鲁西古生代碳酸盐岩中的垂直缝合线及其在华北板块构造演化中的意义

Vertical Stylolites Found in Paleozoic Carbonates in the Western Shandong and Their Constraints on Tectonic Evolution of the Eastern North China Plate

笔者在山东省淄博市博山区中奥陶统马家沟群白云岩和上石炭统本溪组石灰岩中识别出垂直缝合线。垂直缝合线都借助于平面X剪节理发育,缝合面上的"牙齿"与缝合面本身多呈斜交状态,其延伸方向代表着变形期最大主压应力轴(σ1)方向。根据垂直缝合面"牙齿"的突出方向判别:以山东博山地区为代表的华北东部地区在古生代中期和末期先后两次受到NNE—SSW方向的水平挤压作用。其中第一次挤压事件与遍布华北东部的中奥陶统—上石炭统(C2—O2)平行不整合抬升相关,而第二次则与华北东部古生代末期的褶皱隆起相联系。本文的研究为垂直缝合线在盆地构造演化研究中的应用提供了良好的研究实例。

The author of this paper found two sets of verticlal stylolites in Paleozoic carbonates, the Middle Ordovician dolostones and the Upper Carboniferous limestones, in the Boshan area, Shandong Province, east of China. Both sets of stylolites developed along the preexisting vertical shear joints the X conjugate joints during the process of diagenesis. The teeth of both stylolites are not perpendicular, but oblique to the stylolite surfaces. However, it is recognized that all the teeth of the stylolites should track the largest regional compressive stress （σ1）. According to the direction of the teeth, crust compression events in the NNE--SSW direction happened twice separately in the Middle Ordovician and the Late Paleozoic. The first event might be related to the uniformly uplift of eastern North China Plate, which is shown by the parallel unconformity between the Middle Ordovician and the Upper Carboniferous （C2/O2）.The second event coincided with the folding and uplifting of North China Plate by the end of Paleozoic, which is indicated by the angular unconformity between the Upper Permian and Jurassic. Furthermore, the two sets of vertical stylolites also show that the X-type conjugate shear jointing can develop in the early diagenesis and thus provide the sites for the pressure solution, and the shear joint planes can be rotated by the successive crust compression. Therefore, in reality, the direction of the greateast principal stress （σ1） often bisect an abtuse angle （〉90°） rather than an acute angle at which the two conjugate joint planes intersect.