| Abstract |
The island of Java (Sunda arc, Indonesia) contains the largest geothermal resources (potential and known reserves) in Indonesia. For example, five out of seven producing geothermal fields in Indonesia are located in this island. In total around sixty geothermal prospects have been identified, in which mostly are spatially associated with Quaternary volcanoes. However, their spatial distributions are not uniformly distributed along the island; rather the bigger prospects (with potential reserve >100 MW) are concentrated in few locations and they can be related with regional to district-scale geologic segmentation of the Quaternary volcanoes. The Sunda volcanic arc in Java is segmented into the West, Central and East segments that each has distinctive styles of volcanism. Although several geothermal fields are located within large, single stratovolcanoes, the majority of large geothermal fields are concentrated within Upper Neogene to Early Quaternary caldera remnants, in which many Pleistocene volcanic edifices (mostly are monogenic) were emplaced. Most notably is in the eastern part of West Java especially within the volcanic front field. This area is also the most seismically active region and has the highest volcanic density in the whole island. Petrochemical data of Quaternary lavas suggest that volcanism surrounding geothermal system contain some of the most primitive magma erupted in this mature arc. In Central Java geothermal prospects are, on contrary, located within the backarc-side volcanoes. Similarly, the biggest geothermal district in Dieng is also associated with many monogenic volcanoes emplaced within an Upper Neogene-Early Quaternary caldera. Current radiometric data suggest that major geothermal fields are associated with magmas erupted during the Upper Pleistocene, whose ages range approximately 0.5-0.2 Ma. In eastern Java, specific settings for geothermal prospects are less evident in which known prospects are located at both volcanic front and backarc-side stratovolcanoes. The recognition of Upper Pleistocene volcanic edifice is the single most important evidence for the first-pass exploration for geothermal fields. |