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首页> 外文期刊>Journal of Asian earth sciences >New field and geophysical data about transpressional deformation: An improved model for the structural style of Sha Gou fault area in southern Ningxia, northeastern edge of Tibetan Plateau, China
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New field and geophysical data about transpressional deformation: An improved model for the structural style of Sha Gou fault area in southern Ningxia, northeastern edge of Tibetan Plateau, China

机译：转压变形的新领域和地球物理数据：青藏高原东北缘宁夏南部沙沟断裂带构造样式的改进模型

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Situated near the northeastern edge of the Tibetan Plateau, the Sha Gou fault area (SGFA) represents an important area to understand Cenozoic regional interactions between northeastern (NE) Tibetan Plateau and southwestern (SW) Liupan Shan Basin. Within this region, several km-scale arcuate fault systems such as the Lijun fault and the Madong Shan piedmont fault accommodate the transpressive deformation, but their structural style is still controversial. Predecessors regarded these bow-like faults as southwest-dipping thrust systems with large-scale nappes, however, this opinion is not compatible with the new field and geophysical data. In this study, we aim to ascertain the structural pattern of this area based on the analyses of field observation data, interpretation of seismic reflection profiles and two-dimensional gravity forward modeling. According to the present fieldwork, the structural cleavages, low-angle slickenlines, sub-vertical fault surfaces, "ribbon effect" as well as the linear geomorphic features in plane view indicate that these faults belong to a strike-slip system. Newly acquired seismic pro, files, characterized by distinct positive flower structures, strongly suggest that this area is again a strike-slip fault system rather than a thrusting system. Furthermore, gravity forward modeling results show that the reverse strike-slip model without large-scale thrust nappes is closer to the present structural style of this area. The gravity forward modeling is an effective method to identify km-scale thrust nappes, which could be used for reference by the structural style analysis in other similar regions. Based on these evidences, a new transpressional shear model for the structural pattern is proposed. The overall structural style of the SGFA is not characterized by large-scale thrust nappes, but is dominated by a transpressional shear system with significant strike-slip faulting. Such a new model can be an additional evidence for the tectonic escape that is going on in the area north of the Himalaya and is dominated by reverse strike-slip deformation. The stepwise morphology (i.e., the Pre-Cretaceous strata in the west of strike-slip faults are higher than those in the east successively) in this model is also caused by the uplift of the Tibetan Plateau. Furthermore, the strike-slip deformation indicates that the SW Liupan Shan Basin is a continental sub-basin segmented by several km-scale strike-slip faults rather than the imbricated style of purely contractional system in typical foreland basin. (C) 2015 Elsevier Ltd. All rights reserved.
机译：沙沟断裂带（SGFA）位于青藏高原的东北边缘附近，是了解东北（NE）青藏高原与西南（SW）六盘山盆地之间新生代区域相互作用的重要区域。在该区域内，几公里规模的弧形断层系统（如李军断层和马东山前山断层）可容纳超压变形，但其构造形式仍存在争议。前人将这些弓状断层视为具有大规模推覆作用的西南倾推系统，但是这种观点与新的野外和地球物理数据不符。在这项研究中，我们旨在基于对野外观测数据的分析，地震反射剖面的解释和二维重力正演模型来确定该地区的结构模式。根据目前的野外工作，结构分裂，低角度滑移线，次垂直断层表面，“带状效应”以及平面图中的线性地貌特征表明这些断层属于走滑系统。新近采集的地震剖面文件具有明显的正花结构特征，强烈表明该区域还是走滑断层系统而不是逆冲系统。此外，重力正演模拟结果表明，没有大推力推覆的反走滑模型更接近该地区目前的构造样式。重力正演模拟是一种识别千米尺度推力推覆的有效方法，可用于其他类似地区的结构样式分析中作为参考。在这些证据的基础上，提出了一种新的构造型压转剪切模型。 SGFA的整体结构形式并不以大型推覆推覆为特征，而是以具有明显走滑断层的超压剪切系统为主导。这样的新模型可以为喜马拉雅以北地区正在发生的构造逃逸提供补充证据，该逃逸以逆走滑变形为主导。该模型的阶跃形态（即走滑断层以西的白垩纪前地层先后高于东部）是由于青藏高原隆升引起的。此外，走滑变形表明，六盘山西南盆地是一个大陆性次盆地，被数千米规模的走滑断层所分割，而不是典型的前陆盆地的纯收缩系统的镶嵌形式。 （C）2015 Elsevier Ltd.保留所有权利。

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