Geochemical studies of eclogites and marbles from Sujiahe in the western Dabie Mountains

Abstract

The isotope compositions of hydrogen, oxygen, strontium and neodymium and the compositions of rare earth elements (REE) were measured on mineral separates and/or whole-rocks from Xiongdian and Yangchong eclogites and Hujiawan garnet amphibolite in the Sujiahe district, the western Dabie 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 Yangchong eclogite are as low as +4.3‰. The whole-rock δD values range from -55‰ to -75‰. These results indicate that the eclogite precursors exchanged oxygen and hydrogen isotopes with ancient seawater under both high and low temperatures. The Sr and Nd isotope compositions as well as REE distribution patterns 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 and have lower δ 13C values (-2.6‰~+0.1‰) than those from the eastern Dabie 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 18O values of marbles from Xiongdian are as low as +2.0‰~+2.2‰, suggesting a water-rock interaction with a low δ 18O fluid (probably ancient meteoric water) during diagenetic and/or prograde metamorphism.