内蒙古徐尼乌苏逆冲推覆构造的变形特征

发布时间：2018-09-05 14:18

【摘要】：研究区位于内蒙古中部，大地构造位置位于华北板块北缘，紧邻华北板块与西伯利亚板块的拼合带。依徐尼乌苏断裂带研究区分为北部的华北地层大区和南部的北疆—兴安地层大区，同时该条断裂也被认为是槽台界线，即该断裂以南为华北地台区，以北为地槽区。出露的地层主要有太古界色尔腾山岩群，中新元古界长城-蓟县-青白口系白云鄂博群，下古生界寒武-奥陶系温都尔庙群和白乃庙群、下寒武统西井子组以及下中奥陶统五道湾组、志留系徐尼乌苏组和西别河组，上古生界石炭系本巴图组和阿木山组、下二叠统三面井组和额里图组及少量中生界和新生界。经野外观察并结合前人研究，在研究区多处见有白云鄂博群覆盖在古生界之上，白云鄂博群出露不连续，东西向延伸约160km，因其大致沿徐尼乌苏断裂分布，故称该带为“徐尼乌苏逆冲推覆构造带”，本文首次对徐尼乌苏逆冲推覆构造的分布范围、分带特征、构造变形特征、推覆方向、推覆距离以及推覆时代进行了系统研究，补充了前人对于徐尼乌苏逆冲推覆构造中带研究的不足，并结合徐尼乌苏断裂的性质，合理推断徐尼乌苏断层并非研究区的槽台边界。按分布范围和构造特征，将徐尼乌苏逆冲推覆构造进一步划分：锋带主要沿补力太—徐尼乌苏—白乃庙—博日和—章毛乌苏—化德县北一带分布，呈叠瓦状逆冲推覆构造；中带主要沿东、西乌素—爱国村—章盖营—西井子乡一线分布，以发育大量大小不一的飞来峰和构造窗为特征，断层角砾岩发育，推覆构造界面发生褶皱变形；研究中未能识别出根带，逆冲推覆构造根带很可能已经被后期的岩浆活动和构造运动破坏。徐尼乌苏逆冲推覆构造大致可以分为两期：第一期以大规模的水平运动为主，该期为逆冲推覆构造主期次；第二期以挤压变形为主。从研究区中带测得的产状数据进行分析，可以判断该逆冲推覆构造主要受区域上南北向挤压作用，整体的推覆的方向为从南向北；根据飞来峰前缘至构造窗后缘之间的距离，初步确定推覆距离不小于52km；从逆冲推覆构造涉及的地层和侵入构造界面的岩体形成时代两个方面进行限定，确定了该逆冲推覆构造发生的大致时间为早二叠世末期。研究区的徐尼乌苏断裂被认为是传统的槽台界线，但通过本次研究认为该断裂带是由于逆冲推覆构造形成的一系列逆断层组合，断层倾角较小，影响深度较浅，并非区域上的槽台界线，推断真正的槽台界线在该断裂以南约10~20km处。结合区域构造演化背景，暗示本次逆冲推覆构造与中二叠世华北板块与西伯利亚板块的对接碰撞、古亚洲洋的闭合有关。
[Abstract]:The study area is located in the central part of Inner Mongolia, the tectonic position is located in the northern margin of the North China Plate, close to the convergence zone of the North China Plate and the Siberian Plate. The North China Platform is a geosynclinal area to the north. The strata are mainly Archaeozoic Seltenshan Group, Mesoproterozoic Changcheng-Jixian-Qingbaikou Bayan Obo Group, Lower Palaeozoic Cambrian-Ordovician Wenduermiao Group and Bainaimiao Group, Lower Cambrian Xijingzi Formation and Lower-Middle Ordovician Wudaowan Formation, Silurian Xuniwusu Formation and Xibiehe Formation. Formation, Upper Paleozoic Carboniferous Benbatu Formation and Amushan Formation, Lower Permian Sanmianjing Formation and Erlitu Formation, and a few Mesozoic and Cenozoic.
According to field observation and predecessors'research, the Bayan Obo Group is found to cover the Paleozoic in many places in the study area. The Bayan Obo Group is not continuous and extends about 160km in the East-West direction. Because it is distributed along the Xuniwusu fault, it is called the Xuniwusu thrust nappe structure belt. This paper is the first time to study the Xuniwusu thrust nappe structure. Distribution range, zoning characteristics, structural deformation characteristics, nappe direction, nappe distance and nappe age have been systematically studied, which complements previous studies on the middle zone of Xuniwusu thrust nappe structure and reasonably infers that Xuniwusu fault is not the trough-platform boundary of the study area.
According to the distribution and structural characteristics, the Xuniwusu thrust nappe structure is further divided into the following parts: the front belt is mainly distributed along the northern part of Buli Tai-Xuniwusu-Bainaimiao-Bori and Zhangmaowusu-Huade County, showing imbricate thrust nappe structure; the middle belt is mainly along the east, Xiwusu-Aiguo Village-Zhanggaiying-Xijingzi Township. Fault breccia developed and folding deformation occurred at the nappe structure interface. Root zone could not be identified in the study, and the thrust nappe structure root zone may have been destroyed by later magmatic activity and tectonic movement.
Xuniwusu thrust nappe structure can be roughly divided into two stages: the first stage is dominated by large-scale horizontal movement, and the second stage is dominated by compression deformation. According to the distance between the front edge of Feilai peak and the rear edge of the structural window, the nappe distance is not less than 52 km, and the time of the formation of the strata involved in the thrust nappe structure and the rock mass at the intrusive tectonic interface is limited, and the time of the occurrence of the thrust nappe structure is approximately two years earlier. The end of the world.
The Xuniwusu fault in the study area is considered to be the traditional trough-platform boundary. However, this study suggests that the fault zone is a series of thrust faults formed by thrusting nappe structure. The fault dip angle is small and the influence depth is shallow. It is not the trough-platform boundary in the region. It is inferred that the true trough-platform boundary is about 10-20 km south of the fault.
Combining with the regional tectonic evolution background, it is suggested that the thrust nappe structure is related to the collision between the North China plate and the Siberian plate in the Middle Permian and the closure of the Paleo-Asian Ocean.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P542

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