Coexisting High- and Low-Calcium Melts Identified by Mineral and Melt Inclusion Studies of a Subduction-Influenced Syn- collisional Magma from South Sulawesi, Indonesia

Mineral and melt inclusions in olivines from the most Mg-rich magma from the southern West Sulawesi Volcanic Province indicate that two distinct melts contributed to its petrogenesis. The contribution that dominates the whole-rock composition comes from a liquid with high CaO (up to 16 wt %) and low Al2O3 contents (CaO/Al2O3 up to 1), in equilibrium with spinel, olivine (Fo85–91; CaO 0.35–0.5 wt %; NiO 0.2–0.30 wt %) and clinopyroxene. The other component is richer in SiO2 (>50 wt %) and Al2O3 (19–21 wt %), but contains significantly less CaO (<4 wt %); it is in equilibrium with Cr-rich spinel with a low TiO2 content, olivine with low CaO and high NiO content (Fo90–94; CaO 0.05–0.20 wt %; NiO 0.35–0.5 wt %), and orthopyroxene. Both the high- and low-CaO melts are potassium-rich (>3 wt % K2O). The high-CaO melt has a normalized trace element pattern that is typical for subduction-related volcanic rocks