U-Pb ages and Hf isotope characteristics of zircons from Jiangqiao granodiorite in southeastern Hubei Province and their geological implications

Located in the westernmost part of the Middle and Lower Yangtze metallogenic belt,the southeastern Hubei Fe-Cu province possesses extensive magmatism and is hence an important part of the Late Mesozoic magmatic belt in the middle and lower reaches of the Yangtze River.Ore-forming plutons,especially large ones,have been extensively studied,with important progress achieved;nevertheless,the study of barren intrusions is very insufficient.Lying between the Lingxiang pluton and Yinzu pluton,the Jiangqiao intrusion consisting of granodiorite is the largest pluton among the small intrusions in southeastern Hubei Province.In this paper,the authors present high-precision zircon U-Pb age of the Jiangqiao granodiorite by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).The result indicates that its emplacement took place at 144±1 Ma,suggesting a product of Early Cretaceous magmatism.The cathodoluminescence (CL) images of zircons show that a few inherited zircons with ancient cores exist in the sample,except magmatic zircons with obvious overgrowth bands.The eHf(t) values of magmatic zircons are relatively negative and vary from-9.1 to-14.6.The corresponding two-stage model ages range from 1.77 Ga to 2.11 Ga,coincident with U-Pb ages of a few inherited zircons,indicating that the Jiangqiao granodiorite probably originated from Palaeoproterozoic crustal materials.The eHf(t) values of inherited zircons range from-0.6 to-14.6,corresponding to the two-stage model ages of 2.00～3.60 Ga and therefore indicating that Palaeo-Archaean basement might exist in southeastern Hubei Province.These results,in combination with data available,suggest that the formation of the Jiangqiao granodiorite was related to lithospheric extension and thinning,thus being the initial product of tectonic regime transformation in eastern China.