TY - JOUR
T1 - Partial melting experiments on a MORB-like pyroxenite between 2 and 3 GPa
T2 - Constraints on the presence of pyroxenite in basalt source regions from solidus location and melting rate
AU - Pertermann, Maik
AU - Hirschmann, Marc M
PY - 2003/2/10
Y1 - 2003/2/10
N2 - 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.% Al2O3). 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%/GPa and averages ∼59%/GPa through the melting interval, suggesting substantial partial melting deep in basalt source regions: G2 is ∼60% molten at the 3 GPa peridotite solidus. Small percentages of pyroxenite in the source significantly affect oceanic crust production and composition, as the proportion of pyroxenite-derived melt contributed to oceanic crust formation is 5 to >10 times the pyroxenite proportion in the source. Given the overall depleted isotopic character of mid-ocean ridge basalt (MORB), oversampling of fertile G2-like pyroxenite limits the abundance of such lithologies to ∼<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 (230Th)/(238U) in oceanic basalts without requiring marked shifts in other indicators of heterogeneity, such as Sr or Pb isotopes.
AB - 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.% Al2O3). 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%/GPa and averages ∼59%/GPa through the melting interval, suggesting substantial partial melting deep in basalt source regions: G2 is ∼60% molten at the 3 GPa peridotite solidus. Small percentages of pyroxenite in the source significantly affect oceanic crust production and composition, as the proportion of pyroxenite-derived melt contributed to oceanic crust formation is 5 to >10 times the pyroxenite proportion in the source. Given the overall depleted isotopic character of mid-ocean ridge basalt (MORB), oversampling of fertile G2-like pyroxenite limits the abundance of such lithologies to ∼<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 (230Th)/(238U) in oceanic basalts without requiring marked shifts in other indicators of heterogeneity, such as Sr or Pb isotopes.
KW - Eclogite melting
KW - MORB petrogenesis
KW - Pyroxenite melting
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M3 - Article
AN - SCOPUS:0037929696
SN - 2169-9313
VL - 108
SP - ECV 12-1 - 12-17
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - 2
ER -