Crustal Differentiation Processes at Krakatau Volcano, Indonesia

Anak Krakatau is a basaltic andesite cone that has grown following the famous -forming 1883 eruption of Krakatau. It breached sea level in 1927 and since 1950s has been growing at an average rate of ~8 cm a week. We present new and trace element data combined with whole-rock 18O, Sr, and Nd isotope data 1883, 1993 and 2002 Krakatau eruptive products and the surrounding crust. erupted from Anak Krakatau during 2002 contain frothy meta-sedimentary plutonic xenoliths that show variable degrees of thermal metamorphism, plastic and partial melting. Contact-metamorphic minerals such as cordierite and in meta-sedimentary xenoliths are consistent with high-temperature and incorporation at mid- to upper-crustal depth. -constrained assimilation and fractional crystallisation (EC-AFC) modelling of -rock data suggests that the Anak Krakatau magmas have a genetic relationship the 1883 eruption products. The geochemical impact of crustal contaminants on -rock compositions is apparently small, and we conclude that low levels of of a quartzo-feldspathic sediment are recorded in Anak Krakatau magmas. phenocrysts from the 2002 eruption exhibit disequilibrium textures and compositional zoning, however, and are also isotopically variable with a range in 87Sr/86Sr of 0.7043 - 0.7048 as determined by in-situ LA-ICPMS. This that although shallow crustal assimilation appears to have had limited effect whole-rock chemistry, a complex late stage differentiation history is recorded the magma’s cargo of crystals and xenoliths.