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华北克拉通中北部变质基底发育大规模的前寒武纪基性岩墙群,由于基性岩墙同位素定年技术存在问题,因此一直未获得岩墙群的确切年龄数据。本文利用单颗粒锆石U-Pb化学法,首次获得恒山地区北西向基性岩墙群的U-Pb年龄为1769.1±2.5Ma,并证明它代表基性岩墙群的侵位年龄,这一年龄数据也是华北克拉通大规模分布的未变质基性岩墙群已知的最古老年龄。综合分析同期岩浆活动的同位素年龄记录,本文提出中元古代早期华北的岩浆侵位发生于伸展构造背景下。
The large-scale Precambrian basic dyke swarm developed in the metamorphic basement in the north-central part of North China Craton has not obtained the exact age data of the dyke swale due to the problem of isotopic dating techniques of the basic dyke. In this paper, U-Pb dating of the NW-trending mafic dyke swarms in the Hengshan area was obtained for the first time using the single-particle zircon U-Pb chemistry method. The U-Pb age is 1769.1 ± 2.5 Ma, and it is proved that it represents the emplacement age of the basic dyke swarm. The age data is also the oldest age known to the large-scale distribution of un-metamorphic basement dikes in North China Craton. Based on a comprehensive analysis of isotopic age records of magmatism during the same period, this paper proposes that the magmatic emplacement in the early Mesoproterozoic occurred in the extensional tectonic setting.