摘要:小秦岭地区是华北克拉通南缘早前寒武纪基底重要分布区，可见大量构造抬升剥露的基底结晶杂岩带。太华杂岩是小秦岭出露最古老的地质体，对于探讨华北克拉通南缘早期地壳形成和演化及其构造归属等问题具有重要意义。在小秦岭地区，太华杂岩被划分为正片麻岩系和以孔兹岩系为主的表壳岩。利用LA-ICP-MS锆石U-Pb定年方法测得小秦岭地区太华杂岩表壳岩中黑云斜长片麻岩碎屑锆石的源区物质主要形成于2.40～2.11 Ga，经历了两期的古元古代晚期变质事件（～2.04 Ga和～1.91 Ga），限定该套表壳岩的沉积时代介于2.11～1.91 Ga。结合锆石Hf同位素特征，我们认为该表壳岩的碎屑物质可能主要来自中条山的涑水杂岩体及绛县杂岩体、熊耳花岗岩体、小秦岭古元古代花岗岩体等，其初始的源区物质可能为太华杂岩的新太古代正片麻岩系。此外，本研究揭示华北中部造山带可能记录了一个长达约250 Ma（～2.05～1.8 Ga）持续的俯冲—碰撞过程。
关键词: 锆石年代学/
Hf同位素/
太华杂岩/
小秦岭/
华北克拉通
Abstract:Xiaoqinling is an important distribution area of the Early Precambrian basement in the southern margin of the North China Craton. In this area, a great number of basement rocks were tectonically uplifted to the surface. The Taihua complex is the most ancient geological unit in the Xiaoqinling area, and therefore has great significance in understanding the formation and evolution of the early crust at the southern margin of the North China Craton and constraining its tectonic affinity. This complex in this area can be usually divided into two tectonic units, including orthogneisses and supracrustal rocks. The supracrustal rocks are dominated by khondalite series. Zircon U-Pb dating of a biotite plagiogneiss from the Taihua complex indicates that the magmatic grains were formed at 2.40～2.11 Ga whereas the metamorphic grains yielded two upper intercept ages at ～2.04 Ga and ～1.91 Ga, respectively. This suggests that the paragneiss have an Early Paleoproterozoic provenance and experienced two Middle Paleoproterozoic metamorphic events after deposition. Therefore, the deposition age of the paragneiss is defined between 2.11 Ga and 1.91 Ga. Combined with the zircon Hf isotopic compositions, we suggest that the clastic materials of the supracrustal rocks were mainly derived from granitic plutons of the Sushui and Jiangxian complexes, the Xiong’er granitic pluton and the Xiaoqinling Paleoproterozoic granitic pluton. The primitive crustal materials of the supracrustal rocks were probably originated from the Neoarchean orthogneisses of the Taihua complex. In addition, this study reveals that a continuous subduction collision course of about 250 Ma（～2.05～1.8 Ga）may be recorded in the orogenic belt in central North China.
Key words:Zircon geochronology/
Hf isotopes/
Taihua complex/
Xiaoqinling/
North China Craton
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