关键词: 锆石U-Pb年龄, 锆石Hf同位素, 地球化学, I型花岗岩, 早泥盆世, 伊犁地块

Abstract: There are numerous Late Paleozoic acidic intrusive rocks in Wenquan area, which is located on the northern margin of the Yili block. In this paper, we present new zircon U-Pb geochronology, Lu-Hf isotopic and geochemical studies of the Early Devonian granites from Wenquan area, aiming to confirm their timing, discuss their petrogenesis, and explore their tectonic evolution process. The zircon LA-ICP-MS U-Pb age of the monzogranites is (418±7) Ma which indicates that their crystallization age is the product of Early Devonian magmatic activity. Meanwhile, the zircon Hf isotope compositions of the monzogranite are typically characterized by high εHf(t) values (8.2-14.0, with an average of 11.3), and the young two-stage model ages (TDM2=863-492 Ma), implying their derivation from a relatively juvenile crust. These two types of granites are characterized by high SiO2, weakly peraluminous, as well as low CaO and MgO contents. The trace elements of the granites are characterized by depletion in high field strength elements (Nb, Ti, P), and enrichment in large ion lithophile elements (K, Rb). The standardized distribution pattern of rare earth elements in chondrites is enriched in light rare earth elements and depleted in heavy rare earth elements, with significant negative Eu anomalies. The low zircon saturation temperature, negative correlation between P2O5 and SiO2, and other geochemical features suggest the granites are I-type granites. Several tectonic discrimination diagrams shows that they were formed in a continental magmatic arc setting. Combined with the regional tectonic background and the evolution information of magmatic rocks in the adjacent area, it is speculated that the granites were mainly derived from the crustal accretion in response to subduction of the Junggar-Balkhash Ocean. 

Key words: zircon U-Pb age, zircon Hf isotopes; , geochemistry, I-type granite, Early Devonian, Yili block