Reconstruction Of Deformation And Metamorphism During Subduction-Exhumation Of Eclogites/Peridotites In Sulu Ultra-high Pressure Metamorphic Terrain

Abundant information of deformation and metamorphism are preserved in the eclogites and peridotites from the 0～800m-deep main borehole of the Chinese Continental Scientific Drilling Project (CCSD) in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The present thesis investigates them individually in detail and then focus on the interaction between them. Combining field, optical, TEM observations, EBSD measurements for texture and microstructure with investigations metamorphism characteristics of eclogites and peridotites, the P-T-t-D path has been reconstructed which includes 6 stages of deformation and metamorphic process: 1) metamorphic-tectonic differentiation during subduction corresponding to prograde metamorphism, 2) strongly plastic rheologic deformation by recovery-accommodated dislocation creep at the peak metamorphic conditions, 3) dynamic recrystallization characterized by porphyroclast with serrated boundary surrounding by a mosaic of polygonal fine-grains active during coesite eclogite-face retrograde metamorphism at the initial exhumation stage, 4) static recrystallization and growth facilitated from a short low-stress and high-temperature interval corresponding to quartz eclogite-face retrograde metamorphism in the early exhumation stage, 5) slow extrusion along the penetrative shear zones at the main exhumation stage with amphibolite and epidote amphibolite-face retrograde metamorphism and 6) transition from ductile to brittle deformation at the post-exhumation extension stage with green schist-face retrograde metamorphism.The interaction between deformation and metamorphism ran through the whole process from subduction to exhumation. In addition to the band structure benefited from the metamorphic-tectonic differentiation, there are other two typical examples else, i.e. the distribution of phlogopite and enstatite and their coarser-grain features at the touch boundary between eclogites and peridotites, and the occurrence of zircons in peridotites which is characterized by Si dissaturation. All of those phenomena are facilitated from the interaction among different deformation mechanisms, metamorphic reactions and fluid actions. Specially depend on those relationship, it is concluded that there is a short low-stress and high-temperature phase between the first-stage fast exhumation driven by buoyancy and the second-stage slow uplift driven by compression-shear-stress induced probably by the synchronous TanLu strike-slip fault.