Paleozoic deformations of the Eastern Kaakhem magmatic area (East Tuva)

Based on the results of structural-petrological and microstructural studies of Paleozoic complexes in the eastern part of the Kaakhem magmatic area, three stages of tectonic activity were identified. The first stage is marked by the formation of the diorite-tonalite-plagiogranite association of the Tannuola complex (476±4 MA) and the fragmentation of earlier mafic rocks. As a result of tectonic-magmatic activity, a complex with breccia-like textures was formed: fragments of basite cemented by granitoid. The second stage is recorded by the formation of a complex of mafic dikes (~ 450 Ma) in the conditions of the upper crust. Dikes cut gabbro-granite deformation of the first stage, which indicates the presence of a long-lived tectonical weakened zone in this region. The third stage is the deformations that controls the formation of monzodiorite-granosyenites of the Shivey and Chadal massifs (282-293 MA). As a result of the simultaneous intrusion of basic and acidic melts, mingling structures are formed, complicated by synmagmatic deformations - lens-shaped small (up to 3 cm) mafic inclusions in granite material, feathery echelon cracks in mafic rocks filled with acidic material. The nature of the deformations of the first and third stages is brittle-plastic, which is due to different rheology of rocks at the same depth of the Earth crust (about 15 km). Mafic rocks are harder bodies that deform through brittle fault mechanisms. They have a rigid frame of partially crystallized minerals, but still contain a certain proportion of melt, which provides ductile deformations. The duration of all episodes of tectonic activity was insignificant and did not exceed the time of melt consolidation. The second and third stages of deformation are caused by extension and extension and transtension conditions. The submeridional orientation of shear planes in Early Permian rocks and the position of Early Ordovician dikes allow us to consider them as a Paleozoic stage in the evolution of the southern part of the Kaakhem structural zone. Its activation and development in the Paleozoic are associated with the formation of permeable weakened zones at the final stage of the collision stage of development of the area. The data obtained do not allow us to classify the Kaakhem zone exclusively as a rift zone. For this object, the term “tectonic zone” or “zones of deformation concentration” is more appropriate, since it does not include geodynamic interpretation and kinematic characteristics - parameters that change during the long-term evolution of the tectonic structure. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

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