Geological Society of Australia
ABSTRACTS Number 99
24"" Victorian Universities Earth and Environmental Sciences Conference
The University of IVIelbourne
November 2010
Geological Society of Australia Abstracts Volume 99
Victorian Universities Earth and Environmental Sciences Conference November 2010
Editors: Ashleigh V.S. Hood and Scarlett C.J. Blewett
ISSN 0729 011X © Geological Society of Australia Incorporated, 2010
Recommended citation: Hood, A. V.S. and Blewett, S.CJ. (eds), 2010, 24'^ Victorian Universities Earth and Environmental Sciences Conference. Geological Society of Australia Abstracts Number 99, 36p.
Copies of this publication may be obtained from: The Geological Society of Australia Incorporated Suite 706, 301 George Street Sydney NSW 2000 Australia
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 TUF UNIVERSITY Of
MELBOURNE The University of Melbourne School of Earth Sciences
The Petroleum Exploration Society of Australia
MONASH University Science
Monash University School of Geosciences
VICTORIA Droisioir Geological Society of Australia, Victoria Division
>1.
Australisn Cme-niiicnt l^r^au IVfetefimlogy
The Centre for Australian Weather and CHmale Resear:^ A partncrsh^ bctvwcn CSIRO and the &ur«ou of Meteorology
The Centre for Australian Weather and Climate Research
CSIRO
Bronze Sponsors AustralianMeteorologkal ^ OceanographicSociety The Australian Meteorological and Oceanographic Society
The 2010 VUEESC Committee Convenor - Linden Ashcroft Volume Editors - Ashleigh Hood and Scarlett Blewett Sponsorship - Erin Matchan and Helen Green Promotion - Matt Bliss and Matthew Felgate Website - Ben Harrison Catering - Dragana Zovkorajak and Campbell Watson
Foreword The University of Melbourne School of Earth Sciences is proud to host the 24"^ Victorian Universities Earth and Environmental Sciences Conference (VUEESC) in November 2010. 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 VUEESC Commitee
2010 VUEESC Programme 8.00
Registration opens
9.00
Welcome and opening remarks: David Phillips
9.10
Paoe
Keynote address: Robyn Pickering
10.30
Volcanology/Geochemistry Chair: Erin Matchan Alternating magmatic and phreatomagmatic eruption styles of the Mt. Gambler volcanic complex Newer Volcanics Province, S.E. Australia- Jozua van Otterloo Cychcity in fluctuating phreatomagmatic and magmatic eruptive styles at Tower Hill volcanic complex S.E. Australia-GemATia Prafa ' Permian caldera forming rhyolitic explosive volcanism: insights from a case study of the Ora ignimbrite, Southern Alps, Italy - Maddy Willcock Thermometamorphism and partial melting peraluminous granites: a source of KgO-rich rhyolitic melts Andrea Giuliani ^ Ar/ Ar basalt ages and the formation of southeastern highlands in Australia - TJ Chang
10.45
Ar/ Ar dating on the basalts of the Newer Volcanic Province-New ages on seven new locationsRafika Ismail
20
11.30
34
11.45
Meteorology/climate science Chair: Linden Ashcroft Explonng the sensitivity of orographic precipitation to variations in upstream conditions and terrain geometry - Campbell Watson The jumping cirrus phenomenon - Muhammad Hassim
12.00
An examination of southwest Pacific explosive cyclone development •- Mitchell Black
12.15
Constraining parameters in a simple climate model - Roger Bodman
9.30 9.45 10.00 10.15
12.30
Heat induced male stenlity in Drosophila melanogasten the east Australian dine - Brendan Dillon
13.30 13.45
Economic geology/ Geodynamlcs/ Stratigraphy Chair: Sara Jakica Chah-zard, a breccia hosted epithermal silver-gold deposit in the tethyan belt of Iran - Hossein Kouhestani Structures and alteration of world-class gold deposits, Jiaodong Peninsula, East China- Steph Mills
14.00
Characterising 3D mantle flow in the new Hebrides subduction zone- Ken McLean
14.15 14.30
Extension overpnnting shortening in an active convergent setting, the south Tibetan detachment system, NW Himalaya - Melanie Finch Sedimentology and environment of the Merinjina Tillite, northem Flinders Ranges, South Australia Helen Dulfer
14.45
Stratigraphy and sedimentology of a Cryogenian carbonate platform: Northem Adelaide Geosyncline South Australia - Thomas Fromhold
15.20
Palaeontology/ Sedimentology/ Environmental Enqineerina Chair: Ben Harrison The possibility ot early animal life in a Cryogenian reef - Marcus Thompson
15.35
Dolomite Seas: pnmary manne dolomite in the Neoproterozoic Balcanoona Formation, South Australia - Ashleiph Hood
15.50
Investigating the potential for Thiocyanate Biodegradation in mining impacted areas - Jem Baldisimo
16.05
Transportation of Water Molecules via carbon nanotubes - Chao Wu
16.20
The Effect of Planting Ratio on the Treatment Performance of Stormwater Biofiltration Systems Jason Ellerton
16.35
Judges deliberate
16.50
Awards and closing remarks
31 32 35 16 7
17 2 4 10
21 29 26 13 11 14
33 18 1 36 12
2010 VUEESC Poster Abstracts Tectonics, fission-track dating and gaodyna^^ Post Gondwana break-up thermal evolution of Tasmania and the South Tasman Rise: insights from low-temp thermochronology - Ling Chunq Low temperature thermochronology of the eastern sheared margin of the Gulf of California, Sonora Mexico. - Raul Lugo-Zazueta Rheological tests of silicones and putties, and their suitability for analogue modelling of geodynamic processes - Damiano Dell'Ertole
Page 8 24 9
Geochemistry, petrology and mineralogy Polymict Pendotite from Kimberley (South Africa): metasomatic tales from the Kaapvaal litospheric mantle - Andrea Giulliani Research on silicolites in Elashan area on Tibet Plateau - Yang Liu
15 23
Palaeontology South Polar flora and environments: Mid-cretaceous biostratigraphy of the Chatham Islands, New Zealand- Chris Mays 25 Meteorology On the development of the 24-72H forecast probability scheme for tropical cyclone formation in the Fiji region - Savin Chand 6 Physical volcanology A caldera in the Pussy Cat group: is this the story of the Kathleen ignimbrite? - Chris Mediin Relationships between geochemical evolution, eruptive styles and products associated with the phonolitic Vico Volcanic Centre, central Italy, with focus on the Farine formation - Islay Laird A microtextural insight into fluctuating magmatic and phreatomagmatic behaviour at Tower Hill Volcanic Centre, SE Australia - Jacqueline Miles Volcanology of Mt. Rouse, newer volcanics province, Australia - Julie Boyce The eruptive history and subsurface morphology of the Red Rock Volcanic Complex - an insight from physical volcanology and geophysical modeling - Teagan Blaikie Sequential eruption of alkaline and sub-alkaline magmas from a small monogenetic volcano in the Auckland volcanic field, New Zealand- Andrew Needham
27 22 28 5 3 30
Energy Renewable energy in Victoria - Robert Huva 19
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
INVESTIGATING THE POTENTIAL FOR THIOCYANATE BIODEGRADATION IN MINING IMPACTED AREAS J.G. BALDISIMO^ ^Office of Environmental Programs, University of Melbourne, Parkville, Victoria, Australia Bioremediation is a cost-effective way of removing contaminants in the environment. Thiocyanate is a contaminant often associated with industrial processes, like gold ore mining. Certain species of bacteria are capable of oxidising thiocyanate into sulfate, thus removing thiocyanate in the system. However, further understanding of bacterial thiocyanate degradation is needed to improve bioremediation strategies in mining areas. This project aims to investigate current and future applications of bioremedation on thiocyanate contamination in a gold mine in Victoria. The study will involve the identification and isolation of bacteria or microbial communities present in the soil. Cultivation, DNA-tests and statistical analyses will be employed to investigate the influence of these microorganisms on thiocyanate concentrations in soils. Keywords: thiocyanate, biodegradation, mining Email: j.baldisimo@pgrad.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
AN EXAMINATION OF SOUTHWEST PACIFIC EXPLOSIVE CYCLONE DEVELOPMENT MT. BLACK^ & A.B. Pezza^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Cyclonic systems experiencing explosive developnnent, also known as meteorological "bombs", are characterised by a reduction of central pressure at the rate of 24 hPa in 24 hours, relative to 60 degrees of latitude. Explosive cyclones are of concern to Australia and New Zealand (NZ), as general features associated with these systems include destructive winds, flood rains and coastal storm surges. On the 23rd July 2008, an exceptional cyclonic system, coined "no ordinary storm", formed over the Coral Sea, exhibiting rapid deepening as it moved towards the NZ North Island. This system had an observed 24-hr pressure drop of 28 hPa averaged at 30°S, which is double that required to satisfy bomb classification. With record low surface pressures and winds gusting to 130-160 km h , the system struck Auckland as one of the most severe storms in decades. This storm was followed by a second explosive event in a matter of days, giving little chance for NZ to recover. These events rate as the 18th and 11th most costly natural disasters in NZ since 1968, respectively, with a combined cost of NZ$73M. This study compiles a 20-year (1989-2008) climatology of Southwest Pacific wintertime explosive cyclones using 1.5° ERA-lnterim reanalysis data and the automated Melbourne University cyclone tracking algorithm. Measurements of explosive cyclone frequency, intensity and scale are used to place the two case systems into a basic climatological perspective. Keywords: explosive cyclone development, meteorological bombs. New Zealand climatology Email: m.black4@pgrad.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
THE ERUPTIVE HISTORY AND SUBSURFACE MORPHOLOGY OF THE RED ROCK VOLCANIC COMPLEXAN INSIGHT FROM PHYSICAL VOLCANOLOGY AND GEOPHYSICAL MODELLING T.N. BLAIKIE^ & F.E.G Piganis^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia Much of the current understanding of maar volcanoes is derived from surficial observations and techniques. However, in order to fully understand the eruptive process, a greater knowledge of the subsurface morphology of these volcanoes is required. This research forms part of a multi-disciplinary study combining both physical volcanology and geophysics with the aim of better understanding the eruptive history and subsurface morphology of maar volcanoes. The Red Rock Volcanic Complex (RRVC) is located in the Newer Volcanics Province of western Victoria. Over 40 eruption points have been identified within the complex including numerous polylobate maars and scoria cones. Detailed gravity and magnetic surveys have been conducted across each of the maar craters within the complex. Contrasting geophysical anomalies are observed between the different maars and indicate that variations exist in the subsurface morphology even though surface morphologies are similar. Forward modelling of several of the maars has been used to construct a 3D model of the maar diatreme and feeder dykes. Inverse modelling has been used to refine these models and to understand the density distribution within the subsurface. The volcanic deposits of the RRVC display both magmatic and phreatomagmatic explosive styles. Detailed surface mapping, petrographic and geochemical analysis across the area has identified a number of volcanic lithofacies, which have been grouped into three major geological sectors. These include: 1) magmatic scoria in the northwest, 2) phreatomagmatic surge and minor fall-out in the south and 3) phreatomagmatic to magmatic fall-out in the northeast. The northern magmatic to phreatomagmatic deposits are geochemically distinct from the southern phreatomagmatic deposits, suggesting they are sourced from two magma batches. Keywords: maar, diatreme, feeder dyke. Newer Volcanics Province, geophysics, geochemistry Email: Teagan.Blaikie@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
CONSTRAINING PARAMETERS IN A SIMPLE CLIMATE MODEL R.W. BODMAN\ D.J. Karoly^ & I.G. Enting^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia ^MASCOS, The University of Melbourne, Parkville, Victoria, Australia Simple climate models are useful for estimating the global-mean temperature response to increasing greenhouse gases. Parameters are required for the model equations, although uncertainty in the parameter values contributes to the overall uncertainty in projected temperatures. Parameter values have previously been estimated by testing model results against different historical observations and tuning to more complex models. However, the cross-correlation between observations has been a limiting factor. This study discusses an alternative approach using independent constraints that can assist in overcoming this problem. These investigations are based on MAGICC (Model for the Assessment of Greenhouse-gas Induced Climate Change) as the simple climate model; a model that has been used in all of the IPCC reports to date. Recent work has focussed on constraining the ocean vertical diffusivity parameter. Results pertaining to an examination of the ocean temperature profile, as well as a constraint based on a sea-surface temperature to ocean heat content ratio have led to a revision in the standard value used by the model. A different setting for this diffusivity parameter requires a corresponding change in the climate sensitivity parameter. Changing both these parameters results in revised temperature projections, with increased warming for a high emissions scenario. This occurs despite a reduced value for the climate sensitivity. Some implications for future warming are discussed, and the relevance of the findings to climate policy is considered. Keywords: parameter constraints, simple climate model, MAGICC, vertical diffusivity Email: rwbodman@unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
VOLCANOLOGY OF MT. ROUSE, NEWER VOLCANICS PROVINCE, AUSTRALIA J.A. BOYCE\ I. A. Nicholls^ & R.R. Keays^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia Mt. Rouse volcano lies in the Western Plains sub-province of the Newer Volcanics Province (NVP), Victoria, Australia. Lava flows from this volcano are more than triple the size of other NVP volcanoes in terms of both area covered and volume erupted. Mt. Rouse is possibly the most important volcano in the Western Plains, and yet remains little studied. Why are these lavas so voluminous and extensive compared to those of the numerous other eruption sources in the province? What is the cause of the alternating eruption styles (from magmatic to phreatomagmatic) as shown by pyroclastic deposits in the summit cones? Systematic sampling and detailed geochemical analysis of the products of Mt. Rouse are combined to determine petrogenetic evolution and provide mantle source constraints. Recognition of the mono- or polygenetic character of Newer Volcanics complexes will provide important evidence for the depth and degree of mantle melting during magma generation. The more tholeiitic (sodium-rich) the deposits, the shallower the mantle source with a larger percentage of mantle melting. However, the more alkaline (sodium-poor) the deposits, the deeper the mantle source and smaller the percentage of melting. If Mt. Rouse is polygenetic, this would have implications for the entire province, which is thought to be composed of monogenetic volcanoes. Results will be used to evaluate whether or not the NVP relates to movement over small "plume"-type features, which should lead to a trend of tholeiitic to increasingly alkaline over time. Recent research indicates that centres such as Mt. Gambier are actually monogenetic and polymagmatic. This may be the case for Mt. Rouse, as implied by the single geochemical analysis from the spatter rampart. Keywords: Newer Volcanics Province, monogenetic, phreatomagmatic, pyroclastic, lava Email: Julie.Boyce@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
ON THE DEVELOPMENT OF THE 24-72H FORECAST PROBABILITY SCHEME FOR TROPICAL CYCLONE FORMATION IN THE FIJI REGION S.S. CHAND^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia An objective methodology for forecasting the probability of tropical cyclone (TC) formation in the Fiji, Samoa and Tonga regions (the FST region) using antecedent large-scale environmental conditions is investigated. Three separate probabilistic forecast schemes are developed using a probit regression approach where model parameters are determined via Bayesian fittings. These schemes provide forecasts of TC formation from an existing system: (i) within the next 24 hours (W24h); (ii) within the next 48 hours (W48h) and; (iii) within the next 72 hours (W72h). In order to assess the performance of the three forecast schemes in practice, verification methods such as the posterior expected error. Brier skill scores, and relative operating characteristic skill scores are applied. Results suggest that the W24h scheme, which is formulated using large-scale environmental parameters, performs better than that formulated using climatology and persistence variables (CLIPER). In contrast, the W48h (W72h) scheme formulated using large-scale environmental parameters performs similar to (or poorer than) that formulated using CLIPER variables. Keywords: Bayesian, probit regression, cyclones, forecasting Email: schand@pgrad.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
''^AR/^^AR BASALT AGES AND THE FORMATION OF THE SOUTHEASTERN HIGHLANDS IN AUSTRALIA T.J. CHANG' ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia The age of the highlands in southeastern Australia has long been the subject of debate. Despite the efforts put in by many researchers over many years, the age of the highlands remains controversial. The scope of this project is to constrain the age of the southeastern highlands of Australia by providing age data for the Tertiary Older Volcanic Group basalts which lie on plateau surfaces of the highlands, mainly in eastern Victoria. The alluvial sediments that are found directly underneath the Older Volcanic Group basalts in many places indicate these basalts flowed into ancient river beds during Tertiary volcanic activity. Therefore southeastern Australia was uplifted during or after the eruption of the Older Volcanic Group basalt, as seen in these river channels. Erosion following uplift has subsequently removed much of the Palaeozoic bedrock and a large part of the erupted basalts resulting in relief inversion. Today, the preserved basalt outcrops on top of the plateaus and ridges in the eastern Victorian highlands may be remnants of once continuous and extensive basalt flows in the palaeo-river valleys. From the presence of these basalt outcrops on the highland plateaus, I propose that the palaeo-river valleys in this area predate the eruption of the Older Volcanic Group basalts and the uplift. The Older Volcanic Group basalts found on the highlands are dated for this project using the dating technique. The analyses show that the basalts in the highland area range in age from 20 to 40 Ma. The similarity in basalt ages within individual palaeovalleys indicates the Older Volcanic Group basalts were much more extensive than seen preserved in current outcrops. They are likely to represent continuous flows occurring before the uplift and erosion. Therefore, the uplift that gave rise to the southeastern highlands took place between 20 and 40 million years ago. Keywords:
dating, southeastern highlands, Older Volcanics, basalt, palaeovalleys
Email: t.chang3@pgrad.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
POST GONDWANA BREAK-UP THERMAL EVOLUTION OF TASMANIA AND THE SOUTH TASMAN RISE: INSIGHTS FROM LOW-TEMP THERMOCHRONOLOGY L. CHUNG\ BP. Kohn^ & AJ.W. Gleadow^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Evolution of the East Gondwana break-up history of the south-eastern Australia margin has been strongly influenced by two rift systems; Australia and Antarctica (the Southern Rift System (SRS)), as well as the eastern Australian margin and Lord Howe Rise. Tasmania, along with two large submerged continental fragments, the South Tasman Rise (STR) to the south and East Tasman Plateau (ETR) to the southeast, lie in a crucial setting at the junction of the two rift systems, and potentially contain a comprehensive thermal record of recent regional tectonic history. In addition, the Tasmanian transform margin, extending along western offshore Tasmania and the STR, provides an opportunity to evaluate the thermal signature of an evolved transform margin. Here we report the first apatite (U-Th-Sm)/He (AHe) study on mid-Jurassic (-175-180 Ma) Tasmanian dolerites and dredged crystalline basement STR/ETP samples. Together with previous apatite fission track (AFT) and geophysical data, this provides new insights into the post rifting geodynamic evolution of southeastern Australia. Tasmanian dolerite, a precursor to the initiation of Gondwana break-up and widely distributed over the island, forms an ideal geological 'marker' to document the post rift thermal history. Single-grain AHe results from dolerites yield ages ranging from -70-115 Ma (mostly 87-101 Ma), while most of the previously reported AFT data from all lithologies yield ages less than 120 Ma. Combined AFT and AHe results strongly support a rapid mid-Cretaceous cooling episode in Tasmania and suggest that most of the rocks currently exposed in Tasmania cooled from >110°C to -40-50°C within -20 Ma. AHe and AFT ages in this time range have also been reported from offshore Tasmania (STR) and the southeastern Australian margin (NSW and Victoria). The mid-Cretaceous cooling episode corresponds to the time of early formation of the Tasman Basin, related to rifting between the Lord Howe Rise and the eastern Australian margin at 95-83 Ma. It predates transform faulting along the western Tasmania and STR margin, where AFT results yield ages of -40-60 Ma recording the thermal imprint of break-up between southern Australia and Antarctica. Keywords: thermochronology, apatite (U-Th)/He, apatite fission track, Tasmanian dolerite, transform margin, Gondwana breakup Email: I.chung4@pgrad.unimelb.edu.au
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
RHEOLOGICAL TESTS OF SILICONES AND PUTTIES, AND THEIR SUITABILITY FOR ANALOGUE MODELLING OF GEODYNAMIC PROCESSES D. DELL'ERTOLE^ & W. P. Schellart' ^School of Geosciences, Monash University, Clayton, Victoria, Australia The choice of suitable materials for analogue modelling of geodynamic processes is the initial and essential step in model planning. In this work we show the results of rheological tests executed on different viscous materials. The investigated materials are a transparent silicone gum (Rhodorsil Gum FB) and a pink putty (Dow Corning 3176 Dilatant compound). The tests were completed to discover if such materials could be used to build analogue models of rock layers with a high-viscosity contrast, which would be deformed in a special shear-box machine to study the development of sheath folds! Samples of different viscosity can be made by mixing the two compounds mentioned above, in various percentages. The transparent silicone gum has been mixed with 5%, 10%, 15%, 20%, 25%, 30% and 50% of pink putty (% in weight). The tests were performed using an Anton Paar rheometer Physica MCR 301, and for each sample a shear rate ramp, a frequency sweep and a temperature ramp test were done. Tests on pure silicone gum show that this material has a Newtonian behaviour for a wide range of shear rates (2.6 x 1 0 ' - 1 x lO"' s ' ) , while its viscosity is approximately exponentially dependent on temperature, decreasing with increasing temperature. The same test on the pink putty shows that the linear behaviour is present in a very small range of shear rates (1 x 10"^ 3 x 1 0 " s"), and the putty is mainly a power-law material. Also, the pink putty shows a greater dependency on temperature; with the highest viscosity increment at low temperatures. The frequency sweep tests provided indications about the prevailing behaviour (viscous vs. elastic) of the compound in defined oscillation frequency domains. It emerges that in the experimental shear rate range (1x10" - 1 X 10" s"), both materials (and their mixes) are suitable for analogue modelling. Keywords: rheology, silicone gum, shear rate, frequency sweep test, sheath folds Email: Damiano.DellErtole@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
HEAT INDUCED MALE STERILITY IN DROSOPHILA MELANOGASTER: THE EAST AUSTRALIAN CLINE B. DILLON^'^ ^Department of Zoology, The University of Melbourne, Parkville, Victoria, Australia Bio21 Institute, The University of Melbourne, Parkville, Victoria, Australia Climate change will push many species to the end of their physiological tether and change species composition and ecosystem functionality. Such organisms include insects which carry out roles in ecosystems such as the pollination and recycling of organic matter. The fruit fly, Drosophila melanogaster, is a well described model organism which has provided poignant insights into the evolutionary and ecological response of insects to climatic stress. A good system for investigation is the dine in temperature resistance that became established along Australia's east coast following invasion of the species about 100 years ago. This dine is defined by increased resistance of fruit flies towards tropical populations and implies adaptation to the warmer tropical climate in the north. The pattern holds for exposure time-intensity that induces paralysis and death but has not been investigated for male sterility. Temperature induced male sterility should be an important component of male reproductive success in tropical populations and we expect resistance to increase towards the northern end of the coast. Indeed, tropical populations from across the globe have been shown to retain a higher instance of male fertility than temperate populations following development at high temperatures. I tested eight populations spanning northern Tasmania to mid-Queensland for fertility following developmental exposure and five days of adult exposure to sterility inducing temperatures. There was differentiation in resistance between individuals but despite an apparent trend in resistance it was not significant. Male fertility may not be as important as suggested by previous studies. Alternatively, there may not have been sufficient time for the evolution of male resistance to temperature induced sterility in D. melanogaster and developmental stages may be vulnerable under higher temperatures predicted in climate models. Keywords: dine, sterility, thermotolerance, Drosophila melanogaster, climate change Email: b.dillon@ugrad.unimelb.edu.au
10
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
SEDIMENTOLOGY AND ENVIRONMENT OF THE MERINJINA TILLITE, NORTHERN FLINDERS RANGES, SOUTH AUSTRALIA H.E. DULFER^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia The Neoproterozoic is one of the most enigmatic periods in the Earth's history. It is characterised by extreme climatic fluctuations and contains extensive periods of glaciation. Competing hypotheses, such as the Snowball Earth, Zipper-Rift Earth and High Obliquity theories, have been developed in order to explain both the apparent global correlation of glacial sequences into two or three major glaciations and paleomagnetic evidence that indicates some of the Neoproterozoic glacial sequences were deposited at mid to low latitudes. These theories have been highly contentious over the past 30 years. Recently, very little attention has been paid to the glacial sediments themselves. Therefore, the sedimentology of the Merinjina Tillite, a Sturtian glacial deposit located near Arkaroola in the northern Flinders Ranges, has been recorded through detailed stratigraphic sections. The sedimentary evidence that has been collected has been used to reconstruct the glacial depositional environment in conjunction with glacial facies models and information obtained from modern glacial analogues. Keywords: Neoproterozoic, glacial sedimentology. Snowball Earth, Sturtian glaciation Email: h.dulfer@ugrad.unimelb.edu.au
11
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
THE EFFECT OF PLANTING RATIO ON THE TREATMENT PERFORMANCE OF STORMWATER BIOFILTRATION SYSTEMS J.P.ELLERTON\ T.D. Fletcher^ & B.E. Hatt' ^ Department of Civil Engineering, Monash University, Clayton, Victoria, Australia Stormwater biofiltration systems filter diverted runoff through dense vegetation followed by vertical filtration through a porous soil-based media. The vegetation used in a biofilter enhances the pollutant removal performance, however, different plant species vary in their contribution to pollutant removal. Lomandra longifolia and Carex appressa are two plants frequently used in biofilters but little is known about how they behave when planted together. Observations have shown that Lomandra replaces the Carex plants in the planted community over time. Carex appressa is the better performing plant and over time, this shift in community composition may leave a biofilter with a monoculture of Lomandra longifolia and a diminished capacity for filtering stormwater. We investigated the treatment performance of these two plant species grown in different ratios in lab-scale biofiltration columns. The plants were grown in experimental biofilters over five different planting ratios and fed with artificial stormwater. Variations in effluent water quality were found to correlate with planting ratios, suggesting a competitive effect between the plants may be occurring. This work aims to improve our understanding of how plants commonly used in biofilters interact with each other and will describe ideal planting ratios for optimum nutrient removal. Keywords: stormwater, biofiltration, water quality, nitrate, Carex appressa, Lomandra longifolia Email: jason.ellerton@monash.edu
12
Geological Society of Australia
Victorian Universities Earth and Environnfiental Sciences Conference University of Melbourne, November 5, 2010
EXTENSION OVERPRINTING SHORTENING IN AN ACTIVE CONVERGENT SETTING: THE SOUTH TIBETAN DETACHMENT SYSTEM, NW HIMALAYA M. FINCH\ R. Weinberg^ & P. Hasalova^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia The collision of India and Asia at --55 Ma was accommodated by a number of large-scale thrust faults, the northernmost of which is the Main Central Thrust (MCT). To the north of, and parallel to the MCT lies the South Tibetan Detachment System (STDS) which is an extensional system that extends along the entire length of the 2,400 km Himalaya. The MCT and STDS shared a period of broadly coeval movement in the early Miocene which caused extrusion of the High Himalayan Crystalline Series (HHCS), the metamorphic core of the Himalaya. Relatively little research has focused on the NW Himalaya, in the Zanskar Range, where the STDS is known as the Zanskar Shear Zone (ZSZ) and overprints an earlier stage of thrusting. Here, we report the relationships between different generations of structures using field mapping, structural analyses, fabric analysis, and metamorphic petrography. The results indicate that the ZSZ is a 2.7 km normal shear zone which overprints an earlier thrust shear zone. The expression of normal shearing was found to be dependent on structural position and lithology. Less competent lithologies that were at deeper structural positions during normal movement record ductile normal movement only. More competent lithologies at shallower positions preserved earlier thrust shear structures with brittle normal movement overprint. A kilometre scale leucogranite intrusion zone, the Gumburanjon Dome, was found to have been exhumed during this normal movement. Additionally, the normal and thrust shear planes were found to be parallel and with the same but opposite transport directions, suggesting the normal shear zone reactivated earlier thrust planes. As such, this region records structures which reflect a gradual progression from high temperature conditions during thrusting to gradually cooler conditions as normal movement on the ZSZ was activated and extruded the HHCS. Keywords: Himalaya, South Tibetan Detachment System, Zanskar Shear Zone, normal shear zone Email: Melanie.Finch@monash.edu
13
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
STRATIGRAPHY AND SEDIMENTOLOGY OF A CRYOGENIAN CARBONATE PLATFORM; NORTHERN ADELAIDE GEOSYNCLINE, SOUTH AUSTRALIA T A FROMHOLD^ & M.W. Wallace^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Extensive fieldwork carried out in the Cryogenian (mid-Neoproterozoic) succession of the northern Flinders Ranges, South Australia, reveals a complex sedimentary record. A giant reef complex, developed in the Balcanoona Formation, is found to prograde over the deep-water basinal shales and turbidites of the Tapley Hill Formation. The reef complex preserves lithofacies similar in style to Phanerozoic reefs. These include forereef (basinal), reef-margin (slope) and backreef (shallow platform) deposits. Supratidal redbed deposits of the Angepena Formation are found to laterally grade into and interfinger with the backreef facies of the Balcanoona Formation. The Angepena Formation is interpreted as a coastal mudflat deposit. A regional unconformity occurs above the Angepena, Balcanoona and Tapley Hill Formations which finitely constrains the relative depositional ages and lateral equivalency of these units. Keywords: stratigraphy, sedimentology, Adelaide Geosyncline, carbonate platform, Cryogenian Email: t.fromhold@pgrad.unimelb.edu.au
14
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
POLYMICT PERIDOTITE FROM KIMBERLEY (SOUTH AFRICA): METASOMATIC TALES FROM THE KAAPVAAL LITOSPHERIC MANTLE A. GIULIANI^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Kimberlites are unusual volcanic rocks whose importance resides in representing not only the main diamond source, but also an "open window" on the sub-continental lithospheric mantle thanks to their large inventory of entrapped peridotitic xenoliths. Polymict peridotites are a rare xenolithic occurrence in kimberlites worldwide. They are metasomatised ilmenite, phlogopite, rutile, sulphide (IPRS) and orthopyroxene enriched rocks, displaying a substantial xenocrystic contribution, sampled from the garnet-facies of the sub-continental lithospheric mantle by Group I kimberlites. The subject of this study (sample DU1) is a veined harzburgite sampled from the Bultfontein Pipe (Kimberley district. South Africa) that experienced multiple enriching episodes among which the IPRS-type represents the final event. The melt crystallizing the IPRS phases inside this rock depicts a coherent evolution trend, as recorded by DU1 mineral chemistry, attributed to a process of percolative fractional crystallisation. The petrogenesis of this xenolith is summarised as a four-step process: i) an ancient partial melting event, typical of all the cratonic areas, with the production of a depleted olivine-rich protolith; ii) silica re-enrichment leading to the extensive replacement of olivine by orthopyroxene; iii) aqueous fluid-induced metasomatism that crystallised the first generation of phlogopite; and iv) IPRS metasomatism, that introduced abundant clinopyroxene and garnet xenocrysts. The preservation of disequilibrium textures within the IPRS assemblage, together with the strong inter- and intracrystalline chemical heterogeneity recorded by the IPRS metasomatic phases, indicate that this event slightly pre-dates the kimberlite entrainment, but also that a close genetic relationship exists between the metasomatic agent and the kimberlite. It is suggested that the IPRS melt enriched the kimberlite source region in incompatible elements, hence lowering its solidus temperature and promoting the melting process. This is in agreement with the notion that Group I kimberlite petrogenesis is a twostep process involving early incompatible element enrichment imposed on a depleted mantle source followed by partial melting. Keywords: Kimberley, sub-continental lithospheric mantle, multiple metasomatism, IPRS metasomatism, kimberlite petrogenesis Email: a.giuliani@pgrad.unimelb.edu.au
15
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
THERMOMETAMORPHISM AND PARTIAL MELTING OF PERALUMINOUS GRANITES: A SOURCE OF K2O-RICH RHYOLITIC MELTS A. G I U L I A N r & M. Gaeta^'^ ^ School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia ^ Dipartimento di Scienze della Terra, Universita di Roma La Sapienza, P.le Aldo Moro 5,1-00185, Rome, Italy ^ Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Sismologia e Tettonofisica Via di Vigna Murata 605, 1-00143, Rome, Italy The Reddish Granites of the Gennargentu Igneous Complex (central Sardinia) represent the thermometamorphic equivalent of micaceous peraluminous granites fringing the eastern part of a shallow crustal (pressure = 1.9 kbar) late-Permian quartz-dioritic intrusion. They display petrographic and geochemical zoning related to the distance from the heat source inducing the thermal event (i.e. the quartz-dioritic intrusion). The metagranites close to the quartz-diorites display petrographic evidence (e.g. occurrence of granophyric intergrowths and cumulus-textured plagioclase) and geochemical characteristics (Fe203, MgO, CaO, Ba, Zr enrichment; Si02, K2O, Pb, Rb depletion) suggesting that they are the restite of a process involving large degrees of partial melting and subsequent melt loss (about 60 wt% according to a fractional melting model). The elevated melting rate is constrained by the large amount of heat supplied by the successive injections that define the high-temperature (1030-1050°C) emplacement of the quartz-dioritic intrusion and by the protolith composition, which is close to the granitic minimum/eutectic for the estimated 1.9 kbar pressure. Alternatively, a lower melting rate could be triggered by the influx of a highly evolved melt, derived from the differentiation of quartz-dioritic liquid and driven by the pressure gradient imposed by the migration of the granitic melt which mixed with the granitic restite. The K20-rich silicic melt produced in the portion of the aureole closest to the magmatic intrusion affected the chemical composition of the outer metagranites, enhancing the growth of K-feldspar, and migrated upward, contributing to the Permian acid volcanism of the Gennargentu area. The potassic melt displacement was favoured by its high mobility (H20-undersaturated) and the positive thermal anomaly experienced by Sardinia in the Permian. Its bi-directional migration paths arose from the diverse forces operating on it, nominally the high-silica melt buoyancy, as well as the stress induced by the regional extensional regime and by the time-spread quartz-dioritic melt emplacement. Keywords: granophyric granites, red granites, thermometamorphism, partial melting, Gennargentu Igneous Complex Email: a.giuliani@pgrad.unimelb.edu.au
16
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
THE JUMPING CIRRUS PHENOMENON M.E.E. HASSIM^&T.P. Lane^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Very tall cumulonimbus clouds are often indicative of severe thunderstorms and weather. These storms often reach the high altitudes of the upper troposphere (>12 km in the tropics) and some can even penetrate the lower stratosphere (>17.5 km) via overshooting updrafts. These deep convective storms transport copious amounts of water (in the form of ice and water vapour) and thus play an important role in regulating the moisture tendencies of the region. However, the complex dynamics at the top of these storms do give rise to some interesting and spectacular above-cloud top phenomena such as jumping cirrus and chimney-like plumes above the thunderstorm anvils. In this presentation, we will show both observed and modelling evidence which suggest that such phenomena are commonly occurring features above overshooting thunderstorms. In addition, we will discuss the mechanism that causes them, their ohgins (i.e. where the air has come from) and what implications such phenomena might have for the lower stratospheric water budget. Keywords: jumping cirrus, overshooting thunderstorms, cloud phenomena Email: m.hassimi @pgrad.unimelb.edu.au
17
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
DOLOMITE SEAS: PRIMARY MARINE DOLOMITE IN THE NEOPROTEROZOIC BALCANOONA FORMATION, SOUTH AUSTRALIA A.V.S. HOOD^ & M.W. Wallace^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia The unusual abundance of dolomite in the Proterozoic has been the subject of decades of research, yet fundamentally, even the conditions of dolomite formation remain poorly understood. However, the recent discovery of dolomitic Cryogenian reef complexes in the Adelaidian stratigraphy of the northern Flinders Ranges, South Australia may significantly improve our understanding of Precambrian carbonates. The reef complexes provide an ideal setting for the documentation of a range of synsedimentary and early diagenetic processes. While the reef complexes consist entirely of dolomite, allochthonous reef material present in time-equivalent basinal shales displays a range of carbonate mineralogies. These blocks show varying degrees of dolomitisation, with smaller blocks composed of limestone and larger blocks partially or completely dolomitised. The preservation of this transitional mineralogy suggests that dolomitisation occurred early, as a syn-sedimentary process. In the reef facies, abundant neptunian dykes, sheet cavities and growth framework cavities host a variety of fibrous, inclusion-rich dolomite cements. These columnar and fascicular-optic isopachous cements are overlain by internal sediment and are cross cut by later sediment-filled fractures, indicating unequivocally that they are marine precipitates. According to an understanding of Phanerozoic reef diagenesis, these fibrous cements might easily be interpreted as primary calcium carbonate marine cements which have been mimetically dolomitised. However, cathodoluminescence microscopy reveals delicate growth zonation and acicular fabrics within the fascicular-optic and columnar cements. Replacement of aragonite, calcite or even proto-dolomite would destroy this finescale zonation, suggesting that dolomite was the original mineralogy of these cements. Primary marine dolomite cements are essentially undocumented in the geological record, and their very existence is highly contentious. The occurrence of primary dolomite in Cryogenian carbonates suggests unusual ocean conditions at this time, possibly relating to oceanic re-equilibration following the massive Sturtian glacial event. Keywords: dolomite, marine cement, Cryogenian, Balcanoona Formation, reef diagenesis Email: ashleigh.hood@pgrad.unimelb.edu.au
18
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, Novennber 5, 2010
RENEWABLE ENERGY IN VICTORIA R. HUVA^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia With renewed pressure from industry and environmental lobbies to find 'green' solutions to Australia's future energy needs, technologies such as wind and solar power are seen as having an important role in the inevitable switch to renewable energy production. However, given the relatively small observational network across Australia, little can be said about the potential for non-observed locations to produce renewable energy. Thus, this study explores the integration of a numerical weather prediction model (WRF) into the process of co-locating wind and solar power plants, with the aim of meeting electrical demand for Victoria. Analysis across 5 days from each season is used to highlight the general covariance of wind speed and solar irradiance for Victoria, and then a conversion to wind and solar power is made. Importantly, this study uses the BFGS optimisation routine to allocate wind and solar resources to pre-determined locations. The output from these locations is optimised to match demand. It is shown that, as expected, the two resources alone cannot match demand for the whole time period. Significantly though, with only a 24% utilisation of gas back-up this study demonstrates that wind and solar can be combined to meet demand predominantly on their own. Contrary to common belief, these findings show that if care is taken in locating wind and solar power plants, the potential for integrated renewable energy to meet the majority of load requirements is very high. Keywords: wind energy, solar energy, numerical modelling, optimisation, energy demand Email: r.huva@ugrad.unimelb.edu.au
19
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
"^^AR/^^AR DATING OF SELECTED YOUNG VOLCANOES, NEWER VOLCANIC PROVINCE, VICTORIA R. ISMAlU ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia The Newer Volcanic Province represents the youngest chapter of Cainozoic volcanism in Australia. Despite having well preserved outcrops, the region has not been extensively dated and absolute ages of the volcanoes in the region are incomprehensive. Ages obtained from the province were previously determined by the potassium-argon (K-Ar) method, which has been gradually replaced by the Arr Ar method; a more superior technique that overcomes many flaws identified in the K-Ar method. Ten samples^of feldspar megacrysts were provided by the Museum of Victoria and seven were utilised for "^^Ar/^^Ar dating. Samples were selected mainly based on the potassium content determined from geochemical analysis. Most of the basalt samples originated from basalt flows in the Central Upland and Western Plain sub-provinces. In geochronological order, locations of the samples include Red Rock in Alvie (0.102 ± 0.046 Ma), Mount Franklin (0.111 ± 0.015 Ma), Lake Bullen Merri (0.119 ± 0.020 Ma), Ridge Road Quarry in Daylesford (1.999 ± 0.081 Ma) and Mount Kororoit (3.72 ± 0.34 Ma). Two of the samples were taken from the Anakies and the ages determined were 2.119 ± 0.081 Ma and 2.132 ± 0.031 Ma respectively. Data reported in this study provides evidence to support multiple volcanic events within the Newer Volcanic Province which occurred over a period of approximately 4.5 Ma. The analyses and the reported ages not only provide new geochronological data for the province but also elucidate the difficulties in dating very young basalts using the method. Keywords:
dating. Newer Volcanic Province, feldspar megacryst, geochronology
Email: r.ismail@pgrad.unimelb.edu.au
20
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
CHAH-ZARD, A BRECCIA-HOSTED EPITHERMAL SILVERGOLD DEPOSIT IN THE TETHYAN BELT OF IRAN H. KOUHESTANr, M. Ghaderi^ & K. Zaw^ ^Department of Geology, Tarbiat Modares University, Tehran, Iran CODES, University of Tasmania, Hobart, Tasmania, Australia The west-central volcanic mineral belt of Iran, the Urumieh-Dokhtar Magmatic Arc (UDMA) forms part of the pnncipal metalliferous Tethyan belt stretching more than 2000km long and 100km wide, hosts world-class porphyry copper and epithermal gold-silver deposits similar to those of the Andes. The Chah-Zard Ag-Au epithermal deposit is located in the central part of the UDMA. The country rocks form a circular-shaped volcanic complex consisting of poorly sorted-polymictic clast-supported volcanic breccias hosted in altered Miocene (6.24 Ma) intermediate to felsic volcano-plutonic units (andesite, trachy-andesite, dacite, porphyritic dacite, porphyritic rhyolite). The alteration assemblages are quartz, illite-pyrophyllite, K-feldspar, sericite and jarosite occurring in an area greater than 9 kml The mineralisation at Chah-Zard is directly related to the intensity of silicification and is hosted in sulphide-cemented breccia; and gold-bearing quartz-sulphide-gypsum veins, accompanied by illitepyrophyllite and jarosite alterations. Samples collected from trenches and diamond drill holes show up to 21 g/t Au , 92 g/t Ag and 66 g/t Au, 463 g/t Ag, respectively. Ore minerals are pyrite, arsenical pyrite, chalcopyrite, galena, sphalerite, native gold, Ag-tetrahedrite, Ag-tennantite, chalcocite, arsenopyrite, marcasite, sulfosalts and bornite. The major associated gangue minerals are quartz, gypsum and jarosite. Based on the intensity of silicification, argillic and jarosite alteration, with sulphides and gypsum cements in the gold-bearing veins, it is likely that the Chah-Zard deposit could be an overprinting system of low-sulphidation to high-sulphidation Ag-Au epithermal mineralisation, making it a model for exploration of similar deposits in the Tethyan belt. Further mineralogical-textural studies are in progress to fully understand the ore-forming processes. Keywords: epithermal, breccias, Chah-Zard, Urumieh-Dokhtar Magmatic Arc, Tethyan belt, Iran Email: Kouhestani®modares.ac.ir
21
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
RELATIONSHIPS BETWEEN GEOCHEMICAL EVOLUTION, ERUPTIVE STYLES AND PRODUCTS ASSOCIATED WITH THE PHONOLITIC VICO VOLCANIC CENTRE, CENTRAL ITALY, WITH FOCUS ON THE FARINE FORMATION M.I. LAIRD\ R.A.F. Cas' & G. Giordano^ ^ School of Geosciences, Monash University, Clayton, Victoria, Australia Dipartimento di Scienze Geologiche, Universita di Roma Tre, 00146 Roma, Italy Vico Volcano is a well-developed Neogene-Quaternary phonolitic stratovolcano located at the northern edge of the Roman Magmatic Province, approximately 60 km north of Rome in central Italy. The basal part of the stratovolcano is predominantly composed of lavas, with a composite summit explosive caldera. Vico Volcano had a complex history commencing at 419 ka and ending at 95 ka. Three main eruptive cycles have been identified within the Vico Volcanic Complex: the Rio Ferriera Synthem (419 - 400 ka), representing the initial effusive phase intermittent with minor explosive phases of activity; the Lago di Vico Synthem (305 - 144 ka), characterising the major explosive caldera forming phase; and the Monte Venere Synthem (138 - 95 ka) which represents final effusive and phreatomagmatic volcanism. Four major ignimbrite units have been identified in the Lago di Vico Synthem: Farine, Ronciglione, Sutri, and Caprarola Formations. Most of the units examined were leucite-bearing, however, the Ronciglione Formation is leucite-free. The Farine Formation marks the initial caldera-forming phase and multiple lateral and vertical variations have been observed. Pyroclastic fall and flow deposits of the Farine Formation outcrop to the west, northwest and northeast parts of the volcano. Pyroclastic fall deposits range in thickness from 0.2 - 1.2 m, with the thicker deposits occurring towards the northeast. The ignimbrite consists of at least two flow units, and includes lithic-rich lenses, where lithics are up to 3 m in diameter. One of these lenses is observed to the northwest of Vico caldera, approximately 5 km from the source. Observations infer this brecciated lens to be a lag-flow breccia deposit. Farine spatter flow deposits, approximately 1 m thick, are also observed to the northwest of the volcano, and are often welded. Keywords: ignimbrite, phonolite, caldera, Vico Volcano, Central Italy Email: lslay.laird@sci.monash.edu.au
22
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
RESEARCH ON SILICOLITES IN ELASHAN AREA ON TIBET PLATEAU Y. LIU^ & L.Z. W a n g ^ ^Department of Civil Engineering, Monash University, Clayton, Victoria, Australia Changsha Research Institute of Mining and Metallurgy, Changsha, Hunan, China Silicolites have won the attention of geologists due to their special chemical composition and the denotative meanings for mineral exploration, palaeogeographic reconstructions and other applications. Silicolites widely occur in the Elashan area of the Tibet Plateau (which is one of the mineral-rich areas of China). In this research, studies on macro-elements, trace elements and rare-earth elements were conducted to determine the genetic types and palaeogeographic environment of silicolites. In macro-element research, Al203-Si02 relationship graphs showed silicolites are a result of submarine hydrothermal formation. Results of Al/(A|+Fe+Mn), AI/(AI+Fe) and Fe/Ti-AI/(AI+Fe+Mn) reinforced the hydrothermal deposition genetic type of these silicolites. Meanwhile, MnO/TiOs and Fe203/Ti02-Mn0/Ti02 '2 suggested oceanic deposit types for the silicolites. Studies of rare-earth elements showed the palaeogeographic environment of formation is between a continental margin and an oceanic basin; some areas were affected by terrestrial material. Results of research on trace elements showed low Co/Ni and high U/Th, which further improved the theory of hydrothermal formation of the silicolites. In addition, CryTh suggested that composition minerals of silicolites are from diverse sources. Combining with research on the geological background, the origin of the minerals may include terrestrial material, volcanics and later hydrothermal superimposition. Consequently, silicolites in Elashan area on the Tibet Plateau resulted from hydrothermal deposition. The depositional environment is between a continental margin and an oceanic basin; terrestrial material does influence the formation and composition of silicolites, but not majorly. Keywords: silicolites, hydrothermal deposit, Elashan, trace elements, geochemistry Email: Liuyang2585899@163.com
23
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
LOW TEMPERATURE THERMOCHRONOLOGY OF THE EASTERN SHEARED MARGIN OF THE GULF OF CALIFORNIA, SONORA, MEXICO R.E. LUGO-ZAZUETA\ BP. Kohn\ AJ.W. Gleadow\ T. Calmus^ E. RamosVelazquez^ & J. M. Fletcher"^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia ^Institute de Geologia, UNAM, Hermosillo, Sonora, 83000, Mexico ^UABCS, Departamento de Geologia, La Paz, B.C.S., 23080, Mexico ^Departmento de Geologia, CICESE, Ensenada, Baja California, Mexico Since Oligocene time, northwestern Mexico has been under an extensional tectonic regime that ultimately evolved into the current morphology and geology of the Gulf Extensional Province (GEP). In mid-Tertiary time plate interactions changed from compression (Laramide event) to extension (Basin and Range (BR)). The Baja California peninsula commenced its transfer from the North American to the Pacific Plate at --12.3 Ma, as an orthogonal rift that changed to a sheared trans-tensional oblique rift at Ma. Kinematic models used to reconstruct plate evolution suggest that the Pacific Plate has been displaced by up to -700 km, mainly by transform faulting, from the relatively stable North American Plate. As the GEP evolved, spreading centres and relative displacement along the transform faults during oblique rifting are proposed to have migrated to the west-northwest. The eastern margin is considered an abandoned rift margin that has been inactive since ~3 Ma. Due to a lack of tectonostratigraphic indicators in the predominantly granitic basement, details of the timing of deformation and evolution of the eastern margin of the GEP are poorly constrained. Hence, thermochronological dating techniques represent an excellent tool for constraining the timing of evolution of this sheared continental margin. Previous apatite (U-Th-Sm)/He (AHe) ages from the western margin of the Gulf of California reported relatively young ages (1.6 - 3.0 Ma). These were attributed to thermal resetting, probably by hydrothermal fluid circulation, related to evolution of the Ballenas transform fault. We present new apatite fission track (AFT) and AHe ages, obtained from Laramide granitoid rocks on the eastern margin of the Gulf of California along a 270 km coastal strip of the Sonoran coast (from Puerto Libertad to Guaymas). The youngest ages obtained consistently range from 4-7 Ma and do not show any clear indications of hydrothermal alteration (at outcrop or microscopic scale). These are considered to indicate a minimum age for onset of rifting, along the Tiburon transform fault. AFT ages obtained further inland are consistently older and in many cases are thought to be related to cooling associated with BR extension. Further studies are underway to determine whether a discrete cooling pattern between the BR and GEP extensional phases can be distinguished or whether the two overlapped in time and space.
Keywords: thermochronology, Gulf Extensional Province, tectonics, apatite fission track dating Email: raull@pgrad.unimelb.edu.au
24
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
SOUTH POLAR FLORA AND ENVIRONMENTS: MIDCRETACEOUS BIOSTRATIGRAPHY OF THE CHATHAM ISLANDS, NEW ZEALAND C. M A Y S \ J . D . S t i l w e i r & M . H a i r ^School of Geosciences, Monash University, Clayton, Victoria, Australia The Chatham Islands are home to arguably the highest palaeolatitude mid-Cretaceous fossil plant locality of the Southern Hemisphere. As such, the palaeoenvironment may represent the most extreme climatic conditions of the mid-Cretaceous; the floral ecology should reflect this. This study stratigraphically logged two sedimentary sequences of the mid-Cretaceous Tupuangi Formation, Chatham Islands, with 41 palynomorph samples retrieved and processed for biostratigraphic analysis. An age of Cenomanian to lower Turonian was derived, which supports the notion of a failed-rift basin in eastern Zealandia prior to sea-floor spreading between Zealandia and Antarctica in the Late Cretaceous. Relative abundances of pollen and spores indicate a floral ecology dominated by conifers (primarily Cupressaceae, Podcarpaceae & Araucariacae), with minor seedferns, ferns, gingkos, lycophytes, bryophytes and angiosperms. There is a rise in microplankton and angiosperm microfossil abundance and diversity, suggesting increasing marine influence and basinal subsidence, as well as the initial stages of angiosperm dominance at southern polar latitudes.
Keywords: Cretaceous, Chatham Islands, biostratigraphy, floral ecology, terrestrial environments, polar circle, greenhouse Email: chris.mays@monash.edu
25
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
CHARACTERISING 3D MANTLE FLOW IN THE NEW HEBRIDES SUBDUCTION SYSTEM K.A. MCLEAN\ M.A. Jadamec^ & P.M.J. Durance^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia The New Hebrides subduction zone is characterised by slab curvature, variability in slab depth, southward shallowing slab dip, and a lateral slab edge. Such characteristics have been shown to drive mantle flow in subduction zones. The arcuate trench uniquely causes the back-arc spreading ridge to be perpendicular to the subduction zone trench. The Vanuatu arc comprises the island arc system of the New Hebrides subduction zone. The southern Vanuatu arc/Hunter Ridge region is characterised by an abundance of primitive lavas. We model the 3D mantle flow field to determine the interaction between spreading centre upwelling and slab edge toroidal flow, in order to provide a tectonic framework for the crystallisation history of these primitive lavas. We present a 3D instantaneous flow model of the New Hebrides subduction zone to solve for temperature-dependent solid-state Newtonian deformation of the lithosphere and mantle. Model input constraints and observational constraints were derived from the synthesis of available geological and geophysical data. We find that substantial mantle flow around the slab edge toward the mantle wedge occurs by toroidal motion. Additionally, the upward component of mantle flow is enhanced by back-arc upwelling. Mantle flow is a key geodynamic process because it not only transports mantle material, but also mantle partial melts and advected heat. A rapid upward component of flow, combined with an increased geothermal gradient, may provide the magmatic conditions necessary to support the formation, preservation and subsequent eruption of the primitive lavas at the southern Vanuatu arc. The integration of geodynamics with geochemistry allows us to better understand evolutionary processes at subduction zones, indicating that historical 2D models of subduction underestimate the complexity of these inherently 3D processes. Keywords: 3D modelling, Vanuatu arc. Hunter Ridge, geodynamics, primitive magmas Email: ken.mclean@monash.edu
26
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
A CALDERA IN THE PUSSY CAT GROUP: IS THIS THE STORY OF THE KATHLEEN IGNIMBRITE? C.C. M E D L I N \ M. W e n e i ^ & R A F . Cas^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia The Kathleen Ignimbrite is a km thick, rhyolitic, volcanic rock succession thought to be part of an explosive caldera sequence. The primary objective of this research is to investigate if this rock succession really does represent an explosive caldera system, which erupted in Australia during the late Proterozoic, using a combination of field mapping, volcanic facies analysis, and geophysics. The research area is located in the Musgrave Province of Central Australia. The geological setting is a Mesoproterozoic to Neoproterozoic mobile belt which forms a basement inlier, hosting high-grade metamorphic rocks (amphibolite to granulite facies), with widespread volcanic deposits and lesser sedimentary precursors that are intruded by a number of younger granitoids, and a combination of mafic and felsic dykes. The Kathleen Ignimbrite is the formal stratigraphic unit name given to this volcanic rock succession This unit, together with a sedimentary, volcaniclastic, and mafic package of rocks, termed the Glyde Formation, forms the Pussy Cat Group. The Pussy Cat Group is part of the much larger and more widespread Bentley Supergroup. The Bentley Supergroup is made up predominantly of felsic and mafic volcanics, volcaniclastic rocks, and interlayered sedimentary rocks that date between -1075 and -1025 Ma, with the Kathleen Ignimbrite unit dated at 1071 ± 5 Ma. The Kathleen Ignimbrite exhibits interesting volcanic textures, such as well-defined and preserved fiamme populations, remnants of glass shards, autobrecciation and hyaloclastite formation; and structures, such as flow-folds and flow-banding. In addition there are interesting stratigraphic relationships with the underlying and overlying lithologies, including intruding clastic dykes, overlying breccias, epiclastic deposits, bedded tuffs, and genetically-related, contemporaneous, synsedimentary rhyolitic porphyry intrusions. All of these aspects, combined with the volcanic rock succession's vertical thickness and lateral extent, make a strong argument for the proposed explosive caldera setting in which these volcanics were deposited. Keywords: rheomorphic ignimbrite, caldera, Musgrave Province Email: chris.medlin@monash.edu
27
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
A MICROTEXTURAL INSIGHT INTO FLUCTUATING MAGMATIC AND PHREATOMAGMATIC BEHAVIOUR AT TOWER HILL VOLCANIC CENTRE, S.E. AUSTRALIA J. MILES^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia Fluctuating magmatic and phreatomagmatic phases at Tower Hill Volcanic Complex in South Eastern Australia caused the formation of an exceptionally wide (>3km) maar with a rim sequence of fine ash, ash lapilli, lapilli ash and scoria lapilli deposits. The eruption of Tower Hill ended with a purely magmatic episode that resulted in the formation of nested scoria and spatter cones. This location provides an excellent case study for the investigation of factors influencing phreatomagmatism in what would otherwise likely have been an explosive Strombolian, if not Microplinian, monogenetic eruption, based on field observations. Whilst bulk magma composition remained constant throughout the history of Tower Hill, microtextural variations between eruptive products reveal varying ascent rates for different eruptive phases. Juvenile clasts from the maar-rim, forming explosive magmatic phases, have high microlite number densities relative to mafic volcanics elsewhere, but juvenile phreatomagmatic material contains an order of magnitude more crystals. Crystallinity of both deposits also reflect this trend; characteristic crystal sizes less so. Due to the relationship of microlite formation with decompression, and combined with bubble texture analysis, magmas producing magmatic explosive eruptions have been interpreted to have risen at a greater ascent rate than magmas leading to phreatomagmatic explosive events. Both, however, are interpreted to have ascended faster than suggested rise speed rates for eruptions producing Strombolian deposits at other volcanoes. Exceptionally rapid rise rates and low initial magmatic volatile contents may have resulted in rapid and shallow exsolution, providing significant energy for higher than predicted fragmentation efficiency. Keywords: phreatomagmatic, ascent rates, crystallisation, maar, Strombolian eruptions Email: Jacqueline.miles@monash.edu
28
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
STRUCTURES AND ALTERATION OF WORLD-CLASS GOLD DEPOSITS, JIAODONG PENINSULA, EAST CHINA S.E. M I L L S ^ & A . G . T o m k i n s ^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia The gold-rich Jiaodong Peninsula is located on the southeastern margin of the North China Craton. Although this area is host to extensive gold mineralisation, the genesis of the system is still poorly understood, and the area itself is underrepresented in international literature. The deposits are hosted mainly in Mesozoic granitoids, and gold mineralisation is structurally controlled by moderately dipping faults. This project focuses on developing a genetic model specific to Jiaodong, starting by constraining structural influence on the alteration system and associated gold mineralisation. Gold mineralisation is almost exclusively restricted to the footwall. Thin, subvertical pyrite vein accumulations are observed in the shallow levels of the footwall in several deposits and in some cases have proven areas of economic interest. Vertical fractures are typically indicative of extensional movement, although mineralization has generally been thought to have taken place in a dextral strikeslip environment. Evidence of normal movement indicates a need for a reconsideration of the structural regime during mineralisation. Alteration around mineralised zones consists of sericite alteration close to the controlling faults; Kfeldspar alteration becomes dominate approximately 10m away from the fault and can extend for more than 100m, with mineralisation as far as the mid-K-feldspar alteration zone. Sericite alteration appears to overprint earlier K-feldspar alteration but is closer to the fault, implying the lower temperature alteration is occurring proximal rather than distal to the source of the fluids. This could be explained by prolonged fluid flow over the same area, allowing the system to cool and/or deplete in potassium, or, combined with structural evidence, the fluids could migrate vertically through the fractures in the country rock to pool beneath the fault instead. Understanding fluid flow with respect to controlling structures and the evolution of the alteration system with associated gold mineralisation are initial steps to understanding the atypical mineralising system seen at Jiaodong, which is responsible for such rich gold endowment over a relatively limited geographic area. Keywords: gold, Jiaodong, Shandong, China, orogenic, intrusion-related, alteration, K-feldspar, sericite Email: stephanie.mills@monash.edu
29
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
SEQUENTIAL ERUPTION OF ALKALINE AND SUBALKALINE MAGMAS FROM A SMALL MONOGENETIC VOLCANO IN THE AUCKLAND VOLCANIC FIELD, NEW ZEALAND A.J. NEEDHAM\ J.M. Lindsay^ I.E.M. Smith^ P. Augustinus^ & P.A. Shane^ ^ School of Geosciences, Monash University, Clayton, Victoria, Australia ^School of Environment, University of Auckland, Auckland, New Zealand Rangitoto Volcano is the youngest and largest eruptive centre in the monogenetic intraplate Auckland Volcanic Field (AVF). The stratigraphy of Rangitoto pyroclastic deposits that have been preserved in swamps on nearby Motutapu Island and in Lake Pupuke on the mainland reveals that the volcano erupted twice. Radiocarbon dating of 10 samples from two tephra units in the swamps indicates eruption ages of 553±7 and 504±5 cal years BP for the lower and upper tephra layers, respectively. Geochemistry of the lava field and various scoria cones on the volcano itself reveals two distinct compositional groups: an alkaline olivine basalt group (that correlates geochemically with the lower tephra layer) and a group that is sub-alkaline and transitional to tholeiite (that correlates geochemically with the upper tephra layer). Based on this data we infer that following a phreatomagmatic vent-clearing phase, the early magmatic eruption of Rangitoto was Strombolian in character and produced an alkaline olivine basalt scoria cone and an associated thick ash deposit on nearby Motutapu Island. This was followed by a time gap of up to several decades, after which a second eruptive phase built the current summit cone together with an encircling lava field. We suggest this later, sub-alkaline eruptive period was associated with the deposition of the thin upper tephra layer on Motutapu Island. The two suites of Rangitoto samples are chemically quite distinct, and each is associated with a distinct parental composition. Trace element modelling indicates the alkaline and sub-alkaline parental melts could have been derived by and 6 wt% partial melting of an anhydrous garnet peridotite source at - 8 0 and 65 km depth, respectively. The compositional range within each suite is similar and can be explained by major olivine and minor clinopyroxene fractionation within a relatively simple conduit system in which mixing and mingling were not important. Significant olivine fractionation (<25%) suggests that the magma may have spent some time in the upper conduit during ascent. This contrasts with a recently published model for the Crater Hill centre in the AVF, in which deep-seated fractionation followed by relatively rapid ascent to the surface has been invoked to explain the observed compositions. The polycyclic nature of Rangitoto, and in particular, the reuse of the conduit system after a period of quiescence have implications for the concept of monogenetic volcanism. There are also implications for hazard assessment, such that if a future eruption occurs in the AVF, it will be necessary to consider the conduit a possible pathway for another eruption for up to several decades afterwards. Keywords: intraplate volcanism, monogenetic behaviour, Auckland Volcanic Field, Rangitoto Island, basalt geochemistry Email: andrew.needham@monash.edu
30
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
ALTERNATING MAGMATIC AND PHREATOMAGMATIC ERUPTION STYLES OF THE MT. GAMBIER VOLCANIC COMPLEX, NEWER VOLCANICS PROVINCE, S.E. AUSTRALIA J. V A N O T T E R L O O \ R.A.F. C a s ' & J . M . C a s t r o ' ^School of Geosciences, Monash University, Clayton, Victoria, Australia The monogenetic Mount Gambier Volcanic Complex is the youngest (ca. 5000 yrs. BP) volcanic centre in the Newer Volcanics Province of southeastern Australia. This intra-plate volcanic province, which has been active for the past 5 million years, is characterised by large tholeiitic and alkali basaltic lava flows, as well as small monogenetic eruption centres consisting of maars, tuff rings, scoria cones and tuff cones. Multiple eruption styles have been recorded in the deposits of the monogenetic alkali basaltic volcanic complex of Mount Gambier, which consists of WNW-ENE aligned maars and tuff cones, tuff rings and a buried scoria cone. These eruption styles occurred in a wide range; from purely magmatic (i.e. Hawaiian and Strombolian) to phreatomagmatic, producing pyroclastic fallout, surge and flow deposits as well as massive lava flows. The different units and facies were described and based on stratigraphic relationships, the chronology of these differing styles can be constrained showing multiple alternations in magmatic and phreatomagmatic styles occurring over a short time-scale. Results from high-resolution geochemical analyses show that the volcanic centre can be divided into two parts (east and west), which were fed by different small-volume magma batches. Differences exist in alkalinity (basanites vs. ne-hawaiites), MgO, Ni and Cr contents as well as LREE enrichment. However, the wide variety in eruption styles occurred in both parts of the complex, implying that the magmatic compositions did not affect the alternations in eruption styles. This implies that other factors such as initial volatile contents, magma ascent rates, temperatures and aquifer dynamics should be researched. Keywords: monogenetic, alternating eruption styles, phreatomagmatic, explosive volcanism Email: jozua.vanotterloo@ monash.edu
31
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
CYCLICITY IN FLUCTUATING PHREATOMAGMATIC AND MAGMATIC ERUPTIVE STYLES AT TOWER HILL VOLCANIC COMPLEX, S.E. AUSTRALIA G.S. PRATA^ ^School of Geosciences, Monash University, Clayton, Victoria, Australia Many basaltic monogenetic volcanoes display fluctuating styles of behaviour, from magmatic styles such as Hawaiian fire fountaining and mild Strombolian explosions, to intense, pulsatory phreatomagmatic eruptions like those of the April 2010 eruptions of Eyjafjallajokull. The causes of these fluctuations are not well understood and the present study aims to address this. Tower Hill Volcanic Complex is an ideal location as it displays many fluctuations in eruption behaviour, from highly explosive phreatomagmatic activity to more subdued magmatic activity. A statistical Markov chain analysis of the most complete section in the maar rim sequence reveals a significant cyclical pattern of eruptive behaviour in the volcanic system. "Drying" cycles, from phreatomagmatic to magmatic, occur rapidly compared with "wetting" cycles which occur more gradually, from magmatic through an intermediate phase to phreatomagmatic. This is coupled with a deepening of the groundwater interaction level, evidenced by lithic populations throughout the sequence. The causes of the differing eruptive styles are associated with fluctuating water to magma mass ratios and the cyclicity observed is inferred to be either due to systematic damage and recovery of the aquifer or the result of changing magma rise rates within the conduit. Major element geochemistry reflects basanitic composition and trace element signatures are remarkably similar throughout the sequence, suggesting a single magmatic source. Keywords: phreatomagmatic, maar, basaltic volcanism, Markov chain, cyclicity Email: gemma.prata@monash.edu
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
THE POSSIBILITY OF EARLY ANIMAL LIFE IN A CRYOGENIAN REEF M. THOMPSON^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia A detailed mapping project on an interglacial, Cryogenian reef in the Northern Flinders Ranges, South Australia has been conducted. This reef, preserved as dolomite, has been found to be more similar to modern (Phanerozoic style) reefs than to other Precambrian reefs. It has significant relief above the sea floor and features a fore-reef facies (slope), a reef margin facies and a back-reef lagoon facies. The reef-margin facies consists of two distinct frameworks which are hypothesised to have been constructed by different organisms. The uppermost appears to be a typical stromatolite framework consisting mostly of columnar stromatolites, while the lower is a large, rigid, framework consisting of chambers up to 2 cm in diameter with a definite basin-ward growth direction. This chambered framework appears to have existed in water depths below the photic zone, ruling out a photosynthetic origin. Thin section analysis revealed textures resembling that of calcimicrobes similar to Epiphyton and Renalcis, which appear to be overgrowing a pre-existing, fine skeletal framework. Such an organised framework appears most like that which might be built by metazoans (multi-cellular animals). It is speculated that this framework may represent the calcified skeletons of early Poriferans (sponges) or encrusting Cnidarians (corals) that had not yet developed phylumdefining characteristics. The extreme climate of the Marinoan glaciation may have resulted in the death and possible extinction of this unique reef-building organism, which, should it have been metazoan, would make this reef framework the most ancient metazoan structure in the fossil record by 75 million years. Keywords: reef, Cryogenian, early animal life, Precambrian, stromatolite Email: marcus.99t@gmail.com
33
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
EXPLORING THE SENSITIVITY OF OROGRAPHIC PRECIPITATION TO VARIATIONS IN UPSTREAM CONDITIONS AND TERRAIN GEOMETRY C. WATSON^ ^School of Earth Sciences, The University of Melbourne, Parkville, Victoria, Australia Recent advances in numerical weather prediction models have allowed significantly higher resolution mesoscale forecasts. These increases in resolution facilitate explicit treatment of cloud processes and precipitation, and can also capture important small-scale detail in topography. Thus, recent mesoscale models should provide more realistic forecasts of precipitation in regions of complex terrain. However, the skill of these forecasts can suffer due to their sensitivity to small variations in upstream conditions. Such sensitivities can be magnified in mountainous regions because local terrain features can significantly modify an impinging airflow and may be associated with regime transitions. For example, orographic precipitation can be especially sensitive to upstream conditions when those conditions are near the threshold between blocked and unblocked flow. The Weather Research and Forecasting (WRF) model is used to simulate moist-stable, intermediate Froude number flows representative of the North-West Cloud Band: a synoptic-scale weather phenomenon responsible for a large proportion of winter-time precipitation in the Australian Alps. To quantify the sensitivity of orographic precipitation to variations in upstream conditions, a simple ensemble of upstream conditions have been constructed. Also, a range of alpine-scale terrain shapes have been examined to determine the role of specific terrain features in influencing those sensitivities. These experiments highlight the potential uncertainties associated with high-resolution mesoscale forecasts in regions of complex topography that place limits on the predictability of orographic precipitation. Keywords: mesoscale meteorology, orographic precipitation, complex terrain Email: c.watson@pgrad.unimelb.edu.au
34
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
PERMIAN CALDERA FORMING RHYOLITIC EXPLOSIVE VOLCANISM: INSIGHTS FROM A CASE STUDY OF THE ORA IGNIMBRITE, SOUTHERN ALPS, ITALY M.A.W. WILLCOCK\ R.A.F. Cas\ G. Giordano^ & C.Morelli^ ^Monash University, School of Geosciences, Clayton, Victoria, Australia ^University di Rome Tre, Roma, Italy ^Bolzano Provincial Geological Survey, Bolzano, Italy Extremely large volume, crystal-rich ignimbrites are erupted from immense explosive silicic caldera volcanoes and their magma chambers. There are many examples in both modern settings (e.g. the active Altiplano Puna Volcanic Complex); and in the geologic record (e.g. the Late Devonian Central Victorian Magmatic Province, Australia). The formation processes for these voluminous crystal-rich ignimbrite deposits and calderas are not well constrained. The 65 X 40 km Ora ignimbrite and caldera system is one of the largest caldera systems currently identified. The Ora ignimbrite is the youngest eruptive unit of the Athesian Volcanic Group (AVG), Southern Alps, Italy. The AVG is a volcanotectonic, multi-cyclic system, with volcanism occurring over a 10 Ma period (285-274 Ma), and an interpreted seven ignimbrite forming events. The Ora ignimbrite lacks a preceding Plinian fallout deposit, is crystal-rich (40-45%), lithic-poor (<1%), massive, thick (up to 1300m in the intracaldera), has common juvenile clasts and is pervasively jointed with ubiquitous welding. The intracaldera facies association includes: 1) crystal-rich, lithicpoor, lapilli tuff facies 2) 'bimodal crystal population', crystal-rich, lithic-poor, lapilli tuff facies and 3) lithic-rich, crystal-rich, lapilli tuff facies. The extracaldera facies association includes 1) crystal-rich, lithic-poor, coarse tuff facies 2) 'bimodal crystal population', crystal-rich, lithic-poor, lapilli tuff facies and 3) crystal-rich, lithic-poor, vitrophyric, lapilli tuff facies. The intracaldera sequence demonstrates clear vertical and lateral variations in crystal size distribution, mineralogy and geochemistry, with important implications for the evolution of this system, with the potential for multiple collapse events, forming a nested caldera complex. The Ora eruption is suggested as being a 'boil over' type eruption, producing a dense, low column, which underwent rapid collapse, preventing the formation of a Plinian fallout deposit. The eruption sequence appears to have begun with an initial vent clearing episode, evinced by proximal pyroclastic breccia deposits. Large-scale pyroclastic flows associated with column collapse, filled the intracaldera depression, and spilled out over the margins. These flows demonstrate a progression from turbulent, high particle concentration density currents into dense, high particle concentration laminar currents, with final widespread ignimbrite deposition. Pyroclastic flow direction data obtained by anisotropy of magnetic susceptibility (AMS) studies, demonstrate more variable intracaldera flow directions (N-NE-S), with uniform extracaldera flow directions (N-NE). A key vent location has been identified in north of the system. Keywords: caldera, ignimbrite, anisotropy of magnetic susceptibility, welding Email: madelaine.willcock@monash.edu
35
Geological Society of Australia
Victorian Universities Earth and Environmental Sciences Conference University of Melbourne, November 5, 2010
TRANSPORTATION OF WATER MOLECULES VIA CARBON NANOTUBES C . W U \ W . H . D u a n ^ & X . L Zhao^ ^Civil Engineering Department, Monash University, Clayton, Victoria, Australia The unique properties of carbon nanotubes (CNT) allow water molecules to pass through the interior of cylinders while chemical and microbial contaminants cannot pass. This is accomplished at a high rate of flow with very little energy (pressure) input to "push" the water through the nanotubes - thus providing a big advantage over current membrane technologies. The transportation of water molecules via a carbon nanotube, based on an energy pump concept, was investigated by molecular dynamics simulations. A small portion of the wall of a carbon nanotube was initially twisted. The energy was stored and employed to function as an energy pump for possible smooth transportation of water molecules. The momentum and resultant force on a water molecule and the corresponding displacement and velocity of the molecule were particularly observed. The efficiency of the transportation was found to be dependent on the size of the energy pump. The effect of the environmental temperature and fluctuations in the nanotube channel on the transportation was investigated. It is demonstrated that a water molecule can be successfully accelerated in a CNT channel. Moreover, the water molecule is found to move smoothly in the CNT channel before leaving the end of the CNT which forms a barrier to the water molecule. A more efficient transportation of the water molecules has been identified with the application of a shorter pump, as more energy was found to be stored in the shorter pump than its longer counterpart. In the transportation of 20 water molecules, it was observed that the accelerated duration is higher than that of the transportation of single water molecule due to the higher inertia of multi-molecules. In addition, it was found that higher environmental temperature and fluctuations in the CNT channel, due to buckling propagation, will lead to lower water velocities and hence retard the transportation process. Keywords: carbon nanotube, water molecule transportation, pump efficiency Email: chao.wu@monash.edu
36