Geochemistry and Geological Significance of Intermediate-Acid Intrusive Rocks in Chaganganuo Area, East Kunlun

The Chaganganuo area is located in themiddle-east part of Qimantage Mountains, westernsectionof East Kunlun.The intermediate-acid intrusive rocks in this area are mainly granodiorite and adamellite intrusion, which are intruded into the Baishahe Group, varying from granodiorite to adamellite, with the increasing contents of SiO₂ (65.22%~72.42%) and the decreasing values of Al₂O₃ (14.90%~16.79%), CaO (1.97%~4.20%) and MgO (0.61%~2.00%). Their Rittman indexesrange from 1.41 to 2.02, and the total alkali contents of K₂O+Na₂O are 5.04%~8.8%, belonging to high-K calcium-alkali series.The total REE contents are moderate, with ΣREE values of 69.78×10^-6~148.9×10^-6, and their REE patterns show enriched LREE and no Eu anomaly. Rb and Th elements in rocks are quiterich, while Nb, Zr, Ce, Ta and Hf elements are rich, but Y element is weakly loss.LA-ICP-MS zircon U-Pb dating shows that the formation ages of these rocks are (246.8±1.7)Ma, which belong to Middle Triassic.The geological characteristics mentioned above indicate that these intermediate-acidic intrusive rocks are I-type granites.Combining with regional geological information, it's shown that a large number of dark microgranular enclave contained in these granitic rocks, with the evidence of obvious magma-mixing characteristics.In Middle Triassic, this area was experienced the conversion stage from the end of oceanic suduction to the beginning of collision orogeny.Thus, the discovery of these intrusive rocks has a great significance for the further study on tectonic magmatic beltand the evolution history in Qimantage area, East Kunlun.