贵州剑河方陇剖面留茶坡组硅质岩的地球化学特征及其成因意义

Geochemistry of the Chert from the Liuchapo Formation in the Fanglong Section at Jianhe County,Guizhou Province

为研究贵州剑河方陇剖面留茶坡组硅质岩的成因和沉积环境,用X荧光光谱仪和等离子体质谱仪对其主量和微量元素进行了测试。结果显示,硅质岩的Si O2含量较高(平均值为87. 67%),Al2O3、Fe2O3、MnO平均含量分别为5. 21%、1. 15%和0. 005%,Al/(Al+Fe+Mn)、Al2O3/(Al2O3+Fe2O3)、K2O/Na2O和MnO/Ti O2的平均值分别为0. 77、0. 82、36. 07和0. 028;ΣREE值为13. 94×10^-6~89. 36×10^-6,平均值为59. 69×10^-6,低于澳大利亚后太古宙平均页岩(PAAS,ΣREE=184. 8×10^-6),高于扬子地台部分同时期深水盆地硅质岩,LaN/YbN和LaN/CeN平均值分别为1. 17和1. 43,具有一致的弱负Ce异常(平均0. 77),无明显的正Eu异常(平均1. 00),U/Th平均值为0. 21。研究表明,贵州剑河方陇剖面留茶坡组硅质岩的成因倾向于正常海水沉积成因,沉积环境为大陆边缘,沉积过程中有一定程度的陆源碎屑物质的输入。

In order to understand the origin and sedimentary environment of the chert of the Liuchapo Formation at the Fanglong section in Jianhe County of Guizhou Province,major and trace elements of the chert have been analyzed using XRF and ICP-MS,respectively. The results show that the chert has high content of SiO2(averaged 87. 67%). The averaged contents of Al2O3,Fe2O3,MnO in the chert are 5. 21%,1. 15% and 0. 005%,respectively. The ratios of Al/(Al+Fe+Mn),Al2O3/(Al2O3+Fe2O3),K2O/Na2O and MnO/TiO2 of the chert are 0. 77,0. 82,36. 07 and 0. 028,respectively. They have averaged total REE of 59. 69×10^-6,which is lower than the total REE of PAAS(184. 8×10^-6) and higher than that of some synchronous cherts deposited in deep basin. Their(La/Yb)Nand(La/Ce)Nratios are 1. 17 and1. 43,respectively. The chert from the Fanglong Section has weak negative Ce anomaly(averaged δCe is 0. 77) and has no Eu anomaly(averaged δEu is 1. 0). The average of U/Th ratio of the chert is 0. 21. The data of the present study suggest that the chert tends to have formed from normal marine environment at continental margin. The results also suggeat the contribution of terrestrial detritus during deposition of the chert.