LA-ICP-MS zircon dating, geochemistry, petrogenesis and tectonic implications of the Dapingliang Neoproterozoic granites at Kuluketage block, NW China

Abstract The Kuluketage block, located in the northeast Tarim Craton, is one of the largest Precambrian blocks in Xinjiang Province, China. Recently the Dapingliang skarn Cu deposit was discovered at the eastern part of the Kuluketage block. The ore bodies are developed in skarn rocks along the NE fault. This deposit formed at the middle Neoproterozoic (826 Ma) and the ore-related plagiogranite also formed at 826 Ma. Plagiogranite, biotite monzogranite and K-feldspar granite are the major rock types intruded in sequence in the Dapingliang area. The LA-ICP-MS zircon 206 Pb/ 238 U age of the monzogranite is 816 ± 5 Ma. The emplacement age of the Dapingliang granites is then constrained between ca. 816 and 826 Ma. Geochemical characteristics show that the rocks belong to the low-Ca, high-K calc alkaline and shoshonite series. They are typical I-type granites. These series have a negative slope from La to Lu. The plagiogranite and biotite monzogranite show no (or weak negative) Eu anomaly, low (La/Yb) N (9.87–23.39), (Dy/Yb) N (1.01–1.14), high Sr (531–976 ppm) and Sr/Y (30.5–50.7) with no garnet and plagioclase residual. The K-feldspar granite shows weak to high negative Eu anomaly and relative lower LREE/HREE fractionation. The low La/Yb and Sr/Y show that the origin has plagioclase residual and no garnet residual. Trace elements of the plutons show a negative anomaly of Nb, Ta, P, Zr and Ti, and positive anomaly of Ba, K, Sm and Sr with respect to primary mantle. ɛNd ( t ) varies from −6.1 to −14.6 and initial 87 Sr/ 86 Sr ranges from 0.70235 to 0.70912 for all the samples show lower crust origin and are contaminated with Archean rocks. Pb isotope show low radiogenetic 208 Pb/ 204 Pb and 207 Pb/ 204 Pb. The initial 208 Pb/ 204 Pb and 207 Pb/ 204 Pb are well above the Northern Hemisphere Reference Line. The Pb isotopes also indicate lower crust origin. These rocks maybe formed by partial melting of K-rich basalt of the lower crust during a period of transition from crustal compression to extension. There are also K-rich granites formed at the same tectonic setting in the Kuluketage block which contributed to the post-collisional granite belt derived from lower crust.