Combined escape tectonics and subduction rollback-back arc extension: a model for the evolution of Tertiary rift basins in Thailand, Malaysia and Laos

The Tertiary rift basins of Thailand and adjacent countries show considerab le variability in the timing of rift initiation, termination, the timing an d magnitude of thermal subsidence, and the timing and intensity of inversio n episodes. The rift basins developed on continental blocks that were extru ded southeastwards. Hence their development must be tied into Himalayan ext rusion tectonics. Current tectonic models propose that the Tertiary basins opened up as pull-apart basins associated with strike-slip faults. Publishe d geochronology of strike-slip fault zone rocks, mapping of fault patterns in the Tertiary basins and mapped releasing-restraining bend geometries all indicate that in Thailand major sinistral strike-slip motion ceased at abo ut 30 Ma, prior to the formation of most rift basins the Thailand. The effe cts of later dextral slip were minor and probably a result of reactivation during episodes of inversion during NW-SE to NE-SW (Himalayan) compression. Dextral slip was not responsible for opening most of the rift basins, in T hailand. An alternative mechanism to open the rift basins is subduction rol lback of the Indian plate to the west of Thailand. It is proposed that subu ction rollback can help explain some of the characteristics of the rift bas ins such as non-uniform lithospheric extension, deep sag basins, and the di achronous onset and termination of rifting.