GEMOC ARC National Key Centre

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 Earth's 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

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

The research program for the first six years focussed on four strands:

The Research Highlights section gives an overview of major progress in 2001.

The Research Program for 2002 follows the topics of the funded projects listed in Appendix 5.  The new ARC Program Grant (O'Reilly and Griffin) incorporates some of the new research directions in the GEMOC continuation.  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 is testing 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 Highlights) across the Australian continent and globally 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 the research (including industry collaborative) programs.  The 2001 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 the degree of crust-mantle interaction 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 trace-element spectrum 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 2001 the following activities addressed this goal.

• Software development for the high-temperature SQUID spinning magnetometer continued through 2001 in collaboration with Dr Phil Schmidt and Mr David Clark from CSIRO.
• Collaboration with Dr Patrice Rey (University of Sydney) on geodynamic modelling continued and a 2-year Research Fellowship in geodynamic modelling at Macquarie University was advertised to commence in 2002.
• The strategic alliance with Dr Karsten Gohl of the Alfred Wegener Institute, Bremerhaven was strengthened with the success of relevant funding applications on both sides.  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 starting December 2002.  GEMOC participants and 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.
• GEMOC had continuing access to the pool of seismic detectors, which forms 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 GA).
• Dr Yvette Poudjom Djomani, GEMOC Postdoctoral Fellow, continued her work in potential field geophysics (including gravity, magnetic and thermal modelling) in collaborative projects including the SPIRT project with Kennecott Canada (Slave Craton) and Australian lithosphere studies with WMC.
• Collaboration with Professor Paul Morgan (Northern Arizona University, Flagstaff) continued in geophysical modelling.

The published interpretation and documentation of the results of Global Geoscience Transect 21 (from the Philippine Sea to the Barents Sea) with the Geological Survey of China and the Institute for Gravity, Xi'an was distributed in 2001.
• Major advances were again made in understanding the interpretation of geophysical signatures of some types of large-scale lithosphere domains (eg Publications 228, 231, 234, 250 and presentations at the conferences listed below, now submitted as 6 manuscripts).
• Sue O'Reilly was invited to write a "News and Views" article (Nature, 2001, v 412, pp 777-779) on the first group of papers from the "Kaapvaal Experiment".
• Petrophysical study of the upper mantle and lower crustal xenoliths from the Kerguelen Archipelago and integration of acoustic velocity results with seismic profiles was published as Publication 244 (in collaboration with Dr Ian Jackson, ANU).
• Investigation of the paleomagnetism and rock magnetism of rocks from the Lachlan Fold Belt continued.
• Modelling 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 continued (eg Publication 234).
• Magnetostratigraphic study of the Cambro-Ordovician Black Mountain sequence in northwest Queensland continued (postgraduate project by Kari Anderson).
• Investigation of the Mooki and Peel Faults, and the Tamworth Belt using gravimetry began (postgraduate project by Bin Guo).
• 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) were published (Publication 231).
• SPIRT funding commenced on the 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 geophysical modelling and interpretation, including four keynote and six invited presentations by Sue O'Reilly, Bill Griffin, Yvette Poudjom Djomani and Paul Morgan (see Appendix 4 for titles and the GEMOC website for the full text of abstracts):
• The 12th international conference of the Geological Society of Africa
• European Union of Geosciences Conference, Strasbourg, France
• 11th V. M. Goldschmidt Conference, Hot Springs, Virginia, USA
• Australian Society of Exploration Geophysicists, 15th Geophysical Conference and Exhibition, Brisbane
• Slave-Kaapvaal Workshop, Merrickville, Ontario, Canada
• Chapman Conference: Exploration Geodynamics, Perth, Western Australia
• 4th International Archean Symposium, Perth, Western Australia

PROGRAM STRAND LOCATIONS.

RESEARCH PROJECTS FEEDING MAJOR PROGRAMS

Lithosphere Mapping

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

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

Gravity modelling of lithosphere terranes (regional elastic thickness)

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

Basalts as lithosphere/asthenosphere probes

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 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)

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

Tracking mantle plumes through time  Research Highlights
 

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

Crust-mantle interaction: applications of Terranechron^TM  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")

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

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

Resistate minerals and mineral exploration

Base and noble metals in glass inclusions, Bougainville lavas

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

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

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

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

Trace elements in diamonds - possible genetic indicators?
 

Geotectonics

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

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

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

Paleomagnetic studies of the northern New England Orogen Research Highlights

Geodynamic modelling of large-scale processes using constraints from 4-D Lithosphere Mapping results

Evolution of lithospheric composition and Earth geodynamics through time  Research Highlights