Wed 17th January @ noon, Rm 312.222

Abstract:

The physical and chemical properties of the Earth depend on the atomic to nanoscale structure of their constituent rocks, minerals and fluids. During my talk I will focus on two examples to show how nanoscale processes may control geological processes. The first example focuses on nanoscale transport processes during fluid-rock interaction. Using multi-dimensional nano-imaging and (non-equilibrium) molecular dynamics simulations, I demonstrate that in feldspar, the most abundant mineral in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (10-100 nm) can be highly effective. This suggests that metamorphic fluid flow and fluid-mediated mineral replacement reactions can be considerably influenced by nanofluidic transport phenomena and are not solely reliant on tectonic forcing and fluid pressure gradients. In a second example I focus on the deformation of nanogranular media in earthquake-prone fault zones. Using a combination of natural samples from the seismically active Gulf of Corinth (Greece) and rock mechanics experiments I will discuss formation and deformation mechanisms of nanograins within carbonate faults and their impact on crustal fault zone stability and earthquake nucleation.

Short bio:

Oli attended the University of Münster for his BSc and MSc. He then completed his PhD at the University of Oslo. He is now assistant professor at the Department of earth Sciences, Utrecht University (the Netherlands).

Wed 22nd November @ noon, Rm 407.208

Abstract:

Following publication of the first reliable Hadean age from Earth in 1983, the inventory of Hadean zircon grains has grown dramatically in recent years. Initially a preserve of Western Australia, there are now at least sixteen locations globally where Hadean zircon has been recorded. However, the Jack Hills remains the only place on Earth where such grains are abundant, and by far the majority have come from a single location – the W74 conglomerate site on Eranondoo Hill. Mount Narryer is the second most abundant site, but elsewhere Hadean zircon is generally present as just solitary grains within igneous, metamorphic or sedimentary rocks that range from Archean to Cenozoic in age. All locations for which published data are available will be reviewed and, where available their chemical and isotopic characteristics will be evaluated. Since these grains are the only tangible record on Earth of the first 500 Ma of our planet’s history, it is imperative that we glean as much information as possible from these crystals. Of particular importance – and great controversy – is what they tell us about conditions on the early Earth and the evolution of its continental crust. The various viewpoints will be discussed and an attempt made to trace key events during the Hadean and its transition into the Archean.

Short bio:

Simon Wilde has been around for a long time! He joined the Geological Survey of Western Australia in 1972 where he mapped >50,000km² of southwestern Australia on the Perth, Pinjarra, Collie and Pemberton-Irwin Inlet 1:250,000 sheets. He joined Curtin University in mid-1981, was the inaugural Head of the School of Applied Geology from 1991-1997 and established The Institute for Geoscience Research (TIGeR) in 2006, being its Director until 2014. Besides chasing old zircons around the world, he has worked extensively in China for the past 25 years, especially in the North China Craton and the Central Asian Orogenic Belt, and more recently in Tibet. Although primarily focussing on the Precambrian, he has also studied Phanerozoic crustal evolution in several cratons, principally through field, petrological, geochemical and isotopic studies of granitoids.

Wed 15th November @ noon, Rm 502C.102

Abstract:

Monazite is a commonly used accessory mineral for geochronological studies of high-temperature (HT) and UHT metamorphic rocks, because of its extremely high U-Th-Pb closure temperature and low Pb diffusivity. Monazite, which can both grow from prograde apatite incongruent melting, and crystallize from cooling melt, is considered to be more reactive and easier to be linked with major mineral reactions than zircon. Besides, monazite is easily affected by fluid-mediated dissolution-reprecipitation process. Correspondingly, it usually preserves complex chemical zoning in terms of Th, U, Pb and Y abundances, probably implying its episodic growth or recrystallization process. Correct understanding of monazite behavior during UHT metamorphism is crucial to the interpretation of its U-Th-Pb dating results.

The Jining and Dongpo UHT localities in the Khondalite Belt of the North China Craton have yielded metamorphic ages of ca. 1.92 Ga and ca. 1.85 Ga, respectively, using zircon geochronology. These results might suggest two separate stages of Paleoproterozoic UHT metamorphism in the Khondalite Belt. Alternatively, one or both of these dates might not be recording the true age of UHT metamorphism given that the dated zircon grains were selected from crushed samples with no petrographic context.

This presentation reports the results of in situ monazite dating from the Dongpo locality by SHRIMP with associated BSE/CL images, which allows the targeting of grains in specific petrographic settings. These results indicate three stages of monazite growth/recrystallization. The oldest age of ca. 1.92 Ga comes from monazite inclusions in the cores and mantles of garnet grains and is interpreted as the minimum age for the M1 (possibly HP) stage of metamorphism. An intermediate age of ca. 1.86 Ga comes from monazite associated with sapphirine+plagioclase±spinel intergrowths or occurring as inclusion in garnet rims, interpreted as the age of M2 UHT metamorphism. Ages of ca. 1.80 Ga or younger come mainly from BSE-bright monazite rims or grains associated with retrograde biotite, interpreted as the age of fluid-mediated metasomatism that was probably associated with the M3 stage of late sillimanite-garnet growth. In order to link monazite behavior with garnet, their trace elements were/are going to be analyzed by LA-ICP-MS. In summary, monazite if associated with textural setting seems to record multiple ages compared to zircon selected from the UHT rocks.

Short bio:

Shujuan Jiao is a visiting research fellow at Curtin University. Her main interest is in high-temperature and ultrahigh-temperature metamorphism and anatexis. Before joining Curtin, Shujuan obtained her bachelor degree from China University of Geosciences (Wuhan), and then completed her PhD in the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). She is now an associate research fellow in the IGGCAS after two years in a post-doctoral position also in the IGGCAS.The

Wed 1st November @ noon, Rm 312.222

Abstract:

The anomalous sulfur isotopic signature ∆³³S₀ ≠ 0‰ that occurs in a restricted range of sulfur-bearing rock types throughout the geological record has been used to assess the surficial nature of the biological and atmospheric and hydrological sulfur cycle through time. It is widely accepted that ∆³³S₀ anomalies (∆³³S₀ > ±0.2‰) were formed in the Archean eon, largely through mass independent fractionation of sulfur (MIF-S) in an oxygen-poor atmosphere and imparted to the Archean supracrustal rock record (as MIF-S₀). In this talk, I demonstrate examples of how we are harnessing the indelible MIF-S₀ signature to trace sulfur pathways to mineral systems where the signature is recycled as MIF-S₁. For instance, study of the Waroonga Archean orogenic gold deposit demonstrates that gold-bearing arsenopyrite yield ∆³³S₁ = +0.3‰, indicating that sulfur, the complexing ligand for gold transport, was sourced at least partially from the Archean sediment record. When these spatially- and temporally-constrained measurements are combined with detailed chemical maps of arsenopyrite, we demonstrate that the Archean sediment reservoir was likely devolatilised at depth. Ore deposits (leaving aside their economic significance) are loci where mass and energy concentrative processes take place, being the ideal natural laboratories to study volatile pathways. The outcomes from these studies have the potential to greatly enhance the application of MIF-S₁ (∆³³S₁) as a powerful tracer of sulfur pathways through the lithosphere.

Short bio:

Crystal attended Acadia University for her BSc. She then completed regional-scale mapping projects for her MSc at Memorial University of Newfoundland, and PhD at the University of New Brunswick in the Canadian Shield of Labrador and Nunavut. Presently, as a postdoctoral researcher at the Centre for Exploration Targeting, University of Western Australia, she studies how the nature of volatiles can enhance our understanding of lithospheric-scale tectonic processes by linking mineral systems, tectonics and geochemistry.

Mon 16th October @ noon, Rm 312.222

Abstract:

Phase equilibria modelling studies investigating the onset of anatexis in rocks are limited by the assumption of a fixed H₂O content in the bulk composition. This limitation is in conflict with the fact that the water content of fluid-absent subsolidus rocks change as a function of pressure and temperature. Rcrust [1] allows phase equilibrium modelling along P–T paths to be conducted with composition as a variable. This study uses this functionality to investigate the evolution of fully-hydrated but fluid-absent (fhfa) compositions along P–T trajectories that evolve towards granulite (at relatively high dT/dP) and eclogite (at relatively low dT/dP) facies peak metamorphic conditions. The H₂O content of the rock changes as it evolves along each path, as the modelling is set to remove any free phase water formed in the system. The results show that the H₂O content of the rock at the solidus varies by 1.4 wt.% and that modelled OH^– content of biotite varies strongly as a function of temperature and pressure. The fhfa solidus coincides with the wet solidus only at P > 12 kbar. At P < 12 kbar melting behaviour is strongly controlled by the subsolidus mineral assemblages. In fields where biotite coexists with phengite (12–7 kbar) and in fields where biotite coexists with cordierite (4.5–2.5 kbar), the fhfa solidus is located at temperatures lower than the wet solidus by up to 25 °C. Where biotite is the sole hydrous mineral in the subsolidus assemblage (7–4.5 kbar), the fhfa solidus is displaced by up to 50°C above the wet solidus. Additionally, the trajectory of the P–T path exerts a strong control on the shape of the fhfa solidus. Steep P–T paths of increasing pressure emnating from 650 °C and 5 kbar do not cross the solidus, which occurs at ~850 °C at 20 kbar. In contrast, paths of steeply decreasing pressure emnating from 650°C and 10 kbar document a less pronounced solidus step to higher temperature in the 7.5–5 kbar field. These results have important implications for anatectic systems and could provide a mechanism for rocks to remain melt absent until high temperatures after which small amounts of subsequent heating or decompression would produce large amounts of melting.

Short bio:

Matthew obtained his MSc in Geology at Stellenbosch University, South Africa in 2015 after which he began a joint PhD program between Stellenbosch University and Université Jean Monnet, France. Currently his research is focused on the development and use of a new software tool that aids in the modelling of mineral stabilities inside rocks (https://tinyurl.com/Rcrust).

His work aims to improve the techniques with which geologists study natural systems and thereby further our understanding of how earth processes formed, and currently maintain, our world. He is funded by the South African Research Chairs Initiative (SARChl) and the French Embassy of South Africa. In his spare time, Matthew enjoys hiking and rocking out on his drumkit.

Wed 20th September @ noon, Rm 312.222

Abstract:

If we accept that an assumption of thermodynamic equilibrium is reasonable for melt-bearing rocks (> or >>650 °C), phase equilibria modelling provides a powerful tool for the investigation of the processes and geodynamic environment in which they formed and evolved. Until now, quantitative constraints on such high-temperature processes using phase equilibria have mainly been confined to the realm of crustal metamorphism, and used siliciclastic source rocks (mudstone, greywacke, etc.), due to the availability of appropriate thermodynamic models for solid solution phases, including melt. The recent development of solution models for minerals and melt in ultramafic and mafic systems represents a huge advance, allowing consideration of more fundamental questions, including the origin and evolution of basaltic primary (’oceanic’) crust from melting of the mantle, and thereby more evolved (‘granitic’) primitive continental crust from the melting of primary mafic crust. This talk gives a couple of examples of the potential utility of these new models, combining phase equilibria calculations on mafic source rocks with trace element modelling to investigate early Earth processes.

Bio:

Tim joined the Department of Applied Geology in January 2014. Prior to arriving at Curtin he worked for six years as a post-doctoral scientist at the University of Mainz in Germany. Before that he co-owned and ran a pub in Graz, Austria. Tim obtained his Honours degree in 1992 from the University of Derby in England. He was awarded his PhD in 1999 from the same institution for a thesis entitled “Partial melting of Dalradian pelitic migmatites from the Fraserburgh–Inzie Head area of Buchan, north-east Scotland”.

Wed 2nd August @ noon, Rm 312.222

Abstract:

The 260 m diameter Hickman Crater is a circular topographic feature in the eastern Hamersley Range, Pilbara Craton. The partly rimmed crater lies along the contact between lower Paleoproterozoic rhyolite and overlying iron formation. A meteorite impact origin was first proposed in 2007. In 2012 a diamond-cored hole was drilled into the sediment filled centre of the crater in a collaborative project between Atlas Iron Ltd and the Geological Survey of Western Australia. The hole encountered a poorly consolidated sedimentary succession of clay, sandy clay, gravel and boulders to a depth of 48.4 m, underlain by 6.7 m of rhyolite-dominated breccia to 55.1 m, with the remainder of the hole intersecting heavily fractured but in situ rhyolite to total depth of 64.7 m. The breccia unit also contains fragments of vesicular glass and partially melted rock. Geochemical analysis of the core reveals pronounced enrichment in siderophile elements, particularly Ni, Co and PGE (up to 2381 ppm Ni, 85 ppb Ir), in the breccia compared to crater basement or overlying sediments. PGE inter-element ratios in the breccia are near chondritic and are interpreted as contamination by oxidised remnants of an iron meteorite projectile, probably a so called primitive iron belonging to chemical class IVB. No fresh meteoritic material is present. Petrographic examination of the crater basement and overlying breccia reveals abundant grain fracturing, but no uniquely impact-diagnostic structures such as planar deformation features were observed. The lack of obvious shock metamorphism and unusually high meteoritic component of the breccia may be explained by significant atmospheric deceleration of a relatively small projectile prior to impact. The crater has yet to be accurately dated radiometrically, but considering its youthful appearance a late Pleistocene age is considered likely. Drilling of Hickman Crater represents the first scientific drilling of a simple impact crater of this size (<1 km) in Australia, and one of few worldwide.

Short Bio:

Peter Haines holds BSc Honours and PhD degrees from the University of Adelaide. He has held positions with the Northern Territory Geological Survey, University of South Australia, University of Tasmania, and most recently is with the Basins and Energy Geoscience group at the Geological Survey of Western Australia.

Wed 26th July @ noon, Rm 312.222

Abstract:

The giga-annum periodicity in global radiogenic Hf and Sr isotopic trends is investigated by integrating data from tectonics, geodynamics, and palaeomagnetism, in order to build a holistic geodynamic model linking modes of mantle convection to plate tectonic motions over the last 2,500 Myr. The gigacycle reflects an alternating dominance between degree-2 and degree-1 mantle convective flow, manifest as the presence and absence of a hemispheric subduction girdle, respectively. The girdle is currently represented by the circum-Pacific subduction system and is geologically recorded by Phanerozoic circum-Pacific accretionary orogens. Degree-1 convection resulted in the amalgamation of Columbia ca. 2,000 Myr ago and Gondwana ca. 550 Myr ago accompanied by peaks in crustal reworking (-εHf), whereas degree-2 convection produced Nuna ca. 1,600 Myr ago and Pangaea 200 Myr ago accompanied by peaks in mantle input (+εHf). The change from degree-2 to degree-1 coincided with Rodinia amalgamation ca. 1,100 Myr ago, when the circum-Nuna subduction girdle collapsed. The gigacycles are rhymthic oscillations of mantle circulation patterns that control plate motion trajectories and contrasting styles of supercontinent amalgamation.

Short bio:

Professor WJ Collins began his work on A-type granites at ANU with Bruce Chappell, before moving to La Trobe University for a PhD on Archean granites with Prof Allan White. A post-doc on high-grade Proterozoic terranes in central Australia ensued with Prof. Ron Vernon at Macquarie  University before moving to the University of Newcastle as a lecturer. He moved to James Cook University as a Professor before returning to Newcastle as Director of the NSW Institute for Frontiers Geoscience. He became a Curtin Professorial Fellow last year.