中条山同善地区虎坪杂岩锆石U-Pb年龄、Hf同位素特征及地质意义

U-Pb Geochronology and Hf Isotope Geochemistry of the Zircon from Huping Complex in Tongshan Area of Zhongtiaoshan Mountains and Its Geologic Implications

中条山地区是华北克拉通中部造山带的重要组成部分,区内前寒武纪地层广泛出露,新太古代地质体主要分布在北东走向的中条山主山脉和近东西向王屋山'同善天窗'内。'同善天窗'中主要出露虎坪花岗质片麻杂岩及宋家山群。虎坪杂岩中黑云斜长片麻岩的锆石U-Pb上交点年龄为(2 530±13)Ma,εHf(2 530Ma)为3.89～7.12;英云闪长岩207 Pb/206 Pb加权平均年龄为(2 551.4±2.7)Ma,εHf(t)为5.49～9.67。结合近年来华北克拉通新太古代晚期中部造山带镁铁质火山岩Nd同位素及遵化二辉橄榄岩的Hf同位素特征,推测华北克拉通中部造山带新太古代晚期地幔εHf(t)与εNd(t)具有一定的线性关系,中条山新太古代晚期地幔εHf(2.55Ga)为8.2～9.5,显示华北克拉通地幔在2.55Ga之前即发生过大规模的分异。虎坪变英云闪长岩幔源Hf同位素的特征需要新生玄武质地壳俯冲熔融,类似特征的花岗岩往往存在于洋内俯冲带或是洋脊俯冲的特殊构造环境;因此,虎坪英云闪长岩的产出可能代表了中条山2.55Ga的洋脊俯冲或是年轻洋壳的壳内俯冲事件。

The Zhongtiaoshan area in which Precambrian rocks widely occurred is an important part of the Trans-North China Orogen（TNCO）.The Neoarchean TTG is mainly distributed in the Main Range of Zhongtiaoshan Mountain extending in NE direction and the Tongshan ＂window＂ of Wangwushan Mountain in EW direction.There occurs mainly the Huping complex composed of biotite plagioclase gneiss,tonalite and Songjiashan gourp in the Tongshan ＂window＂.LA-MC-ICPMS Zircon U-Pb dating shows that the age of the biotite plagioclase gneiss is（2 530±13） Ma and its εHf（2 530 Ma）values range from 3.89 to 7.12.The weighted average 207Pb/206Pb age of the Tonalitic gneiss is（2 551.4±2.7） Ma,and its εHf（t） values from 5.49 to 9.67,which are higher than that of depleted mantle.The approximate εHf（2.55 Ga） values of the Neoarchean depleted mantle in the TNCO are from 8.2 to 9.5,which is also proved by isotopic composition of the TNCO researched recently and the εHf（t） of the tonalitic gneiss.It can be concluded that the mantle of the TNCO was largely depleted before 2.55 Ga.The εHf（t） values of the tonalitic gneiss in Huping complex suggest that the age of the ocean ridge subduction or inter-ocean subduction of young ocean crust is 2.55 Ga,and the subduction played an important role in formation of the tonalitic gneiss in the Huping complex.