Syn-rift and post-rift modelling of the Pattani Basin, Thailand: evidence for a ramp-flat detachment

Flexural forward modelling of the syn-rift section and flexural backstripping of the post-rift section has been conducted on four cross-sections through the Pattani Basin. The extension (beta) for the syn-rift section of 1.2-1.3 is considerably smaller than that estimated from the post-rift section (beta = 2-2.4). This appears to represent a real discrepancy, rather than just a problem with accurate measurement of extension in the syn-rift section. The syn-rift section, particularly in the northern half of the Pattani Basin, has an overall synformal geometry atypical of rifts. Not all the syn-rift subsidence can be modelled as extension-related (unlike typical half grabens). Consequently it is proposed that the Pattani Basin developed due to both extensional faulting, and as a synformal basin developed over a ramp-flat geometry along a major low-angled extensional fault in the upper crust. Overall the discrepancy in upper crustal extension estimated from forward modelling vs, ductile lithspheric extension estimated from backstripping suggests that active mantle processes (e.g. a mantle plume) or non-uniform extension (subduction rollback) operated beneath the Gulf of Thailand. (C) 2000 Elsevier Science Ltd. All rights reserved.