Melting relations of a magnesian abyssal tholeiite and the origin of MORBs

摘要: Melting relations of a glassy magnesian olivine tholeiite from the FAMOUS area have been studied within pressure range 1 atm to 15 kbar. From 10 kbar, is liquidus phase, followed by plagioclase and Ca-rich clinopyroxene. Above clinopyroxene appears on liquidus, orthopyroxene spinel. Near olivine, orthopyroxene, clinopyroxene, spinel crystallize 10°C liquidus. This indicates that liquid this composition could coexist with mantle peridotite at about result in agreement geochemistry Ni; Ni concentration sample corresponds theoretical primary magma [14,15]. These data suggest least some mid-oceanic ridge basalts (MORBs) be melts segregated depths near transition zone between lherzolite (about kbar). Based model, residual after extraction MORBs should lherzolite, not harzburgite. High-pressure (7–10 kbar) fractionation models involving which proposed several workers (e.g. [36]) explain varieties MORBs, were re-emphasized based melting study. The rare occurrence as phenocryst phase explained precipitation chamber high pressure, or dissolution formed earlier pressure.