Early Paleozoic Tarim Orocline: Insights from paleogeography and tectonic evolution in the Tarim Basin

Abstract

The Tarim Basin, situated between the Paleo‐Asian tectonic domain and the Proto‐Tethys tectonic domain, has undergone a complex tectonic evolutionary process under various geodynamic conditions and has provided abundant information about the dynamic evolution of the peripheral orogens. From the Sinian to Early Ordovician, the Tarim–Qaidam Block was under a regional extensional setting. A carbonate platform developed widely in the basin, flanked by a passive continental margin setting. As the extension enhanced, the spreading of the Proto‐Tethys Ocean was accompanied by subduction and collision, which resulted in a nearly linear subduction zone. Since the Late Cambrian, a continuous oblique subduction and induced sinistral shearing produced an initial bending of the Proto‐Tethys subduction zone, leading to rotation and bend of the original Tarim–Qaidam Block and internal long striped subaqueous paleo‐uplift. During the Middle and Late Ordovician, the Altyn–Qilian Orogen underwent continent–continent collision and continental crust deep subduction. The buckling of the subduction system enhanced under the sinistral transpressional field, resulted in the bending of the Altyn–Qilian Orogen to an S‐shape. The subaqueous uplift areas in the basin were further elevated, rotated, and eroded to show an S‐shape distribution and an unconformity developed between the Silurian sediments and underlying strata. The extent of the carbonate platform decreased, around which developed a high‐energy facies in a platform margin and formed important oil–gas reservoirs. In the Silurian to Middle Devonian, the Tarim Basin evolved into a “two uplifts with a depression” framework under the dual‐directional compressional field. Near the end of the Late Devonian, the S‐shape distribution pattern of paleo‐uplifts was covered by the Upper Devonian and Carboniferous sequence in an angular unconformity. Moreover, the planar distribution of thrust faults with strike‐slip property around the paleo‐uplifts also showed an S‐shape. Accompanying small‐scale strike‐slip faults presented as the radial axial cleavages of plunging vertical folds around a vertical hinge, which indicated that the pre‐existing thrust faults bent around a vertical axis resulting from late strike‐slip faults, demonstrating a coupling between the Tarim Basin and orocline of the Early Paleozoic orogens in the Proto‐Tethys Ocean, called the Tarim Orocline.