Analysis of Thermal Manifestation in Suoh West Lampung Indonesia

Abstract

Suoh Geothermal Field is located in a pull apart basin resulting from a step in the Great Sumatra Fault (GSF) which strikes NW. This Field found within a valley which widens into a broad depression (the Suoh depression) and near the southern end of the Sumatra fault zone. Significant thermal areas which are located near the western and eastern margins of the depression. The Suoh depression is interpreted to have formed as a result of a fault jog, where the Great Sumatran Fault zone is offset dextrally by a pair of north-south faults. One of prospect analysis use geochemistry interpretation indicated by the Na-K-Mg and Cl-SO4-HCO3 ternary plot. The dominant units are young alluvium (Qal) and Asam eruption deposits (Qae). South-west of the Souh depression the primary rock type is Tertiary Andesite (Tat). North-east of the depression are the Tekorberak Volcanics (Qsdt). The youngest volcanics in the area are the Loreng Volcanics (Qlr) located immediately west of the Kalibata thermal area. Thermal areas in Suoh are consist the Kalibata, Way Haru and Srirejo areas. Liquid geothermometry strongly suggest the Kalibata thermal features are connected to a benign geothermal system of 250oC to 260oC. Estimated temperatures at Way Haru and Srirejo are lower, at 210 oC and 175 oC, respectively. The hottest fluids in the system upflow along the deep-seated Great Sumatra Fault and the western graben transform fault, heated by magmas associated with the Loreng Volcanics. These fluids flow out into the basin-filling volcanics and sediments and likely the underlying Tertiary volcanics to form the geothermal reservoir.