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Journal of Volcanology and Geothermal Research
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Item-typ:Veröffentlichung, Boron isotope variations in geothermal systems on Java, IndonesiaThis paper presents δ11B data for hot springs, hot acid crater lakes, geothermal brines and a steam vent from Java, Indonesia. The processes that produce a large range of the δ11B values were investigated, including the possible input of seawater as well as the contrast δ11B compositions of acid sulfate and acid chloride crater lakes. The δ11B values of hot springs ranged from − 2.4 to + 28.7‰ and acid crater lakes ranged from + 0.6 to + 34.9‰. The δ11B and Cl/B values in waters from the Parangtritis and Krakal geothermal systems confirmed seawater input. The δ11B values of acid sulfate crater lakes ranged from + 5.5 to + 34.9‰ and were higher than the δ11B of + 0.6‰ of the acid chloride crater lake. The heavier δ11B in the acid sulfate crater lakes was caused by a combination of vapor phase addition and further enrichment due to evaporation and B adsorption onto clay minerals. In contrast, the light δ11B of the acid chloride crater lake was a result of acid water-rocks interaction. The correlations of δ11B composition with δ18O and δ2H indicated that the B isotope corresponded to their groundwater mixing sources, but not for J21 (Segaran) and J48 (Cikundul) that underwent 11B isotope enrichment by B adsorption into minerals.Wissenschaftlicher ArtikelBand:31175 110 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Geothermal systems on the island of Bali, IndonesiaThis paper presents an overview of the geothermal systems on the island of Bali, Indonesia. Physicochemical data of hot springs and shallow geothermal wells were collected from four geothermal locations: Penebel, Batur, Banjar and Banyuwedang. The concentrations for the three main anions varied significantly indicating a different geothermal history. The values for Cl− ranged from 0.1 to 1000 mg/L, for HCO3− from 20 to 2200 mg/L and for SO42 − from 0.1 to 500 mg/L. Although the island of Bali is underlain by carbonate rocks, a carbonate host rock for the geothermal reservoirs could not be confirmed, because the (Ca2 + + Mg2 +)/HCO3− molar ratios were approximately 0.4, well below 1.0 and the K/Mg ratios were approaching those of a calc-alkaline rock reservoir. The HCO3− of the thermal waters correlated with Ca2 +, Mg2 +, Sr2 + and K+ indicating water–rock interaction in the presence of carbonic acid. Phase separation was inferred for the Bedugul and Banjar geothermal systems, because of relatively high B/Cl ratios. Boron isotopes were determined for selected samples with values ranging from δ11B of 1.3 to 22.5‰ (NBS 951). The heavy δ11B of + 22.5‰ together with a low B/Cl ratio indicated seawater input in the Banyuwedang geothermal system. The hydrogen and oxygen isotopic composition of the thermal water plotted along the global meteoric water line (GMWL) and close to the mean annual value for precipitation in Jakarta indicating a meteoric origin of the geothermal water. Comparison of the Si, Na/K, Na/K/Ca and Na/Li geothermometers with actual reservoir temperature measurements and physicochemical considerations led to the conclusion that the Na/Li thermometer provided most reliable results for the determination of geothermal reservoir temperatures on Bali. Using this thermometer, the following reservoir temperatures were calculated: (1) Penebel (Bedugul) from 235 to 254 °C, (2) Batur 240 °C and (3) Banjar 255 °C. Due to seawater input this thermometer could not be applied to the Banyuwedang geothermal system. There application of a SiO2 thermometer indicated a reservoir temperature below 100 °C.Wissenschaftlicher ArtikelBand:304117 128 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Geothermal systems on the island of Java, IndonesiaThis paper presents an overview of all known geothermal systems on the island of Java by presenting physicochemical data for associated hot springs, cold springs and acid crater lakes. A total of 69 locations were sampled and classified based on their position in either a volcanic complex (volcano-hosted) or a fault zone (fault-hosted). In particular the potential of a magmatic heat source for fault-hosted geothermal systems was investigated. Volcano-hosted geothermal systems had higher HCO3− concentrations and higher Mg/Na ratios than fault-hosted geothermal systems. This geochemical difference is likely due to degassing and subsequent CO2-water reaction in the volcano-hosted systems, which is absent in the fault-hosted geothermal systems. The HCO3 vs. Cl and Mg/Na vs. SO4/Cl systematics indicated that fault-hosted geothermal systems located in the active Quaternary volcanic belt received shallow magmatic fluids, hence should be classified as volcano-hosted geothermal systems. The heat source of fault-hosted geothermal systems located in the old (Tertiary) volcanic belt was investigated by a combination of Li enrichment and calculated reservoir temperatures. There a shallow magmatic heat source was indicated only for the Cilayu and Cisolok geothermal systems. Thus, a deep seated magma was considered to be the heat source for the fault-hosted geothermal systems of Cikundul, Pakenjeng, Parangtritis and Pacitan. In ten of the volcano-hosted geothermal systems, 2H and 18O isotope enrichments were found, but not in any of the fault-hosted geothermal systems. Stable isotope enrichment due to evaporation was recognized in the Kawah Candradimuka and Kawah Sileri, Kawah Hujan and Candi Gedong Songo geothermal systems. A combination of intensive evaporation and magmatic gases input produced very heavy stable isotopes in the hot acid crater lakes of the Kawah Kamojang, Kawah Sikidang and Kawah Putih geothermal systems. The addition of substantial amounts of andesitic water to the geothermal fluid was observed in the Candi Songgoriti, Banyuasin and Pablengan geothermal systems. Contrary to established belief fault-hosted geothermal systems on Java could be considered a potential source for geothermal energy.Wissenschaftlicher ArtikelBand:28598 257 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Stable and radiogenic isotopes as tracers for the origin, mixing and subsurface history of fluids in submarine shallow-water hydrothermal systemsThe shallow-water hydrothermal system in Tutum Bay on the west side of Ambitle Island, Papua New Guinea provides us with an exceptional opportunity to study isotope systematics in a near shore setting. Compared to seawater, the hydrothermal fluids in Tutum Bay have lower values for δD, δ18O, δ13C, and 87Sr and higher values for 3H, δ34S(SO4) and δ18O(SO4). The δ18O and δD records for vents 1 and 4 indicate that fluid compositions remained stable over an extended period. Interpretation of isotope data clearly demonstrates the predominantly meteoric origin of Tutum Bay hydrothermal fluids, despite their location in a marine environment. δ18O and δD values are identical to mean average annual precipitation in eastern Papua New Guinea. The hypothesis that these fluids are a simple product of mixing between seawater and onshore hydrothermal fluids from the Waramung (W-1) and Kapkai (W-2) thermal areas has been rejected, because the observed δ37Cl, 3H, δ34S(SO4) and δ18O(SO4) values cannot be explained by a simple mixing model. The application of δ18O(SO4) and δ13C thermometers in combination with 3H values corroborates the three-step model of Pichler et al. [Pichler, T., Veizer, J., Hall, G.E.M., 1999. The chemical composition of shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New Guinea and their effect on ambient seawater. Marine Chemistry 64 (3) 229–252], where (1) phase separation in the deep reservoir beneath Ambitle Island produces a high temperature vapor that rises upward and subsequently reacts with cooler ground water to form a low pH, CO2-rich water of approximately 150–160 °C, (2) caused by the steep topography, this CO2-rich fluid moves laterally towards the margin of the hydrothermal system where it mixes with the marginal upflow of the deep reservoir fluid. This produces a dilute chloride water of approximately 165 °C, and (3) possibly the entrainment of minor amounts of ground or seawater during its final ascent.Wissenschaftlicher ArtikelBand:139Heft:3-4428 57