龙泉关剪切带眼球状花岗质片麻岩锆石U-Pb年代学和Lu-Hf同位素特征及其地质意义

Zircon U-Pb age and Lu-Hf isotope characteristics of the granitic augen gneiss from the Longquanguan shear zone,and their geological significance

恒山五台阜平地区地处华北克拉通中部造山带的中段,早前寒武纪地体出露较好,是解析华北克拉通早前寒武纪演化过程的最佳地段。龙泉关剪切带位于五台杂岩和阜平杂岩的交接部位,其主要岩石类型为眼球状花岗质片麻岩、变粒岩和斜长角闪岩。本文利用LA-ICP-MS方法对龙泉关剪切带中的眼球状花岗质片麻岩进行了锆石U-Pb年龄和Lu-Hf同位素的测试。结果显示,龙泉关眼球状花岗质片麻岩原岩结晶年龄为(2 547±7)Ma,其εHf(t)值介于+2.7^+9.2,表明其源区主要为相对年轻的地壳物质,与五台地区新太古代花岗岩非常相似。龙泉关花岗质眼球状片麻岩中锆石两阶段Hf模式年龄(TDM2)为2 477~2 872 Ma,具有2.58Ga、2.71Ga和2.81Ga三个峰值,记录了华北克拉通新太古代初始地壳生长事件。

The Hengshan-Wutai-Fuping area,located in the middle part of the Trans-North China Orogen with large outcrop of Precambrian rocks,is becoming an ideal place to reveal the early-phase evolutionary history of the North China Craton.The Longquanguan shear zone situated in the junction area of the Wutai and Fuping Complex,and the main rock types are granitic augen gneiss and amphibolite.We conducted LAICP-MS zircon U-Pb dating and Lu-Hf isotope analysis for the granitic aguen gneiss from the Longquanguan shear zone.The protolith of the Longquanguan granitic aguen gneiss was crystallized at 2547±7 Ma,withεHf(t)values from+2.7 to+9.2,indicating that the rocks were derived from relatively juvenile continental crust with similar features of the late Archean granitic rocks from the Wutai complex.According to the twostage Hf model,the zircon ages from the Longquanguan granitic augen gneiss varied from 2872 to 2477 Ma and peaked at 2.58 Ga,2.71 Ga and 2.81 Ga,coinciding with the Neoarchean continental crustal growth events of the North China Craton.