Gravity Modeling of the Karaha - Telaga Bodas Geothermal System, Indonesia

The Karaha-Telaga Bodas geothermal system couples spectacular surface manifestations with an extensive geological and geophysical data set. Examination of fluid inclusions and mineral relationships has allowed development of a thermal history for the system. These data suggest that a quartz diorite intrusion encountered in drill samples provides the heat that drives this system. Delineation of the intrusion’s geometry, using gravity data, provides a constraint on the deep thermal structure of the system and the basis for future thermal modeling. The gravity data has a linear expression that extends the length of the field. A large closed anomaly coincides with the Telaga Bodas thermal area. Using a sphere model gives a depth to the center of gravity of approximately 2400 m. The excess mass constraint on the radius (in meters) of the spherical model is ∆ρ(R/304.8)3 = 100. The gentle anomaly along the north-south trending volcanic ridge is consistent with a thin sill of quartz diorite with a width of 1600 m, a depth of 2400 m, and with an approximate thickness of 425 m.