| 青藏高原东北缘海原构造带马东山阶区深部电性结构特征及其构造意义 |
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| 引用本文： | 詹艳,杨皓,赵国泽,赵凌强,孙翔宇.青藏高原东北缘海原构造带马东山阶区深部电性结构特征及其构造意义[J].地球物理学报,2017,60(6):2371-2384. |
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| 作者姓名： | 詹艳 杨皓 赵国泽 赵凌强 孙翔宇 |
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| 作者单位： | 地震动力学国家重点实验室(中国地震局地质研究所), 北京 100029 |
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| 基金项目： | 地震动力学国家重点实验室项目（LED2013A01）、地震行业科研专项（20130811）和国家自然科学基金项目（41474057）共同资助. |
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| 摘 要： | 海原一六盘山构造带是青藏高原东北缘地区的一条重要边界,在海原断裂带和六盘山断裂带接触区形成了特殊的马东山挤压阶区,本文对跨过该挤压阶区一条密集测点大地电磁剖面数据进行了处理和二维反演,获得的深部电性结构图像揭示在马东山挤压阶区深部电性结构表现为在高阻背景下镶嵌多个向西南倾斜的低阻条带电阻率结构样式,并在深度约25 km汇聚到中下地壳低阻层内,共同组成"正花状"结构;海原一六盘山构造带西南侧到陇中盆地区间呈现高、低阻相互"楔合"的深部结构特征,而其东北侧的鄂尔多斯西缘带自地表到中下地壳为较完整的高阻块体.另外结合跨过海原断裂带中段和西秦岭造山带的大地电磁探测结果,对海原一六盘山构造带分段性及其两侧的陇中盆地和鄂尔多斯地块的接触关系进行了研究分析.大地电磁探测成果佐证了在海原断裂带中段为具有走滑特点的断裂,而其尾端与六盘山断裂带斜交区域的马东山地区发生了强烈的逆冲推覆与褶皱变形;活动构造研究发现沿海原断裂带所产生的左旋走滑位移被其尾端的马东山、六盘山以东西向的地壳缩短调节吸收,GPS观测表明青藏高原东北缘地区现今构造变形分布在海原一六盘山构造带以西上百公里的范围内,陇中盆地一海原一六盘山构造带和鄂尔多斯地块一线的深部电性结构图像也很好地解释了该区变形状态:海原一六盘山构造带带及西南盘的陇中盆地的中下地壳非常破碎,在青藏高原向北东方向的推挤下容易发生变形,而北东盘鄂尔多斯地块地壳结构完整,很难发生构造变形.对海原一六盘山构造带马东山阶区和龙门山构造带的深部电性结构及变形特征等进行了比较分析,发现该区有与2008年汶川地震相似的深部构造背景,应重视该区强震孕育环境的探测研究.
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| 关 键 词： | 青藏高原东北缘 海原断裂带 马东山阶区 深部电性结构 地壳变形 |
| 收稿时间： | 2016-08-04 |
Deep electrical structure of crust beneath the Madongshan step area at the Haiyuan fault in the northeastern margin of the Tibetan plateau and tectonic implications |
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| ZHAN Yan,YANG Hao,ZHAO Guo-Ze,ZHAO Ling-Qiang,SUN Xiang-Yu.Deep electrical structure of crust beneath the Madongshan step area at the Haiyuan fault in the northeastern margin of the Tibetan plateau and tectonic implications[J].Chinese Journal of Geophysics,2017,60(6):2371-2384. |
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| Authors: | ZHAN Yan YANG Hao ZHAO Guo-Ze ZHAO Ling-Qiang SUN Xiang-Yu |
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| Institution: | State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | On the northeastern margin of the Tibetan plateau, there is a profound Madongshan compressional step area at the conjunction between the Haiyuan and Liupanshan faults. This work has made processing and 2D inversion of a high-density MT profile across this step area, which permits to image the deep struture of this step area and study its relationship with the Longzhong basin and the Ordos block on its either side in combination with other MT surveys across the West Qinling orogen to the southeast. The resultant images show several southwest-dipping low-resistivity belts (LRBs) in a high-resistivity background beneath this area, which merge at about 25km depth in the middel and lower crust, forming a positive flower structure in the vertical profile. Alternating high and low resistivities characterize the deep subsurface from the southwest of the Haiyuan fault to the Longzhong basin. To the northeast, the west edge of the Ordos basin is an intact high-resistivity body which extends from the surface downward to the middle and lower crust. Studies of active tectonics suggest that the left slip of the Haiyuan fault is accommodating the crustal shortening of the Madongshan and Liupanshan Mountains which lie at the end of the Haiyuan fault. GPS measurements show that the current tectonic deformation is distributed in a region over 100 km west of the Haiyuan-Liupanshan fault zone. Deep electric structure derived from MT surveys aforementioned can explain this deformation pattern. As the middle and lower crust of the Haiyuan-Liupanshan fault zone and the Longzhong basin on its southwest wall is highly broken, this area is easy to deform under the northeastword push of the Tibetan plateau. Whereas the west-edge zone of Ordos on the northeast wall of the fault zone has an intact or relatively hard crustal structure, so it experiences little tectonic deformation. |
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| Keywords: | Northeastern margin of the Tibetan plateau Haiyuan-Liupanshan fault zone Madongshan step area Deep electrical structure Curstal deformation |
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