GEMOC ARC National Key CentreGEMOC's research programs
index
- the research aims
- scientific context
- research program
- summary of major strands
- activities 1998
- action 1998
- research projects feeding major strands
- some research highlights
- 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 modelling 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 the 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 and commodity distribution in the accessible crust.
This bottom-up approach involves:
- 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 comprises four strands:
- Lithosphere Mapping
- Geotectonics
- Crustal Generation Processes
- Metallogenic Provinces
The Lithosphere Mapping strand 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 crustal material and metallogenic provinces. The nature of mantle fluids and the mantle residences and abundances of siderophile, chalcophile and noble elements and sulphur, carbon, oxygen and nitrogen are keys to the transfer of mineralising elements into the crust.
The Crustal Generation strand 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.
The Geotectonics strand 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.
The Metallogenesis strand 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.
This section gives a brief overview of the philosophy and framework of GEMOC's Research Projects and the major new activities in 1998. A few of the important research outcomes in 1998 are highlighted and a list of current funded Research Projects is given in Appendix 5.
GEMOC's research programs aim to be interdisciplinary and draw on our mix of geochemical and geophysical expertise and the technology base that allows, for example, application of micron-scale geochemical data to the interpretation of geophysical datasets and to lithosphere-scale modelling as described in the Siberian Platform and "From the micro to the macro" articles in the Research Highlights below. GEMOC's distinctive approach results from the integrative use of geochemical and geophysical datasets and the different scales of detail from micron to global.
1998 was an exciting year for GEMOC's Research Programs as the first stages of many major strands came to maturity with 100 presentations (many invited) at 18 national and international conferences (Appendix 4). 165 publications published or in press (Appendix 2) and convening of workshops and sessions relevant to GEMOC.
1. Timing and distribution of lithosphere formation and modification in the eastern Australian Tasmanide Belt
The Tasman Orogen is a natural laboratory for the study of Phanerozoic crust-mantle interaction. The geological and geophysical coverage is excellent. A very large database on the geochemistry and metallogeny of the abundant granitic rocks gives a reflection of variations in middle to lower crustal composition across the region. Abundant mantle-derived xenoliths occur in widespread Mesozoic-Tertiary basalts, making it possible to study regional variations in lithosphere and asthenosphere composition and relate these to crustal domains defined by structural relations, granitoid chemistry and geophysics.
The Tasmanide project integrates GEMOC's expertise in mantle studies and geophysics with its expertise in granite genesis and metallogenesis. Xenoliths of lower crustal origin occur in several localities scattered across the region; a traverse from Mt. Gambier in the west to the Monaro Province in the east provides mantle samples from several crustal domains defined by geophysics, granite chemistry and structural/stratigraphic data. The traverse also crosses the I-S granite line, which is believed to represent a major discontinuity in the nature of the lower to middle crust. Xenolith-bearing basalts were erupted through Proterozoic basement in western Tasmania, and through the Paleozoic fold belt in the eastern part of the island. Because of this variety of materials and data, this region provides an excellent opportunity to investigate crust-mantle relationships in a major Phanerozoic orogen, and to relate these to tectonics, geophysics and metallogeny.
An explosion seismic traverse across the New England region has been
planned with international cooperation and will interface with detailed
mantle studies of that area in a postgraduate project. This work will provide
resolution of the crust-mantle boundary region to complement seismic tomography
models that give information at deeper levels. Granite and metallogenesis
studies are characterising crust-mantle interaction and fluid processes.
International funded projects (eg southeastern China igneous rocks,
mineral deposits and tectonic setting) provide direct analogues to help
interpret tectonic and magmatic events in the Tasmanide Belt.
2. Lithosphere Generation project
This umbrella project started as the "Western Pacific Lithosphere Project" but research developments have revealed there is secular and apparently irreversible evolution in the composition of newly-formed lithospheric mantle. We therefore have modified this project to include the definition of the nature of lithosphere formed by processes such as accretion/subcretion of oceanic plateaux. The project includes other regions that may be analogues to the mantle beneath accreted continental margins such as eastern Australia and China.
Some of the world's youngest ophiolite sequences outcrop in the Solomon
Islands and different tectonic units represent samples of mantle formed
in different settings: beneath Cretaceous ocean ridges, in a forearc setting,
and during the plume-induced eruption of the basalts of the Ontong-Java
Plateau (OJP). Mantle xenoliths from volcanic rocks on Malaita and
near Lihir Island provide samples of deep OJP mantle and of relatively
shallow forearc mantle, respectively. The Lihir samples have been
affected by fluids that may be related to gold deposits in the overlying
crust. The Kerguelen Plateau yields a unique suite of deep-seated
xenoliths that reflect young plume and oceanic mantle material, and oceanic
plateau lower crust. Regional gravity and seismic data are available
for both areas. Field, petrological, geochemical and petrophysical studies
of the different types of mantle will be integrated with work on the overlying
cumulate and volcanic rocks to understand the processes that have produced
the spectrum of compositions in each mantle type. Comparisons with
similar "ancient" environments in eastern Australia (the Tasmanide Project)
will enable us to understand the processes involved in the creation and
modification of lithosphere at convergent margins and above plumes, and
to relate these to fluid transfer and ore-forming processes.
"to understand the processes involved in the creation and modification
of lithosphere at convergent margins and above plumes, and to relate these
to fluid transfer and ore-forming processes."
Workshops of research groups across nodes set up a strategic plan to address these projects. As a result:
- A project on the geochemical signatures of basalts and lithospheric mantle across the Tasman Line in Tasmania was continued in collaboration with the Tasmanian Geological Survey and the first results of the postgraduate projects were presented at the Australian Geological Congress in Townsville.
- A collaborative project across GEMOC was funded (small ARC grant) for 1999 to extend the correlation of lithospheric mantle domains with tectonic regions mapped at the surface.
- Two PhD projects are focussing on the nature of the lithospheric mantle in the Tasmanides ? one localised in the New England region and one undertaking a broader survey of the sulfur and PGE budget of this mantle.
- A combined seismic/petrology Honours project examined the detailed Moho structure in the Crookwell (NSW) region.
- A seismic study, utilising quarry blasts, was initiated to refine the nature and location of the Moho in the Sydney Basin.
- A seismic program was planned (with Prof. Keller from the University of Texas, El Paso) to use seismic explosion lines across several traverses (including New England and Monaro, NSW) to refine lower crust, upper mantle and Moho structure. This interfaces with seismic tomography projects in the region at ANU and the University of Adelaide.
- 6 relevant Honours projects were completed in 1998; and 7 are commencing in 1999
- A study of the apparent wander path for Australia during Carboniferous to Permian using volcanic units from the New England Orogen in Queensland was completed (see Research Highlights).
- Geochemistry of basalts in eastern Australia revealed new information to interpret the nature of the lithosphere and of asthenospheric convection: the location of Indian- and Pacific-type asthenosphere was located for two timeslices (see Research Highlights) and distinctive mantle domains were identified in northeastern Australia (in time and space) and correlated with Australia's geodynamic evolution.
- a series of papers and conference presentations gave the results of the first stage of the 4-D Lithosphere Mapping Program in GEMOC, integrating individual project strands, with several conference papers under the title "Are Lithospheres Forever?" Some of these results are summarised in "Research Highlights"
- ARC project funded including a component on the geochemistry of the ophiolitic sequence on Solomon Islands
- completion of a strand of collaborative project between Macquarie and CSIRO to characterise the fluid/rock interaction in mantle xenoliths from Lihir Island, PNG, immediately beneath a young gold deposit (see Goldschmidt Conference 1998 and Australian Geological Congress 1998 abstracts, Appendix 4)
- an analogue study of oceanic lithosphere in the Kerguelen Archipelago including laboratory measurement of Vp on lower crust and upper mantle samples was continued and the first results of the geochemical study presented at the Goldschmidt Conference 1998 (Appendix 4)
- "the roots of an arc" study - the Greenhills Ultramafic-mafic complex, South Island, New Zealand, continued
- an analogue study to define plume-type mantle using mantle xenoliths in post-Deccan alkaline basalts from India with Dr Nitin Karmalkar from Pune University was continued
- the project in collaboration with the University Joseph Fourier in Grenoble on the role of accreted/subcreted oceanic plateaux in the evolution of the continental lithosphere of Ecuador continued
Research projects feeding major strands
Lithosphere Mapping
- Geochemical structure and evolution of continental lithosphere and interpretation of geophysical data
- Mantle terranes and cratonic roots: Canada, Southern Africa, Siberia, Sino-Korea, Greenland, Australia
- China - Mongolia - Siberia Lithosphere Transect
- Gravity modelling of lithosphere terranes (regional elastic thickness)
- Evolution of oceanic lithosphere, New Ireland (Papua New Guinea), Kerguelen Plateau, Hawaii, Crozet Islands.
- Diamonds: origin and clues to lithosphere evolution and structure: eastern Australia, Indochina, South America, Canada, Siberia, China.
- Seismic imaging of Moho structure and integration with petrological data: eastern Australia, Indian Ocean, Kerguelen Plateau
- Thermal framework of the lithosphere: palaeogeotherms, 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
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 plateaux in oceanic and continental crustal formation: Kerguelen, Ontong-Java Plateau, Solomon Islands, Ecuador
- Crustal evolution and metallogenesis, southeastern China
- Crustal tectonism: Proterozoic uplift in East Antarctica; P-T studies, central Nagssugtoqidian Orogen, west Greenland
- 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
- 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
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
- 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
- Sulfide and PGE budget of the mantle
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 Fold Belt tectonism and regional volcanology: Tumut-Gundagai region; Louth area; central western NSW; central Queensland
- Palaeomagnetic studies of the northern New England Orogen
- Hot Rock Geothermal Energy: a major new Australian energy source
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