12th GEOSEA 2012, Bangkok, Thailand
Analysis and Modeling of Airborne
Geophysical Data in the Phetchabun Volcanic
Terrane, Northern Part of Central Thailand
Arak Sangsomphong*, Thanop Thitimakorn and Punya Charusiri Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330 Thailand *rak_geo46@hotmail.com
ABSTRACT
Re-processed airborne geophysical data have been used to interpret the complex subsurface structures of the Phetchabun volcanic terrane covered by thick Cenozoic deposits at the western edge of the Khorat Plateau. Reduction to the pole (RTP), high pass (HP), shade relief (SR) and directional cosine filtering (DIR) constitute the main processing approaches applied to the original data using the Oasis Montaj速 v6.1 program. New RTP map displays four distinct magnetic domains including northern, eastern, central and western domains. Within these domains, four magnetic units of high magnetic anomalies are recognized, namely elongate unit, circular unit, flat unit, and spot units. The HP map also illustrates the ring units with the distinct northwest-southeast regional trend. In addition, the RTP modelings show the elongate unit with a northeast dipping. In the central domain, the elongate units display deformation along a northwest-southeast trending fault with sinistral shear slip of about 33 kilometers, an east-west trending fault with dextral slip of about 3-9 kilometers and a northeastsouthwest trending fault with sinistral slip of about 1-2.7 kilometers. The ring units and the circular units are crosscut by east-west trending sinistral faults and northeastsouthwest trending dextral faults. Based on SR and DIR maps, northeast-southwest trending sinistral faults about 47 kilometers long, north-south trending dextral faults about 1-5 kilometers long, and northwest-southeast trending faults about 2-10 kilometers long have been encountered. The younger spot units occur along the latest fault segments. These new results together with relevant current field verification as well as previous geochronological, geochemical and geological investigations lead to the clarification of tectonic setting and evolution of the Phetchabun volcanic terrane. These distinct geophysical features correspond well with the well-established Loei suture between the Nakhonthai and Indochina tectonic plates. During the PermoCarboniferous, the elongate units corresponding to intrusive igneous bodies may have
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GEOSEA 2012