The intergrated delineation of geothermal system area 'Z' using 3D inversion of magnetotelluric data and gravity data

摘要

A study for delineating geothermal system of prospect area "Z" has been done by using three-dimension modeling of magnetotelluric supported unified data just like geological and geochemical and integrated gravity data. Geothermal area "Z" in tectonic setting included in Sumatra volcanic back-arc, right on one of the southern part of Sumatra fault segment, composes by volcanic and clastic sendimentary rock are Tertiary to Quarternary (Andesite-Basalt). The existance of geothermal system in this area is indicated by the presence of thermal manifestation in form of alteration and five hot springs temperature in the ranges 44.4 - 92.5 °C, and pH 8.19 - 9.43 and type of fluid are bicarbonate, sulphate-bicarbonate, and sulfate-chloride. The development of geothermal system is affected by tectonic oblique between the Indian Ocean plate and the Eurasian Continent Plate (direction of the Sumatra fault patterns). Based on the analysis of geothermal water reservoir temperature are taken through the calculation geothermometer SiO_2 Fournier, Na-K Giggenbach, Na-K-Ca, Na-K-Mg diagram and Enthalpi Mixing Cloride Model range 145-155 °C, classified as intermediate temperature. Based on a three-dimensional inversion of the magnetotelluric data obtained depth Top of Reservoir (TOR) geothermal system area "Z" about 400 m (elevation 50 meters above sea leavel), while based on the two dimensional of the gravity data predicted heat sources such as cooling instrusion (estimated gabbro; density 2.95-3.15 g/cc) and reservoar such as sandstone (resistivity 50-250 Ωm; density 2.60 g/cc). The Geothermal systems of research area classified as the type of intermediate temperature tectonic fracture zone with prospect area about 7.5 km~2.