Abstract:
Re-reprocessed and modeling of detailed geophysical data are used for interpreting the continuity of geological units and structures, particularly where most of the pre-Cenozoic rock units are overlain by regolith, recent soils, and alluvial deposits. Aeromagnetic data were run through a series of filter routines including reduction to the pole, analytic signal, vertical derivative, directional cosine filtering, and upward continuation. Interpretation of all the processed aeromagnetic data has been carried out by integrating with electromagnetic data, radiometric data, enhanced Landsat images and GIS geological information. Three geological domains (eastern, central, and western) were interpreted from the enhanced geophysical data corresponding assemblages of contrasting magnetic intensities, as well as different regional magnetic structures. The magnetic data were also used to model the geometry of mafic units and granitic intrusions in 3 dimensions. Magnetic mafic bodies in the Loei Suture Zone were found to display their dip direction mainly to the east. High magnetic intensity units running along the eastern side of the Loei Suture Zone correspond fairly well to folded and thrust faulted basalt lava flows of Devonian age. A few Permo-Triassic felsic to intermediate lava flows are identified by their hummocky magnetic textures. Northeast-trending faults observed in the magnetic data cross-cut Triassic granite intrusions and northwest-trending, mostly producing more than 0.5 km of sinistral offsets. The new interpretation from this study agrees with the existing geological bedrock mapping in a broad sense, but shows differences in the continuity of geological features and extent of granitoid intrusions, The geophysical interpretation also contains more large-scale structural detail, particularly at depth. These new results and other relevant previous work lead to the clarification of tectonic setting and its evolution of the Loei study and nearby areas.
