【摘要】 江西铅山晚石炭世硅质岩大多呈条带状、少量呈层状和结核状产出,赋存于灰岩层内或层间;主要由微晶石英组成,含有少量蛋白石或玉髓,未见硅质生物及硅化特点。地球化学分析结果显示,晚石炭世硅质岩的SiO2含量为74.51%~98.48%,Al2O3,TiO2,MgO及ΣREE含量低,分别为0.10%~3.42%(平均为0.45%),<0.01%~0.12%(平均<0.02%),0.07%~1.46%(平均为0.20%)和<1.52×10-6~24.66×10-6(平均不足4.84×10-6);δCe值为0.15~0.70(平均为0.42),呈负异常。Al2O3与TiO2具有明显的相关性,而两者与SiO2相关性极低。在双变量SiO2-Al2O3,SiO2-MgO和三变量Al-Fe-Mn,Fe-Mn-(Ni+Co+Cu)判别图上,硅质岩几乎都落入热液成因及生物沉积成因区;在双变量Fe2O3/TiO2-Al2O3/(Al2O3+Fe2O3)判别图上,落入大陆边缘沉积区范围。综合地球化学特征及岩石薄片观察结果,可以认为研究区硅质岩形成于大陆边缘,其成因主要与海底热液活动有关。更多还原

【Abstract】 Late Carboniferous cherts interbedded with limestone occur extensively in of the county of Yanshan, Jiangxi Province. In this study, 22 chert samples were analyzed for major and rare earth elements. The results show the cherts have low amount of Al2O3 (0.45%), TiO2 (<0.02%), MgO (0.20%) and ΣREE (<4.84×10-6 ) in average. TheirδCe values vary from 0.15 to 0.70 with an average of 0.42, indicating negative Ce anomaly. Al2O3 shows positive correlation with TiO2 . SiO2 shows correlation neither with Al2O3 nor with TiO2 . In the SiO2 -Al2O3 , SiO2 -MgO binary, and Al-Fe-Mn, Fe-Mn-(Ni+Co+Cu) ternary discriminant diagrams, the chert samples fall mainly within the hydrothermally and biologically deposited areas. Moreover, the chert samples fall in the area of continental margin in the Fe2O3 /TiO2 -Al2O3 /(Al2O3 +Fe2O3 ) binary discriminant diagram. All these geochemical and petrographic characteristics of cherts suggest that the origin of Late Carboniferous siliceous cherts in Yanshan county was chiefly related with submarine hydrothermal solution, and that the cherts were deposited in a continental margin setting with a little terrestrial matter. This study shows that Yanshan area was an marine environment with the activity of hydrothermal solution rich in silica during the deposition of the Late Carboniferous siliceous cherts.更多还原