Zircon U-Pb ages, geochemical features and geological implications of Middle Devonian granite in Wulanbaixing area, Qimantag area of East Kunlun Mountains

The granite in the study area is composed of monzogranite and granodiorite.Its silicon values are 67.47%~73.63%, alkali values are 6.74%~7.89%, K₂O/Na₂O values are 0.59~1.30, and A/CNK values are 0.91~1.08, suggesting that the rocks belong to metaluminous to peraluminous rocks of high-K cala-alkaline series and cala-alkaline series.The average values of ∑REE is 137.28×10^-6; δEu values vary in the range of 0.37~0.89, with average values of 0.57; (La/Yb)_N values vary in the range of 6.72~19.36, with an average value of 10.75.The chondrite-normalized REE patterns of rocks show the right deviation type with obvious negative Eu anomaly.The rocks are significantly enriched in large ion lithophile elements Rb, K and incompatible elements of U and Th as well as LREE and Pb, relatively depleted in high field strength elements Nb, Ta, P, Ti and large ion lithophile element Ba.The Rb/Sr ratios vary in the range of 0.45~1.17, with average value of 0.72, suggesting the upper mantle and the crust.The Nb/Ta ratios vary in the range of 5.36~13.90, with an average value of 10.93, which are overall lower than the average value of the mantle, and exhibit the characteristics of crust-mantle mixture.Using zircon U-Pb dating, the authors obtained the ²⁰⁶Pb/²³⁸U age 384.1±2.4Ma (MSWD) of Wulanbaixing granodiorite, which represents the formation age of the rock.In combination with geochemical and structural features and regional geological setting, the authors hold that the intrusive body was formed in an extension environment during post-collisional development stage in the Late Middle Devonian continent and was closely related to the mineralization of the iron-polymetallic deposit.Attentions should be paid to these phenomena in the further mineral exploration.