Ages and compositions of the Precambrian high-grade basement of the Qilianterrane and its adjacent areas

Based on geological, chronological, geochemical and Nd isotopic studies of the high-grade basement of the Qilian terrane, the authors have drawn the f ollowing main conclusions: (1) the high-grade basement of the Qilian terran e consists mainly of meta-argillo-arenaceous rocks and granites and its bul k part was formed in the period of 0.8-1.0 Ga (the Jinningian period); (2) most of the meta-argillo-arenaceous rocks and granitic rocks have strong ne gative Eu and Ba anomalies (Eu/Eu*=0.47-0.71 and Ba/Ba*=0.16-0.64), with t( DM) and epsilon (Nd) (1.0 Ga) ranging from 1.87 to 2.26 Ga and from -8.54 t o -4.06 respectively, showing relatively high maturity; and (3) the Jinning ian granitic rocks are a typical product of continent-continent collision, being probably related to the formation of the supercontinent Rodinia. Thes e studies, combined with the study of high-grade basement rocks near the Qi lian terrane, suggest that before the Jinningian period, the Qilian-Qaidam northern-margin terrane and Dunhuang-Alxa terrane were separated from each other, belonging to different plate systems of the North China craton and Y angtze platform respectively. The Qilian orogenic belt was the same as or s imilar to the Qiling orogenic belt in terms of the geological evolution his tory at least before the Jinningian period.