大别造山带北缘古生代构造-地层岩片沉积物源区及构造演化的地球化学研究

Geochemical Records of Sedimentary Source and Tectonic Evolution of Paleozoic Strata along the Northern Margin in the Dabie Orogen, Central China

取自大别造山带北缘(北淮阳地区)古生代主要构造-地层岩片中变碎屑岩和碎屑岩的一组元素和Nd同位素地球化学数据与相关资料显示,从早古生代到泥盆纪,再到石炭纪,龟山组、南湾组—佛子岭群和石炭系三个岩片中的碎屑岩类,存在稳定的沉积物源区,源区组成可能相当于北秦岭构造单元中古元古代的秦岭群及秦岭群组分沉积再循环的部分。沉积组分成熟度由高到低和源区剥蚀性质变化的地球化学记录,指示三个岩片代表了华北、扬子两陆块在古生代构造演化过程中,主动大陆边缘一侧一系列构造事件中“俯冲后期-对接-碰撞前奏”的三个片断。这些论证显示,大别造山带北缘不同岩片沉积构造环境和演化的进程完全可以与北秦岭构造单元南部对比,大别造山带北缘应是北秦岭构造单元的东延部分。

Measurements of major, trace elements and Nd isotope were made and discussed on the tectono-stratigraphic slices from the northern margin in the Dabie orogen (northern Huaiyang area) to test the relation between sedimentary source and Paleozoic tectonic evolution. The results show that there were similar provenances in the clastic rocks from the Guishan Formation, Nanwan Formation, Foziling Group and the Carboniferous slices from the early Paleozoic to the Devonian, and to the Carboniferous, to correspond to the Paleoproterozoic Qinling Group and its recycled sediments in the North Qinling belt. The geochemical records of changing component maturity and source erosion indicated that the three slices presented three passages of tectonic intervals during the Paleozoic reaction between the North China Craton and the Yangtze Craton: “late subduction-approach-collision eve”, which had occurred in the active continental margin. This study demonstrates that the Paleozoic tectonic settings and changing processes for sedimentation in the different slices from the northern margin in the Dabie orogen are analogous to that in the south of the North Qinling belt, and the northern margin in the Dabie orogen should be the eastern extension of the North Qinling belt.