The Ailao Shan/Red River metamorphic belt: Tertiary left-lateral shear between Indochina and South China

The relative importance of thickening and strike-slip extrusion in continental collision is debated. Ductile shear in the Ailao Shan/Diancang Shan metamorphic belt, along the Red River in Yunnan, China, yields outstanding evidence of the latter process. For > 500 km, mylonites in this narrow northwest-southeast belt show horizontal lineations on steep, northwest-striking foliation planes, and left-lateral kinematic indicators. U-Pb radiometric ages of ~23 Myr imply that strike-slip movement along this shear zone occurred in the Oligo-Miocene. The strain observed suggests that collision of India with Asia displaced Indochina at least 500km southeastwards relative to South China.