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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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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

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Abstract

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.

Item Type: Article
Keywords: melt inclusions; mineral chemistry; olivine; syn-collisional magmatism; ankaramites; low-Ca magma
Journal or Publication Title: Journal of Petrology
Page Range: pp. 2433-2462
ISSN: 0022-3530
Identification Number - DOI: 10.1093/petrology/egl050
Additional Information: http://petrology.oxfordjournals.org/cgi/content/abstract/47/12/2433?etoc
Date Deposited: 24 Nov 2006
Last Modified: 18 Nov 2014 03:12
URI: http://eprints.utas.edu.au/id/eprint/424
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