论文部分内容阅读
鄂尔多斯盆地延长组火山灰沉积物分布广泛,为研究其岩石地球化学特征和形成机制,通过详细的岩心观察、薄片鉴定、X荧光光谱分析(XRF)、ICP-MS分析、扫描电镜(SEM)分析等手段,对延长组火山灰层进行了细致的岩石地球化学分析.结果表明火山灰沉积物富含晶屑、玻屑等火山物质,整体蚀变强烈,可分为凝灰岩和斑脱岩,以伊利石、伊蒙混层等粘土矿物为主;主量元素SiO2含量为50.29%～79.82%,富钾,K2O+Na2O在3.20%～7.88%之间,SiO2与Al2O3、TFe2O3、MgO之间存在着明显的负相关关系;∑REE在(99.82～550.15)×10-6之间变化,总体特征表现为轻稀土富集,重稀土亏损,曲线形态整体表现为右倾型,Eu负异常,δEu为0.147～0.837,没有明显的Ce异常;大离子亲石元素K、Rb、Ba、Th呈正异常,在Nb/Y-Zr/TiO2图解中,数据点主要落在安山岩-流纹岩之间,说明火山物质主体来源于中酸性岩.综合岩石地球化学和沉积学分析,认为延长组火山灰沉积物包括空降型和水携两种形成机制,大地构造环境判识图解反映了火山灰源于火山弧钙碱性岩浆原区,与晚三叠世秦岭造山带的演化关系密切.
The volcanic ash deposits in the Yanchang Formation in the Ordos Basin are widely distributed. In order to study the geochemical characteristics and formation mechanism of the volcanic rocks, detailed core observation, slice identification, X-ray fluorescence spectroscopy (XRF), ICP-MS analysis and SEM The results show that the volcanic ash deposits are rich in volcanic materials such as crystal and vitreous shale, and the whole alteration is intense and can be divided into tuff and bentonite, with illite, Yimeng mixed layer and other clay minerals. The main element of SiO2 content is 50.29% ~ 79.82%, potassium is rich, K2O + Na2O is between 3.20% ~ 7.88%, SiO2 and Al2O3, TFe2O3 and MgO are obviously negative ΣREE varies from (99.82 to 550.15) × 10-6. The general characteristics are light rare earth (REE) enrichment and heavy RE depletion. The curve shows the right-tilting and the Eu anomaly with δEu ranging from 0.147 to 0.837. There is no obvious Ce anomaly. K, Rb, Ba and Th of large ion lithophile are positive anomalies. The data points mainly fall between andesite and rhyolite in the graph of Nb / Y-Zr / TiO2, indicating that the main source of volcanic material In the acidic rocks. Integrated rock geochemistry and sediment According to the analysis, the formation mechanism of volcanic ash deposits in Yanchang Formation, including airborne type and waterborne type, is considered. The tectonic setting of the tectonic environment reflects the origin of volcanic ash in the calc-alkaline magma of the volcanic arc and the evolution of the Late Triassic Qinling orogenic belt Close relationship.