International audienceMiddle Triassic orogens are widespread around and inside the South China Block (SCB). The southern peripheral belts that develop from northwest to southeast, namely Jinshajiang, Ailaoshan, NW Vietnam, NE Vietnam, Yunkai and Hainan exhibit striking similarities, with Permian–Early Triassic magmatic arc, ophiolitic mélange, northeast- to north-directed synmetamorphic ductile nappes, and fold-and-thrust belt. These collisional belts result from oceanic, then continental subduction of the SCB below Indochina. Eastward of Hainan Island, a Triassic suture is hypothesized offshore of the SCB. Within the SCB, the Xuefengshan is a Middle Triassic intracontinental orogen with northwest-directed folds and thrusts, and an intracrustal ductile décollement. This orogen accommodated the Middle Triassic continental subduction of the western part of the SCB below the eastern part. At variance to the generally accepted models, the inter- and intracontinental Triassic orogens of the SCB are interpreted here as the result of south-directed subductions of the SCB

In the Cretaceous, the subduction of the Izanagi/Paleo-Pacific plates beneath the South China Block (SCB) created a wide back-arc domain characterized by numerous extensional basins coeval with voluminous magmatism. The SCB witnessed the whole evolution by records of widespread extensional structures to accommodate the lithospheric stretching. In the interior of the SCB, the Yuechengling (YCL) Massif preserves a large, low-angle detachment fault, the Ziyuan Detachment (ZYD) at the western margin, and a high-angle ductile normal fault, the Tianhu Fault (THF), in the middle of the massif. Both faults display ductile shearing with top-to-the west kinematics but play different roles in two stages of extension. In the early stage at 140-120 Ma, the THF deformed the eastern YCL pluton at a temperature of~350°C, but the ZYD shows limited movement at this time. On the contrary, the later stage (100-85 Ma) is characterized by pervasive middle-to high-temperature deformation (~400-500°C) and rapid exhumation along the ZYD, but the THF only underwent a near-surface brittle overprint. Across the SCB, the two-phase extension is widely recorded in other extensional structures and coincides with magmatic flare-ups at its eastern margin, suggesting episodic changes in the subduction dip. Combined with two compressional events that took place between the intervals of extension, the SCB experienced two cycles of compression-extension at 155-120 and 120-85 Ma. This periodicity is tentatively interpreted as a combined effect from the Izanagi/Paleo-Pacific subduction angle change and a thickening-foundering process in the arc region.

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