The main reasons for the compositional evolution of the Early Paleozoic granitoids of the Eastern Sayan: Evidence from the Munku-Sardyk massif |
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| Authors: | S V Efremov |
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| Institution: | (1) Vinogradov Institute of Geochemistry and Analytical Chemistry, Siberian Branch, Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia |
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| Abstract: | This paper addresses the reasons for the evolution and genesis of the Early Paleozoic granitoids of the Munku-Sardyk Range, Eastern Sayan. It was established that the massif consists of three phases representing derivatives of mantle and crustal magmas. The major part of the massif is made up of mantle-derived granitoids, which are chemically similar to the exotic NEB-adakite association.The crustal granitoids of pluton were formed under the influence of the thermal field of primary magmas. The protoliths of these granitoids were presumably the metamorphic rocks of the Slyudyanka Group. In terms of geochemistry, they are ascribed to calc-alkaline rocks but bear some signatures of anorogenic granitoids.It was shown that the compositional variations of the granitoids were controlled by many factors, the most important of which are the compositions of primary magmas and their contaminant. The geochemical characteristics and mineral compositions of the granitoids distinctly reflect interaction with the host metamorphic sequences. Carbonate rocks played an important role in this process, causing an increase in the alkalinity and basicity of granitoid magmas. The abundance of carbonate rocks in the region was probably the main reason for the broad variations of alkalinity in coeval granitoids.Using the obtained data, a genetic model was proposed to explain all stages of the formation of the massif and compositional evolution of its rocks. |
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