摘要
广西西部存在晚古生代连续深海沉积,其中各个时代玄武岩广泛分布,具大洋板内地化特征。桂西和柳州地区晚古生代硅质岩有明显的铈负异常,指示本区可能属远洋沉积环境。狭窄的深水地层条带具强烈的构造形变,所环绕的碳酸盐台地却产状平缓。区域地质分析表明,广西在晚古生代可能代表扬子和印支地块之间的古特提斯水道,碳酸盐台地可能为广海中的水下高地。
Guangxi region lies in the South China, facing the South China Sea on the south and joining with Vietnam on the southwest. Traditionally, it is regarded as an area where shallow shelves coexisted with deep basins on the platform background during the Late Paleozoic. In recent years we found the depositional alternations of the cherts, siliceous limestones and thick piles of pillow or massive basalts in the western Guangxi. Conodont fossils indicate the sequence ranging from Late Devonian to Late Permian in age. The obvious negative Ce anomaly and other geochemical characteristics of the cherts mean that they formed in deep-water pelagic environment with hydrothermal input. The geochemical compositions of the basalts also show an oceanic intra-plate setting. Meanwhile, in the southern Guangxi an Upper Devonian-Upper Permian radiolarian chert belt was recognized. The chert belt and an unconformably overlying latest Permian molasse belt mark a suture between the Damingshan terrane and Qinzhou—Yunkai terrane (Wu et al., 1994a). These discoveries suggest that during the Late Paleozoic most part of Guangxi region was occupied by the pelagic environment. Some areas in Guangxi are covered with Late Paleozoic weakly deformed platform-type carbonate rocks. However, the lack of terrigeneous detritus and the presence of negative Ce anomaly from the intercalated siliceous beds indicate the pelagic setting for these carbonate rocks. They might be accumulated on the submerged highlands whic emerged sometimes and formed an archpelago between the Yangtze block and the Indochina block. The stratigraphlc sequences in some carbonate plateforms, such as the Jingxi platform, are similar with those in the North Vietnam terrane and in the Indochina block but different from those in the Yangtze block. These platforms or small terranes, including the Jingxi platform, the Damingshan terrane, the Qingzhou- Yunkal terrane and the North Vietnam terrane etc., together with the deep-water sediments between them constitute a wide and complicated transition area between the Yangtze block and the Indochina block. The spectacaular klippes of Devonian limestones thrust upon the tightly folded middle Triassic clastic rocks near the Sino-Vietnam border. The compression resulted from the convergence of the Yangtze and the Indochian blocks occurred not ealier than late Triassic.
出处
《地质科学》
CAS
CSCD
北大核心
1997年第1期11-18,共8页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金
关键词
广西
古特提斯
沉积环境
构造格局
古生代
Guangxi, Paleo-Tethys, Sedimaentary environment, Tectonic settings
