下扬子地区下寒武统幕府山组黑色岩系地球化学特征及其地质意义

为探讨下扬子地区下寒武统幕府山组底部富有机质黑色岩系的物源属性及源区构造背景特征，在南京幕府山剖面幕府山组底部系统的采集样品，并对其进行地球化学测试与分析。Th/Sc?Zr/Sc图解表明幕府山组黑色岩系未曾经历沉积再循环；通过分析主量元素比值特征、稀土元素（REE）配分模式、δEu、（La/Yb）_N及La/Th?Hf和La/Yb?∑REE判别图解，认为幕府山组黑色岩系源岩主要是花岗岩和富含长英质矿物的沉积岩等上地壳长英质岩石，存在基性岩的混入。从物源属性、地质年代关系、华南大陆构造演化历程等多方面考虑，源岩中花岗岩成分主要为新元古时期岩浆活动形成的岩浆岩，物源区为江南古陆（江南造山带）。通过分析K₂O+Na₂O?SiO₂、K₂O/Na₂O?SiO₂/Al₂O₃、La?Th?Sc、Th?Co?Zr/10和Th?Sc?Zr/10图解，认为幕府山组黑色岩系源区构造背景为被动大陆边缘。

Geochemical Characteristics and Geological Significance of the Black Rock Series at the Bottom of the Mufushan Formation in the Lower Cambrian,Lower Yangtze Area

In order to investigate the provenance and tectonic setting for the source of the organic?rich black rock series from the Lower Cambrian Mufushan Formation in the Lower Yangtze area, samples were collected systematically from the bottom of the Mufushan Formation in the Mufushan section in Nanjing, and geochemical tests and analysis were conducted on the samples. The chemical alteration index (CIA) and Th/U values are important chemical parameters for judging the degree of weathering in the source region. The CIA and Th/U values of the sample indicate that the source rock has experienced weak?medium intensity weathering, and the Th/Sc?Zr/Sc diagram shows that the black rock series in the area has not experienced sedimentary recirculation. By analyzing the ratio characteristics of the major elements, the distribution patterns of rare earth elements (REE), δEu, (La/Yb)N, La/Th?Hf, and the La/Yb?∑REE diagrams, we find that the source rock of the Mufushan Formation black rock series is mainly upper crust felsic rocks such as granite and sedimentary rocks rich in felsic minerals, and there are mixed rocks of basic rocks. Considering the source property, geological age, and tectonic evolution process of the South China continent, the granite composition in the source rocks is mainly composed of magmatic rocks that formed during the Neoproterozoic period, and the source area is Ghiangnania. By analyzing the diagrams of K₂O+Na₂O?SiO₂, K₂O/Na₂O?SiO₂/Al₂O₃, La?Th?Sc, Th?Co?Zr/10, and Th?Sc?Zr/10, we determine that the tectonic setting of the black rock source area of the Mufushan Formation is the passive continental margin.