Pb-Sr-Nd-O Isotope Characteristics of Granitoids in East Kunlun Orogenic Belt

This paper reports Pb, Sr, Nd and O isotopic compositions of gabbro and granitoids formed in East Kunlun orogenic belt in Triassic. Granitoids and potassic feldspar have similar Pb isotopic compositions. Studies show that they were formed in an orogenic environment.Initial ( 87Sr/ 86Sr)t ratios range from 0.70144 to 0.70972,and eNd values from -4.49939 to -9.19258. Nd isotopic model ages (t DM) vary from 1.38 Ga to 1.761 Ga, being close to the age of mesoproterozoic metamorphic rocks. O isotopic compositions range from 7.8 to 9.5, indicating that the granitoids were derived from the crust. Based on all isotope data and mineralogical as well as petrochemical studies, it is held that the granitoids were mainly derived from the crust and mixed with the mantle-derived materials. The mixing process between the crust materials and the mantle-derived materials is responsible for the nearly identical isotope compositions.