吕梁山及邻区新生代构造—沉积演化

【作者】 李建星；

【导师】 于在平；

【作者基本信息】 西北大学 ， 构造地质学， 2009， 博士

【摘要】 山体隆升剥蚀及热历史恢复是国内外新生代地质学和构造地质学的重要研究领域。新生代隆起定型的吕梁山分割了原鄂尔多斯盆地为现今鄂尔多斯盆地和沁水盆地,对比研究吕梁山及其东西两侧的两个沉积盆地新生代构造演化可为研究盆地后期经受的改造作用提供新的信息。同时吕梁山也是越过青藏高原东北部边界的的第一大山系,其隆升过程研究可从时间角度约束青藏高原横向扩展所能影响到的东北部边界。吕梁山山前新生代沉积物组成、空间分布、沉积环境及时代确定是研究吕梁山新生代晚期隆升剥蚀以及黄河形成与演化的关键。本论文分别从山前盆地和山体出发,采用多手段研究吕梁山新生代隆升剥蚀过程。从山体入手,根据定性研究结果将吕梁山分为北中南三段,分别采用裂变径迹定年方法,确立吕梁山隆升的期次、幅度及时间,探讨其新生代隆升的时间阶段性和空间区域性。从山前盆地入手,采用岩相学分析与古地磁定年相结合,约束吕梁山晚期隆升剥蚀过程。结合盆地和山体两方面研究结果恢复吕梁山及邻区新生代构造沉积演化过程。山体不同部位裂变径迹研究表明吕梁山新生代至少经历了58Ma、49-53Ma、38-43Ma和26Ma四次间歇性隆升,隆升幅度北中南有异。吕梁山中段于58Ma发生首次抬升,此次抬升可能未波及到南北两段;49-53Ma吕梁山北中段一起隆升,但中段隆升幅度大于北段,南段未记录此次事件。38-43Ma,吕梁山整体隆升。约26Ma,吕梁山再次发生全面抬升,奠定了吕梁山的主体格局。吕梁山山前砾石层的空间分布特征、砾石成份与毗邻基岩区的耦合关系以及典型剖面沉积学研究表明砾石层是吕梁山新生代隆升剥蚀的产物,10-6.5Ma(古地磁年龄)是吕梁山晚期隆升剥蚀的时间。柳林新近纪地层剖面揭示了剖面尺度上红粘土与水成堆积物的关系,结合前人研究结果认为区域上吕梁山山前的水成堆积物呈楔状“侵入”于红粘土的中下部。新发现了再搬运的红粘土及钙质结核,为红粘土成因解释提供了新的资料,磁性地层学研究表明其形成于8Ma,暗示了吕梁山地区曾经堆积了早于8Ma的红粘土。在柳林剖面新近纪地层精细研究的基础上,结合区域资料认为吕梁山山前新近纪(原)保德组下部砂砾石是水成堆积,上部棕红色粘土与棕黄色钙质结核层为风成堆积,中部则为二者的过渡地段,即原保德组包含了下部水成堆积和上部风成堆积。这有悖于《中国地层指南及中国地层指南说明书》对组的定义,应予解体。解体后保德组下部的水成堆积物称为芦子沟组,相当于初始定义的“芦子沟系”或“芦子沟砾岩”;保德组上部风尘堆积仍称之为保德组。新生代以来,吕梁山及西部鄂尔多斯盆地一直处于抬升剥蚀状态,缺失新近纪以前沉积。10-6.5Ma,吕梁山快速隆升,在山前堆积了芦子沟组。约8Ma起,吕梁山西部的黄土高原地区开始广泛接受风尘堆积。1.6Ma黄河贯通南北新生代地堑,此后不断振荡下切,切入基岩。更多还原

【Abstract】 Reconstruction of Cenozoic thermal history and the uplift processes of mountains is the important research field of the Cenozoic geology.L(u|¨)liang Mountain which uplifted in Cenozoic divided the Pre-Ordos Basin into Ordos Basin and Qinshui Basin.Comparative study the evolution of L(u|¨)liang Mountain and Ordos Basin and Qinshui Basin in Cenozoic can provide new information for the study of basin reformation.In addition,L(u|¨)liang Mountain is the first mountain ranges across the northeastern border of Qinghai-Tibet Plateau.Research on the Cenozoic uplift of L(u|¨)liang Mountains could constrain the eastern border of Qinghai-Tibet Plateau lateral spread from time viewpoint.Composition,spatial distribution and sedimentary environment of Cenozoic sedmnetary in front of L(u|¨)liang Mountain are the keys to study uplift of L(u|¨)liang Mountains and the formation and evolution of Yellow River.In this thesis we subject different methods for the uplift of L(u|¨)liang Mountain from the view of foreland basin and Mountain Body.Based on qualitative study,the L(u|¨)liang Mountain can be divided into three parts(north,middle and south).In Mountain,fission track dating analysis are used in diffirent parts of L(u|¨)liang Mountain to get the information of times and amplitude of the uplift,which can provide information to study the time stage and regional characteristic of uplift.For the foreland basin,Lithofacies analysis and Paleomagnetic dating are the main methods to constraint the process of uplift and denudation of L(u|¨)liang Mountain. Together with the study of foreland basin and Mountain Body,We reconstruct the Cenozoic history of tectonic-sedimentation in L(u|¨)liang Mountain and its adjcient area.Fission track study on Different parts of L(u|¨)liang Mountain shows that there are at least four times intermittent uplift(58Ma、49-53Ma、38-43Ma and 26Ma) in Cenozoic and the amplitude is different in the north、middle and the south part.The middle part of L(u|¨)liang Mountain uplifted in 58Ma firstly which has not sweep other parts.In 49-53Ma,both north and the middle part of L(u|¨)liang Mountain uplift.The upift amplitude of middle part was larger the north.38-43Ma and 26Ma,the whole L(u|¨)liang Mountain experienced two rapid uplifts and the latter established the main pattern of L(u|¨)liang Mountain.Gravel’s spatial distribution characteristics in a wider range,gravel composition and adjacent bedrock’s composition and research of typical profile sedimentology tell us that the gravel bed in front of the L(u|¨)liang mountains is the product of L(u|¨)liang Mountains’s uplift in Cenozoic. Paleomagnetic age(10-6.5Ma) of gravel bed is the uplift date of L(u|¨)liang Mountains. Further research on Liulin Section reveals the relation between red clay and fluvial accumulation.Togeteh with other researcher’s results,the conclusion can be drawn:fluvial deposits wedge red clay base like an asymmetric wedge.The discovery of red clay and calcium nodule transported can provide new information for the cause of red clay. Magnetostratigraphic result reveals that red clay and calcium nodule transported is aged about 8Ma,which indicates that the red clay older than it must exist before 8Ma.Based on study on Neogene Stratigraphy in Liulin profile,together with other researcher’s results,it is concluded that the sandy gravel layer in the lower pre-Baodean is fluvial deposits,but the upper sequence of brownish red clay and brownish yellow calcite nodule interbedded with each other are aeolian clay layers;The middle part is thought to be the transition zone of the lower aqueous deposit and upper interbedding of red clay and calcite nodule.In other words,pre-Baode Formation includes fluvial deposits and aeolian clay layers, which is not accord with the definition of Formtion by the《The Stratigraphic Guide of China and Its Explaination》and should be disassembled.We named fluvial deposits of Pre-Baode Formation as Luzigou Formation and aeolian clay layers as Baode Formation.Luzigou Formation is Equivalent to the original difintion of"luzigou Gravel".L(u|¨)liang Mountain and the Ordos Basin have kept in uplift-denudation condition Since the Cenozoic and missed Paleogene strata.At 10-6.5Ma,L(u|¨)liang Mountain uplifted rapidly and formed the luzigou Formation.At 8Ma,Loess Plateau Region(in the west part of L(u|¨)liang Mountains began to accumulate Aeolian clay layers extensively.The Yellow River transfixion the north and south Cenozoic graben in 1.6Ma,then it intermittent cut and cut into the bedrock.更多还原