三波川エクロジャイトの沈み込みP-T経路の導出とそのテクトニックな意味付け : 包括的岩石学への布石として

概要

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In general, derivation of subduction-stage P-T (pressure-temperature) paths for high-P metamorphic rocks is difficult, because in most cases they are affected by subsequent metamorphism, during which the pre-peak P mineral assemblages are significantly modified. However, petrological studies during the last 10 years in the Sambagawa belt have recognized unusually well-constrained sections of the subduction-stage P-T path. In particular, derivation of the subduction-stage P-T path of the Kotsu glaucophane eclogite was backed-up by insights obtained from a combination of petrological and structural analyses. Application of a new thermal model shows that the derived subduction-stage P-T paths are most likely to have been generated in a setting where an active spreading ridge is close to being subducted. This tectonic interpretation suggests that exhumation of high-P/T metamorphic rocks in oceanic subduction zones is triggered by regional heating events such as ridge subduction. A review of recent studies on the Sambagawa belt indicates the significance of promoting a comprehensive petrology, which encompasses the full set of constraints provided by disciplines such as petrology, structural geology, geochronology and thermal modeling.
社団法人東京地学協会の論文
2004-10-25