TY - JOUR
T1 - Oxygen isotope fractionation between gypsum and its formation waters
T2 - Implications for past chemistry of the Kawah Ijen volcanic lake, Indonesia
AU - Utami, S.B.
AU - van Hinsberg, V.J.
AU - Ghaleb, B.
AU - van Dijk, Arnold E.
N1 - Export Date: 18 November 2021
PY - 2020/5/20
Y1 - 2020/5/20
N2 - Gypsum (CaSO4·2H2O) provides an opportunity to obtain information from both the oxygen isotopic composition of the water and sulfate of its formation waters, where these components are commonly sourced from different reservoirs (e.g., meteoric vs. magmatic). Here, we present δ18O values for gypsum and parent spring waters fed by the Kawah Ijen crater lake in East Java, Indonesia, and from these natural samples derive gypsum-fluid oxygen isotope fractionation factors for water and sulfate group ions of 1.0027 ± 0.0003‰ and 0.999 ± 0.001‰, respectively. Applying these fractionation factors to a growth-zoned gypsum stalactite that records formation waters from 1980 to 2008 during a period of passive degassing, and gypsum cement extracted from the 1817 eruption tephra fall deposit, shows that these fluids were in water-sulfate oxygen isotopic equilibrium. However, the 1817 fluid was >5‰ lighter. This indicates that the 1817 pre-eruption lake was markedly different, and had either persisted for a much shorter duration or was more directly connected to the underlying magmatic-hydrothermal system. This exploratory study highlights the potential of gypsum to provide a historical record of both the δ18Owater and δ18Osulfate of its parental waters, and provides insights into the processes acting on volcanic crater lakes or any other environment that precipitates gypsum.
AB - Gypsum (CaSO4·2H2O) provides an opportunity to obtain information from both the oxygen isotopic composition of the water and sulfate of its formation waters, where these components are commonly sourced from different reservoirs (e.g., meteoric vs. magmatic). Here, we present δ18O values for gypsum and parent spring waters fed by the Kawah Ijen crater lake in East Java, Indonesia, and from these natural samples derive gypsum-fluid oxygen isotope fractionation factors for water and sulfate group ions of 1.0027 ± 0.0003‰ and 0.999 ± 0.001‰, respectively. Applying these fractionation factors to a growth-zoned gypsum stalactite that records formation waters from 1980 to 2008 during a period of passive degassing, and gypsum cement extracted from the 1817 eruption tephra fall deposit, shows that these fluids were in water-sulfate oxygen isotopic equilibrium. However, the 1817 fluid was >5‰ lighter. This indicates that the 1817 pre-eruption lake was markedly different, and had either persisted for a much shorter duration or was more directly connected to the underlying magmatic-hydrothermal system. This exploratory study highlights the potential of gypsum to provide a historical record of both the δ18Owater and δ18Osulfate of its parental waters, and provides insights into the processes acting on volcanic crater lakes or any other environment that precipitates gypsum.
KW - Gypsum
KW - oxygen isotopes
KW - crystalline water
KW - sulfate group
KW - isotope fractionation factor
KW - Kawah Ijen
KW - volcanic lake
UR - https://www.scopus.com/inward/record.uri?eid=2-s2.0-85084742793&doi=10.2138%2fam-2020-7298&partnerID=40&md5=4eeea295b9e93ad16a0d97d33f5fd356
U2 - 10.2138/am-2020-7298
DO - 10.2138/am-2020-7298
M3 - Article
SN - 0003-004X
VL - 105
SP - 756
EP - 763
JO - American Mineralogist
JF - American Mineralogist
IS - 5
ER -