Regional Characterization of Sumatran Geothermal Systems, Indonesia

Abstract

Coexistence of the dextral strike-slip Sumatran Fault System and subduction-related volcanic arc forms the western half of the island, while the eastern part is dominated by Tertiary back-arc basins. Subdivision of the arc into three volcano-tectonic domains is the basis for further characterization of Sumatran volcanic geothermal systems. Compilation of fault kinematics, volcanic facies, and associated geothermal systems is conducted for the Southern Domain where volcanism is concurrent with strike-slip faulting. Series of conceptual models are proposed to represent the influences of tectono-volcanism for geothermal system in the domain. Toba Caldera, a large volcanic region with rhyolithic volcanism, dominates the Central Domain. A regional 2D MT survey has been carried out and resulted deep resistivity image up to moho depth from inversion model then used to constrain a lithospheric-scale thermal modeling. In Northern Domain the volcanism is shifted away from the Sumatran Fault System which then affect the nature of associated geothermal systems. Heat flow values in the Central Sumatra Basin are higher compared to average values for continental crust or even to the other two nearby back-arc basins which share a similar sedimentation history. Again 3D numerical modelling of the lithospheric-scale temperature distribution is conducted to identify the controlling factors of that contemporary elevated heat flow. Lateral variation due to amalgamation of several tectonic terranes is incorporated into the model. It is concluded that a large amount of thinning is needed in order to create such high heat flow condition.