GEMOC - Department of EPS - Faculty of Science

GEMOC's research program

The research aims

• to understand how Earth's core-mantle system controls crustal tectonics, and the assembly and destruction of continents through time

• to map the spatial and temporal distribution of elements, rock types and physical and chemical conditions within this system

• to understand the processes responsible for the evolution of Earth’s chemical reservoirs

• to use quantitative modelling to simulate Earth’s geodynamic evolution

• to define the systematics of element redistribution in the mantle and crust

• to define timescales of magmatic and erosional cycles

• to understand mantle melting dynamics, the influence of recycled components and their ultimate contribution to plumes and the subcontinental lithosphere

• to constrain models of the crust and lithospheric mantle from geophysical datasets, through integration of geophysical, petrological and geochemical information

• to define the tectonic and geochemical processes that have created distinct crustal and mantle domains through time

• to produce and interpret maps of lithosphere thickness and lithospheric mantle type at the present day and for selected time (and location) slices through Earth’s geological evolution

• to provide a new framework for area selection for a wide spectrum of economic deposits, by linking deep Earth models and processes to the formation of metallogenic provinces

• to define the timing of events and processes in the crust and mantle to understand crust-mantle linkages

• to develop collaborative links with international institutions and researchers relevant to GEMOC’s goals

GEMOC aims to achieve an integrated understanding of the evolution of the Earth and other planets to better understand the surface environment.

SCIENTIFIC CONTEXT

Thermal energy transmitted from the deep Earth (core and convecting mantle) provides the energy to drive lithosphere-scale processes. Mantle-derived fluids and the tectonic environment control element transfer across the crust-mantle boundary and control commodity distribution in the accessible crust. The nature of mantle heat transmission reveals information on fundamental deep Earth processes from the core-mantle boundary to the surface. The lithology of the Earth’s lithosphere can be mapped using fragments of deep materials such as mantle rocks and diamonds, and the compositions of mantle-derived magmas. Timescales can be unravelled from billions of years to tens of years.

What drives the heat engine that powers the Earth’s magnetic field and drives mantle convection? We do not clearly understand this, because we do not know the contents of heat-producing radioactive elements (K, U, Th) in the lower mantle and the core, and how these may have changed with Earth’s evolution. Experimental studies of Earth materials at extreme conditions will provide new constraints for modelling of the mantle and the evolution of the early Earth.

The focus of GEMOC's research programs is the driving role of the convecting mantle in Earth processes and its control of element concentration and distribution in the accessible crust. This bottom-up approach involves:

• Understanding Earth's internal dynamics and the generation of the present chemical and physical structure of our planet through time

• Understanding the location of different types of metallogenic provinces by defining the links between:

• mantle evolution, type and processes

• crustal generation

• large-scale tectonics

• heat, fluid and element transport

• Integration of information across disciplines, especially petrology, geochemistry, geodynamics, geophysics and tectonics

Where in the world is gemoc?

RESEARCH PROGRAM

The Research Highlights section gives an overview of major progress in 2007.

The Research Program for 2007 follows the topics of the funded projects listed in Appendix 5. Summaries of funded basic research projects are listed below and some of the collaborative industry research projects are summarised in the section on Industry Interaction.

The research program for the first six years focused on four strands: the current Research Program is pushing into new conceptual and technology frontiers, building on our intellectual capital from the first phase of GEMOC and new expertise in the Earth and Planetary Evolution CoRE.

• Mantle Dynamics and Composition

forms the framework for advancing our knowledge of Earth’s geochemical and physical evolution. The thermal output driving Earth’s “engine” has declined exponentially through time, and the distribution of heat sources must have changed with the geochemical evolution of Earth. How has this secular cooling of Earth affected the internal driving forces, and what does this imply about changes in Earth dynamics through time? When did subduction processes begin? Novel approaches using redox-sensitive metal-isotope systems will be used to examine changes in the mantle’s oxidation state, potentially linked to the initiation of subduction. Modelling of Earth’s thermal history, incorporating information about the present and past distribution of heat-producing elements and processes, will be used to test conceptual models for Earth’s internal dynamics through time. High-pressure experimental approaches will advance our understanding of deep Earth structure and properties.
Lithosphere Mapping provides the fundamental data for defining lithospheric mantle domains in terms of composition, structure and thermal state. Lithosphere profiles built up by this information are interpreted in the context of geophysical datasets (especially seismic tomography) to extrapolate laterally. Relating lithospheric domains to refined models of tectonic evolution will help to define the large-scale evolution of mantle processes through time, and their influence on the development of the crust and metallogenic provinces. The nature of mantle fluids and the mantle residence and abundances of siderophile, chalcophile and noble elements, sulfur, carbon, oxygen and nitrogen and timescales of magmatic processes are keys to understanding the transfer of mineralising elements into the crust.

• Geodynamics

uses stratigraphic, tectonic, and geophysical data to interpret the history and causes of continental assembly and disruption, with a special focus on Australia, East Asia and major cratons (Siberia, Africa, Canada, South America, India). It provides the fundamental framework to link the research on crustal and mantle processes with the localisation and development of metallogenic provinces. Numerical Modelling is a new direction and is being used to test a range of different Earth models.

• Crustal Generation Processes

seeks to understand the large-scale processes that have created and modified continental crust, how these processes may have changed through time, and how crustal processes influence the concentration and localisation of economically important elements. The role of crust-mantle interaction in granite genesis, coupled crust-mantle formation and its influence on tectonism, and transport of elements across the crust-mantle boundary link to the Mantle Dynamics and Composition and Metallogenesis strands.

• Metallogenic Provinces

seeks to define the mantle and crustal reservoirs of economically important elements, the mechanisms by which elements can be extracted from the mantle and transported into the crust, and the mechanisms of fluid transfer in the crust and mantle. The emphasis is on understanding processes of regional scale, and relating these processes to the tectonic framework and the processes of mantle and crustal generation.

RESEARCH PROJECTS FEEDING MAJOR PROGRAMS

Mantle Dynamics and Composition

Lithosphere mapping: Geochemical structure and evolution of continental lithosphere and interpretation of geophysical data

U-series applications to timescales of lithosphere processes

Experimental studies of mantle minerals: high pressure partition coefficients; water in mantle minerals; role of accessory minerals in controlling mantle fluid compositions

Mantle terranes and cratonic roots: Canada, USA, southern Africa, Siberia, eastern China, Australia, Brazil, India, Spitsbergen

Origin of mantle eclogites

The composition of Earth’s core and timing of core formation; core-mantle interaction

Interpretation of deep seismic tomography

Evolution of oceanic lithosphere: Kerguelen Plateau, Hawaii, Crozet Islands, abyssal peridotites

Diamonds: origin and clues to deep mantle and lithosphere evolution and structure Research Highlights and cover Research Highlights

Basalts as lithosphere/asthenosphere probes

Plume compositions, sources and origins Research Highlights

Thermal framework of the lithosphere: paleogeotherms, heat production, conductivity, thermal evolution

Lithosphere extension processes and consequences in East Asia: Taiwan and eastern China

Constraints on the timing of depletion and fluid movements in lithospheric mantle of different ages, using a range of isotopic and trace-element methods, including Re-Os in mantle sulfides Research Highlights

Metal isotopes as tracers of lithosphere processes and Earth evolution

Crustal Evolution and Crustal Processes

Timescales and mechanisms of magmatic processes and movement (U-series applications)

U-series analysis of weathering and erosion processes

Dating lower crust domains and tracking extent of Archean crust

Role of oceanic plateaus in the formation of oceanic and continental crust: Kerguelen

Tracers of magmatic processes: trace elements in accessory minerals

Hf-isotopic signatures of zircons (in situ LAM-ICPMS) as tracers of crust-mantle interaction in granites

Integrated U-Pb, Hf-isotope and trace-element in situ analysis of detrital zircons to characterise the magmatic history of major crustal terrains (“Event Signatures”): applications of TerraneChron®, eastern China, South America, Canada, South

Africa, Australia, India, Norway Research Highlights

Studies of detrital zircons in Paleozoic sediments: origins of terranes in Lachlan Fold Belt

Formation of Earth’s first silicic crust

Metallogenesis

U-series applications to timescales of fluid movement

Metal isotope applications to ore genesis

Geochemistry of mantle sulfides Research Highlights

Area selection and evaluation for diamond exploration

Diamond trace elements as clues to diamond formation Research Highlights

Lithosphere domains through time and location of ore deposits

Effect of deep mantle processes on lithosphere evolution and structure

Identification of plume types fertile for Ni and PGE mineralisation

Crust-mantle interaction, granites and metallogenesis through time

Re-Os dating of mantle sulfides in situ and timing of mantle processes Research Highlights

Highly siderophile element (including PGE) concentrations in sulfides (LAM-ICPMS) Research Highlights

Stable-isotope ratios of some important commodity elements (e.g. Cu, Fe, Zn, Mo) in a range of ore minerals and deposit types

Trace elements in diamonds - source fingerprinting and genetic indicators Research Highlights

Geodynamics

Influence of mantle processes on crustal geology and topography - regional geotectonic analysis: Slave Craton (Canada), Siberia, eastern China, Australia, Kaapvaal Craton, India Research Highlights

Tasman Fold Belt: terrane analysis

Paleomagnetic studies of the northern New England Orogen

Antarctic seismic studies

Deep crustal processes (New Zealand)

Plate margin processes (Papua New Guinea, Macquarie Island)

Geodynamic modelling of large-scale processes, integrating constraints from 4-D Lithosphere Mapping Research Highlights

Evolution of lithospheric composition and Earth geodynamics through time Research Highlights

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GEMOC ARC National Key Centre