難府縫合帶：航空地球物理結果

難府縫合帶：航空地球物理結果

* Corresponding author. E-mail: Punya.C@chula.ac.th.

Nan Suture Using Airborne Geophysical Approach

Rawiwan RITTISIT1), Arak SAENGSOMPONG1), Kachentra NEAWSUPARP2),Thanop THITIMAKORN1), Punya CHARUSIRI1)*
1)Earthquake and Tectonic Geology Research Unit (EATGRU), Chulalongkorn University, Bangkok10330Thailand;
2)Department of Mineral Resources, Rama 6 Rd., Bangkok10330Thailand

Nan suture in northern Thailand, representing a complex zone with complex geology and structures,has been selected for airborne geophysical investigations. The suture has been widely accepted as an early Triassic collision zone between Shan-Thai and Indochina microcontinental blocks. Our field data suggest the occurrence of a mélange zone in response to compression tectonics. Moreover, previous petrochemical and field investigations suggest that the Nan suture may have been formed as a result of a subduction zone.

Results on our enhanced airborne radiometric and magnetic interpretations as well as those of the enhanced remote sensing information and the petrochemistry of chromian spinels in mafic and ultramafic igneous rocks reveal cryptic subsurface geology and structures. The combined interpretation of our current data sets as well as former studies lead us to conclude that the Nan suture has been formed in an island-arc environment of compression tectonic setting and not by the continental collision as previously thought. In addition, our airborne geophysical interpretation also indicates subduction polarlity from the west to the east.Our remote sensing, field, and petrographic surveys show that the occurrence of mafic/ultramafic assemblage in northern Lao PDR suggests that the Nan suture or tectonic line definitely extends northeastward.We, therefore, consider that Shan Thai and Indochina blocks have never been abut against one another and that the closure of the paleotethys may have taken place due to oceanic – oceanic interaction. Although the trend of the suture is almost the same, the new suture shows the better boundary and extension than those of the previous studies.

Nan Suture; Thailand; Paleotethys; Airborne Geophysical Approach

10.3975/cagsb.2012.s1.04