Preservation and retrogression of ultra high pressure (UHP) rocks: case studies of UHP metagranitoids in Western Alps and Su-Lu region

• Main Author: Takao Hirajima
• Format: Report
• Language: English
• Published: Department of Geology and Mineralogy, Graduate School of Earth Science, Kyoto University 1998
• Subjects: ultra high pressure rock; retrogression of metagranitoid; granulite facies over printing; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2337; http://id.nii.ac.jp/1291/00002337/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2337&item_no=1&attribute_id=18&file_no=1

The in situ association of ultra high pressure (UHP) rocks and country gneiss, and possible mechanisms to obliterate the UHP metamorphic minerals during exhumation will be discussed for giving a new insight to a debate between in situ vs. external origin of UHP rocks. The UHP rocks associated with UHP metagranitoids found in southern Dora Maira massif, western Alps and the Yangkou unit in the Su-Lu region, eastern China are distinct examples of the in situ origin. The deformation and accompanied fluid infiltration at lowpressure conditions pervasively erased the precursor UHP evidence without a significant heating in these areas. Granulite facies overprinting on UHP/HP metamorphic rocks is reported in some UHP terranes. Annealing at medium temperature and low-pressure conditions could be another candidate for obliterating the UHP metamorphic minerals pervasively.