Development of the continental crust deruced from deep subducted crustal materials

点击翻译按钮获取中文摘要

In 1996, PCI (High resolution Image capture system) was newly combined to the electron microscope in Kyoto Univ. This new tool improved the quality and precision of micron-scale texture analysis for deeply subducted continental materials. The detail texture analysis was performed for the deeply subducted crustal materials collected from Su-Lu belt, eastern China, Dora Maira massif, western Alps and Sanbagawa belt and it made clear following facts.1) Many UHP rocks in the middle and north parts of the Su-Lu belt experienced a granulite facies overprinting at lower crustal level, and the exhumation path from the upper mantle to the lower crust show an isothermal decompression path. The simple thermal calculation suggests that the UHP rocks should exhumed as a large mass more than 15km in diameter to prevent a loss or addition of heat from the wall rocks, even if it exhumed with fairly rapid speed of l0mm/y. This conclusion gives a strong constraint for the exhumation mechanism of the UHP rocks.2) The texture study of Dora Maira massif suggests that the deformation and accompanied fluid infiltration at upper crust pervasively erase precursor UHP evidence especially in quartz-feldsparthic rock rather than basic rocks.3) Our study and literature compile suggest that the granulite facies overprinting on UHP/HP rocks seems to be a common phenomenon in the continent collision belt and annealing at lower crust could be another candidate for obliterating the precursor UHP evidence. This causes a new problem to reevaluate the thermal history of the granulite region for the comprehensive study of the development of continent.