Carbonated-fluxed melting of MORB-like pyroxenite at 2·9GPa and genesis of HIMU ocean island basalts

We present partial melting experiments on a carbonate-added, mid-ocean ridge basalt (MORB)-like pyroxenite composition (G2C; 5 wt % CO2). Experiments were conducted at 2·9 GPa and 1000^15008C and the resulting partial melt compositions were compared with those of alkalic ocean island basalts (OIBs). The solidus is estimated between 1000 and 10508C and the liquidus is between 1450 and 14758C. The subsolidus assemblage is cpxþgarnetþ rutileþ calcio-dolomitic solid solution, and the near-solidus melt is carbonatitic (55 wt % SiO2, 51·3 wt % TiO2,50·5 wt % Al2O3, 31wt %5CaO525 wt %). At 1245^ 12758C, with the disappearance of rutile, a carbonated basaltic melt is found to coexist with carbonatitic melt, cpx, and garnet.The sili-cate melts are alkalic basalts with SiO2 of 44^47 wt % on a volatile-free basis, and the melt becomes most silica-poor and CO2-rich at the temperature of complete mixing of carbonate and sili