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RESEARCH PRODUCT

The composition of near-solidus melts of peridotite in the presence of CO2 and H2O between 40 and 60 kbar

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Abstract Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H2O and 2.0–3.2 wt.% CO2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46–0.53, which fall to  30 wt.%) and Al2O3 (  9 wt.%) and concomitant decrease in CaO (> 20 to Partial melts of peridotite with CO2 and H2O are too low in MgO to resemble kimberlites, but will act as effective metasomatic agents enriching the lithosphere in K and carbonates, of relevance for ultramafic lamprophyres and kamafugites. Higher-degree melts (15–35%) have > 20 wt.% SiO2, are only mildly enriched in trace elements, and will not cause large time-integrated isotopic in-growth except over long geological time intervals. The temperature interval over which melts are carbonatitic with SiO2 contents