地震地质 ›› 2020, Vol. 42 ›› Issue (1): 163-181.DOI: 10.3969/j.issn.0253-4967.2020.01.011

• 研究论文 • 上一篇    下一篇

利用地貌形态估算西秦岭-松潘构造结及邻区的下地壳黏滞系数

魏聪敏1, 葛伟鹏1,2, 张波1,2   

  1. 1. 中国地震局兰州地震研究所, 兰州 730000;
    2. 兰州地球物理国家野外科学观测研究站, 兰州 730000
  • 收稿日期:2019-04-12 修回日期:2019-09-16 出版日期:2020-02-20 发布日期:2020-06-17
  • 通讯作者: 葛伟鹏,男,1981年生,副研究员,E-mail:geweipeng@gmail.com。
  • 作者简介:魏聪敏,女,1994年生,现为中国地震局兰州地震研究所固体地球物理学专业在读硕士研究生,研究方向为GPS地壳形变观测,电话:13051467088,E-mail:15554186885@163.com。
  • 基金资助:
    中国地震局科技星火计划项目(XH18048)、国家重点研发计划项目(2017YFC1500102)、甘肃省自然科学基金(17JR5RA340)、中国地震局地震预测研究所基本科研业务专项(2014IESLZ05)和国家自然科学基金(41304035,41572197,41802228)共同资助

ESTIMATING THE LOWER CRUSTAL VISCOSITY OF THE WESTERN QINLING-SONGPAN TECTONIC NODE AND ITS ADJACENT AREAS BY USING LANDFORM MORPHOLOGY

WEI Cong-min1, GE Wei-peng1,2, ZHANG Bo1,2   

  1. 1. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China;
    2. Lanzhou National Geophysical Observation and Research Station, Lanzhou 730000, China
  • Received:2019-04-12 Revised:2019-09-16 Online:2020-02-20 Published:2020-06-17

摘要: 西秦岭-松潘构造结下地壳黏滞系数的定量化研究是理解青藏高原东缘及东北缘动力过程的基础。为进一步认识该区域岩石圈动力学的演化过程,建立下地壳流与不同时间尺度岩石圈变形特征的相互联系,文中以下地壳管道流模型为基础,利用地貌形态估算下地壳的黏滞系数,探讨深部岩石圈流变学过程如何作用于上地壳形变和构造地貌特征;同时结合GPS速度场分析现今的地壳形变,进一步研究区域弥散构造变形过程。结果表明:1)若尔盖-红原盆地北侧及东北侧下地壳的黏滞系数小于东侧及东南侧;2)下地壳流具有向NE低黏滞系数区流动的趋势,较好地解释了该区域的造山运动过程、弧形等高线分布及"V"形展布断裂的发育;3)GPS数据揭示的现今地表运动方向与黏滞系数反演的下地壳历史演化方向一致,说明下地壳与上地壳可能具有良好的耦合特征。研究结果最终为解释不同走向和性质的断裂系发育、造山带形成、宏观地貌发育特征以及深入探讨青藏高原东北缘岩石圈的流变学和隆升动力学提供了依据。

关键词: 西秦岭-松潘构造结, 下地壳黏滞系数, GPS速度场, 构造地貌

Abstract: The western Qinling-Songpan tectonic node is located at the intersection of three major tectonic units of Tibetan plateau, the South China Block and the Ordos Block, and is at the forefront of the northeastern margin of Tibetan plateau. It has unique geological and dynamic characteristics from the surface to the deep underground. Based on the model for ductile flow in the lower crust, the geomorphological form is used to estimate the viscosity of the lower crust, and how the rheological process of the deep lithosphere acts on the upper crust deformation and structural geomorphology. And combined with GPS velocity field data, the current crustal deformation is analyzed to further study the regional dispersive deformation process. The results show that the viscosity of the north and northeast of the Zoige-Hongyuan Basin is smaller than that of the east and southeast. Therefore, the lower crust flow has a tendency of flowing to the northeastern low viscosity zone. We believe that when the lower crust flows from the central plain of the Qinghai-Tibet Plateau to the rigid Sichuan Basin with a higher viscosity of the lower crust, it cannot flow into the basin, and part of the lower crust flow accumulate here, causing the upper crust to rise, and the uplifting led to the formation of the Longmen Mountains and a series of NNE-striking faults as well. When the lower crust flows to the northeast direction with a low viscosity, the brittle upper crust is driven together. Because of the remote effects from the Ordos Basin and the Longxi Basin, the mountains in this region are built slowly and the stepped arc-shaped topography of the current 3 000-meter contour line and the 2 000-meter contour line are developed. At the same time, a series of NWW-trending left-lateral strike-slip faults are developed. This explains the seismogenic tectonic model of the western Qinling-Songpan tectonic node as from NWW-trending left-lateral strike-slip faulting to the NNE-trending right-lateral strike-slip faulting and both having a thrust component. The current crustal movement direction revealed by the GPS velocity field is consistent with the direction of historical crust evolution of the lower crust revealed by the viscosity, implying that there is a good coupling relationship between the lower crust and upper crust. The results provide a basis for studying the development of fault systems with different strikes and properties, the formation of orogenic belts, the macroscopic geomorphological evolution characteristics, and the rheological and uplift dynamics of the lithosphere in the northeastern margin of the Tibetan plateau.
In addition, our research differs from the previous studies in the spatial and temporal scale. Previous studies included either the entire Qinghai-Tibet Plateau or only the eastern margin of the Qinghai-Tibet Plateau. However, our analysis on the contours and topographical differences in the topography of the western Qinling-Songpan tectonic knot reveals that the study area is controlled by the lower crust flow. Our results are confirmed by various observations such as seismology, magnetotellurics and geophysical exploration. Moreover, the previous studies did not point out enough that the elevation contours are elliptical, and the elliptical geomorphology further illustrates that the formation and evolution of the Qinghai-Tibet Plateau has rheological characteristics and also conforms to the continuous deformation mode. Meanwhile, in terms of time scale, the evolution time of the study area is divided into three types of simulation time according to geochronology. And the GPS velocity field is introduced to observe the present-day crustal deformation.

Key words: western Qinling-Songpan tectonic node, lower crustal viscosity, GPS velocity field, tectonogeomorphology

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