ND-ISOTOPE CONSTRAINTS ON ORIGIN OF GRANITOIDS IN BEISHAN MOUNTAIN AREA

Abstract

Located in the central-east part of the Central Asian Orogenic Belt (CAOB), the granitoids are widely distributed in Beishan Mountain area, with an outcrop area more than 30,0000 km2. The Nd isotope of the granitoids, however, lacks systematic study. Based on the previous geological work, a large number of granitoid samples are carried on the Sm-Nd isotopic analysis. The results show that the ε Nd(t) values of these granitoids occurred in Beishan Mountain area range from -16.39 to +10.89, some of which are characterized by the positive εNd(t) value. It suggests that the crustal growth existed during Phanozoic in Beishan Mountain area, just like other regions in the CAOB. Comparing with those in northern Xinjiang, eastern Inner Mongolia and Great Hinggan, the granitoids in Beishan Mountain area have much larger range of eNd(t) values, and are more negative, which may be related to the voluminous Precambrian metamorphic rocks exposed in this area.