Formation and evolution of strike‐slip faults, rifts, and basins during the India‐Asia Collision: An experimental approach

The processes which have governed the formation and evolution of large Tertiary strike-slip faults during the penetration of India into eastern Asia are investigated by means of plane strain indentation experiments on layered plasticine models. The steady state deformation of plasticine obeys a power creep flow law (e˙=C(T)σn). The stress exponent (n) is between 6 and 9 at 25°C. Uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening, a process observed for strain rates ranging from 3.5×10−5 to 3.6×10−3 s−1. Fault or shear zones form after only 7–10 % bulk strain. Subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine. A series of nine plane strain indentation experiments shows the influence of boundary conditions, as well as that of the internal structure of the plasticine model on the faulting sequence. The ubiquity of strain softening in experimental deformation of a variety of rocks, as well as the widespread occurrence of shear zones in nature suggest that long-term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain. The deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision-induced strikeslip faulting in Asia, particularly to total offsets and rates of movements on the faults. The experiments simulate the evolution of the western ends of the strike-slip faults, which have probably been analogous to trench-fault-fault triple junctions. The experiments also illustrate mechanisms for the formation of extensional basins, such as the South China Sea, North China Basin, and Andaman Sea, near active continental margins. The basins, which appear to absorb terminal offsets along major strike-slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts. The existence of distinct phases of strike-slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous, non-steady state deformation of the continental lithosphere.