【作者】 赵红格；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2003， 博士

【摘要】 鄂尔多斯盆地西缘构造现象复杂、特征各异，中生代的构造属性及其演化不同学者认识有别，尤其是对晚三叠世的构造属性尚存在较大分歧。笔者广泛收集和系统分析了研究区大量的地球物理、沉积、构造和岩石学等资料，对盆地西缘自南而北进行了两次野外地质实际调查，在此基础上，重点研究了大量地震剖面和在西缘地震勘探空白区新完成的地震剖面及新近重磁电研究成果，结合裂变径迹等测试分析资料，从区域地球动力学背景和盆山耦合的思路入手，对鄂尔多斯盆地西缘的构造特征及其属性进行了详细解剖。 通过对鄂尔多斯盆地西缘构造发育的区域构造背景分析，认为在鄂尔多斯盆地之西，一直没有一个统一的稳定地块相邻，与盆地西缘北部相邻的阿拉善地块，受南北相邻的祁连褶皱带和天山兴蒙褶皱带活动的影响，较稳定地块的范围比较狭窄，其南又有龙首山-中卫走滑断裂构造带存在。这是盆地西缘南、北区构造特征差别甚大，而中区构造特征特殊形成的区域背景。盆地西邻中生代盆地发育，各盆地均有一定厚度的中生代沉积，其中以早中侏罗世地层分布最广。这表明中生代在盆地西邻不存在广泛遭受剥蚀的区域挤压褶皱隆起区。 在盆地西缘北部贺兰山地区，发现典型拉张环境形成的拉斑玄武岩，测年时代为晚三叠世。在贺兰山的中生代地层中，晚三叠世-中侏罗世地层分布广泛、厚度巨大，中侏罗世延安组为贺兰山的优质含煤层。构造特征分析表明，在晚三叠世贺兰山地区处于拉张环境，早中侏罗世构造环境亦无明显挤压迹象。据沉积、构造和裂变径迹测试结果综合分析认为，现今所见的贺兰山逆冲推覆构造形成于晚侏罗世。贺兰山的主隆升期始于始新世，与银川地堑的形成同步。西缘六盘山地区在晚三叠世-中侏罗世，较大面积沉降，接受沉积，上三叠统厚度较大，可与鄂尔多斯盆地沉积环境比较，当时的水体是相连通的。故六盘山地区在晚三叠世-中侏罗世并不是一收缩造山带。 通过对西缘地区在现代地貌、地表地质、沉积环境和构造展布方向等特征和地震、重磁等资料的综合研究，提出盆地西缘在南北向上构造特征差别明显的新认识。将其分为北、中、南三区，其间分别以区域近东西向的青铜峡-吴忠和中卫-中宁断裂带相分隔。 北区以正谊关断层为界，可进一步分为桌子山段和银川地堑及横山堡两大段，其中的横山堡段可根据断层展布方向、构造特征的差异，分为铁克苏庙、陶乐东和色伦卡德庙南三段。桌子山段以发育一系列由西向东逆冲的断裂和背向斜组成的推覆体系为特点，卷入地层多为元古界-古生界，中生界分布有限，其中晚侏罗世地层在逆冲断裂前缘普遍见一套砾岩，故推测该段逆冲构造形成于晚侏罗世。横山堡构造带发育由东向西逆冲的高角度断裂，根据地层接触关系，推断该构造带的逆冲活动发生于晚侏罗世。 中区包括马家滩段及其与横山堡之间的转换带两段。该转换带在西部卫宁山区，表现为一系列东西向展布的断裂和褶皱。在两缘表现为由东向西的横山堡反冲构造带和由西向东的马家滩逆冲推覆构造带之间的转换带，南、北构造线临近和进入转换带均发生明显的向近东西向转变。马家滩构造带分为惠安堡-马家滩大型逆冲推覆构造体系和韦州-石沟驿拆离滑覆构造体两部分。惠安堡-马家滩大型逆冲推覆构造表现为浅层强烈的逆冲推覆活动，对深层影响较小，为薄皮构造，形成于晚侏罗世。韦州-石沟驿拆离滑覆构造体叠加于前者之上，由南向北发生滑覆，发生时期稍晚于前者。 南区以环县-海原和平凉-隆德断裂为界，分为沙井子北、固原和华亭南三段，其逆冲推覆作用明显减弱，断层倾角变陡。其中固原段可分为沙井子南和彭阳两段，其间以兰州-固原断裂为界，两段中盆地西缘与盆地内部的分界断裂在东西方向上差别较大。 对盆地内充填的沉积地层、环境特征和盆地沉积边界等的系统研究，探讨了古沉积边界和盆山关系。地层厚度和各油层组厚度对比表明，晚三叠世石沟驿地区延长组的厚度不超过1500m，且以含砾砂岩为主，与其东西两侧的地层厚度变化不大，向南北方向，厚度则快速减薄。汝箕沟地区的巨厚上三叠统，为拉张环境下的沉积.峡恫山巨厚的延长组沉积，分布范围有限，主要受秦祁造山带活动的影响，故而不能作为整个西缘的代表，所以在晚三叠世盆地西缘不存在有统一成因联系的大型南北向沉降带.而晚三叠世盆地南缘地层剖面上南厚北薄的特点，与秦岭造山带的挤压隆升作用活动密切相关，为其周缘前陆盆地。 晚三叠世一中侏罗世，鄂尔多斯盆地西部的沉积范围远大于现今的沉积边界，向西延伸较远，与六盘山盆地及其西沉积环境相似、地层具可比性。 针对盆地西缘露头区隆升时限和主构造变形期具体定时难度较大、认识不一的难题，本文首次在西缘从南到北系统采样，进行磷灰石和错石裂变径迹年龄测试，进而探讨隆升期次、时限和速率。西缘不同地区(汝箕沟、石沟异、罗山、炭山、窑山、六盘山和安口窑)错石、磷灰石裂变径迹测试结果的中生代年龄在 222.5一78Ma之间，集中在158.l.136.2Ma之间，平均为146.SMa，反映了盆地西缘主构造抬升事件发生于晚侏罗世。这与该时期挤压逆冲构造发更多还原

【Abstract】 The structure phenomena in Ordos basin are complicated and different in various areas. The views to Mesozoic structure attribute and its evolution differ between scholars, especially much diversity on the structure attribute in Late Mesozoic. Based on extensively gathering and sysmatically analyzing much geophysics, sedimentary, structure and petrological materials in research field and taking two field geological explorations from south to north in western Odors basin margin, the paper studied large numbers of seismic sections and newly-finished profiles in former seismic blanked area of western margin as well as up-to-date gravity and magmatic fruits, put views on the regional geotectonic background and basin-mountain coupling and made through research on the structure features and attribute together with the result of fission track testing.Through the regional background analysis in which western structures developed, it suggested that there did not exist a united and steady block to the west of Ordos basin. Alashan Block neighboring on the north of the western margin was largely influenced by the action of Qilian and Tianshan-Xingmeng folded belt which is respectively to the south and north of Alashan Block, was narrow in the steady block and was limited by the Longshou Mountain-Zhongwei strike fracture in the south area. These all formed the regional background of western margin of Ordos basin in which there were extremely difference in south and north area and developed special structures in the middle area. Great many Mesozoic basins in which Mesozoic sediments had certain depth and Early-Mid Jurassic strata were broadly distributed are found nearby western Ordoa basin. So it can be concluded that there did not exsit regional compressional folded-uplifted area which was eroded widely in Mesozoic in the west neighouring district.The tholeiite with Late Trassic age has been found in Helanshan area on the north part of western margin of Ordos basin. Late Triassic to Mid Jurassic strata in which owns the good coal of Van’an Formation distributes widely with huge thickness in Helan Mountain. Structure characteristics show that Helan Mountain was in extensional environment in Late Triassic and no obvious compressional evidence in Early-Mid Jurassic. The present thrust nappe structure formed in late Jurassic according to comprehensive analysis of sedimentary, structure and fission track tesing result. The main uplift age is in Eocene and isochronous to that of the formation of Yinchuan graben. Liupan mountainous area deposited and toke sediments in huge district in which Late Triassic has huge thickness, which is similar to that of Ordos basin and the water is connected. Therefore, Liupanshan area during Late Triassic to Mid-Jurassic is not a compressional orogen.Comprehensively studied the features in present geomorphography, surface geology, sedimentary environment and structural distributed direction and seismic, gravity and magmatic data, the paper proposes the new view that there still lies evident structure difference in western margin of Ordos basin from south to north. The western margin can be divided by Qingtongxia-Wuzhong and Zhongwei-Zhongning fracture with east-west tending into three districts, north, middle and south distict.The north district includes Zhuozishan and Yinchuan graben and Hengshanbu part by the boundary of Zhengyiguan fault. Hengshanbu part have three secondary parts which are Tiekesumiao, eastern Taole and south of Selunkademiao. The Zhouzishan part of is charactered by thrust nappe which is composed by faultsthrust from west to east, anticlines and synclines, involving much of Proterzoic, Palozoic and very limited Mesozoic in which a suite of conglomerate is found in the front of thrust fractures in Late-Jurassic. It is concluded that the thrust structure formed in Late-Jurassic. Faults with high angles appeared in Hengshanbu structure part which is also developed in Late-Jurassic deduced by strata contact relationship.Middle district includes two parts which更多还原