Evolution of Cambrian and Early Ordovician arcs in the Kyrgyz North Tianshan: Insights from U-Pb zircon ages and geochemical data |
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| Institution: | 1. Geological Institute (GIN), Russian Academy of Sciences, Pyzhevskiy pereulok 7, Moscow 119017, Russia;2. Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Road 26, Beijing 100037, China;3. Institute of Geosciences, University of Mainz, Saarstrasse 21, 55099 Mainz, Germany;4. Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Makarova embankment 2, St. Petersburg 199034, Russia;5. Department of Geoscience, Universidad de los Andes, Cra 1 No 18A-70, M1-307, CP: 111711 Bogotá, Colombia;6. Institute of Geology, National Academy of Sciences of Kyrgyzstan, Irkendyk Prospect 30, Bishkek 720481, Kyrgyzstan;7. Dept. of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;1. Institute for Peat and Mire Research, School of Geographical Sciences, Northeast Normal University, Changchun 130024, China;2. The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;3. Research School of Earth Sciences, Australian National University, Mills Road, Canberra, ACT 0200, Australia;1. GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Schlossgarten 5a, D-91054 Erlangen, Germany;2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beituchengxilu Road 19, P.O. Box 9825, Beijing 100029, China;1. Institute of Earth Sciences, St-Petersburg State University, University Embankment 7/9, St-Petersburg, 199034, Russia;2. Geological Institute (GIN), Russian Academy of Sciences, Pyzhevskiy 7, Moscow 119017, Russia;3. New South Wales Institute of Frontiers Geoscience, University of Newcastle, Newcastle, NSW 2308, Australia;4. Department of Earth and Atmospheric Sciences, University of Alberta, 116 Street and 85 Avenue, Edmonton, Alberta T6G 2R3, Canada |
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| Abstract: | Geochronological, geochemical, and structural studies of magmatic and metamorphic complexes within the Kyrgyz North Tianshan (NTS) revealed an extensive area of early Palaeozoic magmatism with an age range of 540–475 Ma. During the first episode at 540–510 Ma, magmatism likely occurred in an intraplate setting within the NTS microcontinent and in an oceanic arc setting within the Kyrgyz-Terskey zone in the south. During the second episode at 500–475 Ma, the entire NTS represented an arc system. These two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature, which led to obduction of ophiolites from the Kyrgyz-Terskey zone onto the microcontinent. The occurrence of zircon xenocrysts and predominantly negative whole-rock ?Nd(t) values and ?Hf(t) values of magmatic zircons suggest a continental setting and melting of Precambrian continental sources with minor contributions of Palaeozoic juvenile melts in the generation of the magmatic rocks. The late Cambrian to Early Ordovician 500–475 Ma arc evolved mainly on Mesoproterozoic continental crust in the north and partly on oceanic crust in the south. Arc magmatism was accompanied by spreading in a back-arc basin in the south, where supra-subduction ophiolitic gabbros yielded ages of 496 to 479 Ma. The relative position of the arc and active back-arc basin implies that the subduction zone was located north of the arc, dipping to the south. Variably intense metamorphism and deformation in the NTS reflect an Early Ordovician orogenic event at 480–475 Ma, resulting from closure of the Djalair-Naiman ophiolite trough and collision of the Djel'tau microcontinent with the northern margin of NTS. Comparison of geological patterns and episodes of arc magmatism in the NTS and Chinese Central Tianshan indicate that these crustal units constituted a single early Palaeozoic arc and were separated from the Tarim Craton by an oceanic basin since the Neoproterozoic. |
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