Wed 16th May @ noon, Rm 312.222

Abstract:

The Petrel Basin is a NW-SE trending graben, orthogonal to and most likely older than the NE-SW trending structures that dominate the North West Shelf. The development of salt structures is closely related to the complex multi-phase evolution of the basin and the adjacent passive margin. Although not penetrated by wells, seismic stratigraphy clearly shows that salt was deposited as part of the syn-rift sequence, most likely of Devonian age. A significant phase of widespread mini-basin formation ensued and was terminated by the end of rifting. Hyper-extension during the Lower Palaeozoic resulted in the development of a thick Carboniferous to Triassic sag sequence during which some of the early formed structures evolved into high-relief point-sourced diapirs by a combination of early salt withdrawal and subsequent passive growth. Extensional fault reactivation in the Middle Jurassic, associated with more widespread rifting further outboard on the continental margin, resulted in accelerated subsidence in the basin centre, with extension on the basin margin being balanced by tightening of compressional salt cored folds and daipirs in the basin centre. A phase of compression, most likely associated with the collision of Australia with SE Asia in the Neogene, resulted in inversion of segments of the basin bounding fault system and a final phase of diapir growth.

Neoproterozoic and Lower Palaeozoic salt occurs in a number of Australian sedimentary basins. Although salt structures are associated with hydrocarbon occurrences in a number of these basins, the Petrel Basin is by far the most prolific. However, despite the large number of salt structures, the number of discoveries in the Petrel Basin is relatively small.  Most hydrocarbon occurrences are associated with broad salt cored anticlines that developed during Jurassic extension, rather than high relief diapirs that experienced Cenozoic growth. The complex multi-phase growth of these latter structures most likely resulted in seal breach.

 

Short bio:

Chris Elders is Professor of Petroleum Geology at Curtin University.  Having spent time at Oxford, in Shell and at Royal Holloway (university of London), Chris has enjoyed spending the last 4.5 years helping to unravel the complex evolution of Australia’s continental margins.

Tues 24th April @ noon, Rm 312.222

Abstract:

Iron oxide minerals are found in almost every surficial environment on Earth where they participate in a variety of biogeochemical processes, record paleo-environmental conditions and host economic quantities of critical metals. Highly crystalline iron oxides (e.g., goethite, hematite) are thought to resist alteration under ambient conditions in aqueous fluids. However, we have recently discovered that dissolved Fe(II) in aqueous solution rapidly and, in some cases, completely exchanges isotopes with structural Fe(III) in these minerals. Dissolved Fe(II) effectively acts as a catalyst to recrystallise these ‘stable’ minerals, thereby cycling iron and associated elements between solid and solution. I will summarise these new reaction pathways and how they can be applied towards quantifying mineral reactivity and calibrating isotopic fractionation factors. These processes have implications for interpreting the trace element contents and isotopic compositions of iron-rich chemical sediments and may be applied to mineral processing technologies for extracting critical metals (e.g., Ni and Co) from laterite ore.

Short bio:

Andrew Frierdich is a Lecturer and DECRA Fellow at Monash University who studies the reactivity and isotope geochemistry of metals and minerals in aqueous environments.

Wed 28th March @ noon, Rm 312.222

Abstract:

Assembly of Rodinia culminated in development of the collisional Grenville-Sveconorwegian orogen at 1.2-1.0 Ga. The tectonic significance of early Neoproterozoic (980-920 Ma) tectonothermal events recorded in the North Atlantic borderlands of Ellesmere Island, East Greenland, Norway and Svalbard is less well understood. This is partly because most rock units were reworked at amphibolite facies during the Lower Palaeozoic Caledonian orogeny, and also because there is controversy over the relative positions of Laurentia and Baltica in Rodinia reconstructions. U-Pb zircon dating of metasedimentary rocks and a range of mafic, intermediate and felsic meta-igneous rocks from the Shetland Islands and mainland northern Scotland provides evidence for a hitherto unrecognised tectonothermal event at 970-930 Ma. Geochemical and isotopic data are consistent with magma generation in a convergent plate margin setting. The identification of subduction-related magmatism at least as far south as the Scottish sector of the eastern Laurentian margin favours a southerly location of western Baltica opposite Rockall Bank. This enables the Scottish margin of east Laurentia to be located relatively close to the periphery of Rodinia, and early Neoproterozoic magmatism and orogenesis to be related to development of an exterior accretionary orogen following supercontinent assembly. Similar-aged calc-alkaline igneous suites have been identified by other workers in Ellesmere Island, Svalbard, and within Laurentia-derived allochthons of northern Norway, and together with the Scottish occurrences these comprise the recently-defined Valhalla accretionary orogen of northeast Laurentia.

Short bio:

Rob did his PhD at the University of Keele, UK, and has since held academic positions at Oxford Brookes University and most recently the University of Portsmouth where he is Professor of Geology. His research is centred around Neoproterozoic and Lower Palaeozoic tectonics in the North Atlantic region.

Wed 21st March @ noon, Rm 312.222

Abstract:

Thousands of exoplanets have been discovered in solar systems with a range of C/O ratios. This ratio has a large control on the oxygen fugacity under which planets in the systems form and evolve. In our solar system, the planet Mercury lies at the extreme low end of oxygen fugacity and may provide insights into how planets in high C/O star system will evolve. As oxygen fugacity decreases, sulfur becomes an important anion, and its solubility in silicate melts increases by 1-2 orders of magnitude. At the same time, the Fe contents of silicate melts all but disappears as FeS and/or Fe-metal are stabilized. Ca and Mg bond with S in the melt, reducing the stability of olivine and Ca-bearing phases such as plagioclase and clinopyroxene. The result is that while Mercury is similar in size to the Moon, its chemical and physical evolution is dramatically different. There is no anorthosite flotation crust, likely no overturn, and Mercury has an enormous metallic core, likely with high Si, S and/or C contents. Pyroclastic volcanism is much more common on Mercury than on the Moon, though what volatile species causes the explosive eruptions is not clear. In this talk I will go over what we know of Mercury from the MESSENGER mission and what we have learned from experimental studies at low oxygen fugacities. Combining the phase equilibria with dynamic models of magma ocean crystallization, I will describe some (highly speculative) models for the internal chemical layering in Mercury and its subsequent evolution.

Short bio:

I received my Ph.D. in Geology and Geochemistry from the Massachusetts Institute of Technology in 2001. I came to Brown after three years as Lecturer at Durham University, Great Britain. I am considered a leading expert on the behavior of volatiles in the Earth’s interior. My work on water in early Earth magmas is providing new insights into the thermal evolution of the Earth. Likewise, my recent research on noble gas solubility in the mantle is challenging the existing models of mantle structure and evolution.

Wed 7th March @ noon, Rm 312.222

Abstract:

A fundamental principle of Earth’s geochemical evolution holds that continental crust is formed by extraction of melts from the mantle, leaving part of the mantle depleted in incompatible elements. The Sm-Nd and Lu-Hf isotope systems have long been used to show that this process has been an essential feature of the Earth throughout its history, but the details of this process in the early Earth—and its implications for addressing questions about mechanisms, timing, and volumes of mantle depletion and crustal production—remain hotly debated. This has led to two very different schools of thought on crustal growth: the first posits that continental crust never existed in any appreciable volume in the early Earth and that crustal growth did not begin in earnest until the Paleoarchean; the other holds that early crust was abundant but has been effectively recycled back into the mantle. This debate endures partly due to the paucity of Archean rocks older than 3.5 Ga available to test these models, and because the rocks that remain typically preserve complex geologic histories. Complexities are often manifest in the whole rock Nd and Hf isotope records where analyses of samples with mixed age and isotope compositions, poor age constraints, and/or open-system behavior, can lead to isotopic artefacts rather than a robust signature of the terrestrial reservoir from which the rock was derived. Exploitation of the zircon Hf isotope record provides the best prospect for unraveling the isotope record of the early Earth, with caveat that even zircon has its limitations, including complex zoning and Pb loss.

The best-constrained Hf isotope data from magmatic zircons (i.e. unambiguous age constraints and uncompromised by multiple components) illustrates a surprisingly simple Hf isotope evolution for the Earth with the development and growth of the depleted mantle beginning at about 3.8 Ga. In this dataset, the most radiogenic Hf isotope compositions are near chondritic from 4.5 to ~ 3.8 Ga and define a nearly linear evolution beginning from e_Hf = 0 at 3.8 Ga to e_Hf ~ +16 at present (Fig. 1). Most significantly, we find no evidence for widespread mantle depletion—a hallmark of voluminous crustal production—from the oldest samples.

Clearly, there was formation of some zircon-bearing crust in the Hadean as evidenced by the Jack Hills zircons [e.g., 2, 3] and the oldest Acasta gneisses [e.g., 4-5]. Based on the Hf isotope record, however, > 3.8 Ga crust was likely small in volume and/or was effectively recycled back into the mantle and did not result in its widespread depletion.  The onset of this mantle depletion at ~ 3.8 Ga likely coincided with the formation of stable continental crust (and cratons) and may signal a change in Earth’s dynamics from a vertical tectonic regime to a more horizontal (rigid plate) tectonic regime that is characteristic of modern-day Earth.

Figure 1: Hf isotope evolution, showing development of the depleted mantle beginning at about 3.8 Ga.

[1] Vervoort J and Kemp T (2016) Chem Geol 425: 65-75. [2] Amelin Y et al. (1999) Nature 399: 252-255. [3] Kemp T et al. (2010) EPSL 296: 45-56. [4] Amelin Y et al. (2000) GCA 64: 4205-4225. [5] Iizuka T et al. (2009) Chem Geol 259: 230-239.

Short bio:

Professor Vervoort is a radiogenic isotope geochemist and geochronologist with interest in the early Earth and how the planet has evolved through time.  Dr. Vervoort received his Ph.D. from Cornell University (USA), worked as a postgraduate researcher at the University of Arizona for several years and is currently at Washington State University where he is a full professor and director of the Radiogenic Isotope and Geochronology Laboratory. Professor Vervoort has published over 150 peer-reviewed papers.  He is a Fellow of the Geological Society of America and American Geophysical Union, and has held over 20 research grants from the US National Science Foundation.  Professor Vervoort will be at the University of Western Australia through mid May.

Wed 28th January @ noon, room 312.222

Abstract:

Arc magmas are oxidised relative to MORB, leading to the controversial proposal that the mantle beneath arcs is more oxidised than the mantle elsewhere.  A cause proposed to explain this oxidation is that the presence of water during peridotite melting beneath the arcs affects the melt structure, thereby increasing the partitioning of ferric iron into the melt.  The validity of this proposal was explored with a series of piston cylinder experiments, the preliminary results of which are inconclusive.  To mitigate the tedium of the inconclusive results, a photo tour through the ocean crust on Macquarie Island will be presented.

Bio:

Katy completed a Ph.D on “Metamorphic Fluid Flow in East Central Vermont” in 1999. This was followed by postdoctoral work at the University of Sheffield (UK) on kinetically-controlled mineral dissolution and precipitation in the unsaturated zone of mine spoil. She moved to Australia in 2002 to take up a position as a Research Fellow at CSIRO Exploration and Mining, where she worked on greenstone-hosted gold deposits and the thermodynamic characteristics of sulphur-bearing, high ionic strength, mixed solvent fluids. In 2005 she was awarded an Australian Synchrotron Research Fellowship, hosted by the ANU, and used this time to undertake experiments on S- and Cl-bearing silicate glasses and CO2-bearing solutions. She began a Research and Teaching Fellowship at Curtin in 2007.

Wed 21st January @ noon, Rm 210.104

Abstract:

Topic 1: A 4463 Ma apparent zircon age from the Jack Hills resulting from ancient Pb mobilization

Hadean (≥4.0 Ga) zircon grains provide the only direct record of the first half billion years of Earth’s history. Determining accurate and precise crystallization ages of these ancient zircons is a prerequisite for any interpretation of crustal evolution, surface environment and geodynamics on the early Earth, but this may be compromised by mobilization of radiogenic Pb due to subsequent thermal overprinting. Here we report a detrital zircon from the Jack Hills (Western Australia) with 4486 – 4425 Ma concordant ion microprobe ages that yield a concordia age of 4463 ± 17 Ma (2σ), the oldest zircon age recorded from Earth. However, scanning ion imaging reveals that this >4.4 Ga apparent age resulted from incorporation of micrometre-scale patches of unsupported radiogenic Pb with extremely high 207Pb/206Pb ratios and >4.5 Ga 207Pb/206Pb ages. Isotopic modeling demonstrates that these patches likely resulted from redistribution of radiogenic Pb in a ~4.3 Ga zircon during a ~3.8 Ga or older event. This highlights that even a concordia age can be spurious and should be carefully evaluated before being interpreted as the crystallization age of ancient zircon.

 

Topic 2: Remnants of Eoarchean continental crust derived from a subducted proto-arc

Eoarchean [3.6 – 4.0 billion years ago (Ga)] tonalite – trondhjemite – granodiorite (TTG) are the major component of Earth’s oldest remnant continental crust, thereby holding the key to understanding how continental crust originated and when plate tectonics started in the early Earth. TTGs are mostly generated by partial melting of hydrated mafic rocks at different depths, but whether this requires subduction remains enigmatic. Recent studies show that most Archean TTGs formed at relatively low pressures (≤1.5 GPa) and do not require subduction. Here we report a suite of newly-discovered Eoarchean tonalitic gneisses dated at ~3.7 Ga from the Tarim Craton, northwestern China. These rocks are probably the oldest high-pressure TTGs so far documented worldwide. Thermodynamic and trace element modelling demonstrates that the parent magma may have been generated by water-fluxed partial melting of moderately enriched arc-like basalts at 1.8 – 1.9 GPa and 800 – 830 ℃, indicating an apparent geothermal gradient (400 – 450°C GPa-1) typical for hot subduction zones. They also locally record geochemical evidence for magma interaction with a mantle wedge. Accordingly, we propose that these high-pressure TTGs were generated by partial melting of a subducted proto-arc during arc accretion. Our model implies that modern-style plate tectonics was operative, at least locally, at ~3.7 Ga and was responsible for generating some of the oldest continental nuclei.

 

Short bio:

Rongfeng Ge obtained a joint PhD from Nanjing University (China) and Curtin University in 2014 – 2015. He has been a research associate working with Prof. Simon Wilde at Curtin since April 2016 on the Jack Hills zircons, aiming to extracting a primary record of the Hadean zircons using various methods. He has also being working on the Precambrian geology of the Tarim Craton, with an emphasis on the origin and evolution of continental crust, as well as reconstruction of the Tarim Craton in the Rodinia and Columbia/Nuna supercontinents.

Wed 14th January @ noon

Abstract:

With its almost inexistant erosion, the lunar surface preserves a good record of the early Earth-Moon system evolution. Over the past decade, lunar science has benefited from a rapid increase in international interest. Many missions from different space agencies have shed a new light on our closest neighbor, but also raised many questions.

The Moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres. The most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the Procellarum KREEP Terrane (PKT), and the mare basaltic lava flows that erupted in or adjacent to this terrane. There is no consensus regarding the extent and cause of this enrichment.

In parallel, improved paleomagnetic measurements of Apollo samples from several groups have strengthened the idea of a long lasting magnetic field. From a period of strong intensity of several hundred millions years (similar in amplitude to Earth’s field), the field decayed by almost two orders of magnitude. Several processes exist to generate a lunar magnetic field, but their relative contribution is debated.

In this presentation I will show integrated evolution models of the lunar mantle and core to discuss both volcanic activity and magnetic field generation and discuss possible implications for the early stages of lunar evolution.

 

Short bio:

I obtained my PhD degree from the Institut de Physique du Globe de Paris (IPGP), under the supervision of M. Wieczorek and D. Breuer, working on the long term evolution of Earth’s moon. I am now working at the Earth-Life Science Institute (ELSI) in Tokyo, Japan. I am interested in how different processes shape the long term evolution of planets. In particular, I’d like to use insights from exoplanetary statistics to improve our understanding of planets in the Solar System.

More information:

http://mlaneuville.github.io/

https://orcid.org/0000-0001-6022-0046

Wed 24th January @ noon, Rm 312.207

Abstract:

After over a century of intensive research, the Kalgoorlie goldfields, home to the giant Golden Mile Au-Te deposit, still hold undiscovered treasures.

The Hidden Secret Ag-Au-Te deposit, located 1 km northwest of the Golden Mile Superpit and 350 m east of the Mt Charlotte mine, is a resource recently discovered by Kalgoorlie Consolidated Gold Mines (KCGM). More specifically, the historical upper Hidden Secret orebody, with bonanza grades of 49.45 g/t Au and 139.45 g/t Ag from 9676 t, was mined in 1904-1925 – but the continuation of the ore (the lower Hidden Secret orebody), with a reported reserve of 665 t at 3.56 g/t Au, wasn’t located until 2011. The Hidden Secret orebodies (both upper and lower) host unusually silver-rich ores in comparison to the greater Golden Mile. Gold is hosted in silver-rich native gold (mostly electrum, >20% Ag) and the Ag-Au telluride minerals hessite and petzite. The deposit also contains a diverse suite of non-economic Bi, Hg, Ni and Pb telluride minerals, assemblages of which were used in thermodynamic modelling of the ore deposition conditions. The assemblage electrum-hessite-coloradoite was used to derive an ore geothermometer for Au-Ag telluride deposits, and produced temperatures of 188-239°C for Hidden Secret ores, which are relatively low compared to typical mineralization temperatures of orogenic gold deposits. Further, the high-Ag telluride ores at Hidden Secret were linked to similar localized Ag-Au-Te occurrences at Mt Charlotte and Mt Percy, pointing to a district scale, lower-T and higher-Ag mineralizing event.

Elsewhere in the Golden Mile, from a location that is now empty space in the centre of the Superpit, a new telluride mineral was discovered in a historical WASM museum specimen from the Associated gold mine. Officially approved by the International Mineralogical Association in March 2016, the mineral was named kalgoorlieite after the type locality. Kalgoorlieite’s empirical formula is [As_1.59Sb_0.41]_2.00Au_0.02Ag_0.01[Te_2.95S_0.01Se_0.01]_2.97, or more simply As₂Te₃. Substantial concentrations of Sb in the mineral structure suggest the existence of a series between kalgoorlieite and tellurantimony, Sb₂Te₃. Observed only in thin section, kalgoorlieite occurs as grains ranging in size from <10 to 50 µm, intergrown with other telluride minerals and native tellurium. The grain size was too small for the traditional XRD characterization of the crystal structure usually required for a new mineral definition, but fortunately, synthetic As₂Te₃ was already well-described and the structure of natural kalgoorlieite was successfully matched to that of the synthetic form using Kikuchi diffraction. Thermodynamic modelling shows that kalgoorlieite has a relatively small stability field, which shrinks dramatically in the presence of tetrahedrite (a common sulphosalt in Golden Mile ores), explaining the rarity of this mineral in telluride ores.

Bio:

Kirsten is originally from Vancouver, where she began her voyage in the earth sciences and completed a BSc at the University of British Columbia in 2002. She then headed to the French side of Canada, where she earned an MSc and PhD in experimental geochemistry, with a focus on the transport of molybdenum in ore fluids, at McGill University. After a brief sojourn as a geologist with a Quebec exploration company in 2008, she began a postdoc at the GFZ German Research Centre for Geosciences in Potsdam, where she did experiments on subsurface CO₂ storage and metal transport in fluids. She moved to the southern hemisphere in 2012, where she began working as a lecturer in ore deposits at the Western Australian School of Mines, Curtin University. Kirsten’s research has focused on various topics in ore genesis, including experiments on metal transport in aqueous and hydrocarbon ore fluids, as well as studies of the gold deposits around Kalgoorlie, where she discovered a new telluride mineral called kalgoorlieite.