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Tectono-metallogenic systems — The place of mineral systems within tectonic evolution,with an emphasis on Australian examples
Institution:1. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;2. Research School of Earth Sciences, Australian National University, Building 142, Mills Road, Acton, ACT 2601, Australia;3. Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;4. Centre for Exploration Targeting, School of Earth and Environment, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, 35 Stirling Highway, 6009 Crawley, Perth, Western Australia, Australia;5. Geological Survey of Victoria, GPO Box 4509 Melbourne, VIC 3001, Australia;1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;1. Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley WA6009, Australia;2. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;3. Dept Earth & Atmospheric Sciences, University of Alberta, 126 Earth Sciences Building, Edmonton, AB T6G 2R3, Canada;4. Centre for Russian and Central EurAsian Mineral Studies (CERCAMS), Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK;1. ARC Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia;2. BHP-Billiton, GPO Box 1777, Adelaide, South Australia 5001, Australia;1. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;2. Université de Lorraine, CNRS, CREGU, GeoRessources, UMR 7359, Boulevard des Aiguillettes, B.P. 239, F-54506 Vandoeuvre-lès-Nancy, France;3. PRISE, Australian National University, ACT 2600, Australia;4. Centre de Recherches Pétrographiques et Géochimiques, UMR 7358, CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, BP 20, 54501 Vandoeuvre-lès-Nancy, France;1. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;2. Geological Survey of New South Wales, PO Box 344, Hunter Region Mail Centre, NSW 2310, Australia;3. Exploration Consultant, 468 Fairy Hole Rd, Yass, NSW 2582, Australia;4. Commonwealth Scientific and Industrial Research Organisation, 11 Julius Avenue, North Ryde, NSW 2113, Australia;5. Argent Minerals, 6 Clerence Street, Sydney, NSW, Australia
Abstract:Tectono-metallogenic systems are geological systems that link geodynamic and tectonic processes with ore-forming processes. Fundamental geodynamic processes, including buoyancy-related processes, crustal/lithospheric thinning and crustal/lithospheric thickening, have occurred throughout Earth's history, but tectonic systems, which are driven by these processes, have evolved as Earth's interior has cooled. Tectonic systems are thought to have evolved from magma oceans in the Hadean through an unstable “stagnant-lid” regime in the earlier Archean into a proto-plate tectonic regime from the late Archean onwards. Modern-style plate tectonics is thought to have become dominant by the start of the Paleozoic. Mineral systems with general similarities to modern or geologically recent systems have been present episodically (or semi-continuously) through much of Earth's history, but most of Earth's present endowment of mineral wealth was formed during and after the Neoarchean, when proto- or modern-style plate tectonic systems became increasingly dominant and following major changes in the chemistry of the atmosphere and hydrosphere. Changes in the characteristics of some mineral systems, such as the volcanic-hosted massive sulphide (VHMS) system, reflect changes in tectonic style during the evolution towards the modern plate tectonic regime, but may also involve secular changes in the hydrosphere and atmosphere.Whereas tectono-metallogenic systems have evolved in general over Earth's history, specific tectono-metallogenic systems evolve over much shorter time frames. Most mineral deposits form in three general tectono-metallogenic systems: divergent systems, convergent systems, and intraplate systems. Although fundamental geodynamic processes have driven the evolution of these systems, their relative importance may change as the systems evolved. For example, buoyancy-driven (mantle convection/plumes) and crustal thinning are the dominant processes driving the early rift stage of divergent tectono-metallogenic systems, whereas buoyancy-driven processes (slab sinking) and crustal thickening are the most important processes during the subduction stage of convergent systems. Crustal thinning can also be an important process in the hinterland of subduction zones, producing back-arc basins that can host a number of mineral systems. As fundamental geodynamic processes act as drivers at some stage in virtually all tectonic systems, on their own these cannot be used to identify tectonic systems. Moreover, as mineral systems are ultimately the products of these same geodynamic drivers, individual mineral deposit types cannot be used to determine tectonic systems, although mineral deposit associations can, in some cases, be indicative of the tectono-metallogenic system.Ore deposits are the products of geological (mineral) systems that operate over a long time frame (hundreds of millions of years) and at scales up to the craton-scale. In essence, mineral systems increase the concentrations of commodities through geochemical and geophysical processes from bulk Earth levels to levels amenable to economic mining. Mineral system components include the geological (tectonic and architectural) setting, the driver(s) of mineralising processes, metal and fluid sources, fluid pathways, depositional trap, and post-depositional modifications. All of these components link back to geodynamic processes and the tectonic system. For example, crustal architecture, which controls the spatial distribution of, and fluid flow, within mineral systems, is largely determined by geodynamic processes and tectonic systems, and the timing of mineralisation, which generally is relatively short (commonly < 1 Myr), correlates with local and/or far-field tectonic events.The geochemical characteristics of many mineral systems are a consequence of their geodynamic and tectonic settings. Settings that are characterised by low heat flow and lack active magmatism produce low temperature fluids that are oxidised, with ore formation caused largely by redox gradients or the provision of external H2S. The characteristics of these fluids are largely governed by the rocks with which they interact, rocks that have extensively interacted with the hydrosphere and atmosphere, both environments that have been strongly oxidised since the great oxidation event in the Paleoproterozoic. In settings characterised by high heat flow and active magmatism, ore fluids tend to be higher temperature and reduced, with deposition caused by cooling, pH neutralisation, depressurisation and fluid mixing. Again, the characteristics of these fluids are governed by rocks with which they interact, in this case more reduced magmatic rocks derived from the mantle or lower crust.
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