Abstract
Magmatic settings involving active volcanism are potential locations for economic geothermal systems due to the occurrence of high temperature and steam pressures. Indonesia, located along active plate margins, hosts more than 100 volcanoes and, therefore, belongs to the regions with the greatest geothermal potential worldwide. However, tropical conditions and steep terrain reduce the spectrum of applicable exploration methods, in particular in remote areas. In a case study from the Lamongan volcanic field in East Java, we combine field-based data on the regional structural geology, elemental and isotopic composition of thermal waters, and the mineralogical and geochemical signatures of volcanic rocks in exploring hidden geothermal systems. Results suggest infiltration of groundwater at the volcanoes and faults. After infiltration, water is heated and reacts with rocks before rising to the surface. The existence of a potential heat source is petrologically and geophysically constrained to be an active shallow mafic-magma chamber, but its occurrence is not properly reflected in the composition of the collected warmed spring waters that are predominantly meteoric in origin. In conclusion, spring temperature and hydrochemistry alone may not always correctly reflect the deep geothermal potential of an area.
Highlights
In a conventional approach, several methods need to be adopted and integrated to understand the geochemical and geophysical signatures of active geothermal systems (e.g., Rybach and Muffler 1981)
This study provides a first survey of the geothermal potential of the Tiris area located on the northeastern slope of Lamongan Volcano in East Java, Indonesia (Figs. 1, 2)
The purpose of this study is to develop a conceptual model of the Tiris geothermal system in the Lamongan Volcanic Field (LVF) by combining field observations and chemical data of hot and warm springs with a reconnaissance structural–geological mapping, which will serve as a baseline study for a subsequent in-depth geological and seismic exploration of the area
Summary
Several methods need to be adopted and integrated to understand the geochemical and geophysical signatures of active geothermal systems (e.g., Rybach and Muffler 1981). Young volcanic zones along convergent plate margins are prime targets for the exploration of geothermal energy sources, as active magma chambers have an intrinsically high geothermal potential (Bogie et al 2005). Heat transfer in those areas is dominated by circulating fluids and, in the case of two-phase systems, by steam. Steep terrain and difficult access could explain why a well-substantiated geothermal concept for East Java is still missing
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