鄂尔多斯盆地延长组火山灰沉积物岩石地球化学特征  

Petrological-Geochemical Characteristics of Volcanic Ash Sediments in Yanchang Formation in Ordos Basin

作　　者：邱欣卫[1] 刘池洋[1] 毛光周[1,2] 吴柏林[1] 

机构地区：[1]大陆动力学国家重点实验室,西北大学含油气盆地研究所,陕西西安710069 [2]山东科技大学地质科学与工程学院,山东青岛266510

出　　处：《地球科学（中国地质大学学报）》2011年第1期139-150,共12页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金(重大研究计划)重点项目(No.90814005);陕西省“13115”科技创新工程重大科技专项项目(No.2008ZDKG-48);国家重点基础研究发展计划“973”项目(No.2003CB214600);西北大学研究生自主创新资助项目(No.09YZZ41)

摘　　要：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.Volcanic ash sediment is widely distributed in Yanchang Formation in Ordos basin,in order to study lithogeochemistry characteristics and formational mechanism of volcanic ashes sediment,the paper use many analysis methods,such as observe the cores,microscope,XRF,ICP-MS,SEM et al.. The results indicate volcanic ash sediment containing much crystal and shard fragments,including tuff and bentonite,the illite and andreattite can be seen under the SEM; SiO2 content between 50.29%-79.82%,rich potassium,K2O＋Na2O at 3.20%-7.88%,the negative correlation present in relationship of SiO2 with Al2O3,TFe2O3 and MgO;∑REE=99.82×10-6~550.15×10-6,and rich in LREE,deplete in HREE,the curve rightward incline,Eu negative abnormity and the δEu between 0.147-0.837,there is no evidently Ce abnormity,and K,Rb,Ba,Th are of positive abnormity. In the illustration of Nb/Y-Zr/TiO2,the data dots are mainly located at the zone of andesite-rhyolite,which suggest that the volcanic ash is primary from middle-acid rocks. Lithogeochemistry and sedimentology illustrate the formational mechanisms of volcanic ash include：falling down from air and carried by water. Through the diagram of tectonic setting,the volcanic ash is primary from volcanic arc and calc-alkalic lavas,which is intimately related the evolution of Qinling orogenic belt.

关 键 词：鄂尔多斯盆地 延长组 火山灰沉积物 凝灰岩 斑脱岩 地球化学 

分 类 号：P584[天文地球—岩石学]