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Geochemistry of hot springs and fumarolic gases from the Banda Arc

1989; Elsevier BV; Volume: 24; Issue: 2-3 Linguagem: Inglês

10.1016/0077-7579(89)90158-0

1873-1406

R.P.E. Poorter, Johan C. Varekamp, T. Sriwana, Manfred J. van Bergen, R.D. Erfan, K. Suharyono, Achmad Djumarma Wirakusumah, Pieter Z. Vroon,

Geological Studies and Exploration

Geothermometry carried out on hot springs occurring on the volcanic non-active Islands of Ambon and Haruku indicates minimum subsurface temperatures of 180°C; for Alor Island we obtained a temperature of 170°C. The hydrothermal systems of these islands are likely crack and fault dominated. Hot springs on the islands with active volcanism indicate subsurface temperatures of 180 to 250°C. The chemical and isotopic compositions of fumarolic gases from the active volcanoes Banda Api in the Banda Archipelago, Serawerna on Teon, Wurlali on Damar and Ili Lewotolo on Lomblen are reported here for the first time. The measured fumarolic gas temperatures ranged from 98°C to 170°C for Banda Api, Laworkawra, Legatala, Serawerna, Wurlali and Sirung volcanoes and reached 490°C for Ili Lewotolo volcano. The main gas components are H2O, CO2 and SO2; CO2 predominates over (SO22 + H2S). The calculated gas equilibrium temperature for Wurlali is 700°C and for Ili Lewotolo more than 1000°C. Stable carbon isotope data for Wurlali (δ13C = −3.3 % 0) and for Ili Lewotolo (δ13C = −2.9 % 0) volcanoes are similar to those for other Indonesian volcanoes. The bulk sulfur is relatively rich in the heavy isotope. The 3He/4He (R/RA) ratios vary between 1.0 and 3.6, which is low for subduction related volcanoes. A contribution from continental crust or sediment-derived radiogenic 4He is suggested.