Formation Age and Geochemical Characteristics of Dishantou Monzonitic Granite in Estern Kunlun Orogenic Belt

Ziron U-Pb dating and petrological geochemistry of Ditoushan monzonitic granite in the middle section of Estern Kunlun Orogenic Belt have carried out in this paper. Ziron U-Pb dating of monzonitic granite yields an age of (225.52±0.76)Ma, showing that the Ditoushan monzonitic granite was generated in late Triassic Indo-Chinese epoch. Petrological geochemistry research show that Al₂O₃ content vary from 14.73% to 16.42% while Rittmann index change from 1.18 to 1.46, suggesting that these rocks belong to calc alkalic series. Their K₂O/Na₂O ratio less than 1, showing the features of enriched sodium and depleted potassium. Their A/NCK range from 0.94 to 0.99, belonging to aluminous magmatic rock, with richment of large ionic lithophile element (LILE, such as Rb, K, Sr and Ba) and high strength field elements (HFSE, including Th, U, La and Ce), but obviously poor of Nb and Ti. Their LREE/HREE ratios vary from 6.06 to 16.98, while δCe values range from 0.95 to 0.99, showing negative anomaly. Their (La/Yb)_N ratios change from 7.46 to 28.35, showing rich LREE; Their δEu values vary from 0.51to 0.92, displaying negative Eu anomaly and showing distinct magmatic differentiations. These rocks belong to I-type granite. Combined with geotectonic discrimination diagram, it's comprehensively judged that the Ditoushan monzonitic granite belongs to late Triassic volcanic arc granitoids formed in the middle Estern Kunlun Orogenic Belt.