Učënye Zapiski Kazanskogo Universiteta. Seriâ Estestvennye Nauki (Mar 2016)
Closing History of the Late Palaeozoic Oceanic Basins between Tarim and Junggar: Geodynamics and Stratigraphic Problems
Abstract
The history of the Late Palaeozoic convergence and collisions in the South Tian Shan, Tarim, and South Junggar has been considered based on new geological and geochronological data. The Late Palaeozoic (Pennsylvanian and Permian) in this region represents a distinct phase in the regional tectonic history and, thus, corresponds to the original meaning of the concept of “geological period (system)”. This phase begins with several events, which occur in the Early and Middle Pennsylvanian as follows: 1) development of a continuous north-dipping subduction zone along the northern edge of the South Tian Shan at ca. 320–315 Ma and beginning of overthrusting in the South Tian Shan; 2) collision of the Bogdoshan arc with the Yili continental arc of Eastern Kazakhstan at ca. 315–310 Ma. This led to elimination of magmatism in these two arcs and was followed by deposition of carbonates and subsidence in the Bogdoshan and Junggar basins; 3) beginning of collisions between the Alai and Tarim microcontinents and the southern margin of the Kazakhstan continent at ca. 310 Ma. Subduction and collisional deformations in the South Tian Shan were accompanied by top-to-the south overthrusting and deposition of turbidites and olistostromes that range in age from the Bashkirian in the north to the Asselian in the south. Amalgamation of two continents in the South Tian Shan led to elimination of the last deeper marine basins with cherty deposits in the Late Pennsylvanian and to termination of turbidite sedimentation in the Asselian. Beginning of the late collisional phase in the South Tian Shan during the late Asselian and Sakmarian is expressed by: 1) overthrusting changed to folding and strike-slip faulting; 2) general uplift of the fold-and-thrust belt that led to elimination of the last marine basins and consequent deposition of coarse continental molasses; 3) initiation of post-collisional granitoid magmatism, which at least by part may also reflect melting of the continental crust due to heating by the Tarim mantle plume. Tectonic events that took place in the Tian Shan-Junggar region during the Triassic and Jurassic are conventionally considered as intraplate, and this allows to define the end of the Late Palaeozoic tectonic phase near the boundary of the Permian and Triassic.
