Zircon SHRIMP U-Pb dating of granites from the Da Qaidam area in the north margin of Qaidam basin, NW China

The granites associated with ultra-high-pressure rocks are very developed in Da Qaidam area which is an important part in the early Paleozoic UHP belt of the north margin of Qadaim Basin, NW China. Two types of granites in the area can be divided based on their petrology and geochemistry. The first type of the granite is characterized by the ratio of Na2O/K2O to be less than 1, obvious negative Eu abnormal, and very low Sr and high Y content, having an affinity like the S-type granite and the other type is by the ratio of Na2O/K2O to be larger than 1, no negative Eu abnormal to positive Eu abnormal, and very higher Sr and low Y content, like the I-type granite, indicating the differences in their protolith and origin. The zircon SHRIMP U-Pb dating shows that the ages of the granites in Da Qaidam area can be divided into three groups, that is (1) 446.3 +/- 3.9Ma, (2) 408.6 +/- 4.4Ma, 403.3 +/- 3.8Ma and 401.8 +/- 3Ma, (3) 374.5 +/- 1.6Ma and 372 +/- 2. 1 Ma. Combined with regional geological characteristics, we think that the first group of ages represents the collision time between Qaidam continental plate and middle-southern Qilian plate, the second group the delemination time and the last stretch of different blocks after plate collisional upheaving.