Geochemical characteristics and geochronology research of diopside syenite and diopside granite of Kuzigan, Taxkorganin Ailaoshan-Jinshajiang

Kuzigan rock mass is the largest alkaline complex in the Taxkorgan region. The rocks are rich in alkali (Na₂O+K₂O=9.12% 12.55%), potassium (Na₂O/K₂O=0.39% 0.76%) and calcium (CaO=1.62% 9.77%). And the large-ion lithophile elements (LILE, Rb, Ba, Th, U and Sr) and Pb are also enriched while the high field strength elements (HFSE, Nb, Ta, Zr, Hf and Ti) are deficient.Rare earth elements (REE) content ranges from 372.37×10^-6 to 1218.07×10^-6. The ratio of LREE/HREE is relatively high (20.83 37.36), and it has weak negative anomaly of δEu (0.66 0.84). The REE distribution pattern shows the rocks are rich in LREE, and the curve of HREE is relatively flat. Electron probe micro analysis reveals pyroxenes in Kuzigan alkaline compound massif are rich in Ca and poor in Na, thus they are mainly diopsides, and Kuzigan alkaline compound massif consist of diopside syenite and diopside granite. LA-ICP-MS U-Pb dating and SHRIMP U-Pb dating of zircon indicates ages of diopside syenite and diopside granite are 11.69±0.15Ma and 11.07±0.34Ma respectively, and they are products of Cenozoic magmatism. Major and trace element geochemical analyses suggest magma of the rocks originate from enriched mantle which are transformed by continental crust materials. Based on regional geological background research by predecessors and geochemical analysis of this study, the paper concludes the potassic alkaline rocks of Kuzigan are formed in tensional tectonic environment.