|
|||||
|
|
| 滑塌堆积在逆冲构造中的作用——以宁夏牛首山中奥陶统米钵山组为例 | |
| 引用本文： | 张进,马宗晋,任文军,雷永良.滑塌堆积在逆冲构造中的作用——以宁夏牛首山中奥陶统米钵山组为例[J].地学前缘,2007,14(4):85-95. |
| 作者姓名： | 张进 马宗晋 任文军 雷永良 |
| 作者单位： | 1. 中国地震局,地质研究所,北京,100029 2. 东方地球物理公司,长庆物探处,宁夏,银川,750006 3. 中国科学院,地质与地球物理研究所,北京,100029 |
| 摘 要： | 宁夏中南部发育的中奥陶统米钵山组中普遍发育着滑塌堆积。综合米钵山组内滑塌堆积的沉积及后期的变形特征,我们认为滑塌堆积在逆冲变形中起着重要的作用,在逆冲构造中滑脱层的发育往往和岩性有关,滑塌堆积也是一种重要而潜在的滑脱层,不仅由于大尺度上其显著的横向不均匀性,中小尺度上其内部也表现出不均一性,因此它的存在使得应力得以在该层集中,变形因此也主要发生在该层中,从而产生滑脱层,而滑塌堆积的围岩变形则很微弱。结合宁夏中宁中南部地区强烈的逆冲推覆作用,我们认为中奥陶统中的滑塌堆积是该区逆冲推覆构造的重要滑脱层,这些滑脱层控制着该地区下古生界的变形。由于这种构造作用的叠加,先前的那些外来岩块逐渐“细粒化”,逆冲作用使得滑脱堆积中的砾石变形成为构造透镜体,这解决了该地区长期存在的有关这些砾石或透镜体是外来体还是本地的争论。我们的研究表明,在宁夏地区中奥陶统中大部分以外来体为主,但也有一定的本地岩层因构造作用成为透镜体,因此在不同地区应该仔细分析。由于牛首山地区逆冲构造比较发育,滑塌堆积转化成广义上的混杂堆积,而同样有滑塌堆积产出的贺兰山地区由于远离祁连山造山带,滑塌堆积得以保存,其中的砾石基本上没有变形。宁夏地区中奥陶统中的滑塌堆积从区域上为我们提供了一个区别滑塌堆积与混杂堆积的例子。 |
| 关 键 词： | 牛首山 米钵山组 滑塌堆积 逆冲断层 滑脱层 |
| 文章编号： | 1005-2321（2007）04-0085-11 |
| 收稿时间： | 2007-04-06 |
| 修稿时间： | 2007-04-062007-05-20 |
The role of olistostrome in thrusting——a case study from the Miboshan Formation of Middle Ordovician in the Niushou Mountain, Ningxia |
|
| Zhang Jin,Ma Zongjin,Ren Wenjun,Lei Yongliang.The role of olistostrome in thrusting——a case study from the Miboshan Formation of Middle Ordovician in the Niushou Mountain, Ningxia[J].Earth Science Frontiers,2007,14(4):85-95. | |
| Authors: | Zhang Jin Ma Zongjin Ren Wenjun Lei Yongliang |
| Abstract: | Olistostromes are common in the Middle Ordovician strata in the central-southern Ningxia Province. These olistostrome may have become decollements during later thrusting. Based on the sedimentary and later deformation characteristics of these olistostromes in the Miboshan Formation, we suggest that these olistostrome played an important role in the thrusting process. The development of a decollement during thrusting is commonly related to the rheology of the rocks. Because olistostromes possess, not only a marked transverse inhomogeneity on a large scale, but also inhomogeneity at the mesoscopic and microscopic scales, olistostromes can be an important potential type of decollement. The presence of olistostromes allow stress and deformation to be mainly concentrated in the olistostrome itself, resulting in the formation of a decollement in this layer. Since strong thrusting did occur in the central-southern Ningxia Province during the Paleozoic, we propose that the Middle Ordovician olistostromes in the sedimentary succession were important surfaces of decollement in this region. Owing to tectonic deformation the former exotics became smaller gradually, which resulted in the lens-shape of inclusions. This resolves the long-term controversy on the origin of these inclusions, i. e. , whether they were exotics or formed by tectonics. The study shows that most inclusions in the Middle Ordovician strata in Ningxia Province were exotics, there were also some inclusions formed by the fragmentation of once cohesive sequences owing to tectonic overprinting. Therefore more detailed work is needed. Moreover, the Niushou Mountain was once a foreland area of Qilian orogenic belt, during the late Early Paleozoic, thrust faults developed widely, and the olistostromes changed into a melange in the broad sense. However, because of the long distance from the Qilian orogenic belt, the Helan Mountain olistostromes cannot have been tectonically overprinted, and the exotics rarely underwent deformation. The regional occurrence of the olistostromes in the Middle Ordovician sedimentary sequence in Ningxia Province provides us a good case for distinguishing the difference between olistostromes and melange. |
| Keywords: | Niushou Mountain Miboshan Formation olistostromet hrust fault decollement melange |
| 本文献已被 CNKI 维普 万方数据 等数据库收录！ | |