Geochemical Studies of Eclogites and from Sujiahe in the Western Dable Mountains

Abstract

The isotope compositions of hydrogen, oxygen, strontium and neodymium and the compositions of rare earth elements (REE) were measured on and/or whole-rocks from Xiongdian and Yangchong eclogites and Hujiawan garnet amphibolite in the Sujiahe district, the Mountains. δ 18O values of whole-rocks for the Xiongdian eclogites and Hujiawan garnet amphibolite are as high as +8.8 % to +11.2%, those for the Yangehong eclogite are as low as +4.3% The whole-rock δD from -55% to -75%. These results indicate the oxygen and hydrogen with seawater under both high and low temperatures. The Sr and Nd isotope compositions as well as REE distribution show that the Sujiahe eclogites resemble island arc basalts and thus were probably originated from subducted ancient oceanic crust between the Yangtze and Sino-Korean plates, Marbles occur as the country rocks of the eclogites in Sujiahe have lower δ 13C values (-2.6%- + 0.1%) than those from the eastern Dable Mountains (+ 0.5%-+5.7%). This indicates a difference in sedimentary environment between these marble protoliths (i.e. limestones), maybe due to a difference in their diagenetic ages. δ 18C values of from Xiongdian are as low as +2.% - +2.2%, suggesting a water-rock interaction with a low δ 18C fluid (probably ancient water) during and/or prograde metamorphism.