Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine

Abstract

Plane indentation experiments on unilaterally confined blocks of plasticine help us to understand finite intracontinental deformation and the evolution of strike-slip faulting in eastern Asia. Several large left-lateral strike-slip faults may have been activated successively, essentially one at a time. The experiments suggest that the penetration of India into Asia has rotated (≈25°) and extruded (≈800 km) Indochina to the southeast along the then left-lateral Red River fault in the first 20 to 30 m.y. of the collision. This process can account for the opening of the South China Sea before late Miocene time. Extrusion tectonics then migrated north, activating the Altyn Tagh fault as a second major left-lateral fault and moving southern China hundreds of kilometres to the east. As this occurred, Indochina kept rotating clockwise (as much as 40°), but the sense of motion reversed on the Red River and other strike-slip faults in the south. Opening of the Mergui basin and Andaman Sea (up to the present) also appears to be a simple kinematic consequence of the extrusion. Recent rifts in northeastern China and Yunnan may be considered incipient analogs of the South China and Andaman Seas. Other Tertiary tectonic features such as the sedimentary basins of the Gulf of Thailand may be explained as collisional effects, if one uses our experiments as a guide. The experiments also suggest that a major left-lateral strike-slip fault and rift system will propagate across the Tien Shan, Mongolia, and Baikal to the Sea of Okhotsk.