Crustal differentiation processes at Krakatau volcano, Indonesia

Gardner, M.F., Troll, V.R., Gamble, J.A., Gertisser, R., Hart, G.L., Ellam, R.M. , Harris, C. and Wolff, J.A. (2013) Crustal differentiation processes at Krakatau volcano, Indonesia. Journal of Petrology, 54(1), pp. 149-182. (doi: 10.1093/petrology/egs066)

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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 18O, 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 meta-sedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism, plastic deformation and partial melting. Contact-metamorphic minerals such as cordierite and tridymite in meta-sedimentary xenoliths are consistent with high-temperature metamorphism and incorporation at mid- to upper-crustal depth. Energy-constrained assimilation and fractional crystallisation (EC-AFC) 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 LA-ICPMS. This suggests that although shallow crustal assimilation appears to have had limited effect on whole-rock chemistry, a complex late stage differentiation history is recorded within the magma’s cargo of crystals and xenoliths.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Ellam, Professor Rob
Authors: Gardner, M.F., Troll, V.R., Gamble, J.A., Gertisser, R., Hart, G.L., Ellam, R.M., Harris, C., and Wolff, J.A.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of Petrology
Journal Abbr.:J. petrology
Publisher:Oxford University Press
ISSN (Online):1460-2415

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