Static stage of exhumation of metamorphic rocks recorded in garnets: Evidence of EBSD-EPMA mapping

Fabrics of various scales observed in the regional metamorphic rocks, such as fold, lineation, and crystallographic preferred orientation of minerals, show that the regional metamorphism is a dynamic process. Combination of X-ray EPMA mapping and EBSD analysis provide us the valuable data of the growth and deformation process of minerals. Whitney et al. (2008_Journal of Metamorphic Petrology) and Whitney and Seaton (2010_Contributions to Mineralogy and Petrology) reported the polycrystalline garnet porphyroblasts in the several metamorphic rocks and discussed the prograde multiple nucleation and coalescence of the garnet polycrystals. On the other hand, Enami et al. (2017_American Mineralogist) reported the examples of the clustered garnet that preserves the similar crystallgraphic orientation during exhumation stage. They interpreted that the garnet did not experience the dynamic deformation after the segmentation of the garnet and may have been exhumed under static conditions. In this study, we will show three examples of the EBSD-EPMA mapping of the garnet grains from the Sanbagawa high-pressure belt, Japan, the Sulu ultra-high pressure belt, China, and the Mogok high-temperature belt, Myanmar. The microstructure and EPMA mapping of these garnets show the segmentation during the exhumation. On the other hand, in the EBSD analysis, garnet grains preserve a nearly common crystal orientation and does not show the evidence of dynamic deformation during the exhumation stage. We consider that a relatively static environment is common at some period of the exhumation stage in several metamorphic belts.