The Late Mesozoic-Cenozoic intracontinental evolution of the West Qinling Belt, Central China

The East Asian continent was formed by the amalgamation of several microcontinents and overprinted by the polyphase of intracontinental reworking and reactivation under the far-field effect of subduction-collision during the Mesozoic to Cenozoic. The Qinling Belt, stretching from east to west in Central China, was formed during episodes of accretion and collision between the North China Block, South Qinling Terrane, and South China Block along the Shangdan suture in the north and the Mianlue suture in the south. The Qinling Belt transitioned from an intercontinental orogenic belt to an intracontinental orogenic belt during the late Mesozoic, whereby it did not cratonize after collision but evolved into a new tectonic regime characterized by intensive intracontinental orogenesis and regional erosion. The Qinling Belt was eventually divided into the East Qinling Belt and West Qinling Belt by the Foping Dome, which represents not only the gradient boundary layers of different lithospheric thicknesses but also the topographic transition zone between the Western and Eastern China mainland regions. Although previous studies have established the pre-Triassic evolution of the West Qinling Belt, the basic intracontinental tectonic setting and geodynamic evolution remain unclear, including whether the intracontinental setting was controlled only by the Pacific subduction system, or was more complex, involving additional tectonic domains. Paleostress inversion refers, traditionally, to mathematical or graphical inversion of the geometrical attributes of faults with the aim of quantifying the stress associated with fault activity in the geological past. In this study, we present a comprehensive paleostress inversion to obtain the intracontinental evolution of the West Qinling Belt. Paleostress inversion of 1215 fault slip vectors from outcrops, combined with defined structural levels and dating results for key lithostratigraphic units, is systematically employed to establish the paleostress fields in the West Qinling Belt during the Late Mesozoic and Cenozoic. Overall, clockwise rotation of the maximum principal stress axes indicates that the intracontinental deformation is reduced by the Pacific regimes but correspondingly strengthened by the Neo-Tethyan regimes. The first generation is considered to involve NW-SE extension (D1, similar to 145-105 Ma) during the sedimentation of Cretaceous intermontane basins caused by the multiplate convergent syncollisional/synorogenic extensional setting. Then, the second generation (D2, similar to 105-65 Ma), N-S extension with minor E-W contraction, is supposed to have occurred after the sedimentation of the Cretaceous intermontane basins. Along with previous work on the cooling/exhumation history of the West Qinling Belt, these data clarify the regional slow exhumation and peneplanation at the D2 stage. Subsequently, the third generation includes two phases (D3, similar to 50-30 Ma), NW-SE and N-S superposed contraction phases, characterized by a widespread contraction deformation related to the multiplate convergent tectonic setting. Finally, the fourth generation of paleostress fields (D4, similar to 22-5 Ma) is determined to have occurred during/after the formation of Cenozoic intermontane basins and is characterized by NE-SW compression driven by lateral expansion of the Tibetan Plateau. After continent-continent collisional ceases to shape the mountain belt and the prevailing compressive force is relaxed, there is a long period of tectonic quiescence accompanied by erosion. Subsequently, the previous collisional belt is eroded to a plain and become part of the craton. Currently, the intracontinental high-elevation belts represent rejuvenation following a relatively recent uplift during the Cenozoic. Intracontinental rejuvenation is generally achieved by reactivation and reworking caused by compressive stress during their incorporation into new tectonic regimes. Therefore, the general rule, a transition from collisional to intercontinental belts, is that the active tectonic regime apparently controls the extension collapse, tectonic quiescence with peneplanation, and reworking and reactivation uplift.