Detrital and xenocrystic zircon ages from Neoproterozoic to Palaeozoic arc terranes of Mongolia: Significance for the origin of crustal fragments in the Central Asian Orogenic Belt |
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| Authors: | Y Rojas-Agramonte A Kröner A Demoux X Xia W Wang T Donskaya D Liu M Sun |
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| Institution: | 1. Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China;2. Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany;3. Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, 119017 Moscow, Russia;4. Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London SW7 5BD, UK;5. Geological Faculty, St. Petersburg State University, University Embankment 7/9, St. Petersburg 199034, Russia;6. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;7. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China;8. Central Asian Geological–Geophysical Association, Bishkek, Kyrgyzstan;9. Institute of Geology, Academy of Sciences of Kyrgyzstan, Bishkek 720481, Kyrgyzstan;10. Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;11. CERCAMS, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK;1. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, PR China;2. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, PR China |
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| Abstract: | The Central Asian Orogenic Belt contains many Precambrian crustal fragments whose origin is unknown, and previous speculations suggested these to be derived from either Siberia, Tarim or northern Gondwana. We present an age pattern for detrital and xenocrystic zircons from Neoproterozoic to Palaeozoic arc and microcontinental terranes in Mongolia and compare this with patterns for Precambrian rocks in southern Siberia, the North China craton, the Tarim craton and northeastern Gondwana in order to define the most likely source region for the Mongolian zircons. Our data were obtained by SHRIMP II, LA-ICP-MS and single zircon evaporation and predominantly represent arc-related low-grade volcanic rocks and clastic sediments but also accretionary wedges and ophiolitic environments.The Mongolian pattern is dominated by zircons in the age range ca. 350–600 and 700–1020 Ma as well as minor peaks between ca. 1240 and 2570 Ma. The youngest group reflects cannibalistic reworking of the Palaeozoic arc terranes, whereas the Neoproterozoic to late Mesoproterozoic peak reflects both reworking of the arc terranes as well as Neoproterozoic rifting and a Grenville-age crust-formation event.The 700–1020 Ma peak does not exist in the age spectra of the Siberian and North China cratons and thus effectively rules out these basement blocks as potential source areas for the Mongolian zircons. The best agreement is with the Tarim craton where a major Grenville-age orogenic event and early Neoproterozoic rifting have been identified. The age spectra also do not entirely exclude northeastern Gondwana as a source for the Mongolian zircons, but here the Neoproterozoic age peak is related to the Pan-African orogeny, and a minor Grenville-age peak may reflect a controversial orogenic event in NW India.Our Mongolian detrital and xenocrystic age spectrum suggests that the Tarim craton was the main source, and we favour a tectonic scenario similar to the present southwestern Pacific where fragments of Australia are rifted off and become incorporated into the Indonesian arc and microcontinent amalgamation that will evolve into a future orogenic belt. |
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