MODEL KONSEPTUAL ZONA OUTFLOW SISTEM PANAS BUMI GUNUNG UNGARAN, SEMARANG, JAWA TENGAH BERDASARKAN STUDI GEOLOGI DAN GEOKIMIA MANIFESTASI

• Main Author: Yuda Kencana, Aditya
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47982
• Institution: Institut Teknologi Bandung

Mount Ungaran geothermal system, Semarang, Central Java is a volcanic geothermal system associated with Ungaran Caldera. Geothermal surface manifestation includes fumarole, thermal springs, steaming ground, travertine, and altered rocks. The upflow zone of Mount Ungaran geothermal system is located in Gedongsongo area, while the outflow zone is located in the northern area (Nglimut) and the eastern area (Kendalisodo). This research is conducted in the outflow zone of Mount Ungaran geothermal system, i.e. Kendalisodo and surrounding which is located in the eastern and southeastern part of Mount Ungaran. The purpose of the study is to build the conceptual model of the Kendalisodo geothermal system, type of the system, hydrothermal fluid characteristics, and subsurface fluid flow. Methods used comprise of literature study, geological traverse mapping in the manifestation area, water sampling, and geochemical study for anions, cations, gas, and stable isotopes ?18O, ?2H, ?13C analysis. Geothermal surface manifestation in the study area includes Kendalisodo, Diwak, Derekan, and Kaliulo warm springs; with travertine and salt deposits in some areas. Fumarole and hot springs appear in the upflow zone of Gedongsongo. The results showed that lithology in the study area, from the oldest to the youngest is limestone (ooids packstone) from Kerek Formation, pyroclastic breccia and vitric tuff from Merangkang Volcanic unit, and Andesite Intrusion unit. In the study area, there are two geothermal systems, i.e. Kendalisodo system (with a discharge of Kendalisodo warm spring) and Diwak system (with the discharge of Diwak, Derekan, and Kaliulo warm springs). These two systems are separated by the Old Ungaran Caldera. Both systems are non-volcanic and medium enthalpy geothermal system. The Kendalisodo reservoir has a temperature of 170 ± 10oC. The hydrothermal fluid of the Kendalisodo system originates from meteoric water catchment on the southeast slope of Mount Ungaran; the meteoric water is heated up by the remaining heat of Mount Kendalisodo intrusion. The fluid has experienced conductive cooling and mixing with cold water, before discharge in the upflow zone at the Kendalisodo area. The Kendalisodo geothermal system, geologically and geochemically, is different from the main geothermal system of Mount Ungaran (Gedongsongo). The Diwak geothermal system has a reservoir with a temperature of 160 ± 10oC. The hydrothermal fluid of the Diwak system is also from meteoric water, which is heated up by high heat-flow and/or overpressure system. The fluid then flows upward through the Derekan Fault and discharges in the upflow zone as the Diwak and Derekan warm springs. The fluid also flows laterally through the Derekan Fault and mixed with formation water to form Kaliulo warm spring in the outflow zone.