Melting Behaviour of Model Lherzolite in the System CaO–MgO–Al2O3–SiO2–FeO at 0·7–2·8 GPa

Fe–Mg exchange is the most important solid solution involved in for Fe–Mg exchange between the coexisting crystalline phases and melt, KdFe–Mg, show a relatively simple and predictable behaviour partial melting of spinel lherzolite, and the system CaO– MgO–Al2O3–SiO2–FeO (CMASF) is ideally suited to explore with pressure and temperature: the coefficients for olivine and spinel do not show significant dependence on temperature, whereas the this type of exchange during mantle melting. Also, if primary midocean ridge basalts are largely generated in the spinel lherzolite coefficients for orthopyroxene and clinopyroxene increase with pressure and temperature. When melting of lherzolite is modeled in the stability field by near-fractional fusion, then Na and other highly incompatible elements will early on become depleted in the source, CMASF system, a strong linear correlation is observed between the mg-number of the lherzolite and the mg-number of the nearand the melting behaviour of mantle lherzolite should resemble the melting behaviour of simplified lherzolite in the CMASF system. solidus melts. Comparison with melting in the CMASN system indicates that Na2O has a strong effect on lherzolite melting behaviour We have determined the isobarically univariant melting relations of the lherzolite phase assemblage in the CMASF system in the only at small degrees of melting. 0·7–2·8 GPa pressure range. Isobarically, for every 1 wt % increase in the FeO content of the melt in equilibrium with the lherzolite phase assemblage, the equilibrium temperature is lower