加里东期扬子板块与华夏板块西南段分界线的岩相古地理制约

Lithofacies Paleogeographic Constraints of Southwestern Boundary between Yangtze and Cathaysian Plates in Caledonian

定量化的岩相古地理分析可以为判别不同大地构造单元的分界线提供制约依据。采用“单元素分析多因素综合作图法”,结合古流向、沉积特征等实际资料,从定量的角度研究了桂北—桂东地区加里东期的岩相古地理,并认为研究区加里东期自南华纪开始新一轮裂解之后,荔浦断裂北西的桂北—桂东北地区逐渐从深海盆地演变为扬子大陆边缘斜坡,其坡面倾向南东,古流向由北西向南东,陆源碎屑来源于西北,属于扬子(或康滇)古地理体系;而荔浦断裂南东的桂东地区为华夏大陆斜坡,并在奥陶纪最终演变为陆棚—滨岸环境,其坡面倾向北西,古流向由南东向北西,陆源碎屑则来自东南,属于华夏古地理体系。岩相古地理证据表明荔浦断裂为加里东期扬子板块与华夏板块西南段的分界断裂。

Quantitalive lithofacies palaeogeographic analysis can provide constraints to the boundary of different geotectonic units. By means of the method of ＂ single factor analysis muhifactor comprehensive mapping＂, integrating several aspects of data such as palaeo-current directions and sedimentary charateristics, a quantitative study is made on the Caledonian lithofacies palaeogeography of NE Guangxi. Since the Neoproterozoic, the whole research area cracked into two different basins along the Lipu fault. On the NW side of the Lipu fault （ N and NE Guangxi ）, The Caledonian basin evolved from deep-sea basin to passive continent margin basin. Its slope dipped to the southeast, and palaeo-current directions were from northwest to southeast. The terrigenous detrital sediments were derived from the northwest. However, on the SE side of the Lipu fault （E Guangxi）, the Caledonian basin had long been an active continent slope environment, and eventually evolved into a continental-shelf- coastal environment in the Ordovician. The slope dipped to the northwest, and the palaeo-current directions were from southeast to northwest. The terrigenous detrital sediments were derived from southeast. All these indicate that they belonged to different palaeogeographic systems. That is, the basin in northern and northeastern Guangxi belonged to the Yangtze plate, while the basin in eastern Guangxi belonged to the Cathaysian plate. The proof of lithofacies paleogeography suggests that the Lipu Fault is a dividing fracture which separates two terrains in the Caledonian.