GEOLOGICAL MODEL OF PRE-KHORAT GROUP IN EASTERN PART OF SAKHON NAKHON BASIN USING GRAVITY AND MAGNETIC DATA

Abstract

Khorat Plateau in eastern part of Sakhon Nakhon basin had been examined to exhume Pre-Khorat aspects via integrated magnetic and gravity data with seismic reflection and exploratory well data. Qualitative and quantitative interpretations have been carried out simultaneously. For qualitative interpretation, the derivative techniques including horizontal derivative in x and y directions, total horizontal derivative, vertical and second order vertical derivatives, analytic signal, tilt derivative and total horizontal derivative on tilt derivative have been employed. The qualitative interpretation solution provides magnetic and gravity anomalous patterns. The magnetic anomaly patterns represent the depth of magnetic sources whereas gravity anomaly patterns roughly indicate the lithology of Pre-Khorat Group. For quantitative interpretation, two sections of 2D forward modeling on residual magnetic and completed Bouguer data have been carried out. The constraint depth of ensemble sources is derived from spectral analysis and subsurface information. The resultant models display subsurface geological aspect of study area. The aeromagnetic data interpretation based on reduction to the pole and its derivatives collaborate with spectral analysis suggests basement form as irregular surface with occasional fault. The derivative techniques are also applied on gravity complete Bouguer map which provided the recognition of four gravity patterns correlated with seismic reflection section. This shows that the west gravity high underneath Phu Phan Ranges coincides with Permian carbonate platform and clastic of Saraburi Group. The moderate to high gravity patterns represent the outlining distribution of Triassic basin on high density basement. The low to moderate gravity patterns indicate Nong Khai High Basement which is not homogeneous texture. The NW trending patterns of low to moderate gravity units suggests that it is possible either sedimentary or metamorphic overly on basement. Last, from Forward modeling of potential field data suggests that the low gravity anomaly pattern with long wavelength may be caused by magnetic basement thickness increasing into middle crust.