LA-ICP-MS zircon U-Pb ages, geochemical characteristics and geo-logical significance of the Neogene Quanshuigou Formation volcanic rocks in the north of Dahongliutan-Qitaidaban area, Xinjiang

The Quanshuigou Formation volcanic rocks are located in northern Dahongliutan-Qitadaban area, western Kunlun Mountains, Xinjiang. The volcanic rocks are mainly composed of pyroxene andesite, pyroxene latite, and biotite trachyte. LA-ICPMS zircon dating indicates that the volcanic rocks were emplaced at 3.71 ±0.05Ma, suggesting that the crystallization age of the Quanshuigou Formation volcanic rocks is Neogene Pliocene. Geochemical analysis shows that major elements are characterized by high Al₂O₃ (13.56%~14.32%) and K₂O (4.46%~5.79%), but low Na₂O (3.68%~4.40%), TiO₂ (1.09%~1.48%) and MgO (2.64%~5.18%), thus belonging to shoshonite series. In addition, they are enriched in total REE (550×10^-6~612×10^-6), and the samples are enriched in LREE (light rare earth elements) and depleted in HREE (heavy rare earth elements) with weak Eu anomalies (δEu=0.55~0.63). The chondrite-normalized REE patterns show rightly-inclined type, and the olcanic rocks have rich LILE(such as K, Rb, Ba, Th, U and Pb)but poor high field strength elements (such as Ti, Nb, Ta, and P). They have typical characteristics of orogenic potassic volcanic rocks.Studies show that the rocks were formed by the partial melting enriched mantle sources mixed with a small amount of materials of the upper crust. Combined with the data of regional geology, the authors hold that the formation of the orogenic belt was related to NNW-striking thrust nappe of Karakoram-Tianshuihai along Dahongliutan-Quanshuigou fault and TianshuihaiGuozhacuo fault in the Pliocene. At that time, the volcanic rocks were formed.