[S-GC38] 固体地球化学・惑星化学

[SGC38-05] Geochemical insights into Sunda Arc magmas genesis: To melt or not to melt?

*Esti Handini¹、Toshiaki Hasenaka²、Takashi Sano³、Nicholas Dewitt Barber⁴、Hikaru Iwamori⁵、Masataka Kawaguchi⁵、Prya Arif Rahman¹ (1.Geological Engineering Department, Universitas Gadjah Mada、2.Center for Water Cycle, Marine Environment, and Disaster Management, Kumamoto University、3.National Museum of Nature and Science, Tokyo 、4.Department of Earth and Environmental Geoscience, Washington & Lee University、5.Earthquake Research Institute, The University of Tokyo)

キーワード：Sunda arc geochemistry, Slab derived component, Machine learning

Fluid fluxing vs melting has always been the center of debate in the arc magmas generation and the subsequent slab-depth dependent material transfer. To further understand this, we: (1) collate 1740 geochemical data from along Sunda arc and run the clustering algorithm and (2) report new slab compositions from IODP sites 211 and 261 which are in the south of central and eastern part of the arc. We simulate the trace element compositions in the fluid, melt, and supercritical fluid phases to evaluate whether each geochemical cluster exhibits distinct affinities for specific slab components. Our result shows that the magma clustering is independent of subduction geometry and slab depth. The mafic-felsic (MgO-FeO-CaO-TiO₂-MnO vs SiO₂-Na₂O) differentiation trend is the main control of most calc-alkaline volcanics. The alkalines of Sunda Arc appear to be strongly controlled by K₂O-P₂O₅-Al₂O₃. The alkalines of eastern Sunda are clustered together with the calc-alkalines, while Muria and Ringgit-Beser form a distinct cluster. All samples are in the mixing line between depleted mantle and the dehydrated basalts from site 211. Most volcanics, except from East Java segment, show closest association with the radiolarian clay from either site 211 or 261; suggesting that the carbonate rich sediment from site 261 shows little influence on eastern Sunda magmas. Furthermore, the model indicates that sediment plays a significant role in the generation of these magmas; however, the specific carrying agents remain unclear and appear to have a limited impact on the process.