EVOLUTION OF THE SAMBAGAWA METAMORPHIC BELT, JAPAN

The high-pressure Sambagawa metamorphic belt evolved within a Mesozoic accretionary prism that developed in the convergent margin along the east of the Eurasian continent. Although extensively researched, recen t studies in this region have revealed a number of important features that allow more complete reconstruction of the tectonic history. (i) T he grouping of radiometric ages suggests the existence of three major structural units with distinct metamorphic histories. One of these has since been completely eroded away. (ii) The differences of ages recor ded by different minerals is, in many cases, small suggesting rapid ex humation after reaching peak metamorphic conditions. (iii) The dominan t ductile deformation of the Sangabawa belt representing major orogen- parallel flow is commonly related to retrograde metamorphic reactions. This shows that the associated fabric developed during exhumation not subduction. (iv) Kinematic studies suggest that the ductile deformati on caused major ductile thinning of the region which was probably a si gnificant factor in causing exhumation of the region.