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湘东北地区早寒武世石煤沉积物源区研究

Sediment source area of early cambrian stone coal in Northeastern Hunan Province, China

  • 摘要: 湘东北地区早寒武世石煤中伴生有多种高含量元素,属性特征鲜明。为查明该区石煤的沉积物来源,从石煤元素地球化学角度入手,利用X射线荧光光谱仪(XRF)、电感耦合等离子质谱仪(ICP–MS)分别测定了研究区12个石煤样品的常量元素和微量元素含量。根据石煤中常量元素组合关系、微量元素含量特征、稀土元素分布特征及相关元素地球化学参数,探讨了湘东北地区早寒武世石煤的沉积物源区。结果表明:湘东北地区早寒武世石煤以无机矿物质为主要组成部分,石煤中SiO2含量占比最高,SiO2与其他常量元素(及其他常量元素之间)关系不明显,石英矿物形态具有陆源输入特征;石煤中微量元素(V,As,Sr,Mo,Cd,Sb,Ba,Bi,U)具有明显富集特征,稀土元素分布特征和Nb/Y–Zr/TiO2 关系表明石煤受到了中性岩影响,LaN/YbN表明石煤沉积物沉积速率自东南向西北有减小趋势,即物源来自东部和南部方向;w(SiO2)/w(Al2O3),w(Al2O3)/w(Al2O3+Fe2O3),w(Al)/w(Al+Fe+Mn)和K2O/Na2O–SiO2构造判别模型显示早寒武世石煤沉积于大陆边缘区域,主要接受陆源输入。通过与研究区东南方向分布的上墅群中酸性岩中稀土元素、Rb、Nb、Pb含量以及双溪坞群出露的岩浆岩中常量元素含量及组合特征综合比较,并结合江南造山带的演化历史,认为江南造山带东南缘发育的中、酸性岩带为湘东北地区早寒武世石煤沉积物源区,亦是石煤富集微量元素的主控因素之一。

     

    Abstract: There were a variety of high content elements associated with the early Cambrian stone coal in northeastern Hunan province, and the attribute characteristics were distinct. In order to find out the sedimentary sources of stone coal in this area, the contents of major elements and trace elements in 12 stone coal samples were determined by X-ray fluorescence spectrometer (XRF) and inductively coupled plasma mass spectrometer (ICP–MS). Based on the combination of major elements, content characteristics of trace elements, distribution characteristics of rare earth elements and geochemical parameters of related elements, the source regions of the early Cambrian stone coal deposits in northeast Hunan province were discussed. The results showed that the early Cambrian stone coal in northeast Hunan province was mainly composed of inorganic minerals, and the content of SiO2 was the highest in the stone coal. The relationships between SiO2 and other major elements (and other major elements) were not obvious, and the quartz mineral morphology was characterized by terrigenous input. The trace elements (V, As, Sr, Mo, Cd, Sb, Ba, Bi, U) in stone coal were obviously enriched. The distribution characteristics of rare earth elements and the relationship between Nb/Y–Zr/TiO2 indicated that stone coal was influenced by neutral rock. LaN/YbN indicated that the deposition rate of stone coal deposits decreases from southeast to northwest. Means, the source comes from the eastern and southern directions; The w(SiO2)/w(Al2O3), w(Al2O3)/w(Al2O3+Fe2O3), w(Al)/w(Al+Fe+Mn) and K2O/Na2O–SiO2 structural discrimination models showed that the early Cambrian stone coal was deposited in the continental margin area, mainly receiving continental sources. Based on the comparison with the contents of rare earth elements, Rb, Nb and Pb in the middle-acid rocks of Shangshu Group distributed in the southeast direction of the study area, and the contents and combination characteristics of major elements in the magmatic rocks of Shuangxiwu Group, and combined with the evolution history of Jiangnan Orogenic belt, the middle-acid rock belt developed in the southeastern margin of Jiangnan orogenic belt was considered to be the source region of the early Cambrian stone coal deposits in northeast Hunan province. It was also one of the main controlling factors for the enrichment of trace elements in stone coal.

     

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