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

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  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 < 10 wt.% narrows with increasing pressure from 30– 60 kbar, meaning that the metasomatic effects of carbonatitic melts may be greatest at 20–30 kbar.