Rock Composition And Elements Abundance Of The Deep Crust In Central Inner Mongolia, China

According to the published data of three crustal sections of trans-Inner Mongolia and related seismic sounding profiles, the structure of central Inner Mongolia’s deep crust is deciphered. The deep crust of all tectonic units could be divided into three parts,the middle crust, the upper part of lower crust and the lower part of lower crust.190 samples were selected in three crustal sections, the elastic wave velocities of 10 sample at high temperature and pressure were measured, and the major and trace elements were analyzed. Then we get the data of 48 elements. The velocitic features of deep crust in central Inner Mongolia region are: middle crust has P-wave velocities between 6.3 and 6.5km/s, the upper part of lower crust has P-wave velocities between 6.7 and 7.0km/s, the lower part of lower crust has P-wave velocities between 7.2 and 7.4km/s, the whole lower crust has P-wave velocities between 6.7 and 7.0km/s, and the whole crust has P-wave velocities between 6.3 and 6.5km/s. The lower crust and crust in central Inner Mongolia have lower P-wave velocities than that of average global crust. The data of deep crust in central Inner Mongolia and the elastic wave velocities of rock samples could be used to establish a deep crust model.The deep crust model indicates that the middle crust is composed dominantly of felsic gneiss and plagioclase amphibolites; the lower crust is composed dominantly of mafic granulite, intermediate granulite and plagioclase amphibolites. We could get the element abundance based on the deep crust model and the elements’data. Compared to other regions, the whole crust and lower crust in central Inner Mongolia are more mafic composition, lower in SiO2,K2O,Cs,Ba,Ta,and higher in TiO2,Feo,CaO . The P-wave velocities of the lower crust is similar to mafic granulite, the value of SiO2 in lower crust was 51% and coincided with the reputed mafic lower crust. The deep crust of central Inner Mongolia has several feature:(1) there are differences between east part of central Inner Mongolia and west part in composition. East part are higher in SiO2,K2O,Ba,Li,Zr,LREE and Lan/Ybn . (2) From north to south, the tectonic units in central Inner Mongolia have a characteristic:the values of SiO2, K2O andΣREE decreases gradually, the values of FeO, MnO and MgO gradually increased.(3) lower crust in Erdos depression is highest in SiO2,K2O,∑REE and Lan/Ybn, lower in MgO,MnO,Rb and Pb.