Late Mesozoic continental deformation, deep processes, and geodynamic evolution of South China
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    Abstract:

    In the Late Mesozoic, South Chinas eastern margin evolved into an active Andean- type convergent margin associated with the subduction of the Paleo- Pacific Plate. The continental crust underwent significant reworking, accompanied by extensive magmatism, providing an ideal natural laboratory to assess the tectono- magmatism, crust- mantle processes, and plate subduction geodynamics along the active continental margin. Here we review the essential constraints of structural deformation, magmatism, and lithospheric architecture. We recognized the Mid- Late Jurassic retro- arc shortening system and the Cretaceous back- arc extensional system, and clarified their spatial- temporal associations and overprinting relationships. The retro- arc shortening involved a northwestward thrust propagation by generating arrays of thin- and thick- skinned thrust systems, multiple decollements, and duplexes in the central Yangtze, possibly associated with the northwestward advancing subduction of the Paleo- Pacific plate. The eastern part of the retro- arc system was tectonically overprinted by several extensional and contractional events during the Cretaceous, accompanied by the flare- up, lull, and resumption of magmatism. The tectonic switching between contraction and extension was governed by changes in the slab dynamics, i.e., slab steepening and shallowing in retreating and advancing subduction settings. Despite these deformation episodes, lithospheric extension dominated the Cretaceous evolution, generating a wide (>800 km) back- arc extensional system comparable to the American basin and range. We analyzed the long- distance lithospheric extension and surface response by compiling all available geophysical and geological observations. The compiled data suggest a depth- dependent deformation mechanism, with vertical and lateral variations in extension modes as a function of lithospheric strength. The extensional strain fields are uniformly orientated ~NW- SE throughout the lithosphere, indicating vertically coherent deformation. Stress transmission across this coherent system likely occurred via basal traction and localized mantle shearing. Basal traction at the lithospheric base, imposed by rollback- induced mantle flow, might have integrated over long distances and caused passive stretching of the lithospheric mantle. Localized mantle shearing generated high- strain mantle shear zones that acted as strain- transfer structures, enhancing the simple shearing at the crust- mantle interface and promoting ductile stretching in the lower crust. We emphasize the tectonic coupling between slab rollback, mantle flow, and lithospheric extension. The driving forces of lithospheric extension are attributed to a combination of ① far- field effects of slab rollback and trench retreat and ② basal shear tractions imposed by mantle flow.

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LI Jianhua, DONG Shuwen, ZHAO Guochun, ZHANG Yueqiao, XIN Yujia, WANG Jinming, LU Yunke.2024. Late Mesozoic continental deformation, deep processes, and geodynamic evolution of South China[J]. Acta Geologica Sinica,98(3):829-861

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  • Online: March 27,2024
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