PTtD Path and Fluid Evolution of HighPressure Eclogites from the Dabie Mountains,Central East China

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PTtD Path and Fluid Evolution of High Pressure Eclogites from the Dabie Mountains, Central East China

In the Dabie high pressure (HP) and ultrahigh pressure (UHP) metamorphic belts, eclogites can be divided into two types, HP eclogites (or cold eclogite) and UHP eclogites. HP eclogites occur in the southern Dabie Mountains and are characterized by the presence of glaucophane. The primary mineral assemblage of the eclogites is garnet, omphacite, phengite, epidote, glaucophane, quartz, zircon and rutile. Garnet contains abundant mineral inclusions, and exhibits apparent compositional zoning with dramatic increases in MgO and decreases in MnO from core to rim. The PTtD path indicates that supracrustal rocks were metamorphosed and deformed from epidote amphibolite to eclogite facies by subduction and collision, then uplifted to the upper crust by thrust faulting in a continuous plate convergence and reworked by retrograde metamorphism of epidote amphibolite facies and by ductile deformation. The HP metamorphic rocks were uplifted to the surface, and modified by greenschist retrograde metamorphism and ductile to brittle deformation in an extensional environment. Fluid inclusions, melt inclusions and fluid bearing minerals indicate that fluid melt rock interaction was widespread in the eclogites. Partial melting occurred during the HP metamorphism, but the migration of melt was limited, and thus magma activity was very limited. Secondary fluid inclusions are abundant in the eclogites of the Dabie Mountains. They are mainly H 2O and CO 2 rich, and halite bearing multiphase fluid inclusions. Primary fluid inclusions have not been found, possibly because rapid uplift caused decrepitation of high density inclusions.