Hydrogen and oxygen isotope geochemistry of high to ultrahigh pressure metamorphic rocks from Southeast Dabie.

The hydrogen and oxygen isotope compositions of single minerals and whole-r ock were measured for coesite-hearing eclogite at Shima and quartz-bearing eclogite at Huangzhen in southeastern Dabie. The delta O-18 values of the e clogites vary from 1.0 to 7.4 parts per thousand at Shima but from -2.1 to 1.3 parts per thousand at Huangzhen; the deltaD values of micas from the ec logites are -79 to -61 parts per thousand at Shima and -89 to -77 parts per thousand at Huangzhen. Hydrogen and oxygen isotope fractionations between the minerals are in both equilibrium and disequilibrium, indicating that th e eclogites have not only inherited the O-18-depletion feature of their pro toliths, but also experienced strong retrograde alteration during exhumatio n. Oxygen isotope temperatures of the eclogite mineral-pairs are cumulated at two peak values of 600 to 640 degreesC and 380 to 430 degreesC, respecti vely, corresponding to retrograde reequilibration at greenschist-facie and high amphibolite-facies conditions; the peak eclogite-facies temperatures o f 750 to 800 degreesC cannot be retrieved due to the strong retrograde alte ration. The high and ultrahigh pressure rocks in southeastern Dabie are geo logically separated by the quartz-bearing eclogite and granitic gneiss, but the oxygen isotope analyses indicate an in situ relationship between the t wo rocks.