GEMOC ARC National Key CentreFunded basic research projects for 2006
Funded research projects within GEMOC are formulated to contribute to the long-term, large-scale strategic goals and determine the short-term Research Plan. Summaries of these projects for 2006 are given here.
The behaviour of geochemical tracers during differentiation of the Earth
Bernard Wood: Supported by ARC Discovery
Summary: The aims of this project are to understand the processes by which the Earth separated its metallic core, to test models of how it developed ‘enriched’ and ‘depleted’ mantle components and to constrain the nature of continuing interactions between near-surface geochemical reservoirs and Earth’s deep interior. These processes have traditionally been followed using chemical tracers, but lack of understanding of chemical behaviour under the conditions of the deep Earth limits their application. This project is aimed at filling the gap, by determining experimentally, at high pressures and temperatures, the chemical behaviour of those trace elements which are central to our understanding of geochemical processes in Earth’s interior. The project is aimed at providing fundamental data which Earth Scientists will use to understand the processes by which Earth separated into its chemically-distinct layers (core, mantle, crust, atmosphere, oceans) and to determine the nature of the continuing interactions between the surface environment in which we live and the deep interior.
Episodicity in mantle convection: effects on continent formation and metallogenesis
Craig O’Neill: Supported by Maquarie University Research Fellowship
Summary: Quantitative numerical modelling will be used to evaluate the links between episodes of intense mantle convection and the production of the continental crust that we live on. These models will assess the degree of melt production and crustal generation resulting from different styles of episodic mantle convection, and will determine which types of mantle evolution through time could produce the age distribution observed in the continental crust worldwide. The research addresses a critical shortcoming in our understanding of the formation and evolution of continents, with important implications for the distribution of major mineral and energy resources.
Isotopic fractionation of the ore minerals (Cu, Fe, Zn): A new window on ore-forming processes
Simon Jackson and Bruce Mountain: Supported by ARC Discovery
Summary: Stable isotopes of common ore metals (eg copper and iron) are new tools for investigating ore deposits. Our data suggest that metal isotopic variations can provide new insights into mechanisms operative during formation of ore deposits. Stable metal isotopes also show promise as a new exploration tool for identifying the location of economic mineralisation within large prospective terrains; eg weakly vs strongly mineralised zones in a volcanic belt.
This project will provide fundamental baseline data that will help elucidate the processes that cause metal isotope variations. This will allow stable metal isotopes to be used much more effectively by the mining and exploration industries.
Spreading ridge sedimentation processes: a novel approach using Macquarie Island as a natural laboratory
Nathan Daczko and Julie Dickinson (University of Sydney): Supported by ARC Discovery
Summary: This project is the first that aims to understand the generation, deposition and lithification of sedimentary rocks at mid-ocean spreading ridges. It will improve our understanding of the construction of significant volumes of oceanic crust that commonly host important economic resources such as cupriferous sulfides. The project will examine spreading-related sedimentary rocks, including processes relating to their depositional system, utilising unique exposures on Macquarie Island, where in situ oceanic crust still lies within the basin in which it formed.
A new approach to understanding the mechanism and deep crustal controls of continental rifting
Nathan Daczko: Supported by ARC Discovery
Summary: The Papuan Peninsula region of Papua New Guinea represents an active plate boundary on the northern Australian margin that is presently rifting. This project will develop models that detail how the rifting is accommodated in continental rocks and compare and contrast this with oceanic rocks. The project aims to understand the tectonics of rifting by examining this active tectonic region, thus investigating a fundamental plate tectonic process that is critical to understanding Earth evolution. Expected outcomes include a deeper understanding of plate tectonics, with special focus on deep Earth processes.
Global lithosphere architecture mapping
Sue O’Reilly and Bill Griffin: Supported by ARC Linkage Project and WMC Resources
Summary: Compositional domains in the subcontinental lithospheric mantle reflect the processes of continental assembly and breakup through Earth’s history. Their boundaries may focus the fluid movements that produce giant ore deposits. Mapping these boundaries will provide fundamental insights into Earth processes and a basis for the targeting of mineral exploration. We will integrate mantle petrology, tectonic synthesis and geophysical analysis to produce the first maps of the architecture of the continental lithosphere, to depths of ca 250 km. These maps will provide a unique perspective on global dynamics and continental evolution, and on the relationships between lithosphere domains and large-scale mineralisation.
Toward the use of metal stable isotopes in geosciences
Olivier Alard: Supported by ARC Discovery
Summary: Metal stable isotopes (MSI: Mg, Fe, Cu, Zn, Ga) have enormous potential applications (basic and applied) in Geosciences and beyond. However the use of these elements as geochemical tracers and petrogenetic tools requires: (i) the definition of their isotopic composition in Earth’s key reservoirs and in reference materials such as the chondritic meteorites; (ii) understanding and quantification of the causes of MSI fractionations during geological processes. By a unique combination of in situ and solution geochemical analytical techniques available now through frontier technology and method development, we aim to establish a conceptual and theoretical framework for the use of metal stable isotopes in Geosciences.
Crustal Evolution in Australia: Ancient and Young Terrains
Elena Belousova: Supported by ARC Discovery
Summary: The mechanisms of crustal growth and the processes of crust-mantle interaction will be studied in selected Archean, Proterozoic and Phanerozoic terrains in Australia, using a newly developed approach: the integrated, in situ microanalysis of Hf and Pb isotopic composition and trace-element patterns in zircons from sediments and selected igneous bodies. The results will provide new information on the evolution of the Australian crust, with wider implications for the development of global crust and mantle reservoirs. The outcomes will define crustal evolution signatures related to regional-scale mineralisation, and thus will be highly relevant to mineral exploration in Australia and offshore.
How has continental lithosphere evolved? Processes of assembly, growth, transformation and destruction
Sue O’Reilly and Bill Griffin (with 5 partner investigators): Supported by ARC Discovery and Linkage International
Summary: We will use new in situ analytical techniques, developed in-house, to date the formation and modification of specific volumes of the subcontinental lithospheric mantle, and to define the temporal and genetic relationships between mantle events and crustal formation. Quantitative modelling will investigate the geodynamic consequences of spatial and temporal variations in lithosphere composition and thermal state. Magmatic products will be used to assess the roles of mantle plumes and delamination in construction of the lithosphere, and xenolith studies will investigate the evolution of oceanic plateaus. The results will provide a framework for interpreting the architecture of lithospheric terranes and their boundaries.
The timescales of magmatic and erosional cycles
Simon Turner (with 4 partner investigators): Supported by ARC Discovery
Summary: Precise information on time scales and rates of change is fundamental to understanding natural processes and the development and testing of quantitative physical models in the Earth Sciences. Uranium decay-series isotope studies are revolutionising this field by providing time information in the range 100-100,000 years, similar to that of many important Earth processes. This project is to establish a dedicated Uranium-series research laboratory and to investigate (1) the processes and time scales of magma formation, transport and differentiation beneath western Pacific island arc volcanoes, (2) the time scales and relative roles of physical and chemical erosion in Australian river basins.
Mantle Melting Dynamics and the influence of recycled components
Simon Turner: Supported by Macquarie University Development Grant
Summary: This proposal aims to use U-series isotopes to constrain the rates of mantle melting and residual porosity. Precise information on the time scales and rates of change is fundamental to understanding natural processes and central to developing and testing physical models in the earth sciences. Uranium series isotopes have revolutionised the way we think about time scales because they can date processes which occurred in the last 10-350 000 years. By contrasting normal and enriched basalts we will constrain the effect of heterogeneities, including volatiles on mantle melting. This will radically improve our understanding of mantle melting which powers Earth’s dynamics.
The oxidation state of the early Earth mantle: new clues from iron isotopes
Helen Williams: Supported by Macquarie University New Staff Grant and Industry (Nu Instruments)
Summary: This project’s goal is to understand how the Earth’s atmosphere became oxygen-rich. Oxygen stored in the Earth’s deep interior (the mantle) was probably released to the surface as water and CO2, allowing the growth of free oxygen in the atmosphere to a significant level by ~2.4 Ga (billion years ago). These processes, and the distribution of oxygen in the mantle, are poorly understood. This project will use iron and chromium isotopes as oxygen tracers in 3.3-2.1 Ga mantle rocks to understand the evolution of oxygen in the mantle and how this is linked to the development of the Earth’s atmosphere.
Thallium isotopes: a novel geochemical tracer to map recycling in Earth’s mantle
Sune Nielsen: Supported by a fellowship from the Danish Research Council and subsequently awarded an ARC Discovery Grant
Summary: The recycling of crustal material back into the mantle at subduction zones is one of the most fundamental Earth processes, but its effect on the evolution of the geochemistry of the mantle, and the ultimate fate of the subducted material, are poorly understood. This project will use the stable isotope geochemistry of thallium as a novel and sensitive tracer to follow subducted oceanic crust through the subduction process, and test for its reappearance in hot-spot volcanoes and the continental lithosphere. The results will provide firm constraints on models of mantle convection, Earth evolution and the generation of continents.
Evolution of the upper mantle beneath the Siberian Craton and the southern margin of the Siberian Platform
Vladimir Malkovets: Supported by Macquarie University Research Fellowship
Summary: This project will contribute new information and concepts about the formation of Earth’s continents over the last 4 billion years. It will use geochemical techniques, recently developed with state-of-the-art instrumentation in the GEMOC laboratories, and apply these techniques to unique suites of mantle-derived samples (xenoliths) from volcanic rocks across Siberia to investigate differences between mantle domains of different age and tectonic setting. The results will provide direct analogues for better understanding of mantle structure and mantle evolution beneath Australia, and will contribute to development of tectonic models relevant to the area selection process in mineral exploration.
Enhancing the use of zircon in crustal studies and mineral exploration: trace-element and statistical approach
Elena Belousova: Supported by Macquarie University Staff Grant
Summary: Zircon is an accessory (low-abundance) mineral present in most rock types and represents a time-capsule carrying significant information about its original host rock, including its age, tectonic origin and composition. Interpretation of the parent rock composition using trace-element signatures of zircons has not been fully exploited. This study will characterise trace-element compositions of zircons from representative rock types and use a robust statistical diagnostic methodology (CART: Classification And Regression Trees) to identify criteria for assigning parent rock types using single zircon grains. Zircons collected from alluvial sources could then be used to unravel regional geology and sediment provenance.