ABSTRACT: Constraints on the magnitude of Neogene extensional and strike-slip fault displacements in Thailand

Morley, Chris , University Brunei Darussalam, Bandar Seri Begawan, Brunei

For regional plate reconstructions Thailand has been somewhat of a black hole, yet a critical region for reconstructing the Tertiary evolution of SE Asia; in particular understanding how much rotation Borneo has undergone. Two models illustrate the problem: Lee and Lawver (1994) place only minor strike-slip displacement through Thailand, with little rotation of Borneo. Hall (1996) honouring paleomagnetic data rotated Borneo counter clockwise by 45° between 20 and 10 Ma, with consequent major strike-slip and extensional displacements in the Gulf of Thailand and onshore along the Three Pagodas Fault. Constraints for these models are given by: 1) The dischronous onset of sag basin development-W. Nantuna Basin (Lower Miocene) vs. northern Gulf of Thailand (Middle Miocene); 2) Evidence from Gulf of Thailand seismic reflection data for and against significant strike-slip faulting accompanying rift basin development, 3) Strain estimates from seismic reflection data in the Gulf of Thailand, and 4) palaeostress data from onshore Tertiary rift basins. Generally the data support modest amounts of extension (b < 1.3). Multiple phases of tectonic inversion occurred in northern Thailand, the Malay Basin and W. Nantuna Basin, with much reduced inversion in the central and Northern Gulf of Thailand and onshore Chao Phraya Basin. The data suggest that significant rotation of Borneo cannot be accommodated by Tertiary structures onshore and in the Gulf of Thailand.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia