Fig. 21

Map view slices at 25 m and 300 m depths of the final inverted 3D-Magnetotelluric resistivity survey of Amatyakul et al. (2016). These slices are from an earlier report on that data by Siripunvaraporn (2015). Traces of faults from geologic mapping of Fig. 9 are dashed black lines. Map a (25 m depth) shows the small area of the shallow, low resistivity (< 30 Ωm, colored orange) anomaly at Fang Hot Springs. Deeper slices show only high resistivity beneath the geothermal area. The map shows low resistivity (colored orange) which is associated with the Paleozoic sedimentary rock overlying the crystalline rock (> 300 Ωm, colored blue) between the Doi Kia fault and the Mae Chan fault. Low resistivity rock south of the Mae Chan fault is the shaly Cenozoic basin fill. Map b (300 m) shows the crystalline rock is beneath the hot springs, and low resistivity Cenozoic basin fill southeast of the Mae Chan fault. The white line shows N–NE trending boundary between crystalline rock to the west and sedimentary rock to the east. This feature is not evident in geologic mapping, and appears only on slices deeper than 200 m. The boundary shows up clearly in cross section on the vertical slice, where it appears to dip 55°SE (Fig. 22a). The structure suggests uplifted crystalline rock to the west and may account for the isolated Paleozoic quartzite outcrop in the basin shown in the map