四川龙门山断裂带高精度地壳/岩石圈黏度结构及其动力学意义  

High-resolution crustal/lithospheric viscosity of the Longmenshan fault zone,Sichuan province and its geodynamic implications

作　　者：朱涛[1,2] 詹艳[2] 孙翔宇[2] 张宇[3] ZHU Tao;ZHAN Yan;SUN XiangYu;ZHANG Yu(Key Laboratory of Seismic Observation and Geophysical Imaging,Institute of Geophysics,CEA,Beijing 100081,China;State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;Institute of Crustal Dynamics,China Earthquake Administration,Beijing 100085,China)

机构地区：[1]中国地震局地球物理研究所(中国地震局地震观测与地球物理成像重点实验室),北京100081 [2]中国地震局地质研究所地震动力学国家重点实验室,北京100029 [3]中国地震局地壳应力研究所,北京100085

出　　处：《地球物理学报》2020年第1期196-209,共14页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2018YFC1504103);地震动力学国家重点实验室开放基金项目(LED2017B08);国家自然科学基金(41474057);中国地震局地壳应力研究所中央级公益性科研院所基本科研业务专项(ZDJ2016-02)资助

摘　　要：岩石圈黏度是大陆动力学研究中一个重要参数,但是岩石圈黏度,尤其是横向小尺度(<100 km)黏度结构的确定是一个挑战.本文根据电阻率和黏度与它们控制因素的相似关系,直接把一条跨过青藏高原东缘和四川龙门山断裂带的大地电磁(MT)探测的电阻率剖面转换成黏度结构作为输入,在GPS速度和地表地形数据的约束下,利用地球动力学数值模拟获得了该剖面的二维地壳/岩石圈黏度结构.本文推断的黏度与前人获得的区域尺度的黏度值一致,但揭示出了更多的细节.本文的黏度结构揭示出研究区域内的地壳/岩石圈黏度存在较大的空间变化范围(约5量级),黏度值分布在1.48×10^17~8.44×10^22 Pa·s之间;龙门山断裂带下的黏度存在强烈的小尺度横向变化,其中、下地壳的黏度分别为1.99×10^18~8.21×10^20 Pa·s(平均1.17×10^20 Pa·s)和4.09×10^19~7.08×10^20 Pa·s(平均1.77×10^20 Pa·s).基于该黏度结构的地球动力学模型表明驱动青藏高原中-下地壳物质流动的可能是热-化学浮力,以及上地壳和中-下地壳可能处于解耦状态.本文获得的黏度结构可以为龙门山断裂带地震成因和机制、岩石圈小尺度变形和构造应力状态的深入研究提供重要的帮助.The crustal/lithospheric rheology is an important factor in the study of lithospheric dynamics.However,estimation of this parameter remains challenging,especially for small-scale(<100 km)lateral variations in viscosity.In this study,a resistivity profile from magnetotelluric(MT)survey,which crosses the eastern margin of the Tibetan Plateau and the Longmenshan fault zone in Sichuan province,is directly converted into a viscosity structure as an input based on the similarity between resistivity and viscosity,then geodynamic modeling is used to infer the two-dimensional crustal/lithospheric viscosity along this MT profile under the constraints of GPS-derived crustal velocity and surface topography.Our inference is consistent with previous regional-scale estimates but reveals more details.The viscosity structure exhibits large spatial variations(~5 orders)in the study area and has the viscosity of 1.48×10^17~8.44×10^22 Pa·s.The viscosity of the Longmenshan fault zone has strong small-scale lateral variations,and its values in the middle and lower crust are 1.99×10^18~8.21×10^20 Pa·s(1.17×10^20 Pa·s on average)and 4.09×10^19~7.08×10^20 Pa·s(1.77×10^20 Pa·s on average),respectively.Our viscosity-based geodynamic model implies probably the middle-lower crustal flow is driven by thermal-chemical buoyancy and the decoupling of the upper crust from the middle-lower crust below the Tibetan Plateau.The viscosity structure presented in this paper may provide an important aid for further research of seismogenic mechanism,fine-scale lithospheric deformation and tectonic stress state of the Longmenshan fault zone.

关 键 词：黏度结构 大地电磁测深 电阻率 地球动力学模拟 

分 类 号：P541[天文地球—构造地质学] P631[天文地球—地质学]