OXYGEN-ISOTOPE CONSTRAINTS ON FLUID-FLOW DURING ECLOGITIZATION IN THESULU TERRANE

The oxygen isotope study has been carried out for quartz-veins within eclogite and associated gneiss from the Donghai district in the wester n part of the Sulu terrane, eastern China. Oxygen isotope equilibrium has been achieved between quartz and other minerals, yielding the isot ope temperatures of 660-840 degrees C for quartz veins, 595-725 degree s C for eclogites, and 505-665 degrees C for gneiss. delta(18)O values of vein-quartz vary from -5.3 parts per thousand to +7.5 parts per th ousand, but resemble delta(18)O values of host eclogites, indicating a close approach of isotopic equilibrium between metamorphic fluids and the host rocks. An interally buffered fluid flow is implicated during ultrahigh-pressure metamorphism and subsequent retrogression. The flu id would be produced by dehydration of hydrothermally altered eclogite precursors and thus its delta(18)O values were governed by the nature of host eclogites. These provide evidence for the fracture flow of me tamorphic fluid during eclogitization.