Application of airbone geophysical and reomote sensing data to the interpretation of geologic setting in Nan-Uttaradit area, Northern Thailand

Abstract

This investigation is aimed to reprocess airborne geophysical and remote sensing data for interpreting subsurface structures in the Nan-Uttaradit area. Airborne magnetic data in conjunction with remote sensing and EM data have been enhanced using various techniques. This study applies that RTP, ANA, AGC, vertical derivative, upward and downward continuation, for interpretation. Airborne radiometric data processed by Cooking Technique and Remote sensing data by Band Combination and Principle Component Analysis Technique. Three domains have been identified, namely northern, central and southern domain. The central domain is a significant highly anomalous NE-SW trending narrow zone situating within the Nan River Basin. This domain possesses high magnetic and low radiometric intensities. The central high magnetic domain is enveloped by very low magnetic and high radiometric intensities referred as the north and south domains, both of which orient in the N-S direction and they generally exhibit the low magnetic and various radiometric intensities with the sporadic high magnetic patterns. The northern domain is quite different from the southern domain, suggesting contrast in the geology. The high magnetic anomalies in each domain have been recognized in 2 patterns, elongate pattern located mainly along the Nan River in the NE-SW direction with high magnetic and low radiometric intensities, and circular pattern located in the northernmost area with low magnetic anomalies zone in southern part area. After using magnetic modeling program to identify polarity of magnetic bodies, their patterns show the well-defined east-dipping direction. After validation with previous petrochemical and field investigations, it is quite reliable that the Nan suture formed in island-arc system, not by the continental collision setting as previously thought. The occurrence of island arc-type mafic/ultramafic rocks and their associated chromian spinels suggest an eastward ocean-ocean subduction that is consistent with the present geophysical model. Therefore, it is ascertained that the Nan suture zone can be well delineated and definitely extends northeastward to the Lao PDR.