Middle 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.

International audienceIn SE Yunnan, the Ailaoshan Belt has been extensively studied for the ductile shearing coeval with the left-lateral Cenozoic activity of the Red River fault. However, the Late Triassic unconformity of the continental red beds upon metamorphic and ductilely deformed rocks demonstrates that the Ailaoshan Belt was already built up by Early Mesozoic tectonics. From West to East, the belt is subdivided into Western, Central, Eastern Ailaoshan, and Jinping zones. The Western Ailaoshan and Central Ailaoshan zones correspond to a Carboniferous–Permian magmatic arc, and an ophiolitic mélange, respectively. The Eastern Ailaoshan, and the Jinping zones consist of deformed Proterozoic basement and Paleozoic to Early Triassic sedimentary cover series both belonging to the South China Block. This litho-tectonic zonation indicates that the Ailaoshan Belt developed through a SW-directed subduction followed by the collision between Indochina and South China blocks. Crustal thickening triggered per-aluminous magmatism dated at ca 247–240 Ma. Field and microscope-scale top-to-the-NE ductile shearing observed only in the pre-Late Triassic formations, but never in Late Triassic or younger formations, complies with this geodynamic polarity. Furthermore, the late collisional two-mica granitoids and felsic per-aluminous volcanites record a ductile deformation that argues for a continuing crustal shearing deformation after the Early Triassic collision up to the Middle Triassic. Therefore, a two-stage tectonic evolution accounts well for the documented structural and magmatic features. The Triassic architecture of the Ailaoshan Belt, and its geodynamic evolution, correlate well to the South and North with the North Vietnam orogens and the Jinshajiang Belt, respectively