GEMOC's research program

THE RESEARCH AIMS

• to understand from the "bottom up" the processes that control the generation and modification of the crust-mantle system and to define the tectonic and geochemical processes that have created different crustal and mantle domains through time
• to map the spatial and temporal distribution of elements, rock types and physical and chemical conditions within this system
• to define the systematics of element redistribution in the mantle and crust during the critical liquid-crystal and vapour-liquid separation events
• to advance the modeling of the crust and lithospheric mantle from geophysical datasets, through integration of geophysical, petrological and geochemical information
• to produce maps of lithosphere thickness and lithospheric mantle type at the present day and for selected time (and location) slices through Earthís geological evolution
• to produce chemical tomography sections of lithospheric mantle in time and space where global datasets can be constructed
• to provide a new framework for area selection for a wide spectrum of economic deposits, by linking these models and processes to the formation of metallogenic provinces
• to develop collaborative links with international institutions and researchers relevant to GEMOC's goals

SCIENTIFIC CONTEXT

THERMAL ENERGY transmitted through the mantle provides the energy to drive lithosphere 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 Earth's interior can be mapped using fragments of deep materials such as mantle rocks and diamonds, and the compositions of mantle-derived magmas.
The focus of GEMOC's research programs is the driving role of the mantle in Earth processes and its control of element concentration and distribution in the accessible crust. This bottom-up approach involves

• 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, geophysics and tectonics

RESEARCH PROGRAM

The research program comprises four strands:

o LITHOSPHERE MAPPING provides the fundamental data for defining mantle domains in terms of composition, structure and thermal state; relating these 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 and sulfur, carbon, oxygen and nitrogen are keys to understanding the transfer of mineralising elements into the crust.

o 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 Lithosphere Mapping and Metallogenesis strands.

o GEOTECTONICS 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, Kaapvaal, Canada). It provides the fundamental framework to link the research on crustal and mantle processes with the localisation and development of metallogenic provinces.

o METALLOGENIC PROVINCES seeks to define the mantle and crustal reservoirs of economically important elements, the mechanisms by which elements can be extracted from theelements, 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.

The Research Highlights section gives an overview of major progress in 2000.

The specific Research Program for 2001 follows the topics of the funded projects listed in Appendix 5. Some of the industry projects are summarised in the section on Industry Interaction.

Funding of the SPIRT Project with WMC for 2001 to 2003 (Lithospheric Architecture of Australia: Relevance to Location of Giant Ore Bodies) is a culmination of one of GEMOC's main original Research Aims. This research project will test the concept that giant magmatic and hydrothermal ore bodies are localised by major structural discontinuities that extend through the Earth's lithosphere. Modelling of geophysical data (see the Research Highlight on the Slave Craton) across the Australian continent will define regional lithospheric domains and their boundaries. Tectonic analysis and geochemical data on crustal and mantle rocks will define the age and composition of the upper mantle beneath each domain, and the history of crust-mantle interaction (magmatism, extension, compression). This history will be integrated with information on the timing and style of large ore deposits to understand the relationship between lithosphere domains and large-scale mineralisation. The new methodologies of using mantle sulfides to date mantle events, and of characterising crustal terrane development using U-Pb dating and Hf isotopic compositions of zircons (see Research Highlights) will be integrated with the geophysical modelling.

Technology developments in GEMOC are driven by the needs of these programs. The 2000 advances in the Geochemical Analysis Unit relevant to in situ trace and isotopic analysis are allowing us to exceed our original goals in the areas of tracking fluid movement during mantle and crustal events and recognising the timing of different generations of major lithospheric events. Foremost in these new methods are the in situ PGE and Re/Os analysis of sulfides; U/Pb, Lu/Hf and a spectrum of trace elements in zircon and Rb/Sr and Nd/Sm analyses in a range of minerals.

STRENGTHENING GEOPHYSICS

A major strategic goal of GEMOC is strengthening Geophysics and bridging the geology/geophysics interface. During 2000 the following activities addressed this goal.

• Dr Mark Lackie, Dr Phil Schmidt and Mr David Clark continued development of the rock magnetism joint facility set up with ARC RIEFP funding (involving CSIRO and SUCOGG Universities, with Macquarie as the lead institution). Software for development for the high-temperature SQUID spinning magnetometer continued through 2000.
• New collaboration with Dr Patrice Rey (University of Sydney) was initiated to undertake geodynamic modelling. This will be enhanced by a 2-year appointment of a Research Fellow in geodynamic modelling at Macquarie University.
• A strategic alliance was set up during 2000 with Dr Karsten Gohl of the Alfred Wegener Institute, Bremerhaven. The first collaboration will be "Structure and dynamics of a submarine continent: evolution of the Campbell Plateau", involving research cruises by the vessel RV Sonne. GEMOC PhD students will have the opportunity for shipboard geophysics experience (and subsequent processing) and GEMOC will be involved in interpretation of mantle structure and composition and basalt geochemistry and origin with German colleagues.
• Collaboration with Professor Paul Morgan (Northern Arizona University, Flagstaff) continued in geophysical modelling.
• Equipment upgrades relevant to geophysics research were funded by Macquarie University:
  • GEOMETRICS G856 Proton Precession Magnetometer
  • Seismic trigger cable modifications
  • Bartington MS2 magnetic susceptibility-temperature system
• GEMOC had continuing access to the pool of seismic detectors which form part of the ARC Seismic Consortium (headed by the University of Adelaide/Flinders University with Macquarie, Monash, Sydney, Queensland and ANU as partners and with strong support from AGSO).
• Dr Yvette Poudjom Djomani, GEMOC Postdoctoral Fellow continued her work in potential field geophysics (including gravity, magnetic and thermal modeling) in collaborative projects including the SPIRT project with Kennecott Canada (Slave Craton) and Australian lithosphere studies with WMC. The project on gravity modeling across the Siberian Platform (collaborative with WMC and Dr Y. Erincheck of VSEGEI (St Petersburg) who provided some geophysical datasets) was completed.
• The interpretation and documentation of the results of Global Geoscience Transect 21 (from the Philippine Sea to the Barents Sea) was completed with the Geological Survey of China and the Institute for Gravity, Xi'an. The impressive transect (also available as CD-ROM) was published in July.

Part of the China Gravity modelling team: L-R, Yuan Binqiang, Yvette Poudjom Djomani, Bill Griffin and Ming Zhang.

• Major advances were made in understanding the interpretation of geophysical signatures of some types of large-scale lithosphere domains (eg Publications 199, 217, 228, 231, 234).
• Petrophysical study of the upper mantle and lower crustal xenoliths from the Kerguelen Archipelago and integration of acoustic velocity results with seismic profiles was completed and submitted for publication (in collaboration with Dr Ian Jackson, ANU).
• Investigation of the paleomagnetism and rock magnetism of rocks from the Lachlan Fold Belt continued.
• Modeling of the density of different types and compositions of lithospheric mantle to assess mechanisms of mantle overturn and thinning in regions of different age, thermal structure and tectonic environment was completed and results published (Publications 228, 234).
• Determination of a Devonian-Carboniferous palaeomagnetic pole from the western Drummond Basin in North Queensland (postgraduate project by Kari Anderson) was completed.
• Results of the project on the origin, structure and composition of the Agulhas Plateau, SW Indian Ocean (in collaboration with the Alfred Wegener Institute Antarctic Survey cruise) are in press (Publication 231).
• SPIRT funding was granted (for 2001-2003) for a project with WMC on recognition of lithospheric domains in Australia and integration with thermal and magnetic signatures and datasets.
• GEMOC had a high profile at international conferences relevant to geophysics (see Appendix 4 for titles and the GEMOC website for the full text of abstracts):
  • 15th Australian Geological Convention
  • Australian Palaeomagnetism, Rock Magnetism and Environmental Magnetism 2000
  • AGU Western Pacific and Fall Meetings

PROGRAM STRAND LOCATIONS.

RESEARCH PROJECTS FEEDING MAJOR PROGRAMS

Lithosphere Mapping

Geochemical structure and evolution of continental lithosphere and interpretation of geophysical data

Mantle terranes and cratonic roots: Canada, southern Africa, Siberia, eastern China (Sino-Korean craton, Yangtse), Greenland, Australia, Brazil Research Highlights

China - Mongolia - Siberia Lithosphere Transect

Gravity modeling of lithosphere terranes (regional elastic thickness) Research Highlights

Evolution of oceanic lithosphere, New Ireland (Papua New Guinea), Kerguelen Plateau, Hawaii, Crozet Islands Research Highlights

Diamonds: origin and clues to lithosphere evolution and structure: eastern Australia, Indochina, South America, Canada, Siberia, China Research Highlights

Seismic imaging of Moho structure and integration with petrological data: eastern Australia, Indian Ocean, Kerguelen Plateau

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

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

Basalts as lithosphere/asthenosphere probes Research Highlights

Lithosphere structure along Global Geoscience Transect 21

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

The nature of lithospheric mantle in arc regions (Japan, Kamchatka, Phillipines, Solomon Islands)

Crustal Evolution

Magma genesis and tectonics in Pacific island arcs and oceanic islands: far east Russia, Japan, Izu-Bonin-Mariana, Solomon Islands, Vanuatu, New Zealand, Papua New Guinea, Hawaii

Role of oceanic plateaus in oceanic and continental crustal formation: Kerguelen, Ontong-Java Plateau, Solomon Islands, Ecuador

Crustal evolution and metallogenesis, southeastern China

Evolution of continental crust: central Queensland; San Francisco Volcanic Field, Arizona; Peninsular Ranges batholith of Baja California, Mexico

Origin of granites and crustal genesis at continental margins: eastern Australia, southeastern China Research Highlights

Experimental studies: diffusion of lead in zircon; eclogite melting

Metamorphic reactions and mineral growth; microstructural processes in metamorphic rocks

Tracers of magmatic processes; trace elements in accessory minerals

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") Research Highlights

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

Metallogenesis

Volatile, chalcophile, and noble siderophile elements in subduction zone magmas

Sulfide partitioning between felsic melts and residues

Geochemistry of mantle sulfides

Chromite chemistry in mantle-derived magmas and residues

Magmatic and hydrothermal evolution of intrusive-related gold deposits

Metals behaviour in ultramafic-mafic intrusions

Resistate minerals and mineral exploration

Mantle fluids beneath a young gold deposit: mantle xenoliths from the Tubaf Volcano, New Ireland, Papua New Guinea

Base and noble metals in glass inclusions, Bougainville lavas

Origin of mineralisation in the Browns Creek Gold Mine, NSW

Corundum in basalts: origin of sapphire

High pressure vapour-melt partitioning experiments

Global kimberlite database

Area selection and evaluation for diamond exploration

Lithosphere domains through time and location of ore deposits

Crust-mantle interaction, granites and metallogenesis through time Research Highlights

Sulfide and PGE budget of the mantle

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

Highly siderophile element (including platinum group element) concentrations in sulfides (LAM-ICPMS)

Zircon composition in mineral exploration

Apatite composition in mineral exploration

Groundwater geochemistry and aquifer lithology Research Highlights

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

Trace elements in diamonds ­ possible genetic indicators? Research Highlights

Geotectonics

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

Neoproterozoic earth history of Australia: Tectonics, isotope-, volcanic- and bio-stratigraphy

Tasman Foldbelt tectonism and regional volcanology: Tumut-Gundagai region; Louth area; central western NSW; central Queensland

Paleomagnetic studies of the northern New England Orogen

Hot Rock Geothermal Energy: a major new Australian energy source

Evolution of lithospheric composition and Earth geodynamics through time

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