关键词: I型花岗岩, 锆石U-Pb年代学, 地球化学, 锆石Hf同位素, 早侏罗世, 张广才岭

Abstract:  To determine the formation age, source characteristics and tectonic setting of the two types of Early Jurassic I-type granites in the southern Zhangguangcai Range, this paper presents zircon U-Pb geochronology, whole-rock geochemistry and zircon Hf isotope data for five biotite monzogranite and granodiorite plutons in the southern Zhangguangcai Range. The results show that the zircons from the four granite samples all exhibit narrow and clear oscillatory zoning, characteristic of typical magmatic zircons, with concordant ages ranging from 196 to 181 Ma, indicating that the granites formed in the Early Jurassic. Geochemical analysis indicates that this suite of granites belongs to the high-K calc-alkaline series, characterized by high silica (Si) and total alkali contents, enriched in large-ion lithophile elements (LILEs) such as K and Rb, and strongly depleted in elements such as Ba, Sr, and Nb, with A/CNK values ranging from 1.01 to 1.05. These granites display the geochemical characteristics of I-type granites. They can be further divided into weakly differentiated typical I-type granites (CJM, SYB, and SHC intrusions) and highly differentiated I-type granites (TG and NSJ intrusions). The latter are distinguished by extremely high SiO2 content (73.52%-76.07%), high alkali content (Na2O+K2O>8%), relatively high Ga/Al ratios (2.56-2.80), and strong negative anomalies of Ba, Sr, Eu, P, and Ti. Both types of I-type granites have consistent zircon Hf isotope compositions, with εHf(t) values ranging from 6.2 to 9.5, indicating that they are derived from the partial melting of juvenile lower crustal materials. Combined with the regional geological background, we propose that the formation of these Early Jurassic I-type granites was controlled by the subduction of the Paleo-Pacific plate beneath the Eurasian plate. 

Key words:  , I-type granite, zircon U-Pb chronology, geochemistry, zircon Hf isotope, Early Jurassic, Zhangguangcai Range ,  ,