Lithospheric Electrical Structure along Shenzha-Shuanghu Profile in Tibetan Plateau and Its Significance
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摘要: 为了研究班公湖-怒江缝合带的壳幔电性结构及构造特征，并为其俯冲极性提供电性约束，对青藏高原中部申扎-双湖大地电磁测深剖面进行全面数据处理分析，获得了可靠的二维电性结构模型，研究表明：沿剖面上地壳分布的是规模不等的高阻体，底面埋深在10~25 km变化，高阻层之下发现由不连续的高导体构成的中下地壳高导层.通过对电性结构的分析，认为班公湖-怒江特提斯洋的俯冲消亡极性可能是双向的，随后拉萨-羌塘地体碰撞带处的上地壳高阻体发生拆沉，以上两次动力学事件可能共同作用于缝合带处的壳幔高导体，同时北拉萨地体的壳幔高导体还可能体现了构造作用、岩浆活动和成矿作用之间的关系.Abstract: To understand the crust-mantle electrical structure and the tectonic feature of Bangong-Nujiang suture, and offer the electrical constraints to its subduction polarity, the magnetotellurics data of the Shenzha-Shuanghu magnetotelluric profile in the central Himalaya-Tibetan Plateau was carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study represents that there are some different scale resistors distributed along the profile in the upper crust and the bottom depth varying from 10 to 25 km, and meanwhile there is a middle-lower conductive layer composed of some discontinuous conductivities beneath the resistive layer. With the analysis of the electric structure, the study indicates that the subduction polarity of the Bangong-Nujiang Tethyan ocean may be double-sided, and subsequently the detachment of the upper crustal resistor was occurred, and so the twice dynamics above may contribute to the formation of the conductor within the suture. Furthermore, the conductor beneath the northern Lhasa terrane may also reflect the relation among the dynamics, magmatism and mineralization.
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图 1 (a) 研究区点位图和(b)青藏高原及邻区地形图
a图包括主要大地构造和MT测点.黑色圆点表示宽频大地电磁测深测点，红色圆点表示长周期大地电磁测深测点，蓝色圆圈表示典型测点；b图红色矩形为研究区.TH.特提斯-喜马拉雅地体；LS.拉萨地体；QT.羌塘地体；SPGZ.松潘-甘孜地体；QD.柴达木盆地；TB.塔里木盆地；IYS.印度-雅鲁藏布江缝合带；LMF.洛巴堆-米拉山断裂；SNMZ.狮泉河-纳木错蛇绿岩带；BNS.班公湖-怒江缝合带；JRS.金沙江缝合带；AMS.阿尼玛卿缝合带
Fig. 1. (a) Topography map showing major tectonic structures, (b) topography of the Tibetan Plateau and its adjacent areas
图 2 宽频(点号530、SD39)及长周期(点号504、554、SD16、SD28)典型数据曲线
Fig. 2. Data curves of broad⁃band (station 530, SD39) and long⁃period (stations 504, 554, SD16, SD28)
图 3 2017线和500线Bahr二维偏离度拟断面
Fig. 3. Pseudo section of Bahr skewness of line 2017 and line 500
图 4 阻抗张量分解图
（a）0.1~1 s，（b）1~10 s，（c）10~100 s，（d）100~1 000 s.玫瑰花图显示相应频段的走向分析结果
Fig. 4. Impedance tensor maps
图 5 二维反演模型粗糙度、拟合误差随正则化因子变化的曲线
Fig. 5. L⁃curve of RMS values and roughness corresponding to different tau values of 2⁃D inversion model
图 6 二维TM模式反演模型
a.2017线二维反演单点RMS；b.2017线二维电性模型，RMS=1.34；c.500线二维电性模型，RMS=1.47；BNS.班公湖-怒江缝合带；C1和C2为高导体；R1为高阻体.莫霍面深度引自Gao et al.（2013）和Lu et al.（2015）
Fig. 6. 2⁃D electrical structure models using TM data
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