Triassic tectonics of the southern margin of the South China Block

Abstract

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.