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Crustal differentiation processes at Krakatau volcano, Indonesia

Gertisser, Ralf

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Abstract

Anak Krakatau is a basaltic andesite cone that has grown following the famous caldera-forming 1883 eruption of Krakatau. It breached sea level in 1927 and since the 1950s has been growing at an average rate of ~8 cm a week. We present new major and trace element data combined with whole-rock d18O, Sr and Nd isotope data for 1883, 1993 and 2002 Krakatau eruptive products and the surrounding crust. Bombs erupted from Anak Krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism, plastic deformation and partial melting. Contact-metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high-temperature metamorphism and incorporation at mid- to upper-crustal depth. Energy-constrained assimilation and fractional crystallization modelling of whole-rock data suggests that the Anak Krakatau magmas have a genetic relationship with the 1883 eruption products. The geochemical impact of crustal contaminants on whole-rock compositions is apparently small, and we conclude that low levels of assimilation of a quartzo-feldspathic sediment are recorded in Anak Krakatau magmas. Plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning, however, and are also isotopically variable with a total range in 87Sr/86Sr of 0·7043–0·7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry. This suggests that although shallow crustal assimilation appears to have had a limited effect on whole-rock chemistry, a complex late-stage differentiation history is recorded within the magma’s cargo of crystals and xenoliths.

Citation

Gertisser, R. (2013). Crustal differentiation processes at Krakatau volcano, Indonesia. Journal of Petrology, 149 - 182. https://doi.org/10.1093/petrology/egs066

Journal Article Type Article
Acceptance Date Aug 30, 2012
Publication Date 2013-01
Publicly Available Date May 26, 2023
Journal Journal of Petrology
Print ISSN 0022-3530
Publisher Oxford University Press
Pages 149 - 182
DOI https://doi.org/10.1093/petrology/egs066
Keywords Anak Krakatau plagioclase crustal xenoliths assimilation and fractional crystallization isotope micro-analysis
Publisher URL https://doi.org/10.1093/petrology/egs066

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