Geochemical evolution of lithospheric mantle beneath S.E. South Australia |
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| Institution: | 1. Department of Geology and Geophysics, Adelaide University, Adelaide, SA 5005, Australia;2. Department of Earth Sciences, University of Bristol, Bristol, UK;1. Institut für Mineralogie, Leibniz Universität Hannover, 30167 Hannover, Germany;2. School of Physical Sciences, University of Tasmania, Hobart 7001, Australia;3. Department of Geology, University of Liege, 4000 Sart Tilman, Belgium;4. Department of Geology, University of Pretoria, Hatfield, Pretoria, 0002, South Africa;5. Department of Mineralogy and Petrology, Technical University Berlin, 13355 Berlin, Germany;6. Perm State University, Geological Department, Bukireva 15, 614990 Perm, Russia;7. School of Geosciences, University of the Witwatersrand, PO Wits 2050, South Africa;1. Department of Earth & Environmental Sciences, School of Physical Science, The University of Adelaide, SA 5005, Australia;2. Mineral Exploration Cooperative Research Centre, Department of Earth & Environmental Sciences, School of Physical Sciences, The University of Adelaide, SA 5005, Australia;3. Northern Territory Geological Survey, Department Industry Tourism and Trade, Darwin, NT 0801, Australia;1. School of Natural and Built Environments, University of South Australia, Adelaide, Australia;2. Department of Earth Sciences, School of Physical Sciences, University of Adelaide, Adelaide, SA, 5005, Australia |
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| Abstract: | The record of mafic magmatism from the Proterozoic to the Holocene in southern Australia reflects episodic incompatible element enrichment of the sub-continental lithospheric mantle (SCLM) recording periodic interaction of asthenosphere and lithosphere. The composition of Jurassic and Cainozoic mantle derived magmas is strongly influenced by the geochemical impact on the SCLM of events which took place during the Neoproterozoic and Cambrian. These events include rifting, passive margin development and orogenesis.Neoproterozoic to Cambrian basalts are widespread in western New South Wales, South Australia and Tasmania and reflect mantle decompression during extension and rifting of the Australian–East Antarctic Craton during the development of the proto-Pacific passive margin. These basalts fall into two regionally extensive and very different suites: (i) a voluminous suite of tholeiites and (ii) a highly undersaturated alkaline (nephelinite–basanite) series.Both Jurassic kimberlite magmas from the Adelaide Fold Belt and highly undersaturated Quaternary analcimites and basanites from the Mt. Gambier district of S.E. South Australia, have geochemical characteristics like those of the Precambrian–Cambrian alkaline suites. They have high concentrations of large ion lithophile (LIL), rare earth (RE) and high field strength (HFS) elements, and high HFSE/LILE and LREE/HREE ratios with TDMNd values of 0.5–0.8 Ga. The Jurassic kimberlites appear to sample lithospheric mantle enrichment zones of Late Neoproterozoic to Early Cambrian age. The Quaternary suites result from mixing of contemporary mantle plume components with this old lithospheric enrichment, which is also identified with the occurrence of metasomatic phlogopite, amphibole and apatite in lherzolite mantle xenoliths from a number of Cainozoic volcanoes in Western Victoria.A very different type of lithospheric mantle enrichment took place during the late stages of the Ross–Delamerian Orogeny. This yielded a crustally contaminated mantle zone that mirrors the Cambro-Ordovician position of that orogen. This zone of contaminated lithospheric mantle interacted with a large plume in the Jurassic to yield the highly anomalous Ferrar–Tasmanian–Kangaroo Island basalts and dolerites. |
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