论文部分内容阅读
通过野外地质调查和系统的岩石化学、主量元素、微量元素以及稀土元素等研究,探讨了藏南地区三叠系涅如组含放射虫硅质岩的地球化学特征及其沉积环境。研究区的硅质岩呈黑色、灰黑色或灰褐色薄层状或透镜状产出,具有较低的SiO_2含量,对研究区的硅质岩的主量元素运用了Fe-Mn-Al三角成因判别图、Al/(Al+Fe+Mn)比值、K_2O/Na_2O比值、Si/(Si+Al+Fe)比值、100×(Al_2O_3/SiO_2)-100×(Fe_2O_3/SiO_2)、Al_2O_3/(100-SiO_2)-Fe_2O_3/(100-SiO_2)及Al_2O_3/(Al_2O_3+Fe_2O_3)-Fe_2O_3/TiO_2图解等,显示硅质岩为具有生物成因的非热水或弱热水的大陆边缘沉积环境;硅质岩的稀土元素ΣREE变化较大,通过对硅质岩的稀土元素北美页岩标准化和球粒陨石标准模式图对比、Al_2O_3/(Al_2O_3+Fe_2O_3)-LaN/CeN图解及特征指数Ce/Ce*和LaN/CeN分析研究,显示硅质岩为大陆边缘、大陆边缘—深海的过渡环境;对硅质岩的微量元素运用了U/Th及Ni/Co比值,显示了非热水沉积物的环境特征。综合研究分析岩石化学、主量元素、微量元素以及稀土元素等因素及生物特征,可以得出研究区的硅质岩具有生物特征的非热水的大陆边缘沉积环境。
The geochemical characteristics and sedimentary environment of the Triassic Nirvie group containing radiolarian cherts in the southern Tibet are discussed through the field geologic survey and systematic petrochemistry, major elements, trace elements and rare earth elements. The siliceous rocks in the study area are black, grayish-black or taupe thin-bedded or lenticular-like with low SiO 2 content. The main elements of the cherts in the study area use the Fe-Mn-Al trigonal genesis (Al 2 O 3 / SiO 2) -100 × (Fe 2 O 3 / SiO 2), Al 2 O 3 / (100), Al / (Al + Fe + Mn) ratio, K 2 O / Na 2 O ratio, Si / SiO 2) and Al 2 O 3 / (Al 2 O 3 + Fe 2 O 3) -Fe 2 O 3 / TiO 2 diagrams, which show that the chert is a continental margin depositional environment with biogenic non-hot or weak hot water. Siliceous The REE of ΣREE varies greatly. Based on the comparison of standard schematics of North American shales and chondrules from the REE of siliceous rocks, the diagrams of Al 2 O 3 / (Al 2 O 3 + Fe 2 O 3) -LaN / CeN and the characteristic indices Ce / Ce * and LaN / CeN analysis shows that the chert is the transitional margin between the continental margin and the continental margin-deep sea. U / Th and Ni / Co ratios are used for the trace elements in the cherts, which shows the environmental characteristics of non-hot water sediments . Comprehensive analysis and analysis of rock chemistry, major elements, trace elements and rare earth elements and other biological characteristics, can be obtained in the study area of the biotite silicate non-hot continental margin depositional environment.