The 1982-83 eruption at Galunggung Volcano, Java (Indonesia); oxygen isotope geochemistry of a chemically zoned magma chamber

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Authors:Harmon, Russell S.; Gerbe, Marie-Christine
Author Affiliations:Primary:
NERC, Isot. Geosci. Lab., Keyworth, United Kingdom
Other:
Univ. Blaise Pascal, France
Volume Title:Journal of Petrology
Source:Journal of Petrology, 33(3), p.585-609. Publisher: Clarendon Press, Oxford, United Kingdom. ISSN: 0022-3530
Publication Date:1992
Note:In English. 81 refs.; illus. incl. 1 table, sect., sketch map
Summary:This historically active volcano has erupted four times in the last two centuries. In the most recent event in 1982-83, some 305 x 106 m3 of medium-K, calc-alkaline magma was erupted. The composition of juvenile material changed during the 9-months interval from initial plagioclase-two-pyroxene andesite with SiO2 approx 58%, to final plagioclase-diopside-olivine- bearing primitive Mg-basalts with SiO2 approx 47%. Mineralogical and compositional relationships indicate a magmatic evolution involving differentiation of a high-Mg parental melt. The eruptive volumes of approx 35 x 106 m3 andesite, 120 x 106 m3 mafic andesite and 150 x 106 m3 basalt are consistent with the eruption progressively tapping and draining a magma chamber chemically stratified through extensive crystal fractionation. The plagioclase and pyroxene have delta18OSMOW ranges of +5.6 to +6.0 and +5.3 to +5.6, respectively, with DELTA18Oplag-px values of +0.4 to +0.6 per mille , indicating internal O-isotope equilibrium at approx 1100-850 degrees C. The magnesian basalts have magmatic 18O/16O ratios similar to those of MORB; the O isotope ratios of compositionally evolved derivative melts show no evidence for contamination of the Galunggung magmas by 18O- rich crust during differentiation. Andesites and transitional mafic andesites have a more variable O isotope character possibly reflecting intramagma chamber processes affecting the upper portion of the differentiating magma body before the 1982-83 eruption. [R.A.H.]
Subjects:Eruptions; Genesis; Igneous rocks; Isotopes; Magma chambers; O-18/O-16; Oxygen; Stable isotopes; Volcanic rocks; Volcanoes; Volcanology; Asia; Far East; Galunggung; Indonesia; Java; Galunggung Volcano
Abstract Numbers:93M/755
Record ID:1992039443
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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