GEOLOGICAL POSITION, SOURCES, AND AGE OF MINGLING DIKES OF THE NORTHWESTERN MARGIN OF THE TUVA-MONGOLIAN MASSIF IN WESTERN SANGILEN, SOUTHEASTERN TUVA
V.A. Yakovlev1,2, I.V. Karmysheva1,2, V.G. Vladimirov1,2, D.V. Semenova1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: Dikes, mingling, mixing, Nb-rich magmas, collision magmatism, U-Pb dating, tectonic settings, Tuva-Mongolian massif, CAOB
Abstract
The best source of information about the specific features of magmatism in collision zones is the late collisional tectono-magmatic stage, which is associated with the largest volume and diversity of the resulting magmatic associations. In this paper, granitoid and mafic late collisional magmatism is considered using the example of Early Caledonian igneous complexes of Western Sangilen (Tuva-Mongolian massif). Results of geochronological, petrographic, petrogeochemical, and mineralogical studies of the rocks of the Saizyral mingling dike and salic dikes are presented. Approximately ~485 Ma, high-potassium granitoid massifs formed simultaneously with the intrusion and occurrence of a complex of granitoid and mingling dikes. The Saizyral mingling dike resulted from the joint intrusion and mixing of basic and silicic magmas in a low-pressure region within the Erzin shear zone at a middle crust depth level. Interaction of contrasting magmas is comprised of two stages. The first stage occurs during the transport of a contrast mixture and comes down to intensive mechanical mixing and the introduction of LIL and HFS elements, as well as Th and U from granitoids into the mafic rocks. This changes the geochemical characteristics of the mafic rocks. The second stage is when the joint crystallization of magmas is accompanied by gravitational sedimentation of denser mafic magmas and the formation of narrow zones of intermediate composition at the contact of contrasting rocks.
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