Syntectonic metamorphism of a collisional zone in the Tuva-Mongolian massif, Central Asian Orogenic belt: P-T conditions, U-Pb ages and tectonic setting

––We present the results of study of the geologic structure, petrologic composition, and age of plagiogranitoid associations in the east of the Kaa-Khem batholith (Eastern Tuva). The batholith is located in the junction zone of the Tannu-Ola island arc (TIA) of Vendian–early Cambrian age and the Precambrian rocks of the Tuva–Mongolian microcontinent (TMM). Plagiogranitoids of this region formed in an accretion–collision setting in the period 490–450 Ma. Three stages of formation of plagiogranitoid associations have been established (~489, ~476, and ~450 Ma). The plagiogranitoid associations in the east of the Kaa-Khem batholith do not differ in petrologic composition and age from the plagiogranitoid associations (500–450 Ma) in the west. Xenogenic zircons in the studied plagiogranitoids of the eastern Kaa-Khem batholith have ages of 2335–517 Ma. Their ages are divided into several clusters (524–517, 549–536, 615–586, 684–647, 739–735, 810–794, 842–827, and 2335 Ma) reflecting the heterogeneity of the crust in the TIA–TMM junction zone. The wide range of ages and the abundance of xenogenic zircons in plagiogranitoids of the eastern Kaa-Khem batholith testify to the contribution of older crustal sources to the granite formation at all stages of accretion–collision processes (from 490 to 450 Ma). The much narrower age range of xenogenic zircon (616–474 Ma) and its low contents in coeval plagiogranitoids of the western Kaa-Khem batholith are consistent with their localization within the TIA and the relative homogeneity of the crust in the area of felsic-melt generation. In the west, the influence of older crustal sources was insignificant and manifested itself only at the final stage (~450 Ma) of accretion–collision processes.

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Geological Position, Sources, and Age of Mingling Dikes of the Northwestern Margin of the Tuva–Mongolian Massif in Western Sangilen, Southeastern Tuva

Yakovlev,

Karmysheva,

Vladimirov

et al. 2024

Russian Geology and Geophysics

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––The best source of information about the specific features of magmatism in collision zones is the late collisional tectonomagmatic 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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Syntectonic metamorphism of a collisional zone in the Tuva-Mongolian massif, Central Asian Orogenic belt: P-T conditions, U-Pb ages and tectonic setting

Cited by 4 publications

References 55 publications

Supra-subduction thickening of a continental back-arc: Ediacaran–early Cambrian (Baikalian) metamorphism in the NE Baidrag block (Mongolian Collage)

Supra-subduction thickening of a continental back-arc: Ediacaran–early Cambrian (Baikalian) metamorphism in the NE Baidrag block (Mongolian Collage)

Magmatic and Xenogenic Zircons from Granitoids of the Kaa-Khem Batholith as Age Markers of the Crust in the Junction Zone of the Tannu-Ola Island Arc and the Tuva–Mongolian Microcontinent (Eastern Tuva)

Geological Position, Sources, and Age of Mingling Dikes of the Northwestern Margin of the Tuva–Mongolian Massif in Western Sangilen, Southeastern Tuva

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