桂北-桂东加里东期盆地构造沉降史分析

对造山带各地史阶段的沉积盆地进行构造沉降分析,进而探讨其地球动力学过程,是近年来盆地分析的前缘研究之一。本文采用回剥分析技术,分别编绘了桂北、桂东地区加里东期盆地沉降曲线,并进行了构造沉降史分析。结果表明,桂北、桂东加里东期盆地演化均经历了从拉张裂解到挤压闭合的完整过程。但与桂东大瑶山地区相比,桂北兴安地区在裂陷阶段的沉积速率和构造沉降速率明显偏低;热沉降阶段的持续时间偏长;裂陷阶段与前陆挠曲阶段的分界拐点偏晚;前陆挠曲阶段,由构造宁静期的缓慢沉降向构造活动期的快速沉降转化的分界拐点也偏晚。这些差别这一方面说明了两地区具有不同的构造背景,另一方面也反映了华夏板块由南东逐渐地向北西扬子板块靠拢,沉积盆地相应地向西北迁移的动力学过程。

TECTONIC SUBSIDENCE HISTORY OF THE CALEDONIAN BASIN IN NORTHEAST GUANGXI

One of the frontier recearch of basin analysis in recent years is to analyze the tectonic subsidence history of depositional basins which occur in orogens at different geohistory stage, and to discuss the geodynamic processes involved with the basins. Based on the updated cross sections of regional geological survey at a scale of 1∶50,000 in recent years and the data from field section measurement, subsidence curves of Caledonian basin in north and east Guangxi were drawn up respectively by means of the back-stripping method, and their tectonic subsidence history was analyzed. The results indicate that both Caledonian basins in north and east Guangxi evolved from fracturing to closure. Compared to the basins in east Guangxi, the basin of north Guangxi is characterized by lower depositional and tectonic subsidence rate during rifting, longer thermal subsidence, later inflexion point from rifting to foreland buckling, as well as later inflexion point separating stable stage from active stage during foreland-buckling. The different subsidence history not only demonstrates that the two areas have different tectonic settings, but also proves that the Caledonian basin migrated to northwest when the Cathaysian plate was gradually subducted toward Yangtze plate from southeast to northwest.