Abstract
The upper Paleozoic Yakuno ophiolite in the Asago body, southwest Japan exposes a 3.0 km-thick middle to lower crustal section of intra-oceanic island arc, which is composed of metabasites (metagabbro and schistose amphibolite) of MORB-like affinity and granitoid intrusives of island arc affinity (Hayasaka, 1990; Suda, 2004). Mafic migmatite develops in the lower crustal section, whereas the granitoid intrusives forming plutons and dykes develop in the middle crustal section. Mmorphological change of the migmatite with increasing structural level suggests the melt segregation process. Small-scale primary melt formed at the lowermost horizon (metatexite migmatite), which moved upward, accompanied by increasing degree of melt segregation (melt-enriched migmatite), and finally led to the formation of plutons.
