恒山中元古代早期基性岩墙群的单颗粒锆石U-Pb年龄及其克拉通构造演化意义

Single-Zircon U-Pb Age of the Initial Mesoproterozoic Basic Dike Swarms in Hengshan Mountain and Its Implication for the Tectonic Evolution of the North China Craton

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。

Precambrian basic dike swarms are developed extensively in the north-central part of the North China era-ton , but no precise age data have been obtained owing to the problem of the isotope dating technique of basic dikes. The authors used the single-zircon U-Pb chemical method to date the NW-trending basic dike swarm in the Hengshan Mountain area and for the first time obtained a single-zircon U-Pb age of 1769. 1 ± 2. 5 Ma. They have proved that this age represents the emplacement age of the basic dike swarm and is also the known oldest age of unmetamorphosed basic dike swarms distributed extensively in the North China craton. This age combined with the isotope age records of the contemporaneous magmatism suggests that the intial Mesoprotero-zoic magma series in the North China craton occurred in the extensional tectonic setting.