Structure of Phu Phan Range in the Khorat Plateau: Its Apatite Fission Track Ages and Geological Syntheses

Abstract

Phu Phan area in northeastern Thailand has been selected for apatite fission track (AFT) geochronological analyses. Geological transects have been made over the region. Non-marine Mesozoic continental sediments only 4 formations have been encountered in the study area. Structurally, the rocks have been deformed and series of anticlinal structures have been encountered with their fold axes mostly trend in the northwest – southeast direction. The major fold has been displaced by a few of short left-lateral strike slip faults whose trend is in the northeast – southwest direction. Samples of the Khorat Group rocks were identified and collected for AFT analyses. The AFT result along with those of the previous studies reveals an interesting scenario. Three age ranges have been recognized viz., 78 to 60 Ma, 55 to 42 Ma, and about 37 Ma, the oldest range is a very mild event.  The first episode corresponds to the movement along the northeast – southwest strike slip fault which may have been in turn caused a compressive stress within the Khorat. Two successive basins within the Khorat region may have been developed. The second episode indicates an extensive exhumation (uplift and erosion) which perhaps took place for the whole Khorat region, becoming a Khorat Plateau. The final episode is marked by the minor movement along the strike slip fault which slightly displaced the main structure of the Phu Phan area. The AFT results from this current and previous studies advocate an average exhumation rate of the Phu Phan Mountain range to be ca. 0.0139 mm/yr.