Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 63 – 76
1 Department of Mineral Resources, Bangkok, Thailand
2GETECH and School of Earth Sciences, University of Leeds, England
Abstract: The N-S oriented central floodplain of Thailand is situated between the NE-SW-trending strike-slip Uttaradit Fault Zone (UTFZ) to the north, the northern shoreline of the Gulf of Thailand to the south, and irregular paths of normal faults to the east and west. Major structures of the area include the NW-SE-trending sinistral strike-slip Mae Ping and Three Pagoda Fault Zones (MPFZ and TPFZ) located to the west and a N-S-oriented Central Volcanic Belt (CVE) located to the east of the plain. Tertiary basins located within the Central Plain have geometries indicating that they were formed due to the reversed movement from sinistral to dextral of the major NW-SE-trending strike-slip fault zones during Late Oligocene-Early Miocene times.
Geophysical data interpretation results (magnetic, gamma-radiometric, digital terrain data and regional gravity data) show the N-S-trending CVE, outline the known major fault zones, discover the Chao Phraya Fault Zone (CPFZ) and other subsurface lineaments and magnetic bodies within the Central Plain, as well as suggest a new fault path for the TPFZ.
The findings indicate that the tectonic evolution of the Central Plain was controlled by the movement along the CVE, which may represent an ancient suture zone, and strike-slip faults bounding small subcontinental blocks. These movements include: extension (oblique) along the old sutures and volcanic arcs, reversed sinistral-to-dextral movement on the NW-SE-trending MPFZ, TPFZ and CPFZ, and reversed dextral-to-sinistral UTFZ. Indochina‘s southeast extrusion tectonic setting associated with the collision of the Indian and Eurasian plates may have reactivated these lithospheric weak zones and caused the opening of the Central Plain and the Gulf of Thailand since Late Oligocene time.