【作者】 李瑞保；

【导师】 裴先治；

【作者基本信息】 长安大学 ， 构造地质学， 2009， 硕士

【摘要】 南大巴山构造带位于上扬子地块与南秦岭造山带的交接部位,西与米仓山为邻,东与川东高陡构造带相连,宏观上为一整体向南西凸出的弧形构造带。该构造带是印支期与燕山期两期逆冲推覆构造的复合产物。两期运动造就了南大巴山现今富有特色的弧形构造体系,也形成了类型特殊的前陆盆地（陆内前陆盆地）。通过现代构造地质学方法、地球物理及同位素年代学等多学科综合研究,对南大巴山镇巴—城口段现今构造按照“横向分带、纵向分段和垂向分层”的思路进行构造剖析,并利用锆石年代学资料对大巴山前陆盆地进行物源示踪,在此基础上重点讨论其构造演化及盆山物质耦合关系。至此,取得了以下进展和初步认识:1.在岩石地层方面,重点比对扬子北缘和高川盆地两类不同二叠系沉积,发现扬子北缘二叠系总体为一套台地相碳酸盐岩,而高川盆地二叠系郭家垭组为一套黑色岩系。结合区域构造分析,郭家垭组是扬子板块与秦岭微板块之间裂谷—有限洋盆的一部分被残留下来,是在区域拉张背景之下形成的,与峨眉山二叠纪玄武岩喷发事件所表征的拉张构造背景相吻合。2.通过对研究区地表地质构造的详细路线调查,对重点区段辅以大比例尺面积填图,基本查清南大巴山镇巴—城口段现今构造基本特征。根据构造样式及变形组合对南大巴山进行“横向分带、纵向分段和垂向分层”研究,横向上分为叠瓦冲断带、冲断褶皱带、逆冲推覆扩展变形带和低缓褶皱带,纵向上分为西段、中段和东段,垂向上根据区域滑脱面及地球物理资料分为上、中和下三大构造层。从南大巴山根带到前陆盆地方向,变形强度渐弱,褶皱形态逐渐开阔,地表出露地层时代愈新,滑脱层由北向南逐层抬升直至三叠纪膏盐岩。地表构造样式以箱状褶皱、紧闭褶皱、扇状褶皱和隔档式褶皱为主。3.认为米仓山东段与大巴山西段构造交接区发育两期褶皱,通过大比例尺填图对西乡县司上叠加褶皱研究,确定近东西向—北东东向褶皱形成在先,近南北向—北北西向褶皱形成在后。结合区域不整合事件及前人年代学资料,表明这两期褶皱均形成于J₃-K₁,其中近东西向褶皱形成时代相对南北向褶皱形成时代稍早。4.通过对大巴山陆内前陆盆地三叠系须家河组与侏罗系上沙溪庙组碎屑锆石年代学研究,发现碎屑锆石年龄与秦岭—大巴地区地质体年龄相似,并结合区域资料分析,认为大巴山前陆盆地的碎屑沉积物主要为源自秦岭造山带中生代中晚期陆内造山岩浆活动的产物（213 Ma～283Ma;163 Ma～274Ma）、北秦岭（312 Ma～448Ma;404Ma）、南秦岭（694 Ma～710Ma;712Ma）、秦岭（1430 Ma～1988 Ma;1742 Ma～1972 Ma）、秦岭造山带基底（2133 Ma～2708 Ma;2116 Ma～2594 Ma、3025 Ma～3140 Ma）。研究显示,前陆盆地与秦岭—大巴造山带具有物质上的沟通关系,从物源角度可以说明两构造单元具物质上的耦合关系。5.恢复南大巴山中新生代以来构造活动序列:①受早期华南华北两大板块印支期碰撞造山影响,南大巴山地区已被波及,造成城口坪坝三叠系须家河组角度不整合覆盖在下三叠统之上,此时,城口、坪坝断裂可能形成并活动,但此次活动并未使南大巴山发生广泛的褶皱变形;②燕山期扬子地块向秦岭之下的大型陆内俯冲导致北大巴山地区瓦房店中下侏罗统被逆冲掩覆,南大巴山地区再次被连带卷入到此次变形中,造成南大巴山地区褶皱变形,褶皱系统及逆冲断裂系统相继形成,并可能叠加有右行走滑;③晚白垩纪以来,在喜山运动影响之下整体抬升剥蚀,终成今日之面貌。更多还原

【Abstract】 South Dabashan Mountain tectonic belt is seated at the north margin of the Upper Yangtze block, the connection area of Sichuan basin and south Qinling orogenic belt, which lies adjacent to the Micangshan Mountain in west and to the high and steep orogenic belt in east and takes on a southwest-protruded arc orogenic belt in the whole at a macro view. The belt is the compound production of thrust movement of two periods both in Indosinian stage and Yanshanian stage. Thus two stages’ movements forged the distinctive arc orogenic system of present South Dabashan Mountain, together with the special foreland basin（intra-continental foreland basin）. After synthesized study of modern tectonics methods, geophysics and isotopic chronology and so on, following the thought of "section-divide in strike, belt-divide in inclination and layer-divide in vertical direction", the present tectonic of South Dabashan Mountain Zhenba-Chengkou section is analyzed in detail. What’s more, with the help of Zircon chronology data in tracing the provenance area of Dabashan Mountain foreland basin, its tectonic evolution and mountain-basin coupling relativities are discussed in particular. From these studies, some advances are acquired as follows:1. After comparing the Permian strata of northern margin of Yangtze and Gaochuan basin in special, we discover that the Permian deposit is predominated by carbonate rocks of platform facies in northern margin of Yangtze（especially the Zhenba area） while black rock series of Guojiaya Formation of Permian distributes in Gaochuan basin. Considering the regional tectonic, Guojiaya Formation is the residual of the rift-limited oceanic basin between Yangtze block and Qinling micro-plate, and is formed under the background of regional extensional environment, which is consistent with the Permian basalt eruption event of Emei mountain resulted by regional extensional environment.2. The paper is based on detail route survey towards geological structures on the ground surface of the study area and large scale mapping for key area, and basically makes clear the present tectonic characteristics of South Dabashan Mountain Zhenba-Chengkou section. According to tectonic patterns and deformation assemblages, the principle of section-divide in strike, belt-divide in inclination and layer-divide in vertical direction are put in the study of South Dabashan Mountain, which is divided into east, middle and west in strike, imbricate thrust belt, fault fold belt and thrust stretched deformed belt in inclination and upper, middle and lower in vertical direction through regional decollement and geophysics data. From the root of South Dabashan Mountain to the foreland basin, the deformation becomes weaker and weaker, the shape of fold gets wider and wider and the strata of outcrop turns newer and newer. Meanwhile, the decollemen lifts to plaster salt rocks of Triassic from north to south. And the structures shape on the ground surface is mainly the box-shaped folds, tightly closed folds, fan-shaped folds and Jurassic folds.3.We believe that two periods’ folds developed at the connection between eastern Micangshan Mountain and western Dabashan Mountain and identify that nearly east-west-northeast by east orientated fold formed earlier than the fold of nearly south-north-northwest by west orientated through superimposed study of large scale mapping towards Sishang area of Xixiang county. Combined with regional unconformity event and chronology data of predecessors, it can be concluded that both two periods’ folds formed in J₃-K₁ and the nearly east-west orientated fold formed earlier that that of south-north orientated.4.Through Zircon chronology study of clastic rocks of Xujiahe Formation of Triassic and upper Shaximiao Formation of Jurassic in intra-continental foreland basin of Dabashan Mountain, we find that the clastic Zircon age is similar to that of Qinling-Daba area. Considering regional data, we put forward that the detrital deposits of Dabashan foreland basin is mainly derived from the productions of intra-continental orogenic magmatism in middle-late period of Mesozoic of Qinling orogenic belt（213Ma～283Ma; 163Ma～274Ma）, northern Qinling（312Ma～448Ma; 404Ma）, southern Qinling（694Ma～710Ma; 712Ma）,Qinling（1430Ma^～1988 Ma; 1742Ma～1972Ma）, the basement of Qinling orogenic belt（2133Ma～2708Ma; 2116Ma～2594Ma、3025Ma～3140Ma）. Study shows that the foreland basin keeps communication with Qinling-Daba orogenic belt in material and the two tectonic units exist mutual coupling relativities in material composition.5.Recovering the tectonic events sequence of South Dabashan mountain since Mesozoic-Cenozoic:①Suffering the early effect between the South China block and the North china block, South Dabashan area was deformed and which resulted in Xujiahe Formation of Triassic angular unconformity overlaid on the lower Triassic in Chengkou and Pingba area. At that time, Chengkou-Pingba fault may be formed and active, but the major area of South Dabashan were not folded and deformed;②The large-scale intra-continental subduction of the Southern Qinling in Yanshanian resulted in the thrust of Middle-Lower Jurassic strata in Wafangdian of North Dabashan area, and involved in the South Dabashan again, which caused the fold and deformation in the area . And folds and thrust faults formed in line, yet dextral strike-slipping may superposed at the same time;③Since Cretaceous Period, the study area has been uplifted and denuded in the whole with the impact of Himalaya movement and comes to today’s visage finally.更多还原