TECTONIC ZONING OF THE CENTRAL ASIAN FOLD BELT AND PALEOGEODYNAMIC RECONSTRUCTIONS FOR THE VENDIAN–PALEOZOIC AGE

This paper presents a synthesis of published and new geological, geochronological, biogeographic, paleomagnetic, and petrological-geochemical data. The goal is to substantiate the tectonic zoning of the Central Asian Fold Belt and its Vendian–Paleozoic geodynamic evolution as a complex folded structure composed of deformed fragments of collisional and accretionary orogens. It is shown that the belt formed at the junction of the collisional and accretionary margins of the Siberian Craton. This setting is analogous to the modern tectonic interactions between the Indo-Atlantic and Pacific global tectonic segments of the Earth and their respective interactions with Eurasia. During the Vendian and Early Ordovician, two active margins existed along the periphery of the Siberian Craton: the collisional Tuva-Mongolian margin and the accretionary Kuznetsk-Altai margin. These margins separate the craton from the tectonic plates of the Paleo-Asian Ocean (Indo-Atlantic segment) and the Paleo-Pacific Ocean (Pacific segment), respectively. A distinctive feature of the Paleo-Asian Ocean plate is its complex structure, which includes fragments of oceanic crust and Precambrian Gondwanan continental blocks that contain fragments of the Grenvillian orogeny. Grenvillian detrital zircons (1.3–0.9 Ga) are widely found in Vendian–Paleozoic sedimentary deposits from various geodynamic settings of the collisional orogen. In contrast, a distinctive feature of the accretionary orogen is the widespread presence of oceanic crust fragments and the absence of Precambrian Gondwanan blocks. Consequently, there are no Grenvillian detrital zircons in the Vendian–Paleozoic sedimentary rocks of various geodynamic settings that represent the accretionary orogen. The early to middle Paleozoic Charysh–Terekta–Ulagan–Sayan–Olkhon suture–strike-slip zone separates the collisional orogen from the shelf of a back-arc basin. This basin is located in the northern part of the Altai-Sayan Folded Area, which frames the Siberian Craton. The suture–strike-slip zone consists of fragments of Vendian–early Paleozoic oceanic crust from a back-arc basin, Ordovician blueschist, and Ordovician–Silurian turbidite, as well as late Silurian–Devonian collisional metamorphic rock and granite. Based on the structural position of the suture–strike-slip zone, petrology, and geochronology, this zone is interpreted as a subduction-collision complex. It formed in the back-arc basin of the Vendian–Cambrian Tuva-Mongolian island arc. Late Paleozoic strike-slip faults and thrusts manifested in the Central Asian Fold Belt during the Late Devonian and early Carboniferous. These structures resulted from the collision of the Kazakhstan-Baikal orogen (a composite continent) with the Siberian Craton, which led to the formation of the North Asian continent. Subsequently, during the late Carboniferous and Triassic, the collision of the East European and North Asian continents led to the formation of Eurasia. As a result of these collisional events, the originally linear structures of the collisional and accretionary orogens were deformed into large oroclinal folds. These structures were further fragmented by strike-slip faults and thrusts into numerous blocks. Within these blocks, the Vendian–Paleozoic structures are complicated by thrust-fold deformations.