Volcanic Neck of Mount Iyang Argopuro Revealed from Gravity Study

Abstract

Mount Iyang Argopuro is a volcanic complex which has geothermal prospect located in the eastern part of Java Island. The prospect itself is still in exploration stage. The gravity survey has already conducted in 2013 with total 200 number of stations which covering 50 x 50 km of Mount Iyang Argopuro area. Scintrex CG-5 was used to measure the gravity data in each station and High Precission GPS to measure the elevation to collect high quality of gravity data. 2D inversion model within conjugate gradient scheme with rectangular mesh forward operator was used to reconstruct the subsurface density distribution. The length of line for 2D inversion is 50 km crossing the Mount Iyang Argopuro from the low land to the overlaying volcano. The model shows an interesting vertical dense body having a density contrast up to 0.35 gr/cm3 from average rock density. The dimension of the dense body is 5 km width x 4 km height located near the top of the volcano. The dense body is interpreted as the volcanic neck of the old Iyang Argopuro volcano which currently known as Mount Tengah. However, this dense body will be eliminated from consideration of geothermal prospect since the geological dan geochemical data showed no indication of the presence of geothermal activity. Furthermore, the low residual gravity anomaly in the crater of Mount Iyang Argopuro, after integreted with other geoscientific data is concluded as the most prospective region for geothermal exploitation.