| Title | The geothermal reservoir characteristics of metamorphic terrain, an initiative of geological and geophysical survey of Qingshui, Tuchang, and Renze, NE Taiwan |
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| Authors | G. Ho, J. Lee, C. Chen, H. Huang, S. Song, C. Chiang, Y. Lu, C. Wang |
| Year | 2023 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Metamorphic terrain, Ilan geothermal system, Taiwan |
| Abstract | Tectonic investigation of northeast Taiwan using seismicity, structural mapping, and geochemistry supports that the rocks and fluids have experienced post-collisional extension. Active rifting and lateral spreading can be observed in this metamorphic terrain (e.g. slates, phyllites, metasandstones, and quartzites mapped with normal faults). GPS and palaeomagnetic observations also show about 45-50° clockwise rotation along the Lanyan River. Since the 1970s, the Ilan area has been the largest exploration anddevelopment area for geothermal exploitation in Taiwan, such as Qingshui (an experimental power plant from 1981, transferred to commercial in 2021), Tuchang, and Renze, where ~50 exploration wells have been drilled. A synthesis of available data of magnetotellurics (MT), seismic profiles, drilling, and field measurements has resulted in interpretative geological cross sections along the Lanyang River at different depths, and here we document: (1) the geothermal pathway is confined by faults and secondary fractures near the surface. Mineral veins strike 320 and indicate the late-stage of extension of about 050; (2) normal faults and reactive strike-slip faults may play an important role as the upflow zones at depth of ~2 km. (3) MT measurements suggest two electro-stratigraphic packageswithin 3 km, high resistivity caprock sitting on top of the geothermal reservoir; low resistivity hydrothermal fluids were recognized from high porosity sandstones and fault zones. (4) seismic tomography also observed two different heat sources from 10-15 km. (5) two geothermal systems are suggested at different depths: one with a deep upflow at ~2 km, entering a fractured zone at <200°C and generating ~5 MW of electricity; the second in rocks at 4-5 km close to the brittle-ductile transition where deep-seated fluids are probably produced, and present-day temperatures are in the range of 400-500°C. |