Structure, Magmatism, and Paleozoic Tectonic Evolution of the Uakit Zone in the Context of the Formation of the Angara-Vitim Batholith in the Western Transbaikal Region

摘要

The problem of the tectonic evolution of the Angara-Vitim batholith, the largest igneous complex of the western Transbaikal region, is discussed. This problem is still far from an unequivocal solution; however, it is evident that the Late Paleozoic stage was crucial in the evolution of the Angara-Vitim batholith, and precisely this stage has determined the main structural features of the western Transbaikal region. The geodynamicsrnthat controlled the batholith formation in the Late Paleozoic is exemplified in the Uakit Zone. New data are presented on the stratigraphy of country rocks and on the age and composition of the Vitimkan granitoid complex, the most abundant complex in the batholith. It has been shown that the main tectonic events in the Uakit Zone occurred from the Devonian to the Late Carboniferous. The ensialic orogeny in the form of a reduced Wilson cycle that developed under within-plate conditions was the main mechanism of structure formation. The effect of collision is a self-sufficient mechanism of superplume evolution provided by the origin and passing away of particular, relatively short lived streams of the superplume. The short-lived rifts (aulacogens) arose above the ascending streams during the most active development of superplume and then closed up under tangential compression caused by spatially conjugated younger plumages. The closure of rifts was controlled by pseudosubduction and particular collision. As a result, the mosaic block megastructure was created, being underlain by the hydrated mantle necessary for extensive granite formation. Such a mechanism probably was dominant during a "vague time" in the Riphean geological history of the Earth after the breakdown of Rodinia.