Juvenile versus recycled crust in the Central Asian Orogenic Belt: Implications from ocean plate stratigraphy,blueschist belts and intra-oceanic arcs |
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| Institution: | 1. Earth Sciences, Earth Studies Building C02, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia;2. Department of Geoscience, University of Calgary, ES 274, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada;3. Faculty of Science, Yamaguchi University, 1677-1 Yoshida, Yamaguchi City, Yamaguchi Prefecture 753-8512, Japan;1. College of Earth Sciences, Jilin University, Changchun 130061, PR China;2. College of Marine Geosciences, Ocean University of China, Qingdao 266003, PR China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, PR China;4. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, PR China;1. Department of Earth and Planetary Science, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo 152-8551, Japan;2. Division of Earth and Planetary Sciences, Graduate School of Science, The University of Kyoto Yoshidahoncho, Sakyo-ku, Kyoto 606-8501, Japan;3. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo, Japan;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;3. Department of Applied Geology, Curtin University, G.P.O. Box U1987, Perth, Western Australia 6845, Australia;4. Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, Beijing 100049, China;1. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague, 12843, Czech Republic;2. Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, Prague, 16500, Czech Republic;3. Czech Geological Survey, Klárov 3, Prague, 11821, Czech Republic |
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| Abstract: | New or “juvenile” crust forms and grows mainly through mafic to andesitic magmatism at Pacific-type or accretionary type convergent margins as well as via tectonic accretion of oceanic and island-arc terranes and translation of continental terranes. During the last decades the juvenile or recycled nature of crust has been commonly evaluated using whole-rock isotope and Hf-in-zircon isotope methods. However, evidence for the accretionary or Pacific-type nature of an orogenic belt comes from geological data, for example, from the presence of accretionary complexes (AC), intra-oceanic arcs (IOA), oceanic plate stratigraphy units (OPS), and MORB-OIB derived blueschist belts (BSB). The Central Asian Orogenic Belt (CAOB) represents the world's largest province of Phanerozoic juvenile crustal growth during ca. 800 m.y. between the East European, Siberian, North China and Tarim cratons. From geological point of view, the CAOB is a typical Pacific-type belt as it hosts numerous occurrences of accretionary complexes, intra-oceanic arcs, OPS units, and MORB-OIB derived blueschist belts. In spite of its accretionary nature, supported by positive whole rock Nd isotope characteristics in CAOB granitoids, the Hf-in-zircon isotope data reveal a big portion of recycled crust. Such a controversy can be explained by presence of accreted microcontinents, isotopically mixed igneous reservoirs and by the tectonic erosion of juvenile crust. The most probable localities of tectonic erosion in the CAOB are the middle and southern Tienshan and southern Transbaikalia because these regions comprise a predominantly recycled crust (based on isotope data), but the geological data show the presence of intra-oceanic arcs, blueschist belts and accreted OPS with oceanic island basalts (OIB) and tectonically juxtaposed coeval arc granitoids and accretionary units. This warrants combination of detailed geological studies with isotopic results, as on their own they may not reflect such processes as tectonic erosion of juvenile crust and/or arc subduction. |
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