上部マントルにおけるマグマの形成過程：マントル物質科学における近年の展開

Abstract

Recent developments in studies on the generation of magmas in the upper mantle are reviewed in this paper. This review focuses on mid-ocean ridges, where melting processes are believed to be simpler than those in other tectonic environments, thereby facilitating extensive application of clear-cut models. There are, however, still fundamental unsettled issues in magma generation beneath mid-ocean ridges. They are : (1) depth of initial melting, (2) depth of final melting, (3) style of melt transportation, (4) initial source composition, and, (5) heterogeneity. An attempt is made to clarify these points on the basis of petrologic and geochemical studies on abyssal peridotites and mid-ocean ridge basalts (MORB). A change in the style of melt transport from near fractional (chemical isolation) to near batch (permeable flow) melting is necessary to reconcile the observed behavior of major and trace elements in abyssal peridotites, suggesting the importance of resolving the melting history for each peridotite that has kept its own identity throughout the melting processes.