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Late Paleozoic granitoids in western Transbaikalia: sequence of formation,sources of magmas,and geodynamics
Institution:1. State Key Laboratory of Isotopic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;1. Department of Geology, Trinity College Dublin, College Green, Dublin, Ireland;2. Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK;1. Departamento de Geología, Facultad de Ciencias, Universidad de Salamanca, 37008 Salamanca, Spain;2. Departamento de Geología, Facultad de Geología, Universidad de Oviedo, 33005 Oviedo, Spain;1. Department of Geomorphology and Quaternary Geology, University of Gdańsk, J. Ba?yńskiego Str. 4, 80-309 Gdańsk, Poland;2. Institute of Geology, Adam Mickiewicz University, B. Krygowskiego Str. 12, 61-680 Poznań, Poland
Abstract:The evolution of Late Paleozoic granitoid magmatism in Transbaikalia shows a general tendency for an increase in the alkalinity of successively forming intrusive complexes: from high-K calc-alkaline granites of the Barguzin complex (Angara–Vitim batholith) at the early stage through transitional from calc-alkaline to alkaline granites and quartz syenites (Zaza complex) at the intermediate stage to peralkaline granitoids (Early Kunalei complex) at the last stage. This evolution trend is complicated by the synchronous development of granitoid complexes with different sets and geochemical compositions of rocks. The compositional changes were accompanied by the decrease in the scales of granitoid magmatism occurrence with time. Crustal metaterrigenous protoliths, possibly of different compositions and ages, were the source of granitoids of the Angara–Vitim batholith. The isotopic composition of all following granitoid complexes points to their mixed mantle–crustal genesis. The mechanisms of granitoid formation are different. Some granitoids formed through the mixing of mantle and crustal magmas; others resulted from the fractional crystallization of hybrid melts; and the rest originated from the fractional crystallization of mantle products or the melting of metabasic sources with the varying but subordinate contribution of crustal protoliths. Synplutonic basic intrusions, combined dikes, and mafic inclusions, specific for the post-Barguzin granitoids, are direct geologic evidence for the synchronous occurrence of crustal and mantle magmatism. The geodynamic setting of the Late Paleozoic magmatism in the Baikal folded area is still debatable. Three possible models are proposed: (1) mantle plume impact, (2) active continental margin, and (3) postcollisional rifting. The latter model agrees with the absence of mafic rocks from the Angara–Vitim batholith structure and with the post-Barguzin age of peralkaline rocks of the Vitim province.
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