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

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。

华北克拉通中部中元古代岩墙群的古地磁学研究及其地质意义

华北克拉通中部(主要在晋北、五台和吕梁地区)广泛发育着中元古代的基性岩墙群, 这些基性岩墙群未变形、未变质、具有较强的磁性, 分布广泛, 成为利用古地磁对比前寒武纪高级变质岩区的理想标志. 从这一地区基性岩墙群的古地磁结果分析, 华北板块向南掀斜18°左右, 晋北地区相对五台地区翘起并左旋10°左右, 而吕梁地区的岩墙群比晋北五台地区的岩墙群形成晚. 并且在吕梁地区NNW向和WNW向岩墙形成过程中, 华北板块持续向北漂移, 因此造成吕梁地区NNW向和WNW向岩墙群与晋北-五台地区的岩墙群具有较大的古地磁差异.

The paleomagnetism and geological significance of Meso-proterozoic dyke swarms in the central North China Craton

The Mesoproterozoic mafic dyke swarms are extensively distributedin the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, so the dyke swarms become the mark to compare the high meta-morphic rock areas in magnetism. Based on the analysis of paleomagnetism of mafic dyke swarms in North Shanxi, Wutai and Lüliang areas, NCC inclined southward about 18° so that North Shanxi lifted up and rotated 10° left to Wutai area. The dyke swarms in Lüliang developed later than in North Shanxi and Wutai area. The NNW-trending and WNW-trending dyke swarms developed in Lüliang while the North China Plate moved northward consistently so that the paleomagnetism of dyke swarms in Lüliang is greatly different from North Shanxi and Wutai area.