[SMP41-P11] Petrological and Geochemical Study of Sundoro Volcano, Central Java, Indonesia: Temporal Variations in Differentiation and Source Processes in the Growth of an Individual Arc Volcano
Keywords:Sunda arc, Temporal variation, Multiple magmas, Slab contribution, Sundoro volcano
Against progressive silica content, evolution trend of the three magma types are separated: relatively parallel to each other in 87Sr/86Sr, ratios of Ba/Zr, and La/Yb, diverge in ratios of Th/Yb, and discretely varied in Pb-isotope. Combination of these discrete geochemical evolution trends with petrographic disequilibrium features and wide-range bimodal compositions of plagioclase crystal core (An46-94) suggest that 1) magma mixing is dominant process in intra-crustal level. 2) The three magma types correspond to mixing of three distinct couples of mafic- and felsic-end member magmas. 3) The felsic end-member magma cannot be produced from fractionation of corresponding mafic end-member magma and might come from different melt source. 4) The three mafic-end member magmas are not related co-genetically, thus relative correlation of their mafic rocks might represent magma source characteristics.
Trace elements as proxies of slab contributions (e.g. Ba/Zr, Th/Yb, La/Yb) of the representative mafic rocks of the three magma types show positive correlation to Sr- and Pb-isotopic compositions but negative to Nd-isotopic ratios. We proposed that magma of A-, B-, and C-type corresponds to three distinct slab-derived fluxes containing sediment-derived melt contributions approximately 50%, 55%, and 60%, respectively, which were added to the mantle wedge in a rates of ~1%, ~1.5%, and ~2%, respectively. Temporal variations of the magma type shows the existence of A-type in 20-9 ka, co-existence of A- and B-type in 14-17 ka, and abrupt change from A- to C-type after 9 ka. Reconstruction of the supply magma system in these periods indicate that time interval between the three slab-derived fluxes is about 3-8 ky and shows increasing portion of sediment contribution and rate of slab-fluxes through time. Further application of these approaches to dataset of Merapi volcano revealed increasing rate of slab-derived flux to the magma genesis beneath volcanic front region of central part of Java through time.