Mesozoic and Cenozoic deformations in the Raggyorcaka area, Tibet: implications for the tectonic evolution of the North Qiangtang terrane
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The Mesozoic and Cenozoic deformations of the North Qiangtang terrane reflect a portion of the collisional tectonics of the Tethys Ocean, involving Late Triassic, Early Cretaceous and Cenozoic intraplate structures of shallow to superficial tectonic levels. The structural mapping of the Permian–Triassic structural layer indicates that the Mesozoic structural style is dominated by Early Cretaceous horizontal contractional deformations characterized by NW–SE-trending thrust faults and flexural-slip folds. These folds and thrusts were superimposed on Late Triassic buckle folds. Structural analysis of deformations of the Neogene and Quaternary sedimentary layers indicates that there was an obvious transition in the Cenozoic tectonic evolution of the North Qiangtang terrane, which can be divided into two deformation stages. In episode I (50–40 to 18 Ma), the crust experienced large-scale north–south horizontal shortening and vertical thickening shown by buckle folds and thrust faults. In episode II (18 Ma–present day), east–west passive extension formed conjugate strike-slip fault systems and pull-apart basins. During episode II, the Qiangtang basin was extruded eastwards, and a number of superficial north–south-trending buckle folds were formed.