Geological Society of Australia
ABSTRACTS Number 107
26**^ Victorian Universities Earth and Environmental Sciences Conference
The University of Melbourne
October 2013
October 2013 Geological Society of Australia Abstracts Volume 107
Victorian Universities Earth and Environmental Sciences Conference
Editors: Toni Cox Caitlin Gionfriddo Kieran lies Ing Tzu-Ying Kuo Song Lu Annie Ngoc Nguyen Catherine Wheller
ISSN: 0729 01IX © Geological Society of Australia Incorporated, 2013
Recommended citation: Cox, T., Gionfriddo, C., lies, K., Tzu-Ying Kuo, I., Lu, S., Nguyen, N., and Wheller C. (eds), 2013, 26'^ Victorian Universities Earth and Environmental Sciences Conference. Geological Society of Australia Abstracts No. 107, 32p.
Copies of this publication may be obtained from: Geological Society of Australia Incorporated Suite 61, 104 Bathurst Street Sydney, NSW 2000 Australia
Foreword The University of Melbourne School of Earth Sciences is proud to host the Victorian Universities Earth and Environmental Sciences Conference (VUEESC) in October 2013. The VUEESC is an annual event that allows Honours, Masters, and Ph.D. students to present their research to the local scientific community, industry representatives, and other students in their fields. Every year the conference provides a valuable forum for students to gain experience in communicating their research, to promote their talents to future employers, and to facilitate collaboration between universities. The conference also aims to promote earth and environmental science research to the wider community. This year the VUEESC features oral and poster presentations under several different themes, showcasing a wide variety of research. We are grateful to our sponsors for making this event possible. Thanks, The 2013 VUEESC Committee
Sponsors This event is made possible by:
The Geological Society of Australia The Victorian Universities Earth & Environmental Sciences Conference Committee acknowledges the participation and support of the following sponsors:
Gold Sponsors
rUF UNIVFRSI FY OF
MELBOURNE The University of Melbourne School of Earth Sciences
MONASF1 University
Science
Monash University School of Geosciences
PESA The Petroleum Exploration Society of Australia
VICTORIA DIVISION
/ A MANDALAY RESOURCES
Committee Members Convenor Caitlin Gionfriddo Volume Editors Toni Cox Kieran lies Ing Tzu-Ying Kuo Song Lu Annie Ngoc Nguyen Catherine Wheller Sponsorship Matt Consolmagno Keith Dimech Ash Hood Promotion & Website Max Lechte Angus Keillar Catering Simone de Morton
2013 VUEESC Program 8:00
Registration opens
9:00
Welcome and opening remarks: A/Prof David Phillips
9:10
Page
Keynote: A/Prof Malcolm Wallace Volcanology/Geochemistry/Geochronology
Chair: Kieran lies
9:30
Modelling progressive melt extraction during partial melting of granitic sources: a calculated phase equilibria approach -Gordon Webb
9:45
New insights into the geochemistry of early Cenozoic volcanism in Victoria, Australia-T.J. Chang
7
10:00
Geochemistry and geochronology of the Aileu formation, Timor-Leste-Tamarah King
17
10:15
Apatite fission track anomaly within the Archean-Proterozoic Gawler Craton: The thermal record of a paleoaquifer system? -Samuel Boone
4
10:30
Using Thermal Remanent Magnetisation (TRM) to understand emplacement temperatures of block and ash flow and debris flow deposits: Lava dome eruption at Mount Unzen Volcano, Japan -Dan Uehara
30
10:45
The role of steady-state thermal models in a young volcanic province: The Newer Volcanics Province, Southeast Australia -Ben Mather
23
11:00
Morning Tea (Poster session run concurrently) (30 mins)
11:30
Mechanism behind the occurrence of secondary diurnal peak in rainfall over Darwin, Australia Surendra Rauniyar
11:45
Relationships between tropical cyclones and climate in several general circulation models Michael Horn
16
12:00
Nonlinear Indian Ocean dipole feedbacks and their response to a warming climate -Benjamin Ng
24
12:15
Farm dam development trends in Western Victoria in relation to climate and land-use change Rakhshan Roohi
27
12:30
Lunch Break (Poster session run concurrently) (45 mins)
13:15
Variability and geodiversity analysis of geological maps -Lachlan Grose
13:30
Structural evolution and controls on the North Portia Cu-Au-Mo deposit, Curnamona Province, South Australia -Sheree Armistead
3
13:45
Structural and kinematic evolution of the Indi-long plain fault and Tumut trough -Karen Martins
22
14:00
Controls on Au mineralisation within the Kalpini Au Deposit, Yilgard Craton, Western Australia Kenneth Bush
6
14:15
Geodynamic models of Tethyan style ophiolite obduction -Sarah Edwards
10
14:30
The significance of Tournaisian Tectonism in the Dublin Basin: Implications for basin evolution and zinc-lead mineralization in the Irish Midlands -Simone de Morton
9
14:45
Afternoon Tea (Poster session run concurrently) 30 mins)
Meteorology/Climate Science
Economic Geology/ Geodynamics/ Stratigraphy
Sedimentotogy/ Environmental Geoscience
32
Chair: Maxwell Lechte 26
Chair: Toni Cox 14
Chair: Annie Ngoc Nguyen
15:15
Holowilena ironstone: Insights into Neoproterozoic iron formation deposition -Maxwell Lechte
18
15:30
The formation of solution pipes on Cape Bridgewater, Western Victoria -Matej Lipar
20
15:45
Inland acid sulphate soil environments in the Corangamite region, South-Eastern Australia Fiona Glover
13
16:00
Trace metal mobility during mineral carbonation -Jessica Hamilton
15
16:15
Neutralisation of aluminium-rich acid mine drainage to form a magnetic sludge -Wendy Stanford
29
16:30
Judges deliberate
16:50
Awards and closing remarks
17:00
Conclusion of conference: Drinks and nibbles in the tea room
2013 VUEESC Poster Abstracts Poster Presentations: Running concurrently (Morning Tea, Lunch, and Afternoon Tea)
Page
Significant and episodic recharge in the Loddon River catchment, Victoria -Sanjeeva Manamperi
21
Comparison of the salt budget in paired catchments (pasture and tree plantation) in south-western Victoria -Fahmida Perveen
25
Application of alkalinity producing covers to waste rocks from Mt. Lyell copper mine, Western Tasmania Michael Sephton
28
Microbial geographical distribution in high organic carbon contained wetland in three aspects: Metabolic guilds, biodiversity, and communities similarity-V't;-C/7en Ling
19
Mercury cycling over the Southern Ocean during polar spring: Results from SIPEX II -Caitlin Gionfriddo
11
The influence of biotite/phlogopite dissolution on AMD neutralisation at the Brukunga Pyrite Mine, South Australia -Farah Ali
1
Peak oil and oil vulnerability: What are the implications for industrial agriculture and rural communities? With a case study based in the Southern Gulf region of Queensland -Donald Coventry
8
Controls on gold mineralisation at the Navachab gold deposit, Namibia: Application of the liquid bismuth collector model -Lachlan Urquhart
31
Provenance of the western Lachlan Orogen turbidites: "^^Ar/^^Ar step-heating of detrital muscovite Scarlett Blewett
5
Circumferential petrophysical thermal conductivity imaging -Anson Antriasian
2
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
THE INFLUENCE OF BIOTITE/PHLOGOPITE DISSOLUTION ON AMD NEUTRALISATION AT THE BRUKUNGA PYRITE MINE, SOUTH AUSTRALIA F, ALI\ J. Webb\ J. Taylor^ ^Environnnental Geoscience, La Trobe University, Melbourne ^EarthSystenns Ltd, Suite 17, 79-83 High Street, Kew, Melbourne, Victoria, Australia 3101
Brukunga Pyrite Mine is an abandoned pyrite mine in South Australia, 40 km NE of Adelaide. The mine was operational for 20 years and mined for pyrite and pyrrhotite within mica schists until 1972. As a result of mining the sulphide ore was exposed to the atmosphere, which caused acid mine drainage (AMD) production. A characteristic of the AMD at this site is the high magnesium levels (250 - 2000 ppm) found in surface water and groundwater. The AMD is collected in a central pond, which has magnesium concentrations of about 350 ppm, and treated using lime neutralisation which removes the heavy metals and reduces the magnesium concentrations, by approximately 325 ppm. Analysis of 38 surface water and groundwater samples, 14 waste rock samples and 3 tailings samples showed that the waste rock dumps are responsible for the abundance of Mg in the contaminated water through the attack on phlogopite and biotite, which are the only magnesiumbearing minerals in the waste rock and tailings. Dissolution of these minerals by the AMD releases not only magnesium, but also iron, potassium, aluminium and silica into solution. However, Fe, K and Si are being removed through acid releasing precipitation, which reduces the neutralising capacity of phlogopite and biotite dissolution. The sludge formed by neutralisation of the AMD at Brukunga is composed of gypsum, ettringite (Ca6Al2(S04)3(OH)i2.26H20) and amorphous ferric oxide-hydroxide. Ettringite precipitation has an added benefit since it has absorbed vanadium oxoanions into its structure. The sludge contains - 2 wt% magnesium, accounting for the reduction in Mg concentration of the water as it passes through the treatment plant. XPS analysis of the sludge Indicates that magnesium carbonate (magnesite) is present, and the treatment plant water is saturated with respect to this mineral. Key words: biotite, phlogopite, acid mine drainage, magnesium Email: f.ali@latrobe.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
CIRCUMFERENTIAL PETROPHYSICAL THERMAL CONDUCTIVITY IMAGING A, ANTRIASIAN\ D. Belton^ ^School of Earth Sciences, AGOS, The University of Melbourne, Parkville, Victoria, Australia A procedure has been developed to provide a surface thermal conductivity image of rock-core specimens. An already developed non-contact Thermal Conductivity Scanner (TCS) is used to make the measurements. The apparatus utilizes IR temperature sensors to detect an increase in surface temperature of a core specimen when heated by a moving optical heat source. The TCS is used in this procedure by moving an IR sensor and optical heater assembly along the axis of the core specimen and calculating for thermal conductivity on the millimeter scale based on the IR measurements; the core specimen is then rotated and the scanning is repeated every 10 degrees around the specimen, making for a total of 36 (or more) scans which are assembled and graphically represented to form a surface image of thermal conductivity. The overlay of thermal conductivity images with photographic images of the same specimen reveals a strong relation to visual lithologic structure, and also provides a furthering for the interpretation of visual features. Thermal conductivity structures are revealed during imaging that are not apparent from visual inspection of the rock, such as faulting, veining, and micro-mineralogical thermal conductivity anisotropy (possibly illuminating on stress history). Thermal conductivity measurement has application in Enhanced Geothermal System (EGS) resource exploration, where crustal heat flow measurement and temperature projections are achieved through application to Fourier's Law of heat conduction. Also, thermal conductivity measurement has application towards direct use geothermal heat pump applications and mining engineering. Keywords: thermal conductivity, geothermal, petrophysics E-mail: anson.antriasian@hotdryrocks.com
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
STRUCTURAL EVOLUTION AND CONTROLS ON THE NORTH PORTIA CU-AU-MO DEPOSIT, CURNAMONA PROVINCE, SOUTH AUSTRALIA S. ARMISTEAD\ P. Betts\ L. Ailleres\ R. Armit^ ^School of Geosciences, Monash University, Victoria 3800, Australia Iron oxide copper gold (lOCG) deposits are a valuable but poorly understood source of Cu and Au. The Curnamona Province that straddles the South Australia and New South Wales border is an emerging region of lOCG exploration interest, with several lOCG deposits already recognised. Within the Curnamona Province is the Benagerie Ridge Magnetic Complex (BRMC) which contains the North Portia Cu-Au-Mo deposit. We integrate detailed drillcore logging, petrophysics, petrology, 3D and 2D modelling, with high resolution aeromagnetic data to produce a detailed structural interpretation of the BRMC and North Portia deposit. A major control on Cu mineralisation in the Curnamona Province is the extensive regional redox boundary which separates reduced, lower magnetic units from upper non-magnetic units. The boundary is well represented at North Portia with the most significant Cu-Au-Mo mineralisation occurring at or proximal this redox boundary. Significant sulphide mineralisation also occurs along bedding parallel shear structures, which coupled with the redox boundary mineralisation supports a strong sedimentary control on Cu mineralisation at all scales. Due to pervasive iron oxide alteration throughout the North Portia sequence, it has previously been classified as an lOCG deposit. We propose a new deformation model for the BRMC which is consistent with the c. 1620-1590 Ma Olarian Orogeny. This framework involves the development of a Di early layer-parallel foliation (Si), D2 recumbent style folding, D3 upright folding, and several phases of late Olarian deformation. The overprinting of D2 structures during D3 has resulted in a type 2 interference pattern recognisable in aeromagnetic images. We propose that the Cu-Au-Mo mineralisation occurred syn to post Di before the onset of D2 recumbent folding. This suggests that Cu mineralisation in the North Portia deposit is associated with the earliest phase of the Olarian Orogeny, and is controlled predominantly by the redox boundary and layer-parallel structures. Key words: lOCG, structure, redox boundary, Olarian Orogeny, Curnamona Province, Benagerie Ridge E-mail address: sheree.armistead@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
APATITE FISSION TRACK ANOMALY WITHIN THE ARCHEAN-PROTEROZOIC GAWLER CRATON: THE THERMAL RECORD OF A PALEOAQUIFER SYSTEM? S. BOONE^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Apatite fission track thernnochronology results fronn basement samples from the Archean-Proterozoic Gawler Craton, South Australia, reveal a pronounced Cretaceous to Paleogene (-120-40 Ma) heating that is significantly younger than the Paleozoic (-400 Ma) exhumation of the craton recorded regionally. Overprinted samples exhibit shorter mean track lengths (MTL) (-11-11.5 nm) than the background samples (MTL of -12-12.5 pm), which experienced slow cooling from the partial annealing zone (60120 °C) during the Archean-Paleozoic before remaining at near-surface temperatures (20-40 °C) until the present day. By comparison, modeled thermal histories of overprinted samples suggest a more complex cooling history with reheating to maximum paleotemperatures of >120 in the Cretaceous. Overprinting patterns, lack of major fault structures in the region and neotectonic quiescence do not support a regional thermal event associated with reburial and later exhumation. However, the sporadic distribution of overprinted samples in close proximity to partially overprinted and nonoverprinted samples is consistent with reheating by hydrothermal fluids as the primary overprinting source. The most probable heat source that controlled this reheating event is the CretaceousPaleogene Eromanga Basin aquifer system, whose modern discharge margin (-400 km north of the study area) is marked by thermal mound springs that produce water with temperatures up to >100 °C. The widespread distribution of Eromanga Basin outliers suggests that this region was once covered by a more extensive blanket of these sediments. Removal of the overlying sediment due to erosion associated with a regional exhumation event during the Tertiary likely resulted in the cessation of the abnormal paleothermal regime, consequently cooling the basement rocks to modern surface temperatures. The onset of fast spreading in the Southern Ocean during the Paleogene and the resulting northward tilting of the Australian continent was the likely catalyst for the erosional event that removed the the overlying sedimentary cover. Key words: apatite fission track thermochronology, hydrothermal fluids, Gawler Craton, geothermal system, Eromanga Basin, Great Artesian Basin Email: samcboone@gmail.com
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
PROVENANCE OF THE WESTERN LACHLAN OROGEN TURBIDITES: "^^AR/^^AR STEP-HEATING OF DETRITAL MUSCOVITE S. C. J. BLEWETT^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia During the Late Cambrian to Early Devonian period, the Palaeo-Pacific margin of east Gondwana was inundated with large volumes of continentally-derived sedimentary detritus. Crustal shortening during the Lachlan Orogen accreted these turbidite sediments to the Australian craton, forming part of a 20,000 km long orogenic system along the Gondwanan margin. Previous provenance studies attributed the source of the western Lachlan Orogen turbidites to the Delamerian Orogen (utilizing detrital muscovite 40Ar/39Ar ages) or more distal Pan-African sources (based on detrital zircon U-Pb SHRIMP ages). In an effort to provide further constraints on the sediment source terranes, this study employed 40Ar/39Ar step-heating of detrital muscovite grains selected systematically from sandy turbidite units of the Stawell, Bendigo and Melbourne structural zones that comprise the western Lachlan Orogen. Detrital muscovite grains were extracted from a total of 7 turbidite samples. Step-heating of individual muscovite grains yielded broadly similar ages for each step. Low temperature steps were systematically younger than high temperature (fusion) ages, this is attributed to minor alterationinduced argon loss. These results demonstrate that the high temperature steps provide more accurate provenance ages for detrital muscovite and that the step-heating approach can reduce (or eliminate) the effects of alteration. The single-step total fusion ages reported in previous provenance studies may underestimate the age of detrital muscovite grains. All samples from the western Lachlan Orogen yielded a major age population peak at ca. 500-475 Ma, coinciding with detrital zircon populations from the same or similar stratigraphic units. These detrital muscovite ages are indistinguishable from cooling ages of Delamerian Orogen granites and associated metamorphosed host rocks. 40Ar/39Ar muscovite ages for Late Silurian and Early Devonian samples (Kilmore Siltstone and Cathedral Group) of the Melbourne Zone revealed Neoproterozoic ages (ca. 700 Ma) that have not been detected in any previous provenance study. The broad distribution of 40Ar/39Ar detrital muscovite ages for the Kilmore Siltstone (480-700 Ma) is likely to represent reworking of older detritus or mixing of multiple sources. Defining a primary source for the older age populations observed in the Kilmore Siltstone and Cathedral Group sediments of the Melbourne zone was made difficult by the paucity of detrital zircon studies and the lack of detrital muscovite studies in potential source areas such as the Benambran Terrane, east of the Melbourne Zone. The detrital muscovite age spectra recorded in the upper Melbourne Zone sediments cannot be related to a particular source terrane. Nevertheless, the Melbourne Zone turbidites show similarities with other sediments spanning eastern Gondwana suggesting they are the product of the erosion of reworked local and distal terranes. Key words: Lachlan Orogen, turbidites, detrital muscovite, "^^Ar/^^Ar, step-heating, provenance. Email: scarlett_blewett@hotmail.com
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
CONTROLS ON AU MINERALISATION WITHIN THE KALPINI AU DEPOSIT, YILGARN CRATON, WESTERN AUSTRALIA K. BUSH\ S.M Jowitt\ P. Durance^ ^School of Earth Science, Monash University, Melbourne, VIC 3800, Australia The Kalpini gold deposit is an orogenic lode-gold deposit within the Kurnalpi terrane in the Eastern Goldfields Superterrane of Western Australia and has a resource of 3.24 Mt of ore at 1.8 g/t Au. Here, we present the results of a combined geochemical, petrological, and stable isotope investigation of this deposit, and provide new insights into the controls of Au mineralisation in this area. Three suites were identified in the area, a low Zr and Fe dolerite unit (suite 1), a high Zr and low Fe andesite (suite 2) and a high Zr high Fe dolerite (suite 3). Mineralised contacts within the deposit are often associated with quartz-carbonate vein arrays and strong sericite alteration or 'bleaching' of the surrounding host rock. These contacts are variably mineralised, with gold concentrations (1-2 ppm) significantly higher than background levels located proximal to or within shear zones along the contacts between suites 1 and 2, although the higher gold concentrations within the deposit (5-59 ppm) are restricted to the contacts between suites 1 and 3. Sulphur, carbon and oxygen isotope data provide evidence of a single reduced auriferous fluid derived from a magmatic, metamorphic or potentially mixed magmaticmetamorphic source, with mineralisation occurring at temperatures of 310°C-450°C. The contacts between units most likely acted as preferential fluid conduits, although the differences in Au concentrations outlined above indicate that the location of fluid pathways were not the dominant control on the formation of the Kalpini Au deposit. Instead, the preferential location of Au mineralisation at the contacts between suites 1 and 3 suggests that the Fe-rich nature of the suite 3 dolerite controlled sulphidation and the precipitation of gold, leading to preferential Au enrichments along the sheared contacts between these two dolerite units. Key words: Yilgarn Craton, orogenic gold, whole-rock geochemistry, stable isotope. Email: Kenneth.Bush@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
NEW INSIGHTS INTO THE GEOCHEMISTRY OF EARLY CENOZOIC VOLCANISM IN VICTORIA, AUSTRALIA T-J. CHANG\ J. Hergt\ G. Holdgate\ M, Wallace\ D, Phillips^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia, 3010 The newly acquired geochemical data for the early Cenozoic volcanism in Victoria (resulting in the socalled 'Older Volcanics' province) reveals wide geochemical variations both locally and regionally. These rocks are dominated by alkali basalts and basanites, and all samples are reasonably fresh with typical mineral assemblages including olivine, clinopyroxene, and plagioclase, with or without nepheline. Mantle xenoliths have been observed in 4 samples. The MgO and Si02 contents range between 3.2-11.1 wt% and 41.1-52.1 wt% respectively. The wide range of magnesium numbers (3064) indicates that the magmas vary from near primitive to highly evolved in composition. Although trace element compositions broadly resemble those of modern OIB; in detail, mantle-normalised patterns show distinct differences between subprovinces. The transitions between subprovinces coincide with large-scale faults, indicating possible structural control over the magma chemistry. Ce/Pb and Nb/U ratios range between 11.4-33.3 and 23.8-60.9 respectively, with lower values reflecting the effects of crustal assimilation. Initial (0.70285-0.70507) and ^'^^Nd/^^'^Nd (0.512659-0.513021) ratios are corrected using new "^^Ar/^^Ar or ages. Isotopic compositions of the younger basalts (20-30Ma) form a distinct trend along the mantle array, whereas the older basalts (-40Ma) scatter around Bulk Silicate Earth. In Summary, these new observations reveal that most Pre-10Ma magmas experienced some degree of modification prior to eruption. The earliest period of volcanism in the Pre-IOMa Volcanics province tapped a relatively homogeneous mantle source, and that magmas migrated to the surface without significant assimilation of continental crust. The younger magmas experienced the opposite, however. The extent to which the mantle source rocks for this younger group may also have varied is under investigation. In addition, the role of the large-scale structures in chanelling magmas to the surface, and/or influencing their ability to interact with crust, is an important component of this study. Key words: volcanism, alkali basalts, basanites, magma Email: t.chang3@student.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
PEAK OIL AND OIL VULNERABILITY: WHAT ARE THE IMPLICATIONS FOR INDUSTRIAL AGRICULTURE AND RURAL COMMUNITIES? WITH A CASE STUDY BASED IN THE SOUTHERN GULF REGION OF QUEENSLAND D. COVENTRY^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia. Modern agriculture's high levels of production and global markets have been made possible through vast inputs of fossil fuels for machinery, transport, fertilizer, chemicals, crop and processed food production. Consequently, the peaking and depletion of oil, which eventually will be followed by gas, will challenge how we both produce agricultural output and live in rural and remote Australia. Current analysis estimates that maximum global oil production will plateau before supply begins to decline at a rate between four and six percent per annum by the end of this decade. Despite the imminent decline of global oil production, Australia's academic research and responsive government policy and planning development for this event has been marginal. Agricultural production methods and rural and remote communities will need to adapt to these changes, which will take place in varying ways depending upon production/industry type, location and community resilience. Rural society has already been challenged by decades of neoclassical economic policy, structural adjustment, population decline, environmental degradation and climate change induced drought. Oil vulnerability introduces another layer of change that will seriously alter rural and remote Australia's ability to remain viable. This research explores the question of oil vulnerability presented by the peaking of global supply both at a macro level and through a case study focussing on a remote community in North West Queensland. The research then attempts to contextualise both oil vulnerability and the absence of policy signals via case study interviews from a remote rural community, examining their oil use and oil vulnerability. Key words: peak oil, vulnerability, agriculture, remote and rural communities Email :donald.h.coventry@gmail.com
8
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
THE SIGNIFICANCE OF TOURNAISIAN TECTONISM IN THE DUBLIN BASIN: IMPLICATIONS FOR BASIN EVOLUTION AND ZINC-LEAD MINERALIZATION IN THE IRISH MIDLANDS S. D E M O R T O N \ M. W a l l a c e \ C. R e e d ^ C, H e w s o n ^ P. R e d m o n d ^ E. C r o s s ^ C. M o y n i h a n ^ ^School of Earth Sciences, The University of Melbourne, 3010, Australia ^Teck Namibia Linnited, Widhoek, Namibia ^Teck Ireland Ltd., Wicklow, Ireland The Early Carboniferous stratigraphy of the Irish Midlands is host to significant Zn-Pb mineralisation. Yet despite the global significance of these deposits, their mode of occurrence remains controversial. The majority of research relating to sediment-hosted ore deposits concentrates on understanding the geology in the immediate vicinity of the mineral occurrence. However, the large-scale nature of most sedimentary fluid flow systems that produce ore deposits would suggest that an understanding of the wider host basin is required. The Irish Carboniferous succession is an example of one such mineral field, where study of the host basin is a prerequisite for understanding the nature of mineralization. Recently acquired onshore seismic reflection data, in combination with detailed subsurface stratigraphic analysis have facilitated an innovative approach to understanding the tectonostratigraphic history of the Carboniferous Dublin basin. Consequently, a new view of Lower Carboniferous stratigraphy and tectonism in Ireland is presented. Seismic stratigraphic relationships and stratal thickness variations within Tournaisian units indicates that the Ballinalack High (and associated faulting) was produced by tectonism during the mid to late Tournaisian (Moathill Event, -348 Ma). A second major tectonic event, dominated by regional subsidence (rather than faulting), occurred during the Lower Visean (Tober Colleen Event, -345 Ma). Each of these tectonic events was associated with major subsidence in the basin, producing strong transgressions. We suggest that the Moathill Event was responsible for producing the structural setting of the Ballinalack deposit and could be applied to other Zn-Pb deposits in the Irish Midlands. The suggested earlier timing of fault movement in the basin has implications for arguments about the origin of Irishtype Zn-Pb deposits and the necessity (or not) for having active faulting during mineralization. Key words: Irish-type deposits, seismic reflection, basin analysis, tectonic subsidence Email: s.demorton@student.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
GEODYNAMIC MODELS OF TETHYAN STYLE OPHIOLITE OBDUCTION S.J. EDWARDS\ W.P, Schellart\ J.C. Duarte' ^School of Earth Sciences, Monash University, Clayton, Victoria, Australia Tethyan style ophiolite obduction is a conceptual ophiolite emplacement model involving the thrusting of overriding oceanic lithosphere on top of subducting continental lithosphere. Four-dimensional fully dynamic analogue models have been constructed to evaluate the mechanical feasibility of this ophiolite emplacement model. The role of continental crust thickness, passive margin width and subducting lithosphere thickness were investigated to determine the maximum horizontal obduction distance, passive margin depth, obduction velocity and ophiolite deformation. The experimental setup includes (1) a sub-lithospheric upper mantle modelled using a low viscosity glucose syrup, (2) a negatively buoyant subducting plate modelled using a high viscosity silicone mixed with fine iron powder, (3) a positively buoyant continental crust located on the down going plate modelled using a mixture of two highly viscous silicone materials, (4) a neutrally buoyant overriding plate modelled using a highly viscous silicone mixed with fine iron powder, (5) a subduction interface lubricant (applied to the entire subducting plate) representing weak sediments and serpentinised oceanic crust. No external velocities or forces were applied to the system, rather the model was left to evolve on its own allowing the slab negative buoyancy force to be the primary driving force of obduction. Experiments indicate that the Tethyan style ophiolite obduction model is a mechanically feasible ophiolite emplacement mechanism that can be driven purely by negative slab buoyancy. Results indicate that increasing the continental crust thickness decreases the maximum horizontal obduction distance, passive margin depth and obduction velocity. Conversely, increased passive margin width and subducting lithosphere thickness resulted in increased maximum passive margin depth, horizontal obduction distance and obduction velocity. Negligible trench perpendicular shortening was associated with the obduction process. Model obduction velocities and horizontal obduction distances were found to be comparable with natural examples in Oman and Papua New Guinea. Key words: ophiolite, obduction, Tethys, analogue model, geodynamics, subduction Email: sarah.edwards@monash.edu
10
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
MERCURY CYCLING OVER THE SOUTHERN OCEAN DURING POLAR SPRING: RESULTS FROM SIPEX II C. G I O N F R I D D O \ M. T a t e ^ D. K r a b b e n h o f t ^ A. K l e k o c i u k ^ K. M e i n e r s ^ A, B o w i e ^ D. L a n n u z e l ^ R. S c h o f i e l d \ J . W . Moreau^ ^School of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia ^Wisconsin Water Science Center, U.S. Geological Survey, Middleton, Wl, USA ^Australian Antarctic Division, Kingston, Tasmania, Australia ^Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Sandy Bay, Tasmania, Australia ^The Institute for Marine and Antarctic Studies, University of Tasmania, Sandy Bay, Tasmania, Australia Polar sea-ice plays a critical role in defining marine food webs. Despite of this, very little is known about the contribution of methylmercury (MeHg) from the sea-ice environment to resident aquatic organisms in the Southern Ocean. Sea-ice provides a unique ecological niche that may host microorganisms capable of methylating mercury (Hg). During the Sea Ice Physics Ecosystem experiment (SIPEX) II, snow, sea-ice, brine, and seawater samples were collected for total Hg (THg) and MeHg analysis to understand the speciation and distribution of Hg at the sea-ice/water interface. Real-time atmospheric elemental Hg concentrations were measured over the duration of the voyage, to identify Hg depletion events, which regularly occur in polar spring and result in Hg deposition in the snowpack. THg concentrations in snow, ice, and brine samples ranged from 0.20-179.1 ng/L, with a median value of 4.03 ng/L. MeHg concentrations ranged from 0.020-0.17 ng/L, median: 0.023 ng/L. The highest concentrations of MeHg and THg were found in ice core samples, but only -0.7% was methylated. Seawater samples collected from depths of 15-1000 m had the lowest THg concentrations (0.22-2.48 ng/L, median: 0.47 ng/L), but higher methylation proportionally (11% MeHg). Thus, MeHg concentrations in the seawater profile were similar to ice core samples (median: 0.035 ng/L). In the snowpack, the highest concentrations of THg were found in the upper 2 cm, and decreased with depth, indicating Hg deposition, but loss over time. Our results provide useful constraints on fluxes and bioavailablity for mercury across the atmosphere-sea-ice-seawater continuum for the under-sampled Antarctic region. Key words: polar ecosystems, Antarctica, sea ice, biogeochemistry, mercury. Southern Ocean Email: cgio@student.unimelb.edu.au
11
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
DATING MANTLE METASOMATISM BY U/Pb AND METHODS: WHICH ONE WORKS BETTER? A. GIULIANr, D. Phillips\ M.K. Kendrick\ R. Maas\ A. Greig\ R. Armstrong^, M.R. Felgate\ V.S, Kamenetsky^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia ^Research School of Earth Sciences, Australian National University, ACT, Australia ^School of Earth Sciences, University of Tasmania, Hobart, Tasmania, Australia Precise dating of fluid processes in the Earth's mantle remains a major challenge for geoscientists. The U/Pb and Ar/Ar dating techniques have both been used in an attempt to constrain the timing of mantle metasomatic events; however, the Ar/Ar results have proven contentious. Here we compare the "^^Ar/^^Ar ages obtained for large phlogopite grains from 7 mantle xenoliths from the 84 Ma Bultfontein kimberlite (Kimberley, South Africa), with U/Pb ages from metasomatic zircon and LIMA minerals coeval with phlogopite. LIMAs are unusual titanates that occur in phlogopite-rich metasomatised peridotites. LIMA minerals are enriched in incompatible elements (e.g., LILE, LREE, HFSE), with high U (250-400 ppm) and Pb (200-700 ppm) contents. U/Pb geochronology on LIMA minerals is limited by the low U/Pb ratios and high common Pb. In this study, the U, Th and Pb isotopes of LIMA minerals from three mantle xenoliths were measured by in-situ LA-ICP-MS. Common Pb values were determined from isotope dilution MC-ICP-MS measurements of coeval clinopyroxene grains. LIMA U/Pb ages are - 170-180 Ma, in agreement with a U/Pb age of 184±2 Ma obtained for a single zircon from one of the LIMAbearing xenoliths. These results suggest a link between mantle metasomatism and Karoo magmatism in southern Africa. Ar/Ar step-heating analyses of phlogopite grains were conducted using a new generation ARGUSVI multi-collector mass spectrometer. All the phlogopite samples yielded much older ages (up to 780 Ma) than coexisting zircon and/or LIMA minerals. We attribute these anomalously old Ar/Ar ages to the presence of excess "^^Ar in the metasomatic fluid that crystallised phlogopite. We conclude that the "^^Ar/^^Ar phlogopite technique cannot be used to date mantle metasomatism. Key words: geochronology, lithospheric mantle, metasomatism, U-Pb, titanate, Ar-Ar, phlogopite, kimberlite Email: a.giuliani@student.unimelb.edu.au
12
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
INLAND ACID SULFATE SOIL ENVIRONMENTS IN THE CORANGAMITE REGION, SOUTH-EASTERN AUSTRALIA F. G L O V E R \ J . W e b b ' ^Department of Agricultural Science, La Trobe University, Bundoora VIC 3086 Inland acid sulfate soils (ASS) have beGon^ie a prominent environmental problem in recent years, with inland ASS having been recognised in a wide range of Australian environments. A variety of factors are believed to affect their formation, including being associated with dryland salinity, as the main source of sulfate in inland environments is saline groundwater. However, within the Corangamite region in southwestern Victoria, sites containing sulfidic sediments occur in environments not associated with dryland salinity. At Boundary Creek, near Colac, an actual acid sulfate soil (AASS) has developed in a partially drained swamp within the northern part of the Otway Ranges. The site has begun to oxidise, resulting in the release of acid into the environment. The swamp at Boundary Creek does not show any associated salinity; the water in the swamp is very fresh (-360 jjS/cm). Chromium reducible sulfur (CRS) and titratable sulfidic acidity (TSA) analysis confirmed the presence of sulfides at the site, indicating that while oxidation has occurred, significant potential acidity still remains within the sediment, which lacks any carbonate buffering capacity. A similar site was found on the Anglesea River; however, the Anglesea swamp has a high source of sulfate, as the proximity to the coast allows a higher input of sea spray to mix with rainfall. The swamp is outside the range of tidal inundation and also above the sea level recorded during the Holocene highstand (+ 2.1m), and is therefore an inland ASS rather than a coastal ASS. North of Colac in the Warrion Water Supply Protection Area (WSPA), two drained swamps on the basalt plains also contained sulfidic sediments. However, these swamps contained high levels of carbonate minerals (aragonite and dolomite), indicating the swamps have a high buffering capacity and will not go acidic if the sulfide minerals within the sediments are oxidised. The results of this study have large potential impacts for the future degradation of inland wetlands and swamps, as well as regional groundwater issues. Key words: acid sulfate soils, oxidation, acid neutralising capcity Email: fsglover@students.latrobe.edu.au
13
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
VARIABILITY AND GEODIVERSITY ANALYSIS OF GEOLOGICAL MAPS L GROSE\ L. Ailleres\ G. Laurent' ^School of Geosciences, Monash University, Clayton, Victoria, 3800 Australia Geological maps are created fronn a combination of observation and human interpolation between outcrop observations. Both observation and the geologist's interpretation (manual interpolation) are subject to geological uncertainty. This study uses geological variability as a proxy for geological uncertainty and we present methods for identifying and analysing geological variability surrounding geological structures. Geodiversity will be used to characterize maps differences by a number of geometrical measurements assessing geologically significant map properties. Geodiversity analysis is performed using Self-Organising Maps (SOMs) which allow for n-dimensional datasets to be reduced to 2 dimensions for visualization and analysis. Using k-means clustering on SOMs, the varying maps can be categorised into groups with similar geological characteristics. We use 40 maps from a field course in Broken Hill. The maps cluster in 3 different groups according to their geological variability. Stratigraphic variability maps identify regions of high variability associated with the overall geological structure. Information entropy maps allow for the identification of uncertainty associated with varying geological interpretation. The local gradient of both variability maps and the geometry of highly variable regions can be used to assess the source of variability: varying location, differing interpretations and/or reliability of observations. Variability maps highlight a number of faults in the Eldee structure which are sparingly mapped in the input maps. High regions of variability are associated with the hinge of folds. Key words: Self-organising Maps, geological uncertainty, stratigraphic variability, information entropy, k-means clustering, geodiversity Email: lachlan.grose@monash.edu.au
14
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
TRACE METAL MOBILITY DURING MINERAL CARBONATION J. HAMILTON\ S. Wllson\ B. Morgan^ ^ C. Turvey\ S. Jowitt\ G- Southam^ ^School of Geosciences, Monash University, Clayton, VIC 3800, Australia ^CSIRO Process Science and Engineering, Clayton South, VIC 3169, Australia ^School of Earth Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia Mineral carbonation describes a natural silicate weathering process on Earth which results In CO2 sequestration within carbonate minerals. Magnesite formation (MgCOs) is kinetically inhibited under ambient conditions; thus, in natural systems hydrated magnesium carbonates such as nesquehonite (MgC033H20), and hydromagnesite (Mg5(C03)4(0H)2-4H20) form instead. Carbonation reactions are accelerated with increased mineral surface area, making mine tailings storage facilities an ideal place to observe and promote mineral carbonation. Mine tailings also tend to contain significant concentrations of toxic metals which may be mobilised during enhanced weathering and carbonation. In order to determine whether metal mobilisation represents a risk in this CO2 sequestration technology, we assessed the trace metal concentrations and identified the metalliferous phases in samples from Woodsreef chrysotile mine, a known site for mineral carbonation. XRF revealed that both serpentinites and carbonate crusts contain Ni, Cr, Mn and Co, while mine pit water samples contained no detectable trace metals. Metals were concentrated in magnetite inclusions and chromite, within serpentinite and harzburgite source rocks. We believe metals also substitute for Mg in serpentine minerals and hydromagnesite after mineral carbonation; however SEM was unable to detect low concentrations. Experiments were also conducted to determine whether precipitating Mgcarbonate minerals could sequester metals in a metal rich environment. Nesquehonite was precipitated in the presence of Cu, Co, Cr, Ni and Mn at concentrations up to 100mg/L. ICP-MS confirmed that generally >99% of metals were sequestered in the precipitates and XRD revealed the precipitates contained nesquehonite, sylvite (KCI) and minor baylissite (K2Mg(C03)2-4H20). Crystal chemistry and mineral solubilities indicate nesquehonite is the most likely metal bearing phase. These results indicate that Mg - carbonates may have great capacity to sequester metals during mineral carbonation. This research has implications for potential uses of carbonate minerals as value-added products, and geoengineering mine tailings to accelerate mineral carbonation. Key words: sequestration.
mineral
carbonation,
metals,
nesquehonite,
Email: jessica.hamilton@monash.edu
15
Woodsreef,
mine
tailings,
CO2
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
RELATIONSHIPS BETWEEN TROPICAL CYCLONES AND CLIMATE IN SEVERAL GENERAL CIRCULATION MODELS M. H O R N \ K. W a l s h ^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Tropical cyclones (TCs) are among the nnost destructive nneteorological phenomena. It is therefore of great interest, both scientifically and socially, to determine how climate change is likely to effect TC activity in the future. Much modelling has suggested a decrease in TC frequency overall, with an increase in the frequency of the most intense TCs. However, our current understanding of the links between TC activity and climate is limited, making it difficult to place these projections on a solid theoretical grounding. In order to address this issue of poor basic understanding, members of the U.S. Climate Variability and Predictability (CLIVAR) Hurricane Working Group (HWG) performed a series of idealised experiments in atmospheric general circulation models (AGCMs), forced with specified sea-surface temperatures (SSTs) and greenhouse gas concentrations. These experiments included a present day climatology run, a run with SSTs increased globally by 2 K, a run with doubled atmospheric carbon dioxide concentrations, and a run with both doubled carbon dioxide and 2 K raised SSTs. These experiments were aimed at teasing apart some of the fundamental relationships governing TC activity. Here we present analysis of the trends obtained in these experiments across several models. We find broad agreement on a decrease in TC frequency due to the influence of doubled carbon dioxide, but greater uncertainty in the influence of increased SST. We also examine the relationship of these trends to changes in a range of atmospheric variables and indices, and investigate the dependence of the trends on the tracking scheme used to detect the TCs. Key words: tropical cyclones, climate, climate change Email: mjhorn@student.unimelb.edu.au
16
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
GEOCHEMISTRY AND GEOCHRONOLOGY OF THE AILEU FORMATION, TIMOR-LESTE T, KING' ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia The Banda Arc in southeast Indonesia provides unique insight into initial evolution of an orogenic system, evidence of which is often overprinted or destroyed in more mature orogens. Timor is the largest island in the non-volcanic outer Banda Arc and formed during initial collision of the Australian passive margin and proto-Banda Arc (Sunda Plate). The Aileu Formation on the north coast of TimorLeste has been the subject of much conjecture regarding its pre-tectonic origin and metamorphic history. This has led to various contrasting models to describe collision in Timor, leaving key aspects of tectonic evolution in the Banda Arc poorly understood. New geochemical and geochronological data constrains the origin and prograde metamorphic history of the Aileu Formation. Whole rock major and trace element data refute an island-arc affinity for Aileu Formation igneous units. Features of their composition are more consistent with a rift or within-plate basaltic origin. This supports a Gondwanan provenance and Australian Plate origin for the Aileu Formation. New U/Pb ages of titanite and zircon from the north-east of the Aileu Formation constrain peak metamorphism to 7 ± 0.16 Ma, far later than previous estimates. These results contradict cooling ages of 10-8 million years that have been used to define timing of collision. Felsic units contain zircons that yield an 8.5 ± 0 . 1 Ma age, which may represent a protolith age. This would redefine the northeast volcanic section of the Aileu Formation as a younger distinct unit. Timing of collision in the Banda Arc region and formation models for Timor must be reassessed based on these new data. Any model must explain U/Pb defined peak metamorphism of the Aileu Formation at 7 Ma, "^^Ar/^^Ar cooling ages through 500°C at 6 Ma and stratigraphically controlled uplift at - 4 Ma. Key words: Aileu Formation, Geochemistry, U/Pb dating, titanite, zircon. East Timor, Banda Arc, metamorphism, arc-continent collision Email: t.king@student.unimelb.edu.au
17
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
HOLOWILENA IRONSTONE: INSIGHTS INTO NEOPROTEROZOIC IRON FORMATION DEPOSITION M.A, LECHTE\ M.W. Wallace' ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Iron formations are the complex product of the interaction between the ocean, atmosphere, biosphere and tectonic processes, and as such are key to our understanding of the environmental evolution of the Earth. However, a model for their deposition remains widely debated, and nearly all of the conditions considered necessary for their deposition are contended. The Holowilena Ironstone is an iron rich sedimentary unit in the Flinders Ranges, South Australia, that has a strong association with glaciogenic sediments. While iron formations are almost exclusively confined to the Archean and Paleoproterozoic, this unit is Neoproterozoic in age, and therefore represents the reappearance of iron formations in the geological record after a hiatus of around one billion years. Neoproterozoic iron formations of the same age have been found on all continents, and following this relapse more recent iron formations are extremely rare. The reasons behind this brief reprisal are poorly understood and the subject of much contention. Importantly, the Holowilena Ironstone is closely linked with glacial deposits from the Sturtian glaciation, one of the extreme "Snowball Earth" events. This unique association is consistent across all Neoproterozoic ironstones, and suggests that the low latitude glaciation experienced during this time may have been a major factor in creating the conditions required for the deposition of iron formations. A detailed stratigraphic, geochemical and sedimentological study of the Holowilena Ironstone has been undertaken In order to better constrain the depositional processes and environment of these enigmatic iron formations, with the aim of developing a genetic model that helps to explain the recurrence of ironstone during extensive glaciation. Key words: iron formation, paleoclimate, Snowball Earth, chemical sediments, ocean chemistry Email: m.lechte@student.unimelb.edu.au
18
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
MICROBIAL GEOGRAPHICAL DISTRIBUTION IN HIGH ORGANIC CARBON CONTAINED WETLAND IN THREE ASPECTS: METABOLIC GUILDS, BIODIVERSITY, AND COMMUNITIES SIMILARITY Y. LING\ R. Bush^ A. Rose^ J. W. Moreau' ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia ^Centre for Acid Sulfate Soil Research, Rese School of Environmental Science and Managenrient, Southern Cross University, NSW, Australia Redox sequences in a subsurface ecosystem are based on the concept that limited organic carbon leads to competition among different metabolic microorganisms. This causes the dominant metabolic guild to expel other groups until its electron acceptors are consumed. However, low energy accessibility is not the only threshold, the enzyme reaction efficiency must also be considered. When organic carbon exceeds the upper threshold that microbial enzymes can process, different metabolic guilds may be co-active in the same place. In the Michaelis-Menten Model, a system has maximum enzymatic reaction rate when all enzymes are bonded substrates. Higher concentrations of substrate will not further increased rate. The East Trinity Wetland (Cairns, Queensland) is a high organic carbon containing coastal wetland. This area suffered soil acidification during a drainage period in the 1970s. The acid sulfate soils are formed by oxidation of iron sulfide, which releases acid. The acidic solutions will dissolve attached heavy metals from iron oxyhydroxides. Soil acidification and heavy metal contamination are both hazards to nearby ecosystems. Microbial activity plays an important role in sulfide formation and iron redox reactions. To better understand microbial metabolic mechanisms, microbial community distribution is investigated in this study. In this research, we compared microbial geographical distributions in three different aspects: metabolic groups, diversity, and compositional similarity. The soil layering and saturation shape the microbial community structure and composition into four zones: high organic carbon/high acidity zone, surface tidal zone, groundwater intrusion zone, and sandy clay-seawater interaction zone. Acidity shows more influence on diversity than organic carbon abundance. Methanogens are inhibited by acidity. For the other three metabolic groups including nitrogen-dependent, iron-dependent, and sulfate/sulfur reducing, their distribution implying a overlap redox zones under excess organic carbon. Key words: coastal acid sulfate soil, 16S ribosomal DNA, microbial biogeography Email: ycling@student.unimelb.edu.au
19
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
THE FORMATION OF SOLUTION PIPES ON CAPE BRIDGEWATER, WESTERN VICTORIA M. LIPAR\ J. Webb^ ^Environmental Geoscience, La Trobe University, Bundoora, Victoria, Australia Solution pipes are tubular vertical cavities formed in very porous limestones with matrix porosity, such as calcarenite. Their diameter varies from <0.2 metres to >1 metre, and their termination is usually round or slightly pointed. Average depth is 2 - 5 metres, but can reach more than 20 metres. They sometimes form vertical entrances to cave systems. Solution pipes are surrounded by rims a few millimetres to 5 centimetres wide that are more cemented and erosion resistant than the surrounding calcarenite. Solution pipes have been described as a syngenetic karst feature and interpreted as vertical karst voids, formed by focused vertical solution. Much discussion and many experiments have been published on triggers for focused solution in calcarenites or focused water flows in unconsolidated sediments, but opinions are still divided. Solution pipes are abundant in Pleistocene calcarenites at Cape Bridgewater in western Victoria. Based on field work at this site, combined with morphometrical analysis, thin section examination, and mineralogical, chemical and isotopic analysis, it appears that sufficient but limited dissolution (i.e. rainfall) is crucial for development of the solution pipes. The focused flows that trigger solution pipe development may be initiated in several different ways, mainly dependent on the climate, rock/sand characteristics, and flora and fauna. The shape of the solution pipes is then modified by later calcrete development and weathering. Key words: karst, syngenetic, solution pipe, calcrete, calcarenite E-mail: mlipar@students.latrobe.edu.au
20
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
SIGNIFICANT AND EPISODIC RECHARGE IN THE LODDON RIVER CATCHMENT, VICTORIA S. M A N A M P E R r J .
Webb^'^
^National Centre for Groundwater Research and Training, Australia ^Environnnental Geoscience, La Trobe University, Victoria, Australia Climate studies suggest that the future changes of rainfall and tennperature will lead to changes in the seasonality of surface water availability, thereby changing the recharge pattern in groundwater aquifers. Climate modelling predicts an increasing trend of extreme events such as floods and droughts in much of northern Victoria in the future. However, these events also have positive effects, such as ground water recharge and enhanced water availability in surface water bodies, but which are not well understood and documented. The Loddon River catchment, northern Victoria, has three main aquifers, the Newer Volcanics, Shepparton Formation and underlying Calivil Formation. Groundwater trends in these aquifers for the last 30 years were calculated as normalized anomalies (difference from the mean / standard deviation) and compared to regional rainfall and stream flow anomalies, to understand the sensitivity of the aquifer systems to change. Changes in groundwater storage during the periods that show a significantly high anomaly (1983, 1992, 1995 and 2010/11) were calculated using the water level fluctuation method. Results suggest that, regionally, the Loddon aquifers respond strongly to episodic flooding events. The substantial increase in groundwater storage after a flood event was due to direct recharge in the inundated areas, leakage through overlying aquifers and decreased groundwater abstraction for agriculture. Overall, the anomalies of the groundwater data suggest that aquifer characteristics, episodic events, topography of the region and groundwater demand for agriculture all play a role in the impact of climate change on water levels in the Loddon River catchment. Key words: normalized anomaly, episodic events, groundwater, aquifer response Email:
s.manamperi@latrobe.edu.au
21
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
STRUCTURAL AND KINEMATIC EVOLUTION OF THE INDILONG PLAIN FAULT AND TUMUT TROUGH K. MARTINS' ^School of Geoscience, Monash University, Clayton, Victoria, Australia The Tasnnanides is an accretionary nnargin along the eastern edge of Gondwana. This accretionary nnargin, from Queensland to Tasnnania, is subdivided into several orogens, one of which, the Lachlan Fold Belt, extends fronn northern New South Wales to Tasnnania. The fold belt records a long lived orogenic event which began in Early Ordovician, and continued to the Carboniferous. Three terrains can be distinguished with in the Lachlan Fold Belt the Western, Central and Eastern Terrains. The Indi-Long Plain Fault is one of the largest structures within the Tasminides, located within the Benambra Terrain of the Lachlan Fold Belt. It is truncated near the border of New South Wales and Victoria by the Gilmore Fault. The Tunnut Trough lies at the junction of these two faults, and is postulated to be a transtentional basin that opened in the Mid-Silurian and closed during the MidDevonian. Sediments within the Tumut Trough represent a shallow marine environment. The IndiLong Plain Fault juxtaposes the shallow marine sediments of the Tumut Trough in the west, against the deep marine sediments and MORB-like volcanic rocks (Cambrian to Ordovician) on the Tantangara Block to the east. These deep marine sedimentary and mafic volcanic rocks form the Kiandra Volcanic Belt, perhaps one of four remanent slivers of the Macquarie Arc. Structural analysis indicates that the southern portion of the Indi-Long Plain Fault is an east dipping thrust fault. The northern extent of the Indi-Long Plain Fault has a history of early dextral movement, followed by sinistral movement. These movement senses of the Indi-Long Plain Fault are fundamental in understanding the evolution of the Tumut area. At a large scale the observed movement history, deformational events and stratigraphic relationships contribute to the evolution of the eastern Lachlan Fold Belt Key words: Tasminides, Lachlan Fold Belt, Macquarie Arc, Indi, Long Plain, Kiandra Volcanic Belt, Tumut Trough Email: karen.martins@monash.edu
22
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
THE ROLE OF STEADY-STATE THERMAL MODELS IN A YOUNG VOLCANIC PROVINCE: THE NEWER VOLCANIC PROVINCE, SOUTHEAST AUSTRALIA B. MATHER\ L Moresl\ A. Cruden^ ^School of Geoscience, Monash University, Clayton, Victoria, Australia The Newer Volcanics Province of south-eastern Australia is a Pliocene to recent intraplate basaltic province, which occupies > 20,000km^. Little is known about the origin and controls of volcanic activity within the province with processes including mantle plumes, edge-driven convection, and asthenospheric shear all suggested. It has been theorised that a shift to east-west compression in the Late Neogene produced trans-tension along parallel fault surfaces allowing seismic-controlled decompression melting and volcanism. To validate this, a 3D model of Victorian crust has been imported into Underworld, a finite element Lagrangian particle-in-cell code, to solve for steady-state heat transfer. Temperatures at the base of the crust are forward modelled against surface heat flow data with depth-dependent thermal conductivity and heat production accounted for. Impossibly high Moho temperatures (>900°C) were modelled between Bendigo and Ballarat, which means a steadystate approach to crustal heat flow breaks down. The anomalous zone between Bendigo and Ballarat correlates with a region of low teleseismic velocity and high electrical conductivity that intrudes well into the mid crust. This suggests transient heat flow, arising from magma migration, dominates this part of the crust. Finite difference models of thermal diffusion show multiple pulses of magma migration at shallow depth are required to reproduce the heat flow signature observed at the surface. This work demonstrates the value of heat flow data in constraining the transient thermal effects of volcanism. Future work will examine the flow dynamics of magma migration through preferred fault pathways, and coupling this with a convecting upper mantle. Key words: numerical modelling, geothermal, intraplate volcanism. Newer Volcanics Province Email: ben.mather@monash.edu
23
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
NONLINEAR INDIAN OCEAN DIPOLE FEEDBACKS AND THEIR RESPONSE TO A WARMING CLIMATE B . NG^ ^ W . C a i ^ K. W a l s h ^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia ^CSIRO Marine and Atmospheric Research, PMB 1, Aspendale, Victoria 3195, Australia The Indian Ocean Dipole (lOD) is positively skewed with cold sea surface temperature anomalies (SSTAs) over the eastern Indian Ocean (10) showing larger amplitudes than warm SSTAs. Positive lOD events have the potential to cause devastating droughts in parts of Australia and several processes have been proposed for the positive skewness. These are the positive Bjerknes feedback, the negative SST-cloud-radiation (SCR) feedback, and nonlinear dynamic heating (NDH). However there is debate over which feedback is the dominant cause of skewness. While the asymmetry of the Bjerknes feedback is expected to decrease under climate change, the response of the SCR and NDH feedbacks is not well known. Using the GFDL coupled-climate ESM2M model, representative concentration pathway (RCP) scenario RCP8.5 is analysed to determine how these nonlinear processes behave under global warming. In response to climate change, the asymmetry of the Bjerknes feedback decreases due to a weakening of westerly winds and a shoaling thermocline. The NDH process is largely driven by anomalous zonal advection, which shows a weaker reinforcement of cold SST anomalies but stronger damping for warm SST anomalies under global warming. The SCR feedback shows an increase in asymmetry but this Increase is driven by the shoaling of the mean thermocline depth. However as this study focuses on one model, there is some uncertainty in the response of these feedbacks and their behaviour in a multi-model ensemble remains to be seen. Key words: Indian ocean dipole, nonlinearity, interannual tropical variability Email: benjamin.ng@csiro.au
24
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
COMPARISON OF THE SALT BUDGET IN PAIRED CATCHMENTS (PASTURE AND TREE PLANTATION) IN SOUTHWESTERN VICTORIA, AUSTRALIA F. PERVEEN\ J. A. Webb\ P.E. Dresel' ^Environmental Geoscience, La Trobe University, Melbourne, Vic, Australia ^Department of Primary Industries, Bendigo, Vic, Australia The Crawford River catchment in southwestern Victoria has experienced extensive development of tree plantations. As part of a study looking at the impact of afforestation on water resources in this region, paired catchments under pasture/tree plantations were instrumented with loggers in groundwater bores and weirs on the catchment outlets. Three catchments were studied, two adjacent subcatchments, the northern farm catchment and the southern farm catchment under a pasture and a nearby catchment planted with Eucalyptus globulus in 2001. The catchments were believed to have very similar physical characteristics (geology, soil, topography, and climate). The salt budget for each catchment was determined by calculating salt input, storage and export using CI" as a proxy for total salinity. Compared to the plantation site, the farm sites have greater salt storage in the unsaturated and saturated zones, because the soil water and groundwater are more saline. As a result, the streams in the farm sites are three times more saline and salt export is nine times higher compared to the plantation catchment. However, a net export of salt is occurring from the three catchments (output/input ratio >1). At other paired farm/plantation catchments in SW Victoria, surface water salt export is much greater than input for both pasture and plantation catchments, and plantation catchment has lower streamflow (due to tree transpiration).The Crawford River catchments contradict this story because they are not underlain by uniform geology (contrary to expectations). While magnitude of the streamflow at the plantation catchment is less compared to the farm catchments, it flows longer than the southern farm catchment. Surface sediments at the plantation catchment are much sandier than at the farm catchments, allowing swift percolation of rainfall so the soil water and groundwater are relatively fresh. Furthermore, the low stream flow from the plantation catchment is due largely to substantial leakage into an underlying karst aquifer that also allows substantial salt export within the groundwater. The salt budgets of paired catchments under different land use can be useful to assess the impact of land use change, but only if differences in geology and therefore hydrogeology do not overwhelm any such impacts. Key words: tree plantation, salt budget, paired catchments, southwestern Victoria Ema//.-fperveen@students.latrobe.edu.au
25
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
MECHANISM BEHIND THE OCCURRENCE OF SECONDARY DIURNAL PEAK IN RAINFALL OVER DARWIN, AUSTRALIA S. RAUNIYAR\ K, Walsh' ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia
The mechanisms controlling variations in the characteristics of the diurnal cycle of tropical rainfall under the influence of large-scale circulations are not fully understood. To better understand the physics behind such variations during the Australian summer season, this study used hourly rainfall data from rain gauges and the C-band polarimetric (CPOL) radar located near Darwin. Furthermore, the skill of four numerical weather prediction (NWP) models are also evaluated. The hourly diurnal cycle of rainfall is composited for total days, for each phase of the Madden-Julian Oscillation (MJO) and also for the different large-scale regimes. The composite diurnal cycle at Darwin shows two peaks in the observation, one during early morning (0200-0400 LT) and other during late afternoon (15001700 LT). The sea breeze circulations are found to be a dominant mechanism for the rainfall during the MJO phases 1-3 and 8 and also during the break/ build-up periods of monsoon. These conditions exhibit easterly winds and the atmosphere remains drier than normal, resulting below average rainfall over most of the radar domain, except over the Tiwi Islands. During these conditions, the rainfall is found to be concentrated over land and has a strong diurnal cycle with an afternoon maximum. In contrast, the large-scale circulations are found to be the controlling factors for the widespread rainfall during the MJO phase 4-7 and during the active monsoon periods. During these periods, low-mid level westerly winds are prevalent that make the atmosphere more humid and above normal rainfall occurs, except in phase 7. In addition, the occurrence of early morning maximum rainfall is dominant only during the MJO phases 4-6, but not during the active monsoon periods. This study found that while the models reproduce an early afternoon peak in the diurnal cycle, none of the models are able to reproduce the early morning peak, suggesting that models require a better representation of eastward propagating MJO and or the active periods of monsoon. Key words: Diurnal Cycle, Rainfall, MJO, monsoon Email: s.rauniyar@student.unimelb.edu.au
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
FARM DAM DEVELOPMENT TRENDS IN WESTERN VICTORIA IN RELATION TO CLIMATE AND LANDUSE CHANGE R, ROOHr, J. Webb^ ^School of Agricultural Sciences, Latrobe University, Bundoora, Melbourne, Victoria, Australia In the past four decades, with increasing climatic uncertainty, high annual and seasonal rainfall variability and changing landuse practices, the development of small water storage structures like farm dams has increased tremendously in Western Victoria. These small water storage bodies are primarily used as stock watering points; larger dams are also used for irrigation and domestic uses. Though record of the large farm dams is available with the catchment management authorities; the comprehensive historical record of small farm dam development is not available. Using medium-resolution Landsat data from 1973-2004, in conjunction with high resolution Google earth images, historical development of these water bodies were extracted. Various image enhancement and manipulation techniques were used to augment the contrast of these small water bodies from the surroundings. In comparison with the Google earth images, all the dams were spotted at Landsat image. Over a period of 32 years, there was 178% increase in farm dam numbers. Initially the annual rate of increase was high (5-7% per annum), however it reduced to 0.2% following 1992. The serious droughts of 1982-1983 and 1997-2010 had some influence on the rate of increase in farm dam numbers. After 1993 there was a slow rate of dam construction, due to the fact that most suitable dam sites had already been utilized. Since 1990 there was a shift from dryland pastures to dryland cropping, with a concomitant decrease in demand for watering points. Up to 1979 the increase in sheep population was in line with increasing farm dams but the drought of early 1980s resulted in a decline of sheep population. Following this drought, there was sharp increase in farm dams and though initially there was an increase in sheep population, due to shift in production system from livestock to crop sheep population was reduced. Key words: farm dams, Western Victoria, Landsat, climate change, landuse change Email: r.roohi@latrobe.edu.au
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
APPLICATION OF ALKALINITY PRODUCING COVERS TO WASTE ROCKS FROM MT LYELL COPPER MINE, WESTERN TASMANIA M.G. SEPHTON\ J.A Webb' ^Environmental Geoscience, La Trobe University, Bundoora, VIC Alkalinity-producing covers applied to waste rock heaps and tailings are designed to reduce the generation of acid mine drainage by inhibiting the mechanism of acid generation at its source. The dissolution of alkalinity from the material by rainwater raises pH of the waste rock heaps and causes precipitation of secondary minerals such as ferrihydrite, which can passivate pyrite surfaces. This study investigates the applicability of this method to waste materials from Mt Lyell Copper Mine near Queenstown, Western Tasmania using column leaching experiments. The Mt Lyell Copper mine has around 53 million tons of waste rock spread over an area of around 90 hectares; these contribute a large fraction (around 40%) of the acid mine drainage generated from the site. The waste rock materials on site have been subjected to weathering for varying periods of time and consequently vary in terms of secondary mineral content and acidity generation rates. Alkalinityproducing covers are being tested on both fresh and old waste rock materials. Altogether 10 leach columns have been set up: 4 with fresh waste rock and 4 with weathered waste rock (control, hydrated lime cover, limestone cover, control with oxygen-consumption monitoring) and 2 control columns with quartz gravel (hydrated lime cover, limestone cover). Preliminary results show that the old waste rocks generate acidity and have a higher oxygen consumption rate than the fresh waste rocks, which did not go immediately acidic. Monitoring of leachate composition suggests that leachate acidity is due both to pyrite oxidation and dissolution of secondary minerals. A key question for alkalinity-producing covers therefore becomes whether reduction in acidity generation is due mostly to direct neutralisation or passivation of pyrite. The relative impacts of these two processes will be determined by using the control columns and the total acidity reduction to calculate the magnitude of pyrite passivation. Key words: acid mine drainage prevention, alkalinity-producing covers, alkaline addition Email: mgsephton@student.latrobe.edu.au
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
NEUTRALISATION OF ALUMINIUM-RICH ACID MINE DRAINAGE TO FORM A MAGNETIC SLUDGE W, STANFORD^ and J. Webb^ ^Environmental Geoscience, La Trobe University, Bundoora, Victoria, Australia The active rennediation of acid mine drainage (AMD) typically employs hydrated lime as the neutralising agent, and forms a voluminous sludge. Sludge composition varies depending on initial AMD chemical composition and the neutralising process utilised. The production of a high density magnetic sludge consisting of magnetite is desirable, as this is relatively low volume, more resistant to leaching and neutral in colour compared to the standard ferrihydrite/schwertmannite sludge. Previous studies have shown that aluminium in AMD is detrimental to the formation of magnetite, favouring less stable iron oxy-hydroxides such as ferrihydrite and schwertmannite. Aluminium solubility is strongly determined by pH, and at normal surface temperatures it precipitates as amorphous aluminium hydroxide at pH levels between 4.5 and 5.0. A two-step neutralisation process was applied to an aluminium-rich synthetic AMD solution with a Fe/AI molar ratio of 12:1. After initial neutralisation using hydrated lime, the pH was stabilised at -4.7 for 10 minutes to allow aluminium precipitation to occur, followed by seeding with magnetite. Neutralisation recommenced until pH -11.5 was reached. This treatment successfully removed 91 - 100% of the heavy metals out of solution and produced a magnetic sludge composed of 24-34% magnetite/maghemite with a density of 1.08 - 1.35 g/mL. Seeding was a pivotal step in the formation of a magnetic sludge, with nonseeded experiments resulting in the less stable non-magnetic iron oxy-hydroxide sludge. The ratio of ferrous to ferric iron in the AMD also impacts the production of magnetic sludge. Ratios of (Fe^VFe^^) proved detrin^ 1:3 (Fe^VFe^"') detrimental, with an inverse relationship between Fe^''/Fe^"'ratios and proportion of magnetite in final sludge. Key words: acid mine drainage, magnetic sludge Email: wjstanford@students.latrobe.edu.au
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
USING THERMAL REMANANT MAGNETISATION (TRM) TO UNDERSTAND EMPLACEMENT TEMPERATURE OF BLOCK AND ASH FLOW AND DEBRIS FLOW DEPOSITS: LAVA DOME ERUPTION AT MOUNT UNZEN VOLCANO, JAPAN D. UEHARA^ R.A.F. Cas^ C, Folkes^ S- Takarada^ ^School of Geosciences, Monash University, Clayton, Melbourne, Australia 3800 ^Geological Survey of Japan, AIST, Site 7, 1 -1 -1, Higashi, Tsukuba, Ibaraki JAPAN 305-8567
This study used thermal remanent magnetisation (TRM) of juvenile clasts to determine the emplacement temperatures and to differentiate block and ash flow and debris flow deposits, from the 1991-1995 Mount Unzen eruption, Japan. During the 1991-1995 Mount Unzen eruption 9400 block and ash flows were produced from gravitational collapse events of 13 dacitic lava domes, which resulted in 44 deaths. 64 samples were collected from eight sites from a variety of block and ash flow and debris flow deposits, and from various distances away from the summit. The progressive thermal demagnetisation method was used to show that the clasts have three major trends. Two deposits contain clasts that have one single component orientated to the geomagnetic field at time of emplacement. This indicates clasts in the deposit were cooled from above the blocking temperature of magnetite or Curie temperature of magnetite (580 °G) to ambient temperature. If the clasts from the same unit have magnetic components oriented in similar directions, the unit is interpreted as a hot block and ash flow deposit. Two deposits showed a second trend where clasts had single components but the orientations of the magnetic components within each unit were random. This indicates the deposits could be a cold debris flow deposit, or a hot block and ash flow, but that clasts have been remobilised by external processes. The remaining four units showed a third trend, where clasts had two magnetic components. The emplacement temperatures ranged from 250480°C. These units can be interpreted as warm block and ash flows or hot debris flows. It was shown that this method can be used to determine the emplacement temperature of some block and ash flow deposits, however TRM shows it is still difficult to distinguish between warm block and ash flow and hot debris flow deposits. Key words: Thermal remanent magnetisation, block and ash flow, debris flow deposits Email: dan.uehara@monash.edu
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
CONTROLS ON GOLD MINERALISATION AT THE NAVACHAB GOLD DEPOSIT, NAMIBIA: APPLICATION OF THE LIQUID BISMUTH COLLECTOR MODEL L URQUHART\ A. CRUDEN\ A. TOMKINS\ S. VOLLGGER^ ^School of Earth Sciences, Monash University, Clayton, Victoria, Australia The liquid bismuth collector model (LBCM) is gaining increasing recognition for creating and enhancing economic gold deposits. Au-mineralisation at a growing number of deposits (i.e. Stormont, Tasmania; Escanaba Trough, Gordo Ridge) has recently been attributed to the presence of a Bi-melt during mineralisation. Bi-melts have the unique ability to scavenge ionic Au from Au under-saturated hydrothermal fluids. As a result, fluids and regions previously assumed to be unsuitable for mineralisation now have the potential to host economic Au deposits. The Navachab gold deposit, Namibia was studied to determine if Au mineralisation could be attributed to the LBCM due to conditions within the lower amphibolite facies promoting the transportation of large volumes of Bi during peak metamorphism. The presence of a syn-metamorphic intrusive lamprophyre created a redox front which would reduce the Bi-complex causing a Bi-melt to form. Correlations between Au and Bi, along with diagnostic textural features, indicates this Bi-melt was scavenging Au from coexisting hydrothermal fluids. A highly efficient LBCM requires focused fluid conduits, an extended mineralisation period, high volumes of Bi, and the stability of Bi over bismuthinite. These conditions were present at Navachab and as a consequence, Au/Bi ratios reveal that 95% of Au-mineralisation can be attributed to the LBCM. Since Au-mineralisation at Navachab was dependant on the LBCM, the surrounding regions and larger Damara Belt should be re-examined for Au deposits using LBCM conditions. Areas with high temperature fluids and focusing conduits constrain viable mineralisation zones. For example, fold hinges in close proximity to large intrusive bodies provide necessary conditions for the LBCM. Lamprophyres within these zones can be used as a proxy for high volumes of Bi and therefore enhanced Au concentrations, presenting targets within the Damara Belt for future exploration. Key words: liquid bismuth collector model, gold refinement, hydrothermal ore deposits. Email. Idurq1@gmail.com
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Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, October 31, 2013
MODELING PROGRESSIVE MELT EXTRACTION DURING PARTIAL MELTING OF GRANITIC SOURCES: A CALCULATED PHASE EQUILIBRIA APPROACH G. WEBB\ R, Poweir and S. McLaren^ ^School of Earth Sciences, University of Melbourne, Melbourne, Victoria, 3010, Australia Progressive partial melting and segregation of melt from granitic (sensu lato) source rocks is modeled at 4 and 8 kbar in the system Na20-Ca0-K20-Fe0-Mg0-AI203-Si02-H20-Ti02-02 (NCKFMASHTO). Melt extraction is assumed to occur in batches of 5% once a critical melt fraction of 7% is attained with increasing temperature. This results in the formation of a series of residues comprising solid phases plus 2% remaining melt at each melt loss step. The 7% melt fraction is based on the melt connectivity threshold (MCT) which defines the degree of melting at which individual melt pools begin to coalesce along grain boundaries. The MCT is an important end-member representing efficient, deformation-induced melt-loss during crustal anatexis. The earliest formed melt batches have the highest water content. Subsequent melt batches are extracted at progressively higher temperatures, corresponding to changes in the position of the 7% melt contour as a function of varying bulk composition. These 'residual' melts have lower water contents (-3-4 mol%) which are similar to the water contents observed in most natural granites (3-6 mol%) suggesting that natural granitic melts may have water activities much less than unity. This may have important implications for the viscosity and other rheological properties of granitic melts. The cumulative melt production resulting from the modeled progressive melt extraction during heating from the solidus up to 1000 °C at 4 kbar is -22%. In comparison, modeled bulk melting over the same temperature interval at 4 kbar produces 67% melt. These observations suggests that melt fertility may be strongly influenced by the presence or absence of deformation in supra-solidus rocks. This process has important implications for the quantities and rates of advective mass transfer during anatexis in actively deforming crust. Key words: partial melting, granites, melt loss, deformation Email: gwebb@student.unimleb.edu.au
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