太平洋北西縁の藍閃石片岩変成作用

抄録

There are distinct three ages of the glaucophanitic metamorphism in this region from Chukotok to Taiwan; that is, the late-Paleozoic (Devonian-Carboniferous), early- to middle-Mesozoic, and late-Mesozoic. The glaucophane-schist metamorphic belts of the Chukotok-Kamchatka are the Penjinsky belt of the late-Paleozoic, the Pekurinei-Vaejusky and Ganarsky belts of the early- to middle-Mesozoic, and the Karaginsk-Kuronotsuky belt of the late-Mesozoic. They are respectively accompanied by the later metamorphism of the prehnite-pumpellyite facies. For example, the Penjinsky belt of about 330m.y. age has been superimposed by the metamorphism of prehnite-pumpellyite facies of about 180 m.y. age.
The glaucophane schist metamorphic belts of the Japanese islands are the Sangun and the Matsu-gadaira-Motai belts of the late-Paleozoic and the Sanbagawa and Susunai-Kamuikotan belts of the early-middle Mesozoic. They have been also superimposed by the later metamorphism of the prehnite-pumpellyite facies. That of the Taiwan-Ryukyu islands is the Yuli-Ishigaki belt of the early- to middle-Mesozoic.
In these glaucophanic metamorphic belts, dunite-harzburgite series of ultrabasic rock bodies (H-series) or dunite-wehrlite series of ultrabasic rock bodies (W-series) occur, but dunite-lherzolite-pla-gioclase-lherzolite series bodies (L-series) never occurs. Moreover, in one glaucophanitic metamorphic belt only one ultrabasic rock series occurs; for example, W-series in the Sanbagawa, H-series in the Susunai-Kamuikotan and so on. If ultrabasic rocks are the early crystallization products from basaltic melts, the phase diagram of the Di-En system tells us that the H- or W-series may be formed under high pressure in such a belt of gentle thermal gradient as glaucophanitc belts. The L-series may be formed under the region of steep thermal gradient. However, it is not known why the difference of H- and W-series appears in the glaucophane schist metamorphic belts.