LA-ICP-MS Zircon U-Pb Dating and Geochemical Characteristics of Kalajiareke Rock Mass in Northern Altay Orogenic Belt and Its Geological Significance

The Kalajiareke rock mass is composed of gneissic granite porphyry, with formation age of (450.6±3) Ma, which is the Late Ordovician intrusive rock. The geochemical data suggests that this rock mass belongs to peraluminous cal-alkaline rock series. It's inferred that the mantle-based magma is located at the bottom of the young mantle in the forming process of this intrusion, and a large amount of heat causes the overlying crust material to partially melt for forming the crust-mantle mixed granite magma. In the unsaturated water conditions, this intrusion was formed by the dehydration melting of rich muscovite and biotite metamorphic sandstone. The Ba, Nb, Sr and Ti elements show obvious negative anomalies, while the Rb, U, La, Nd, Zr, Hf and Y have positive anomalies. The loss of Nb is not obvious, but the K and Rb contents have a significant increase. All of these characters reflect the basic characteristics of collision granite. Rare earth elements show the enrichment of light rare earth and the loss of heavy rare earth, with not obvious fractionation of light and heavy rare earth and weak negative anomalies of Eu element. Combined with the tectonic evolution, it is believed that the Kalajiareke granite granodiorite porphyry was formed in the syn-collision subduction environment.