深水阻塞盆地陆源碎屑岩地球化学特征分析——以鄂尔多斯盆地桌子山地区上奥陶统拉什仲组为例  

Geochemical characteristics analyses of terrigenous clastic rocks in deep-water ponded basin:A case study from Upper Ordovician Lashenzhong Formation in Zhuozishan area,Ordos Basin

作　　者：李向东[1,2] 魏泽昳 陈海燕 LI Xiangdong;WEI Zeyi;CHEN Haiyan(School of Land Resource Engineering,Kunming University of Science and Technology,Kunming,Yunnan 650093,China;Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institude of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;China National Offshore Oil Corporation(CNOOC)China Limited Hainan Branch,Haikou,Hainan 570312,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093 [2]中国地质科学院地质研究所,自然资源部深地动力学重点实验室,北京100037 [3]中海石油(中国)有限公司海南分公司,海南海口570312

出　　处：《中国矿业大学学报》2024年第1期158-175,共18页Journal of China University of Mining & Technology

基　　金：自然资源部深地动力学重点实验室开放课题基金项目(J1901-16);国家自然科学基金项目(41272119)。

摘　　要：中、晚奥陶世是鄂尔多斯盆地西缘由被动大陆边缘向主动大陆边缘转换时期,发育各种深水重力流和牵引流沉积.浊积砂岩大地构造环境判别指标总体上显示为介于被动、活动大陆边缘和大陆岛弧之间的性质,反映出该时期大地构造环境的非典型性;同时深水牵引流沉积构造多发育在高钙质含量的岩石中.本文针对上述2个问题,选取桌子山地区上奥陶统具有阻塞浊流沉积的拉什仲组为研究对象,采用沉积学和沉积地球化学相结合的方法开展研究.结果表明:拉什仲组砂岩和黏土岩普遍存在高CaO和低Na_(2)O的特征,砂岩的CaO和Al_(2)O_(3)含量约是黏土岩的2倍和0.5倍.深水牵引流发育和CaCO_(3)沉淀的有利区均为盆地中的高盐度水体作用区,在空间上重合.在使用含有SiO_(2),Na_(2)O,Al_(2)O_(3)和CaO的指标及与这些元素呈良好线性相关性的指标进行大地构造环境判别时会出现一定的偏差.因此,在深水阻塞盆地中,水下隆起或古陆在向陆方向对陆源碎屑物质和淡水的限制(隔离)作用,导致深水牵引流沉积构造多发育在富含钙质的岩石中;在向海方向对岛弧火山物质的阻挡作用,导致在用砂岩地球化学指标进行大地构造环境判别时出现相互矛盾的现象.The Middle and Upper Ordovician of western margin of Ordos basin are an transition geologic age from passive to active continental margin for which the various of deep-water gravity and traction flow deposits were developed.In contrast,one phenomena of western margin of Ordos basin is that the geochemical index of turbidite sandstones proposed the tectonic environments have been among passive,active continental margins and continental island arcs which perhaps reflected an atypical tectonic environment,another pervasive geological phenomena was that the sedimentary structures of deep-water traction flow were mostly developed in calcareous rocks.These two contradictions mentioned above were focused on in this paper,and proposed the studies using sedimentology and sedimentary geochemistry methods based on the ponded turbidity current deposits of the Upper Ordovician Lashenzhong Formation in Zhuozishan area.The results show that the sandstones and claystones in Lashenzhong Formation commonly have the high CaO and low Na_(2)O contents,and the contents of CaO and Al_(2)O_(3) of sandstones are almost twice and half as much as claystones respectively.the favorable area of deep-water traction flow and CaCO_(3) depositions is both coinside well with the action area of high salinity water bodies.the limited deviations is existed in the results of tectonic environments when using the index which contents major elements such as SiO_(2),Na_(2)O,Al_(2)O_(3) and CaO or the index which have a good linear independence with these elements.In conclusions of subaqueous ponded basin,the sedimentary structures induced by deep-water traction flows are devoloped in calcareous rocks perhaps due to the restriction(isolation)of terrigenous detrital material and freshwater(landward direction)by subaqueous uplift or archicontinent.the actions to prevent volcanic material from island arc(seaward direction)induced by subaqueous uplift or archicontinent are perhaps leading to the contradictions in the results of tectonic environments as disting

关 键 词：阻塞浊流 深水牵引流 地球化学 大地构造环境 鄂尔多斯盆地 

分 类 号：P512.2[天文地球—地质学] P594.2