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作者最近在北京延庆高于庄组张家峪亚组上部发现了凝灰岩,并测得了该凝灰岩中锆石1559±12Ma的SHRIMPU-Pb年龄和1560±5Ma的LA-MC-ICPMS U-Pb年龄。这一新的高精度定年结果表明,华北北部高于庄组形成于中元古代初期的盖层纪(Calymmian Period,1600~1400Ma)早期。结合早先大红峪组火山岩的锆石U-Pb年龄(1622~1625Ma),现在可以确切地将高于庄组的底界年龄限定在1600Ma左右。结合最近在铁岭组斑脱岩获得的锆石U-Pb年龄(~1440Ma),本文再次建议,应将华北中元古界蓟县系的底界下拉到高于庄组底界,自该组底部(1600Ma)到铁岭组顶部(1400Ma)的巨厚碳酸盐岩序列都属于新定义的蓟县系,并对应于国际中元古界的盖层系,高于庄组与大红峪组之间的界线则可作为蓟县系与长城系的分界标志。高于庄组凝灰岩锆石的精确定年,为华北北部中元古界年代地层划分等研究,提供了直接的年代学约束。
The authors recently discovered tuffs in the upper part of the Zhangjiayu sub-group of the Yu-Chuang-Zhuang Formation in Beijing and measured the SHRIMPU-Pb ages of 1559 ± 12 Ma and the LA-MC-ICPMS U-Pb ages of 1560 ± 5 Ma for this tuff. The new high-precision dating results show that the Gaoyuzhuang Formation in the north of North China was formed in the early Mesoproterozoic Calymmian Period (1600-1400 Ma). Combined with the previous U-Pb zircon ages (1622-1625 Ma) of the volcanic rocks in the Dahongyu Formation, the bottom boundary age of the Gaoyuzhuang Formation can now be limited to about 1600 Ma. Combined with the recent zircon U-Pb age (~ 1440 Ma) obtained from the Tieling Formation bentonite, it is suggested here again that the bottom boundary of the Mesoproterozoic Jixian system in North China should be pulled down to the bottom of the Gaoyuzhuang Formation, (1600 Ma) to the top of the Tieling Formation (1400 Ma) all belonged to the newly-defined Jixian series and corresponded to the caprock of the Proterozoic in the world, higher than that between the Zhuang and Dahongyu formations The boundary line can serve as the boundary marker between the Jixian Department and the Great Wall. The precise dating of the Gaozhuangzhuang tuff zircon provides a direct chronological constraint for the study of stratigraphic division of the Mesoproterozoic in North China.