【作者】 沈中延；

【导师】 肖安成； 陈汉林；

【作者基本信息】 浙江大学 ， 构造地质学， 2009， 博士

【摘要】 米仓山位于秦岭以南的上扬子西北缘地区,属于秦岭前陆冲断褶皱带,其沉积和构造演化与秦岭碰撞造山过程息息相关。目前普遍认为秦岭于晚三叠世全面碰撞造山,然而对于全面碰撞前的早期碰撞事件却缺乏具体研究工作。另一方面,对于米仓山印支期以来的演化特别是米仓山何时以及如何隆升一直没有很详细的研究工作。本文对米仓山地区晚二叠世-早三叠世的沉积和构造进行了研究,并且综合分析来自沉积、地震剖面、裂变径迹、古地磁等方面的资料对中生代米仓山的隆升时间和方式进行探讨,得出以下结论:1.前人认为米仓山地区下三叠统内部各组地层之间均为整合接触,然而作者通过对米仓山野外12条剖面进行沉积构造研究发现米仓山地区下三叠统内部存在一个不整合面,反映为古风化壳,砾岩、角砾岩、砂岩等碎屑岩的出现。2.在米仓山南缘的地震剖面上同样也识别出了早三叠世的这期构造事件,表现为嘉陵江组二段底面与下伏地层的削截现象、上覆地层的超覆现象,及断层上、下盘的嘉陵江组一段-上二叠统地层厚度的巨大差异。前人认为铜街子组大致相当于广义的嘉陵江组一、二段,因而在作者的研究尺度内可认为早三叠世碎屑岩沉积事件和构造事件是同期的,认为构造运动造成了下三叠统铜街子组的碎屑岩发育。3.通过分析开江-梁平裂谷—汉南-米仓山隆起—佛坪地体和城口—鄂西裂谷—神农架-黄陵地体—武当山地体”的时空配置关系,结合裂谷与造山带的形态,提出开江-梁平裂谷和城口-鄂西裂谷是南秦岭与上扬子地块在晚二叠世发生点式碰撞时产生的碰撞裂谷群。4.在上述研究的基础上,提出了晚二叠世—三叠世研究区的大地构造演化经历了晚二叠世吴家坪期（P₂w）洋壳俯冲阶段,晚二叠世长兴期-早三叠世印度期早期（P₂c-T₁f¹）碰撞裂谷阶段,早三叠世印度期中期-晚期（T₁f²-T₁f⁴）的裂谷消亡阶段,早三叠世奥伦尼期早期（T₁t）持续碰撞阶段,早三叠世奥伦尼期中晚期-安尼锡期（T₁j-T₂l）构造平静期,拉丁期-卡尼期全面碰撞造山期。5.综合分析来自沉积、地震剖面、磷灰石裂变径迹和古地磁等证据,作者提出米仓山真正意义上的隆升发生在中生代晚期的早白垩世,并且具有前展式冲断隆升的特点,早白垩世的隆升速率大于晚白垩世的隆升速率。更多还原

【Abstract】 The Mt.Micangshan locates on the north margin of Upper Yangtze Block south to Qinling orogen.It is a part of the foreland fold-and-thrust belt of Qinling.Thus,its sedimentary and deformational evolution is inferred to be closely related to the tectonic evolution of the Qinling orogen.The Late Triassic collision between North China Block（NCB） and South China Block（SCB） and consequent uplift of Qinling which stands for the final collision was widely accepted by most geologists. Nevertheless,few works have focused on the history before the final collision along the whole northern margin of SCB.Thus,we took research work focusing on the Late Permian-Early Triassic sedimentary and deformation evolution to discover the pre-final-collision history of the Qinling orogen.Some new evidences and understanding are concluded as below:1.The three formations of Lower Triassic in northern Sichuan basin are Feixianguan Fm.,Tongjiezi Fm.,and Jialingjiang Fm.,respectively from the bottom up and are thought to be conformable contact with each other in the previous literature.Our research work find that there exits an unconformity within the Lower Triassic characterized by weathering crusts,conglomerates, breccias,sandstones etc.2.The unconformity can been found in the seismic profiles south to Micangshan characterized by truncation and onlap phenomena near the bottom of the 2^nd See.of Jialingjiang Fm.In our research scale,the unconformity in the seismic profiles and in the field can be considered as contemporaneous.Thus,we infer that the Early Triassic tectonic event resulted in the formation of the unconformity.3.By analyzing the spatio-temporal configuration of the Kaijiang-Liangping rift—Hanhan-Micangshan uplift—Foping dome trinity and Chengkou-Exi rift—Shennongjia-Huangling terrane—Wudangshan terrane trinity,we proposed that the Kaijiang-Liangping and Chengkou-Exi rifts on the northern margin of SCB which strike approximately orthogonal to the Qinling orogen are related to the early collision by South Qinling Block and SCB.In other words,they are twin impactogens（collional rifts）.4.On the basis of the research work mentioned above,with a synthetic consideration of the whole tectonic evolution of Qinling,we proposed the tectonic evolution modal of Micangshan area from P₂-T.5.Integrating evidences from sedimentary,seismic profiles,AFT data,and paleomagnetic data,we put forward that the Mt.Micangshan was uplifted in the Early Cretaceous.The uplift of the mountain itself took place before that of the basin south to Micangshan which was thought to happen in the Late Cretaceous.Furthermore,the apparent uplift rate of the Mt.Micangshan is greater than that of the basin area south to it.更多还原