- 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 GEMOCís 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 Earthís 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 GEMOCís 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
- 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 crust 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 understanding 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.
Technology developments in GEMOC are driven by the needs of these
programs. The 1999 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 analyses
U/Pb, Lu/Hf and a spectrum of trace elements in zircon and Rb/Sr and Nd/Sm analyses in a range of minerals (see Research Highlights).
GEMOC Board suggested producing a map of lithospheric domains
for global regions where relevant data are available. GEMOCís
role in the Global Geoscience Transect 21 is providing
an interpretation of the physical and chemical state of the lithosphere
along a traverse over 20% of the Earthís circumference. Integrated
geophysical and geological modeling involving elastic thickness interpretations
as highlighted in our 1998 Report, were also used in 1999 to image the
lithosphere on a regional basis. These approaches complement the
Lithosphere Mapping where samples of mantle material are available from
This section gives a brief overview of the philosophy and framework of GEMOCís Research Projects and the major new activities in 1999. A few of the important research outcomes in 1999 are highlighted and a list of current funded Research Projects is given in Appendix 5.
GEMOCís 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 modeling. GEMOCís distinctive approach relies on the integrative use of geochemical and geophysical datasets and the different scales of detail from micron to global.
1999 was another exciting year for GEMOCís Research Programs as we embarked on a raft of new projects and developments and the first stages of many major strands came to maturity with presentations (many invited and keynote) at 18 national and international conferences (Appendix 4), 71 publications published or in press (Appendix 2).
Two major themes were set up in GEMOCís first year, as a result of discussions in GEMOC and at Board Meetings, to provide a vehicle for accommodating an interdisciplinary approach for sub-projects consistent with our Research Program structure and addressing relevant problems of both global and Australian geological importance.
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 in widespread Mesozoic-Tertiary basalts, can reveal 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 GEMOCís expertise in mantle studies (basalts and xenoliths) with its expertise in granite genesis and metallogenesis. Xenoliths of lower crustal origin occur in many 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. Studies of granite and metallogenesis 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 expanded this project to include 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 worldís 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 are being 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 construct a broad picture of 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.
PROGRAM STRAND LOCATIONS
- 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, Brazil Research Highlights
- China - Mongolia - Siberia Lithosphere Transect
- Gravity modeling 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 Research Highlights
- 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
- 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 News Flash
- 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 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
- 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
- Sulfide and PGE budget of the mantle Research Highlights
- Highly siderophile element (including platinum group element) concentrations in sulfides (LAM-ICPMS) Research Highlights
- Trace element and isotopic composition of apatite and titanite as indicators of mineralisation News Flash
- Zircon 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 Research Highlights
- 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 Research Highlights
- Hot Rock Geothermal Energy: a major new Australian energy source
A window to the lithosphere across more than 20% of the Earthís circumference
The Global Geoscience Transect 21 is an International Lithosphere Program that has resulted in a multidisciplinary geophysical and geological transect extending from Taiwan, through the Altai region (completed by the Chinese Academy of Geoexploration now incorporated into the newly-formed Chinese Geological Survey), and connecting with the Russian transect from Kyzyl to Murmansk. GEMOC projects have characterised lithospheric sections at key localities where mantle samples are available. Information from these localities provides constraints for interpreting the lithosphere composition and architecture in other parts of the transect from geophysical data. Gravity modeling to define elastic thickness of lithosphere terranes is being carried out in collaboration with Professors Wang Ping and Yuan Xuecheng from the Chinese Geological Survey and with Yuan Bingqiang from the Gravity Centre, Xiían.
Regional MAGSAT data around the Global Geoscience Transect 21.