http://eprints.utas.edu.au/424/ Coexisting high- and low-calcium melts identified by mineral and melt inclusion studies of a subduction-influenced syn-collisional magma from South Sulawesi, Indonesia Elburg, MA Kamenetsky, VS Nikogosian, I Foden, JD Sobolev, AV 260101 Mineralogy and Crystallography 260300 Geochemistry 260102 Igneous and Metamorphic Petrology 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, with negative Ta-Nb and Ti anomalies, positive K, Pb and Sr anomalies, and a relatively flat heavy rare earth element (HREE) pattern. The low-CaO melt shows Y and HREE depletion (Gdn/Ybn 41), but its trace element pattern resembles that of the whole-rock and high-CaO melt in other respects, suggesting only small distinctions in source areas between the two components. We propose that the depth of melting and the dominance of H2O- or CO2-bearing fluids were the main controls on generating these contrasting magmas in a syn-collisional environment. The composition of the low-CaO magma does not have any obvious rock equivalent, and it is possible that this type of magma does not easily reach the Earth's surface without the assistance of a water-poor carrier magma. 2006-12 Article PeerReviewed application/pdf http://eprints.utas.edu.au/424/1/JPet47-Sulawesi.pdf http://dx.doi.org/doi:10.1093/petrology/egl050 Elburg, MA and Kamenetsky, VS and Nikogosian, I and Foden, JD and Sobolev, AV (2006) Coexisting high- and low-calcium melts identified by mineral and melt inclusion studies of a subduction-influenced syn-collisional magma from South Sulawesi, Indonesia. Journal of Petrology, 47 (12). pp. 2433-2462. ISSN 0022-3530 http://eprints.utas.edu.au/424/http://eprints.utas.edu.au/424/1/