Melt compositions in pyroxenites M5–103, M5–40, and M7–16 at 1 GPa plotted as a function of temperature.
The temperature interval of 1245–1305 °C represented by yellow boxes corresponds to the range of temperatures (at 1 GPa) of a mantle undergoing adiabatic decompression melting (assuming potential temperatures in the range 1280–1400 °C, McKenzie and Bickle (1988)). Symbols are as follows: diamonds, M5–103; triangles, M5–40; squares, M7–16. Green fields correspond to liquids produced by peridotites PHN1611, MM3, DMM1 and Depma. Error bars (1σ on oxide concentrations; ±5 °C on temperature) are shown in the bottom right corner of each diagram.
Main result from this study: (1) Most of pyroxenites produce liquids that are similar to peridotite-derived melts for most major elements (SiO2, Al2O3, CaO, MgO, and FeO). This may explain why MORB have relatively uniform major-element compositions, but may have variable trace element and isotopic compositions. (2) Pyroxenite melts are not enriched (and may even be depleted) in incompatible elements (Na2O, TiO2 and K2O) in comparison to peridotite-derived melts. Therefore, the concentrations of these elements cannot be used as markers of pyroxenites in MORB mantle sources. (3) Some pyroxenites yield melts with a distinct signature, such as a low-SiO2 content and/or a high FeO content, two features usually ascribed to a high average pressure of melting (of a peridotitic source).

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