Tonalite Drv Hill Granodiorite Hallets Road Tonalite Silver Flat Porphyries Horsehair Creek Tonalite Bundara Muniie Quartz Diorite Dry Gully Granodiorite Hinno Munjie Granite Ludrik Muniie Granite Penderlea Granite Connlevs Track Granodiorite Pretty Valley Tonalite Bundara Tonalite Wollonaby Granite

Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Late Silurian - Early Devonian Late Silurian - Early Devonian Late Silurian - Early Devonian Late Silurian - Early Devonian Late Silurian - Early Devonian Silurian - Early Devonian Silurian - Early Devonian Silurian - Early Devonian mid-Silurian mid-Silurian mid-Silurian mid-Silurian mid-Silurian mid-Silurian Early-Late Silurian

G119

Mountain Maid Granite

Early Silurian

G111 G115 G156 G170

Mount Wills Granite Taylors Crossina Tonalite Timms Sour Leucoaranite Booraunvah Granite

Silurian Silurian Silurian Silurian

G152b G153 G160 G161 G162 G164 G167 G189 G548 G81 G143 G147 G148 G535 G462 G467 G468 GB0

G82 G83 G117

G154

Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian Early Devonian

Early Devonian

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