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 backstrippi ng of the post-rift section has been conducted on four cross-sections throu gh 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 j ust a problem with accurate measurement of extension in the syn-rift sectio n. The syn-rift section, particularly in the northern half of the Pattani B asin, has an overall synformal geometry atypical of rifts. Not all the syn- rift subsidence can be modelled as extension-related (unlike typical half g rabens). Consequently it is proposed that the Pattani Basin developed due t o both extensional faulting, and as a synformal basin developed over a ramp -flat geometry along a major low-angled extensional fault in the upper crus t. Overall the discrepancy in upper crustal extension estimated from forwar d 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.