中条山前寒武纪花岗岩地球化学、年代学及其地质意义

Zircon U-Pb geochronology,geochemistry and its geological implications for the Precambrian granitoids in Zhongtiao Mountain, Shanxi Province

涉及华北克拉通基底拼合的时、空演化近年已成为华北克拉通研究的热点之一。开展对华北克拉通中部带中条山前寒武纪涑水杂岩中非TTG质花岗岩的研究有可能为讨论这一问题提供重要信息。涑水杂岩中非TTG质的花岗岩以横岭关、解州黑云二长花岗岩和烟庄钾长花岗岩为代表,岩相学、地球化学和LA-ICP-MS锆石U-Pb定年结果显示,横岭关和解州黑云二长花岗岩具有相似的岩相学、地球化学特征和几乎一致的形成年龄(锆石年龄分别为2609±31Ma和2620±14Ma),表明它们属于同一期岩浆活动的产物。烟庄钾长花岗岩形成于古元古代(2351±37Ma)。横岭关、解州黑云二长花岗岩锆石εHf(t)值分别为-2.3～+4.8和+4.4～+7.6,对应的模式年龄分别为2791～3222Ma和2628～2823Ma。新太古代横岭关和解州黑云二长花岗岩属于高钾钙碱性I型花岗岩,源自～2.7Ga的TTG岩石和下地壳镁铁质岩石部分熔融混合而成。烟庄钾长花岗岩中锆石的εHf(t)值为-1.8～+7.8,对应的模式年龄为2408～2996Ma,类似低Sr、Yb的喜马拉雅型花岗岩,其成因与地壳加厚引起陆壳熔融相关。综合前人及本项研究成果发现,华北克拉通中部带在2.8～1.8Ga这一长达10亿年的地壳演化过程中,并不存在明显的地壳生长"幕式"特点,而显示出小频率持续脉冲生长的特点,表明华北的东部、西部和中部带在晚太古代末之前已经是统一的陆块。

The geometry and timing of amalgamation of the North China Craton （NCC） have been controversial. The research on the Precambrian Sushui Complex in Zhongtiao Mountain, located in the Trans-North China Orogen, can provide important information for Early Precambrian geological evolution of the NCC. This paper concentrates mainly on the Henglingguan, Xiezhou and Yanzhuang granites, which are the representative components of cala-alkaline granitoids of the Precambrian Sushui Complex. Henglingguan and Xiezhou biotite adamellites are similar in the petrography and geochemistry feature, and have almost same forming age （with a zircon age of 2609±31Ma and 2620±14Ma）, suggesting that the two granitoid instrusions are the product of the same magmatism. Yanzhuang K-feldspar granite was formed in Paleoproterozoic （2351±37Ma）. In-situ zircon Lu-Hf isotopic analyses for three granitoids show that their εHf（t） range from -2.3 to ＋4.8, ＋4.4 to ＋7.6 and -1.8 to ＋7.8, and the corresponding two-stage model age are 2791～3222Ma,2628～2823Ma and 2408～2996Ma, respectively. Through multidisciplinary analysis lithology, litho-chemistry and Hf isotopic of the granites and combined with the setting regional structure, we suggested that the two Neoarchean granitic rocks belong to high-potassium cala-alkaline I-type granites and probably the result of the partial melting of ～2.7Ga TTG rocks and mafic lower crust. The Paleoproterozoic Yanzhuang granite is typically characterized by low Sr and Yb and similar to Himalayan-type granitic rocks, which is related to the partial melt of continental crust caused by crustal thickening. The paper, based on previous and the author’s own research results, summarizes that there is no obvious episodic character of crustal growth of the central North China Craton in the long period of 1.0Ga between ～2.8Ga and ～1.8Ga, but displays a feature of small frequency persistent pulsing growth, indicating that the eastern and western NCC and the Trans-North China Orogen should be a unified continental block in the Late Archaean.