Defect microstructures of minerals as a potential indicator of extremely rapid and episodic exhumation of ultrahigh-pressure metamorphic rock: implication to continental collision orogens

Exhumation of subducted continental crust to the Earth’s surface was presumably rapid, though at an uncertain rate, to retain coesite, diamond and α-PbO2-type TiO2. Here we report unique defect microstructures of minerals as a potential indicator of a rapid and episodic exhumation process in a fossil fracture zone of coesite eclogite from the Sulu terrain, eastern China having the most negative δ18O value ever reported for eclogite-facies metamorphic rock. Analytical electron microscopy indicates that semi-brittle deformation occurred in kyanite/omphacite/spinel with extensive and unusual fine-scale twin lamellae and that brittle deformation occurred in garnet with hardly healed {110} microcleavages. These unique defect microstructures can be rationalized by a high strain rate at local weakening and deep faulting of continental collision orogens.