班公湖-怒江缝合带中段深部电性结构及其构造意义  

Electrical Resistivity Structure in the Vicinity of the Middle Section of the Bangong-Nujiang Suture Zone,Tibet,as Revealed by Magnetotelluric Data

作　　者：薛帅 卢占武[1] 梁宏达 李文辉[1] 王海燕[1] XUE Shuai;LU Zhan-wu;LIANG Hong-da;LI Wen-hui;WANG Hai-yan(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037;Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang,Hebei 065000)

机构地区：[1]自然资源部深地动力学实验室,中国地质科学院地质研究所,北京100037 [2]中国地质科学院地球物理地球化学勘查研究所,河北廊坊065000

出　　处：《地球学报》2022年第6期925-935,共11页Acta Geoscientica Sinica

基　　金：“第二次青藏高原综合科学考察研究”项目(编号:2019QZKK0701);国家自然科学基金项目(编号:42174094;41704099;42174124);中国地质调查局地质调查项目(编号:DD20221647);中国地质科学院基本科研业务费项目(编号:J2015)联合资助。

摘　　要：班公湖—怒江缝合带作为青藏高原拉萨地块和羌塘地块的重要缝合带,具有比较复杂的构造演化史,然而其深部结构和俯冲极性仍存在较大争议。本文利用横穿班公湖—怒江缝合带中段的近南北向大地电磁测线,处理和分析大地电磁测深曲线和相位张量特征,并通过三维大地电磁反演获得了班公湖—怒江缝合带两侧的深部电性结构。三维大地电磁反演结果显示,沿测线分布显著的中下地壳高导异常。大致以班公湖—怒江缝合带为界,可将中下地壳高导异常分为两部分,北拉萨地块近水平展布的高导异常层和南羌塘地块下方明显北倾的高导异常。结合早期的研究资料,分析认为中下地壳高导异常应该为地壳部分熔融所致,且深部电性结构符合沿测线观测的大地热流值变化。同时,中下地壳高导异常可能指示了中生代班公湖—怒江洋的俯冲闭合痕迹,北倾的中下高导异常支持大洋向北俯冲至羌塘地块之下,而北拉萨地块下方的高导异常层可能为低角度俯冲的小洋盆。The Bangong–Nujiang Suture zone(BNS),a tectonic boundary separating the Lhasa and Qiangtang terranes of the Tibetan Plateau,has had a relatively complex evolutionary history.However,the deep structures and subduction polarity of the BNS remain points of contention.To comprehensively characterize deep structures in the vicinity of the BNS,we employed Magnetotelluric(MT)data along a north-south profile in the middle of the BNS.The MT sounding curves and phase deep electrical resistivity structure in the vicinity of the BNS.The 3D MT inversion shows that there is a significant high-conductivity anomaly in the mid-to-lower crust along the N–S profile.Roughly bounded by the BNS,the conductive anomaly can be subdivided into two parts:the near-horizontal,distributed conductive anomaly beneath the northern Lhasa terrane;and the north-dipping anomaly beneath the Qiangtang terrane,which gradually disappears to the north.Analyzing these results within the context of previous studies,the conductive anomaly may be the result of partial crustal melting;additionally,its electrical resistivity structure is consistent with the variation of the heat flow observed along the N-S profile.Meanwhile,the north-dipping conductive anomaly to the north of the BNS may be indicative of the northward subduction of the Mesozoic Bangong–Nujiang Ocean,whereas the conductive layer to the south of the BNS may be the trace of a small ocean basin with a low underthrusting angle.

关 键 词：班公湖—怒江缝合带 大地电磁 北拉萨地块 南羌塘地块 部分熔融 

分 类 号：P631.325[天文地球—地质矿产勘探] P548[天文地球—地质学]