【作者】 张进；

【导师】 马宗晋；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2002， 博士

【摘要】 陕甘宁交界地区地处我国东部构造域和西部构造域的交接地区，亦为我国中部南北向构造带的北段。构造带向北以及向南可能延出国境。该地区自中、新生代以来以其明显的地貌特征、陡变的地球物理场、强烈的地震活动性、特殊的构造样式、“多旋迴”式的构造活动以及丰富的资源而受到了许多中外学者的注意。在漫长的研究过程中，不同的理论都先后对该地区作出过不同的解释：各大地构造学派都赋予该构造带不同的名称和性质；本文研究的陕甘宁交界的地区，地质上包括鄂尔多斯地块西缘及走廊过渡带东部地区；北起桌子山、贺兰山，向南到达宝鸡附近。西北与阿拉善地块相连，西南以六盘山西麓断裂与北祁连山褶皱带相邻，东面是长期稳定的鄂尔多斯地块。经过多年的研究，鄂尔多斯西缘的变形方式以冲断为主已经得到广泛共识；70年代末期至80年代以来，随着国际上推覆构造研究的重新兴起以及相关油气田勘探的重大突破，许多学者对鄂尔多斯西缘构造带的认识又有了进一步的深化，取得一批水平很高的研究成果，同时也在该地区陆续找到一些油气田。然而这并不表明我们已经完全准确地认识了该构造带，恰恰相反，在一些问题上还存在着许多争论，如对早古生代该地区的构造变动及样式认识不清，对鄂尔多斯西缘逆冲褶皱带缺乏统一的认识等等，这些都直接影响到对该构造带的正确认识，因此对该构造带的研究还有待于进一步的深入。 通过论文期间的工作，在野外地质调查与综合前人资料的基础上，针对该地区一些重要的构造现象重点讨论了鄂尔多斯西缘构造带以及走廊过渡带东部的古生代以及中生代的构造变形和一些沉积学特征；选择贺兰山中、南段、牛首山、卫宁北山以及鄂尔多斯西缘构造带南、北段过渡地区为研究区域，对该地区的古生代以及中生代地层的沉积特征、变形特征以及构造背景进行了研究，得出了一些与以往不同的新看法，取得了以下主要认识： 通过对牛首山地区的褶皱、劈理、断层以及脉体的分析，识别出至少3种类型的劈理，是识别牛首山米钵山组变形过程的重要标志，它们分别代表了导致米钵山组变形弯滑褶皱作用的不同阶段；并表明牛首山地区的褶皱属于断层相关褶皱；在露头尺度上大型断裂比较的少见，往往见到的断层属于褶皱所派生的突破断层；由于形成褶皱的断裂基本上都发育于层理之间，没有明显的切层断坡出现，可见牛首山地区的褶皱多数属于滑脱褶皱与断层传播褶皱的过渡类型。牛首山褶皱可能属于早古生代时期的结果，是该期运动推覆构造的前缘构造带；牛首山的这些特征与其南侧的大、小罗山以及北侧的贺兰山东麓地区很相似，它们可能是一个相连的构造带，代表了早古生代末期北祁连弧后前陆盆地关闭并变形的前缘地带。 根据构造变形特征的对比和构造背景分析，本文明确了狭义的(中生代)鄂尔多斯西缘构造带南北两分的构造特征以及该构造带南北两部分各自的形成机制，指出传统上将鄂尔多斯西缘构造带作为一个有统一形成机制的构造带是不妥当的。实际上，该构造带南北两部分具有各自相对独立的形成机制与过程。北段的形成来自于阿拉善地块与鄂尔多斯地块的相互挤压，而南段的形成主要来自于西南方向上古特提斯洋关闭的作用。鄂尔多斯地块在中生代很可能存在一定程度逆时针方向的旋转运动。北段主要包括桌子山段、贺兰山中、北段、银川地堑和横山堡段，由于结晶基底卷入变形之中，因此厚皮构造是该段变形的重要特点，由于将贺兰山以及银川地区也包括进北段，因此北段地表宽度较南段大，整个东西方向上的中生界地层缩短量也比以往的结果大的多;南段主要包括贺兰山南段、马家滩段以及沙井子段，该段的变形主要集中在沉积盖层，薄皮构造是该段变形的重要特点。阐明在中生代，狭义的鄂尔多斯西缘构造带南北两部分形成的时间以及持续的时间是不同的。北段活动时间短，而南段持续时间长。 通过对晚古生代地层分布及厚度的分析，论文确认了在鄂尔多斯西缘构造带南北两部分之间存在着一个比较大的侧断坡。该侧断坡沿青铜峡一线东西向延伸。侧断坡以北的奥陶纪古地貌表现出一个明显的低地，而且北部在石炭纪以及二叠纪也是一个沉积坳陷，而南部同时期则没有明显的沉积坳陷。由于石炭系一二叠系非能干层(煤层与暗色泥岩)的厚度在两侧不同以及侧断坡的存在，造成了两者从变形特征到影响范围都发生了分化，即使在两部分同时活动的时期(晚侏罗世)，也造成了鄂尔多斯西缘构造带中南北两部分之间的分化。该构造带在平面上的凹凸展布也反映了这种分化;在两部分活动不同时间时，南部的活动基本上没有影响到北部地区的变形。该侧断坡是否受断裂控制现在还不清楚，但根据鄂尔多斯内部资料的显示，该侧断坡可能受区域性断裂所控制。同时在北段也存在着一个侧断坡，因此北段的变形主要发生在这两个侧断坡所夹持的地区之中。 在鄂尔多斯西缘构造带和走廊过渡带东部地区可以识别出三期逆冲活动。早古生代(晚奥陶世一泥盆纪):早古生代地层中存在着逆冲构造，这些逆冲构造的以牛首山及其西南地区古生界的变形为代表，它们都是走廊过渡带弧后前陆盆地早古生代末关闭的结果;在鄂尔多斯西缘?更多还原

【Abstract】 This study is based on the field work of structural geology and sedimentology and synthesizing the data of previous work. It is focused on the Paleozoic and Mesozoic deformation and sedimentology on the western edge of the Ordos Block and the eastern part of Corridor Transitional Zone. And selecting the central and southern parts of Helan Shan, Niushou Shan, Weiningbei Shan and the transitional area between the southern part and northern part of fold-and-thrust belt along the western edge of Ordos Block as objects investigated, the author has studied the geological setting and the sedimentary characteristics, deformation of Paleozoic and Mesozoic strata in these areas, put forward some new points different from those taken by early researchers for granted, and gotten main results as below.By analyzing the folds and cleavages, the author recognized three-stage cleavages at least. These cleavages are important symbols for identifying the different stages of deformation of the Miboshan formation in Niushou Shan. They are representatives of different stages of flexural-slip mechanisms producing the folds in the Niushou Shan. And these folds could be produced by the orogeny movement acting in the early Paleozoic. They were part of the foredge belt of the thrust in that time. Although the folds in the Niushou Shan belong to the fault related fold, the large faults are rare in the outcrops. Many faults are break-through faults which are the results when folds are locked and with the stress going on then the faults are produced cutting the limbs of the folds. Many of the folds in Niushou Shan belong to detachment folds.Based on the analysis of the different characteristics of deformation and geological setting, the author thinks that the northern part is different from the southern part of the western Ordos fold-and-thrust belt in narrow sense, and brings forward the mechanism resulting in thesegmentation of the this fold-and-thrust belt. The author thinks that the opinion taking the western Ordos fold-and-thrust belt as a whole with uniform mechanism by many researchers is not right. In fact these two parts have their own mechanics and processes. The northern part includes the northern and central parts of Helan Shan, Zhuozi Shan segment and Hengshan Pu segment, which was produced by the compression between the Alashan Block and the Ordos Block. The southern part includes the southern part of Helan Shan, Majiatan segment and Shajingzi segment, which was produced by the compression from southwest. It is illustrated that these two parts of the western Mesozoic Ordos fold-and-thrust belt in narrow sense were active and produced in different time. The duration of the northern one was short and that of the southern part was much longer.On the basis of the distribution and thickness of the strata along the western Ordos, a large lateral or oblique ramp is identified between the northern and southern parts of the western Ordos fold-and-thrust belt. The northern part of the western Ordos was a sub-basin that was much deeper than that of southern part during the Carboniferous and Permian. Because of different thickness of strata and lateral (oblique) ramp, even when these two parts were active simultaneously (late Jurassic period), the processes of deformation varied from each other, which led to the segmentation of the western Ordos fold-and-thrust belt, and the salient and recess of the belt shown in the plane also illustrate the segmentation. And when these two parts were active in different time, the activity to the south did not affect the deformation of the northern part basically. It is not clear whether this lateral (oblique) ramp was controlled by fault or not. But the data from the internal Ordos Block show that it was probably controlled by the fault crossing the Ordos Block from west to east.The fieldwork, seismic profiles and data of other researchers demonstrate that there were at least three thrusting activities at different times in these areas. (1) Early Paleozoic period (late Ordovician-middle Devonian)更多还原