首页|Geothermal prospects of Flores Island in Indonesia viewed from their volcanism and hot water geochemistry
Geothermal prospects of Flores Island in Indonesia viewed from their volcanism and hot water geochemistry
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Lavas of the Flores volcanic arc have a range of compositions from basalt to dacite but mostly andesite, containing pigeonite and olivine in island arc tholeiitic series and amphibole and biotite in calc-alkaline series. Chemically, the rocks show a wide variety of SiO_2 (51 - 67 wt. percent), Al_2O_3 (14 - 20 wt. percent) and low TiO_2 (<1 wt. percent), together with relatively high Rb, Sr and Ba. These K group elements represent an increase of SiO_2 with increasing depth of the Benioff zone. Strontium isotope ratios of tholeiitic to calc-alkaline lavas are 0.7042 - 0.7045, assumed to be correlated with the depth of the subducted slab across the island. Flores geothermal prospects are situated in young volcanic terrains of andesite and basalt between 500 to 1000 m above sea level (a.s.l.) and associated with post volcanic fractures, faults and caldera structures. Rot water discharges represent a wide variety of chemical water types; sulfate, bicarbonate and chloride waters. Sulfate type is mostly associated with fumaroles and located on high volcanic terrains (700 - 1100 m a.s.l.), indicating the near-surface H_2S oxidation (Ulumbu, Mataloko, Nage and Sokoria). Bicarbonate waters are located at the moderate slope of volcanics (400 - 700 m a.s.l.), shown by Langageda and Sokoria 2. Neutral chloride waters are located at the lower volcanic terrains approximately 5 - 600 m a.s.l., indicating an outflow from geothermal reservoirs with a temperature of 210 to 280 deg C. Geothermal wells that were drilled at the Ulumbu and Mataloko prospects to a depth of 700 - 1800 m and 200 m, respectively have a subsurface temperature of 200 to 240 deg C, indicating that the high sulfate concentration is associated with a vapor-dominated system. The same system probably occurs in the Sokoria field. While the geothermal prospects of high chloride water type are probably associated with hot-water or mixture system (Wai Sano, Wai Pesi, Jopu, Lesugolo and Oka).
FloresIndonesiageothermal prospectvolcanismvolcanopetrologyrock serieshot springhot spring typegeochemistry
Asnawir NASUTION、Hirofumi MURAOKA、Mawardi RANI
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Directorate of Volcanology and Geological Hazard Mitigation. Jl. Diponegoro No.57, Bandung, 40122 Indonesia
NSTL
