【作者】 胡召齐；

【导师】 朱光；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 上扬子地区是我国具有代表性的中生代强烈板内变形区，具有复杂与长期演化的挤压变形构造。该地区也是我国具有海相油气前景的重要地区。因而，认识与理解该地区中生代的变形方式与演化规律具有重要的理论与实际意义。本论文主要以构造地质学与同位素年代学的方法，重点对上扬子地区湘鄂西褶皱带、川东褶皱带与南大巴山褶皱带开展了详细的研究。在对雪峰隆起北部基底构造进行分析的基础上，本论文选择了7个基底板溪群板岩样品进行了伊利石X射线衍射分析与K-Ar年代学研究。这7个样品给出的冷却年龄为419-389Ma（晚志留世-中泥盆世），表明该隆起经历过加里东期构造热事件与相应的隆升。由此认为，华南加里东期变形事件直接影响到雪峰隆起本身，向西的影响边界可能为张家界-花垣-凯里断裂带。本论文选择了城口—房县断裂带房县-青峰段进行了详细的野外与室内显微构造研究。该段断裂带明显经历过两期上盘向南南西的逆冲变形，第一期为韧性逆冲变形，而第二期为脆性逆冲变形。工作中选择了该断裂带下盘变形变质的下志留统地层，从7块糜棱岩化浅变质粉砂岩中分选出绢云母样品进行了⁴⁰Ar/³⁹Ar同位素测年。其中5个样品给出了225—218Ma（晚三叠世早期）的理想坪年龄，被解释为冷却年龄。由此认为城口—房县断裂带第一期逆冲活动发生在中三叠世末，是扬子板块与秦岭地块陆—陆碰撞中发生的。再结合本次在该断裂带与坪坝断裂带之间新发现的角度不整合印支面（代表中晚三叠世之交发生的印支运动的构造界面），认为扬子板块北缘的印支期前陆变形带发生在坪坝断裂带以北。本论文在雪峰隆起上发现了高角度不整合的印支面，而发现张家界-花垣-凯里断裂带与雪峰隆起之间的印支面为微角度不整合。研究区坪坝飞来峰与张家界-花垣-凯里断裂带之间的印支面呈现为平行不整合现象（15处观察点）。这表明华南的印支期变形明显影响到了雪峰隆起，向西波及的界线为张家界-花垣-凯里断裂带，而区内坪坝断裂带与张家界-花垣-凯里断裂带之间没有发生过印支期褶皱。野外观察表明，研究区内上三叠统至上侏罗统之间的地层皆为整合或假整合接触，表明其间没有发生过褶皱变形。而湘鄂西褶皱带与雪峰隆起上一系列下白垩统与下伏地层之间的角度不整合现象，以及前者内上侏罗统及以下地层一起卷入褶皱，指示湘鄂西褶皱带形成于晚侏罗世末，其影响的西界峰带为齐曜山断裂带。该褶皱带呈弧形展布，向北西突出，其中为背斜宽、向斜窄的隔槽式褶皱。该褶皱带内的轴面倾向与逆冲断层皆指示了自南东向北西的推挤。根据被卷入褶皱地层的最新时代及上白垩统与下伏地层之间的角度不整合现象，本次工作认为川东褶皱带形成于早白垩世末。该褶皱带形成时还使其东侧的湘鄂西褶皱带内叠加了一系列北北东向的褶皱。介于华蓥山与齐曜山断裂带之间的川东褶皱带，为一典型的隔档式褶皱带，具有背斜窄、向斜宽的特征，向斜多为箱型褶皱。内部多数的背斜轴面西倾，但总体上的运动学规律仍是自东向西的推挤。推断震旦系底与志留系泥岩是该褶皱带形成中的重要滑脱层。南大巴山褶皱带内被卷入的最新地层时代也是下白垩统，其明显对川东与湘鄂西褶皱带的北部造成了叠加褶皱，因而形成于晚白垩世初。该褶皱带是一总体向南南西突出的弧形褶皱带，自北向南可以划分出城口—房县与坪坝断裂带之间的根带，坪坝至铁溪—巫溪断裂带之间的中带和铁溪—巫溪断裂带南侧的锋带。根带以冲断岩片为特征，早期还经历过印支期冲断变形；中带以隔档式褶皱为特征，常为箱形褶皱；而锋带主要出现短轴宽缓褶皱。南大巴山褶皱带明显是向南南西推挤中形成的。城口—房县断裂带上第二期向南南西的脆性逆冲就是这一阶段发生的。秦岭造山带南侧的北大巴冲断带在此活动中大规模地向南逆掩在扬子板块北缘之上。本论文通过对被卷入褶皱地层内的逆冲断层进行系统擦痕数据测量，获得了113组有效应力方位，进而划分出三期应力场。通过与区内的褶皱演化对比，认为上扬子北部晚侏罗世末的挤压方向为北西—南东向，对应于湘鄂西隔槽式褶皱带的形成；早白垩世初的挤压方向这近东西向，对应于川东隔档式褶皱带的形成；而晚白垩世初的挤压方向为北东—南西，对应于南大巴山弧形褶皱带的形成。这一古应力场分析工作，也进一步验证了上述关于上扬子地区构造演化阶段的划分。综合本次研究成果，认为上扬子北部张家界-花垣-凯里断裂带以西的研究区内，没有发生过加里东期褶皱。该区中生代经历过四期的褶皱演化，具体的演化序列为中三叠世末北大巴山冲断带北缘与雪峰隆起及其西缘的印支期褶皱→晚侏罗世末湘鄂西弧形隔槽式褶皱带→早白垩世末川东隔档式褶皱带→晚白垩世初南大巴山弧形褶皱带。古特提斯与新特提斯洋的闭合及太平洋板块的俯冲这三大动力先后作用于该地区，从而造成了长期而复杂演化的上扬子板内变形。更多还原

【Abstract】 The upper Yangtze region is a representative, intense intraplate deformation zone in China. Itexperienced complicated, long-term shortening deformation. The region also show important, oilprospective in marine deposits in China. Therefore, understanding of the Mesozoic deformationprocesses and evolution have important theoretical and actual implications in this region. Usingstructural and isotopic methods, this work undertaken detailed studies on the western Hunan-Hubei，eastern Sichuan and southern Dabashan fold belts in the upper Yangtze region.After structural analysis in the basement rocks in the Xuefeng uplift,7slate samples from theBanxi Group in the basement were chosen for elite XRD and K-Ar analyses. The7samples gavecooling ages of419-389Ma, i.e. Late Silurian to Middle Devonian, suggesting that the upliftexperienced a Caledonian tectono-thermal event and uplifting. It is proposed therefore that theCaledonian deformation event in South China affected the Xuefeng uplift and reached westwards tothe Zhangjiajie-Huayuan-Kaili fault zone.Field investigation and microstructural analysis were made along the Fangxian-Qingfengsegment of the Chengkou-Fangxian fault zone in this work. This fault zone was subjected to twophases of top-to-the-SSW thrusting. Ductile deformation was involved in the first phase of thethrusting whereas brittle deformation was involved in the second phase of the thrusting. Sevenmylonitized siltstones from metamorphosed strata of Lower Silurian in the footwall of the fault zonewere chosen for sericite separation and⁴⁰Ar/³⁹Ar dating. Five sericite samples yielded good plateauages of225-218Ma （Late Triassic） which were interpreted as cooling ages of the thrustingdeformation. It is proposed that the first thrusting along the Chengkou-Fangxian fault zone tookplace at the end of Middle Triassic when the Yangtze Plate collided with the Qinling Block. It isinferred from the newly-found angular unconformity at the Indosinian interfaces between the Pingbaand Chengkou-Fangxian fault zones that the Indosinian foreland deformation zone on the YangtzePlate occurred between the two fault zones.It is found in this field work that highly angular unconformity at the Indosinian interfacesexists in the Xuefeng uplift whereas slightly angular unconformity at the Indosinian interfacesoccurs between the uplift and Zhangjiajie-Huayuan-Kaili fault zone. The region between the Pingbaand Zhangjiajie-Huayuan-Kaili fault zones show disconformity at the Indosinian interfaces at15localities. These demonstrate that the Indosinian shortening deformation affected the Xuefeng upliftand reached westwards to the Zhangjiajie-Huayuan-Kaili fault zone, and there is no Indosinianfolding in the region between the Pingba and Zhangjiajie-Huayuan-Kaili fault zones. Field investigation shows that interfaces among upper Triassic and upper Jurassic showconformity or disconformity in the study region, indicating that no folding took place between LateTriassic and Late Jurassic in this region. Several angular unconformities between Lower Cretaceousand underlying strata as well as folding of upper Jurassic and older strata in the westernHunan-Hubei Fold Belt indicate that the fold belt developed at the end of the Late Jurassic. Thefolding reached westwards to the Qiyaoshan fault zone. The fold belt is an arc-shaped beltprotruding NW. Folds in the belt are trough-like with box anticlines and chevron synclines. Dipdirections of axial planes and thrusts in the belt all show pushing from SE to NW during the folding.The youngest folded strata and angular unconformities between upper Cretaceous andunderlying strata demonstrate that the eastern Sichuan Fold Belt formed at the end of EarlyCretaceous. Superposition of many NNE-trending folds also happened in the western Hunan-HubeiFold Belt east of the eastern Sichuan Fold Belt. The eastern Sichuan Fold Belt between theHuayinshan and Qiyaoshan fault zones show typical comb-like folds with chevron anticline and boxsynclines. Axial planes of the anticlines mostly dip westwards, and still suggest pushing from east towest. It is inferred that predominant detachment layers are the base of Sinian and Silurianmudstones.The youngest folded strata in the southern Dabashan Fold Belt are lower Cretaceous.Shortening of the fold belt caused clear fold superposition in the northern segments of the easternSichuan and western Hubei and Hunan fold belts. These indicate that the southern Dabashan FoldBelt developed at the beginning of Late Cretaceous. This is a arc-shaped fold belt protruding SSW,which can be divided into a root belt between the Chengkou-Fangxian and Pingba fault zones, amiddle zone between the Pingba and Tiexi-Wuxi fault zones and a front zone just south of theTiexi-Wuxi fault zone. The root zone is characterized by thrust sheets experiencing the Indosinianthrusting deformation, the middle zone by comb-like, box folds and the front zone by open foldswith short axes. The fold belt was developed by pushing SSW. The second phase of thrusting alongthe Chengkou-Fangxian fault zone took place at this stage. The northern Dabashan Belt in thesouthern of the Qinling orogenic belt thrusted over the northern margin of the Yangtze Platesouthwards on a large-scale.Many fault-slip data measurements on thrusts in the folded strata give113sets of stress data,which can be divided into three phases of stress fields. By comparison with the above-mentionedfolding evolution, it is proposed that a compression direction at the end of Late Jurassic is NW-SWrelated to the formation of the western Hubei-Hunan Fold Belt, the compression direction at the endof Early Cretaceous is nearly E-W related to the development of the eastern Sichuan Fold Belt, andthe compression direction at the beginning of Late Cretaceous is NE-SW related to formation of thesouthern Dabashan Fold belt. This paleo-stress analysis further proves the above division of the structural evolution stages.It is proposed from these studies that the region west of the Zhangjiajie-Huayuan-Kaili faultzone did not experienced the Caledonian folding. Four phases of folding in the Mesozoic arerecognized in this region. The region evolved from the Indosinian folding along the northern marginof the northern Dabashan Belt as well as the Xuefeng uplift and its western margin at the end ofMiddle Triassic, formation of the western Hubei-Hunan arc-shaped, through-like Fold Belt at the endof Late Jurassic, development of the eastern Sichuan comb-like Fold Belt at the end of EarlyCretaceous to formation of the southern Dabashan arc-shaped Fold Belt at the beginning of LateCretaceous. Three dynamics from closure of the paleo-Tethys and neo-Tethys as well as subductionin the Pacific Ocean acted in this region respectively, leading to long-term, complicated evolution ofthe intraplate deformation in the upper Yangtze region.更多还原