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 presum ably rapid, though at an uncertain rate, to retain coesite, diamond and alp ha -PbO2-type TiO2. Here we report unique defect microstructures of mineral s as a potential indicator of a rapid and episodic exhumation process in a fossil fracture zone of coesite eclogite from the Sulu terrain, eastern Chi na having the most negative delta O-18 value ever reported for eclogite-fac ies metamorphic rock. Analytical electron microscopy indicates that semi-br ittle deformation occurred in kyanite/omphacite/spinel with extensive and u nusual fine-scale twin lamellae and that brittle deformation occurred in ga rnet with hardly healed {110} microcleavages. These unique defect microstru ctures can be rationalized by a high strain rate at local weakening and dee p faulting of continental collision orogens. (C) 2001 Elsevier Science B.V. All rights reserved.