| Title | Geology and Geothermal Systems in the Bajawa Volcanic Rift Zone, Flores, Eastern Indonesia |
|---|---|
| Authors | Hirofumi Muraoka, Asnawir Nasution, Janes Simanjuntak, Sjafra Dwipa, Masaaki Takahashi, Hiroshi Takahashi, Koji Matsuda and Yoshikazu Sueyoshi |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | Indonesia, Flores, Bajawa, Mataloko, geothermal heat source, volcanic rift zone, monogenic volcano, geothermal system, vapor-dominated geothermal system |
| Abstract | An Indonesia-Japan bilateral research cooperation project has been carried out in Bajawa City and its surrounding areas, Flores Island, Indonesia, from 1997 to 2002. Regional tectonic setting of the Bajawa geothermal field is characterized by the NNW-SSE left-lateral shear stress accommodated between the north-moving Australia continent in the east and relatively stable "Sundaland" continent in the west. In accordance with this stress regime, an inner volcanic arc of Lesser Sunda Islands forms en echelon volcanic islands. Each echelon element shows a combination of a large-scale anticline of volcanic basement units and overlying a cluster of young volcanoes. If a concept of mantle diapir is assumed, geneses of a large-scale anticline and a cluster of volcanoes can be explained at the same time. The Bajawa volcanic rift zone consists of 60 monogenetic breccia cone volcanoes along the NNW-SSE trending zone, each of which was derived from the phreato-magmatic eruption. Genesis of each cone probably corresponds to each dike-filling event at a depth. A small phreato-magmatic eruption occurred at one of the summits, January 2001, having formed a fissure at the surface. This suggests that an upper tip of the dike reached very shallow-depth near the surface, characterizing that the geothermal heat sources are small, but numerous, shallow and very active in the Bajawa rift zone. These cones are composed of homogeneous calc-alkaline andesite and their phase relation indicates that the magma were derived from a depth of ca. 10 km near the bottom of the immature crust in this region. Three steaming grounds, Mataloko, Nage and Bobo, are known along the Bajawa rift zone with many hot springs. The well MT-2 was drilled to a depth of 162.35 m in the Mataloko steaming ground and constantly produced 15 tons per hour of dry steam. A temperature profile estimated from phase analyses of cutting samples shows that the field is characterized by a vapor-dominated geothermal system. Most areas of the Bajawa rift zone seem quite prospective on the geothermal potential, because of the ubiquitous heat sources and uniform hydrological settings. |