中下扬子北缘中二叠统孤峰组层状硅质岩沉积环境、成因及硅质来源探讨

Discussion on Sedimentary Environments,Origin and Source of Middle Permian Gufeng Formation Bedded Cherts in the Northern Margin of the Middle-Lower Yangtze Area

硅质岩中蕴含着重要的古地理、古构造及古海洋等信息,是进行岩石大地构造学研究的重要手段。针对中下扬子北缘孤峰组层状硅质岩的沉积环境、成因及硅质来源存在的较大争议,基于沉积-构造演化过程,从正反两方面进行论证:正向论证通过对前人关于孤峰组层状硅质岩成因的观点进行归纳总结,并广泛搜集已发表的相关地球化学原始数据,建立硅质岩主量、稀土元素数据库,重新系统地进行沉积环境、成因及硅质来源判别;反向论证通过对华南中二叠世主要地质事件进行时间及成因的梳理,建立构造演化序列,以检验或解释目前存在的系列争议,结果表明:①除个别地区如安徽贵池唐田、铜陵花树坡和巢湖平顶山受火山活动及断裂影响向热液成因过渡,中下扬子北缘孤峰组层状硅质岩主要为非热液成因或生物成因,且沉积于被动大陆边缘深水环境;②华夏古陆隆升及海平面升降控制了研究区孤峰组层状硅质岩中部分陆源物质的输入,但陆源物质对硅质岩的硅质贡献并不明显;③孤峰组硅质岩的研究对峨眉山玄武岩的喷发时间及动力学机制具有重要的启示意义。

Cherts contain important information of paleogeography,paleostructure and paleo-ocean,which is the important means of studying petrotectonics. With regard to the major disputes on the sedimentary environments,origin and source of Gufeng Formation bedded cherts in the northern margin of middle-lower Yangtze area,demonstrations from both forward and reverse aspects from the perspective of the sedimentarytectonic evolution were given. By summarizing previous views on the genesis of bedded cherts in Gufeng Formation,and extensively collecting published original geochemical data,in the forward demonstrations we created the database of the cherts about rare earth elements to systematically identify the sedimentary environments,origin and source of cherts. By sorting out the time and cause of the main geological events in the middle Permian in south China,in the reverse demonstrations we established the sequence of tectonic evolution to verify or explain the current series of disputes. The results show that:① Except some areas,such as GuichiTangtian,Tongling-Huashupo and Chaohu-Pingdingshan in Anhui province,which were affected by volcanic activities and faults,the bedded cherts of Gufeng Formation in the northern margin of middle-lower Yangtze area are mainly of non-hydrothermal origin or biological origin,and deposited in the passive continental margin deep water environments. ② Paleocontinental uplift in cathaysian and sea level eustacy controlled the input of some terrestrial materials in the the Gufeng Formation bedded cherts in the study area,but the contribution of terrestrial materials to cherts is not obvious. ③ The study of cherts in Gufeng Formation is of great significance to the eruption time and dynamic mechanism of Emeishan basalts.