Reconstructing geothermal geological models by combining geophysical, geochemical and geological studies in Tatun volcanoes area, Northern Taiwan

In this study, we conduct a multi-disciplinary study, including geophysics, geochemistry, and geology, with help of tens of previously drilled exploration wells, to reconstruct geothermal geological models at the shallow 3-5 km, for a geothermal exploration project in the Tatun volcano area, northern Taiwan. Our reconstructed geological profiles show that the Tatun volcanoes have a ~1-2-km thick of lava flows and pyroclastic deposits, erupted on top of the 6-8-km-thick fold-and-thrust belt of Miocene sedimentary rocks. The seismic velocity imaging indicates a likely main magma reservoir of high anomaly of Vp beneath the Tatun at the depths of 8-15, with an estimated volume of ~250-300 km³.  

Incorporating the regional geology with the newly acquired magnetotelluric (MT) results, we found three high-resistive areas at different depths, which we tend to interpret as possible “heat bodies”. Surrounding these three high-resistivity areas, there exists overlying low-resistive zones or layers, which we interpreted as “cap rocks” and the potential geothermal reservoirs in-between the “cap rocks” and “heat bodies”: 1) two shallow reservoirs, at the depth of 600-1200 m (downhole temperature of 150-250°C), and 2) a deeper reservoir, at the depth of ~ 2-3 km, seemingly in the uppermost basement of quartz-rich sandstone, underneath low-resistive lobs.

At least four high micro-seismicity zones with cylinder shape are interpreted as conduits of hot fluid derived from deep over-pressured zones, either along the frontal thrust of the Jinshan fault (at the depth of ~2 km), or the outer edge of the fluid saturated magma reservoir around 4-6 km depth, which is also of potential for “super-hot or super-critical geothermal” exploration.