内蒙古阿拉善地块北缘石炭系本巴图组地质特征及沉积环境分析
发布时间：2018-11-10 15:54
【摘要】：研究区位于内蒙古自治区阿拉善盟阿拉善右旗。区内古生界以恩格尔乌苏缝合带为界,分为西北部的塔里木-南疆大区和东南部的华北地层大区,上古生界的上石炭统本巴图组(C2bb)位于华北地层大区,主要出露于恩格尔乌苏-东德乌苏-撒拉-查干楚布一带。根据岩石组合特征,将研究区本巴图组自下向上分为三段:一段以中厚层大理岩(原岩为灰岩)为主,夹有变质中细粒含钙质岩屑砂岩和变质粉细砂岩,为浅海碳酸岩台地沉积;二段为变质砾岩、变质含钙质粉细砂岩和大理岩,砾岩多呈透镜状发育,变质含钙质粉细砂岩呈薄层状发育,为半深海斜坡沉积;三段包括变质砂岩和千枚岩,部分层位变质砂岩中可见黄铁矿晶体和鲍马序列,反映深水还原环境,为深海-半深海浊积扇沉积。根据在恩格尔乌苏本巴图组剖面(PM122)上采集的本巴图组变质砂岩和侵入其中岩脉的样品进行锆石年龄测定。本巴图组变质砂岩中碎屑锆石的最小年龄407±3Ma和侵入本巴图组中的岩脉的岩浆锆石的最大年龄267±3Ma,结合邻区古生物资料大致确定本巴图组时代应为晚石炭世。研究区本巴图组三段砂岩化学成分中Si O2含量变化较大,在42.96%-78.41%之间变化,平均61.74%。变质砂岩中Al2O3含量较高(7.52%-16.95%),平均含量为13.34%。本巴图组砂岩的化学蚀变指数(CIA)较高,介于58.66-76.4之间,平均值为65.82,表明沉积物源区的风化作用较为强烈或者经历了沉积物再循环作用。利用(Fe2O3t+Mg O)-Ti O2图解和(Fe2O3t+Mg O)-Al2O3/(Ca O+Na2O)图解进行判别,表明本巴图组三段的形成环境与活动构造背景相关。稀土元素分析结果显示:样品均为轻稀土元素富集型,Eu呈现负异常。样品∑REE值较大,平均为平均为143.85×10-6,反映与岛弧相关的特征。综合岩性组合特征、沉积构造和地球化学分析可知:本巴图组一段沉积环境为稳定背景下的浅海碳酸盐台地;二段沉积环境为过渡带,此段代表了大地构造背景由稳定到活动的转换;三段沉积环境为活动背景下的深海—半深海。
[Abstract]:The research area is located in the right flag of Alashan League of Inner Mongolia Autonomous region. The Paleozoic is divided into the Tarim and South Xinjiang regions in the northwest and the North China stratigraphic region in the southeast, and the Upper Carboniferous Ben-Gbatu formation (C2bb) in the Upper Paleozoic is located in the North China stratigraphic region. Mainly exposed in the Engloussu-East Germany Usu-Sara-Chaganchub area. According to the characteristics of rock assemblage, the BenGbatu formation in the study area is divided into three sections from the bottom up: the first section is composed of medium and thick marble (primary limestone), intercalated with metamorphic fine-grained calcareous lithic sandstone and metamorphic silty sand. It is a shallow carbonate platform deposit; The second stage is metamorphic conglomerate, metamorphic calcareous silty sand and marble, the conglomerate is mostly lenticular, metamorphic calcareous silty sand is thin layer, it is semi-deep sea slope deposit. The three formations include metamorphic sandstone and phyllite, and pyrite crystals and Baoma sequences can be found in some of the metamorphic sandstone, reflecting the deep-water reduction environment and the deep-sea and semi-deep-sea turbidite fan deposits. Zircon dating was performed on the metamorphic sandstone and intrusive veins of the Ben Gbatu formation collected from the PM122 section of the Englesu Ben Gbatu formation. The minimum age of detrital zircon in metamorphic sandstone of the Ben Gbatu formation is 407 卤3Ma and the maximum age of magmatic zircon intruding into the vein of the Ben Gbatu formation is 267 卤3 Ma. combined with the paleontological data of the adjacent area, it is generally determined that the age of the Ben Gbatu formation should be the late Carboniferous. The content of Si O 2 in the chemical composition of sandstone of the third member of the Benjiao formation in the study area varies greatly, ranging from 42.96% to 78.41%, with an average of 61.74%. The content of Al2O3 in metamorphic sandstone is higher (7.52% -16.95%), and the average content is 13.34%. The chemical alteration index (CIA) of the sandstone of the Gbatu formation is higher, ranging from 58.66 to 76.4, with an average value of 65.82, which indicates that the weathering in the source area of the sediments is relatively strong or has experienced sediment recirculation. The (Fe2O3t Mg O) Ti O 2 diagram) and (Fe2O3t Mg O) Al2O3/ (Ca O Na2O) diagram are used to distinguish the formation environment of the third member of the Gbatu formation is related to the active tectonic background. The results of REE analysis showed that all samples were light REE enriched type and Eu showed negative anomaly. The mean 鈭，
本文编号：2322882
[Abstract]:The research area is located in the right flag of Alashan League of Inner Mongolia Autonomous region. The Paleozoic is divided into the Tarim and South Xinjiang regions in the northwest and the North China stratigraphic region in the southeast, and the Upper Carboniferous Ben-Gbatu formation (C2bb) in the Upper Paleozoic is located in the North China stratigraphic region. Mainly exposed in the Engloussu-East Germany Usu-Sara-Chaganchub area. According to the characteristics of rock assemblage, the BenGbatu formation in the study area is divided into three sections from the bottom up: the first section is composed of medium and thick marble (primary limestone), intercalated with metamorphic fine-grained calcareous lithic sandstone and metamorphic silty sand. It is a shallow carbonate platform deposit; The second stage is metamorphic conglomerate, metamorphic calcareous silty sand and marble, the conglomerate is mostly lenticular, metamorphic calcareous silty sand is thin layer, it is semi-deep sea slope deposit. The three formations include metamorphic sandstone and phyllite, and pyrite crystals and Baoma sequences can be found in some of the metamorphic sandstone, reflecting the deep-water reduction environment and the deep-sea and semi-deep-sea turbidite fan deposits. Zircon dating was performed on the metamorphic sandstone and intrusive veins of the Ben Gbatu formation collected from the PM122 section of the Englesu Ben Gbatu formation. The minimum age of detrital zircon in metamorphic sandstone of the Ben Gbatu formation is 407 卤3Ma and the maximum age of magmatic zircon intruding into the vein of the Ben Gbatu formation is 267 卤3 Ma. combined with the paleontological data of the adjacent area, it is generally determined that the age of the Ben Gbatu formation should be the late Carboniferous. The content of Si O 2 in the chemical composition of sandstone of the third member of the Benjiao formation in the study area varies greatly, ranging from 42.96% to 78.41%, with an average of 61.74%. The content of Al2O3 in metamorphic sandstone is higher (7.52% -16.95%), and the average content is 13.34%. The chemical alteration index (CIA) of the sandstone of the Gbatu formation is higher, ranging from 58.66 to 76.4, with an average value of 65.82, which indicates that the weathering in the source area of the sediments is relatively strong or has experienced sediment recirculation. The (Fe2O3t Mg O) Ti O 2 diagram) and (Fe2O3t Mg O) Al2O3/ (Ca O Na2O) diagram are used to distinguish the formation environment of the third member of the Gbatu formation is related to the active tectonic background. The results of REE analysis showed that all samples were light REE enriched type and Eu showed negative anomaly. The mean 鈭，
本文编号：2322882
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