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Coexisting High- and Low-Calcium Melts Identified by Mineral and Melt Inclusion Studies of a Subduction-Influenced Syn-collisional Magma from South Sulawesi, Indonesia |
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| Authors: | ELBURG MARLINA; KAMENETSKY VADIM S; NIKOGOSIAN IGOR; FODEN JOHN; SOBOLEV ALEXANDER V |
| Institution: | 1 MAX PLANCK INSTITUTE FOR CHEMISTRY, GEOCHEMISTRY DIVISION MAINZ, 55020, GERMANY 2 FACULTY OF EARTH AND LIFE SCIENCES, DEPARTMENT OF ISOTOPE GEOCHEMISTRY, FREE UNIVERSITY AMSTERDAM, 1081 HV, THE NETHERLANDS 3 DEPARTMENT OF GEOLOGY AND SOIL SCIENCE, GHENT UNIVERSITY KRIJGSLAAN 281 S8, 9000 GHENT, BELGIUM 4 SCHOOL OF EARTH SCIENCES AND CODES SRC, UNIVERSITY OF TASMANIA HOBART, TAS 7001, AUSTRALIA 5 FACULTY OF GEOSCIENCES, UTRECHT UNIVERSITY UTRECHT, 3508 TA, THE NETHERLANDS 6 DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF ADELAIDE ADELAIDE, SA 5005, AUSTRALIA |
| Abstract: | Mineral and melt inclusions in olivines from the most Mg-richmagma from the southern West Sulawesi Volcanic Province indicatethat two distinct melts contributed to its petrogenesis. Thecontribution that dominates the whole-rock composition comesfrom 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 0·2–0·30wt %) and clinopyroxene. The other component is richer in SiO2(>50 wt %) and Al2O3 (19–21 wt %), but contains significantlyless CaO (<4 wt %); it is in equilibrium with Cr-rich spinelwith a low TiO2 content, olivine with low CaO and high NiO content(Fo90–94; CaO 0·05–0·20 wt %; NiO0·35–0·5 wt %), and orthopyroxene. Boththe high- and low-CaO melts are potassium-rich (>3 wt % K2O).The high-CaO melt has a normalized trace element pattern thatis typical for subduction-related volcanic rocks, with negativeTa–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), butits trace element pattern resembles that of the whole-rock andhigh-CaO melt in other respects, suggesting only small distinctionsin source areas between the two components. We propose thatthe depth of melting and the dominance of H2O- or CO2-bearingfluids were the main controls on generating these contrastingmagmas in a syn-collisional environment. The composition ofthe low-CaO magma does not have any obvious rock equivalent,and it is possible that this type of magma does not easily reachthe Earth's surface without the assistance of a water-poor carriermagma. KEY WORDS: melt inclusions; mineral chemistry; olivine; syn-collisional magmatism; ankaramites; low-Ca magma |
| Keywords: | : melt inclusions mineral chemistry olivine syn-collisional magmatism ankaramites low-Ca magma |
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