内蒙古大青山地区寒武系与奥陶系之间的一个重要的层序界面

An Important Sequence Interface Between the Cambrian and the Ordovician in Daqingshan, Inner Mongolia

大青山地区寒武纪—奥陶纪地层分布零星,是由中生代逆冲推覆构造就位于此的一系列近东西向延展的构造岩片组成。下寒武统色麻沟组直接覆盖在太古界变质岩之上,缺失中元古界什那干群,寒武系与奥陶系之间呈假整合接触,标志着区内寒武纪与奥陶纪之间发生过一次抬升构造运动,其形成机制与古亚洲洋内的稳定陆快向华北板块拼贴事件有关,是早奥陶世末期华北板块整体抬升的序幕。这个层序界面的识别,对于恢复华北板块北部边缘构造演化历史具有重要意义。

The Cambrian and Ordovician strata are scattered mostly in the region from Hetangou to Tianlinbei. They are composed of a series of structural slabs distributing latitudinally and were formed in the Mesozoic by thrust-napping. Since the of the Lower Cambrian Semagou Formation covers the Archaeozoic metamorphic rocks with anglulare conformity, it may be concluded that the Mesoproterozoic Shinagan Group is absent in the region. The connection of the Cambrian and Ordovician is parallel unconformity, implying that a tectonic movement must have taken place between the Cambrian and Ordovician, which is a part of the rising process of the North China Plate. The forming mechanism of the movement may have some connections with the collision between the North China Plate and the massif in the Paleo -Asia ocean. The discovery of the movement has a great significance in recovering the tectonic evolution history of the North China Plate.