Carbonated, alkaline hybridizing melts from a sub-arc environment: Mantle wedge samples from the Tabar-Lihir-Tanga-Feni arc, Papua New Guinea

Details Carbonated, alkaline hybridizing melts from a sub-arc environment: Mantle wedge samples from the Tabar-Lihir-Tanga-Feni arc, Papua New Guinea Carbonated, alkaline hybridizing melts from a sub-arc environment: Mantle wedge samples from the Tabar-Lihir-Tanga-Feni arc, Papua New Guinea

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.122..125m&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 122, no. 1/2, p. 125-141

Computer Science

22

Aluminum Silicates, Basalt, Earth Mantle, Geochemistry, Papua New Guinea, Subduction (Geology), Carbonates, Glass, Pyroxenes

Scientific paper

Xenoliths and xenocrysts from a high-K, alkaline arc volcano on Simberi Island, Papua New Guinea contain alkali-rich aluminosilicate glasses with crystals of calcite, anhydrite, sodalite and fluorapatite. The glasses are quenched equivalents of a Sulfate-, Carbonate-, H2O-, Alkali-Rich aluminosilicate Melt (SCHARM), similar to phonolite in composition, which is believed to have been derived from a subducted slab. At mantle pressures, SCHARM contained substantial dissolved F, Cl, Sr, Ba, H2O, CO3(2-) and SO4(2-), and had a high oxygen fugacity (f O2 is approximately FMQ + 4). SCHARM hybridized mantle peridotite, reacting with mantle minerals to produce a vertically zoned mantle wedge containing phlogopite-clinopyroxenite at P greater than 2 GPa, and amphibole-clinopyroxenite at lower pressure. REE patterns of the Simberi basalts show a negative Ce and a positive Eu anomaly, with an overall depletion in the HREE relative to LREE. Partial melting of a seawater-altered basalt slab, in which a feldspathic phase (possibly scapolite) contributes significantly to an early incremental liquid, could produce a sulfate-, carbonate-, H2O- and alkali-rich melt with a negative Ce and positive Eu anomaly. Preliminary results of experiments with anhydrous, calcite-bearing basalt, analogous to altered oceanic crust, shows that melting occurs at temperatures of 875 C at 1 GPa, and 975 C at 2 GPa to produce a carbonated, nepheline-normative melt with major element and dissolved CO2 contents similar to SCHARM, but more enriched in Fe and Mg.

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