Partial melting experiments on a MORB-like pyroxenite between 2 and 3 GPa: constraints on the presence of pyroxenite in basalt source regions from solidus locations and melting rate,

Abstract

[1] We present partial melting experiments at 2-3 GPa on a basaltic pyroxenite (G2) similar in composition to typical oceanic crust. The 3.0 GPa solidus is located at 1310 ± 12°C and the liquidus is 1500-1525°C. Clinopyroxene, garnet, quartz, and rutile are subsolidus phases. Garnet, quartz, and rutile are absent above 1475°C, 1365°C, and 1335°C, respectively. At the solidus, the garnet mode is low (18 wt.%) because clinopyroxene is unusually aluminous (13.8-15.5 wt.% Al 2 O 3 ). In adiabatically upwelling mantle near 2-3 GPa, G2-like pyroxenite begins melting 35-50 km deeper than peridotite. The calculated near-solidus adiabatic productivity for G2 is $13$59%/GPa through the melting interval, suggesting substantial partial melting deep in basalt source regions: G2 is $60$<2% of the MORB source. Owing to high extents of partial melting, the effect of modest amounts of pyroxenite on Sm/Yb ratios of aggregated basalts is limited and depends largely on the average bulk composition of the pyroxenite source. Low near-solidus adiabatic productivities could allow small ($1-2%) proportions of basaltic pyroxenite to enhance