长江中下游地区早古生代沉积岩地球化学特征及其构造背景与物源分析

长江中下游地区位于扬子板块北缘,自晋宁期结束至晚三叠世一直接受长期而稳定的沉积。粉砂岩和泥岩的主量、微量和稀土元素(REE)分析表明,研究区早古生代沉积岩的源岩主要来自大陆上地壳,物源区岩石类型主要为长英质沉积岩和火成岩,以及少量基性岩,构造背景为主动和被动大陆边缘。样品具有非常一致的REE配分曲线,表明研究区早古生代沉积物具有稳定且均一的物源。综合微量和稀土元素特征以及前人获得的Nd同位素模式年龄,判断长江中下游地区早古生代沉积岩物源区主要为北淮阳地块卢镇关群,而与上溪群、大别造山带和崆岭群没有联系。

Geochemistry of Early Paleozoic Sedimentary Rocks in the Middle-Lower Reaches of the Yangtze River and its Constrains on Tectonic Setting and Provenance

The Middle-Lower Reaches of the Yangtze River region is located in the northern margin of Yangtze Block. This region has been receiving long-term and stable deposition from the end of Jingningian Period, when the collision of North China and Yangtze Block occurred, to the Late Triassic. Geochemical analyses of the siltstone and mudstone samples from the study area indicate that the source rocks of the Early Paleozoic sedimentary rocks were mainly felsic sedimentary and igneous rocks and a minor basic rocks of the upper crust. Based on the SiO2-K2O/Na2O and Sc/Cr-La/Y diagrams, the trace element ratios, the REE ratios and the REE diagrams, we can conclude that the source rocks of the Early Paleozoic sedimentary rocks in the study area were mainly formed in active and passive continental margin settings. The unanimous REE diagrams of the samples suggest that they were formed from the same source rocks and tectonic settings. By combining the trace elements and Nd isotopic model ages in literature, we propose that the Early Paleozoic sediments in the study area were mainly from the Luzhenguan Group of the North Huaiyang zone, but not from the Shangxi Group, the Kongling Group or the Dabie area.