THE SONGPAN-GARZE TRIASSIC BELT OF WEST SECHUAN AND EASTERN TIBET - A DECOLLEMENT FOLD BELT ON PASSIVE MARGIN

The Songpan-Garze fold belt covers a triangular area of about 500,000 km2. It is bounded by the old continental blocks of South China, North China, North Tibet, South Tibet and Indochina. It was formed during Upper Triassic by shortening of a large Lower to Middle Triassic flyschoid basin. Compressional tectonics is related to the development of a subduction zone below the North China block. The folded Triassic series were detached and thrusted upon the continental margin of South China, previously thinned. A large-scale ductile decollement located in the Paleozoic cover of the South China basement induces important crustal thickening, inducing rise of late-orogenic granites. India-Eurasia collision tectonics has strongly modified the Triassic belt during the Tertiary.