鄂尔多斯地块—扬子地块深部电性结构特征及其动力学意义  

Deep electrical structure characteristics of Ordos Block-Yangtze Block and their dynamic significance

作　　者：吕宏斌 叶高峰[1] 金胜[1] 魏文博[1] 董浩[1] 张乐天[1] 谢成良[1] 尹曜田[1] Lü Hongbin;YE Gaofeng;JIN Sheng;WEI Wenbo;DONG Hao;ZHANG Letian;XIE Chengliang;YIN Yaotian(School of Geophysics and Information Technology,China University of Geosciences(Beijing),Beijing,100083)

机构地区：[1]中国地质大学(北京)地球物理与信息技术学院,北京100083

出　　处：《地质论评》2020年第4期813-828,共16页Geological Review

基　　金：自然科学基金面上基金项目(编号:41274003、41674101和41974112);Sinoprobe专项(编号:Sinoprobe-01)的成果

摘　　要：位于青藏高原东北缘的秦岭造山带在大地构造上南接扬子地块、北接华北地块,是特提斯构造域和古亚洲洋构造域的转换带。本文基于对一条起始于扬子地块,穿过秦岭造山带和鄂尔多斯地块,到达河套地堑的南北向大地电磁测深剖面的研究,探讨秦岭造山带和其北侧的鄂尔多斯地块、南侧的扬子地块之间的接触关系,以及青藏高原物质东北向逃逸等地学问题。对实测数据进行了张量阻抗分解和维性分析等工作,并对剖面进行了二维反演,获得岩石圈电性结构模型。根据电阻率模型认为:在秦岭造山带北部发现大规模"瓶颈状"分布的低阻异常体(C2),可能为华北、华南地块双向俯冲前缘地幔物质的上涌通道,或者是青藏高原中、下地壳物质沿秦岭造山带中构造薄弱位置向东逃逸的通道;在秦岭造山带和大巴山弧形带边界处发现南倾的低阻异常(C1),解释为大巴山弧形带北缘的逆冲断裂在电性上的反映;电性结构模型中,扬子地块高阻异常体(R2、R3和R4)向北倾斜至秦岭造山带下方,而北部鄂尔多斯地块的高阻异常体(R5和R6)向南倾斜至秦岭造山带下方;高阻异常通常被认为是稳定岩石圈的反映,据此推断这两组相向俯冲至秦岭造山带下方的高阻异常是华北地块和扬子地块向秦岭造山带下方汇聚的电性结构探测依据;鄂尔多斯地块南、北电性差异较大,北部中、下地壳大规模分布电阻率值在3~100Ω·m之间的低阻异常体,可能为地幔上涌导致的局部熔融或含盐流体共同作用的结果。The Qinling orogenic belt located on the northeast margin of the Qinghai-Xizang(Tibet) Plateau is connected to the Yangtze block to the south and the North China block to the north, and is the transition zone between the Paleo Asian Ocean tectonic domain and Tethys tectonic domain. It is also an important boundary between China’s tectonic pattern and topographic differentiation. This paper uses a north-south magnetotelluric sounding profile which starts at Sichuan basin of Yangtze block, passes through the Qinling orogenic belt and Ordos block, and reaches the Hetao graben. With the resistivity model produced by two-dimensional inversion, the contact relationship between the Ordos block in the north and the Yangtze block in the south along Qinling orogenic belt, and the northeast escape of material of the Qinghai-Tibet Plateau, can be discussed. Dimensionality analysis and strike analysis were performed on the impedance tensor decomposition and phase tensor analysis. Based on the obtained structural strike angle, the MT soundings was rotated, and resistivity model was obtained by two-dimensional inversion. According to the resistivity model, large-scale"bottleneck" low-resistivity anomaly(C2) found in the northern Qinling orogenic belt may be upwelling channels for mantle material in the opposite subduction edge of the North China and South China blocks, or channel of middle and lower crustal material to escape eastward along the structurally weak area in the Qinling orogenic belt. A south-dipping low-resistivity anomaly(C1) was found at the boundary between the Qinling orogenic belt and the Dabashan arc zone, which is interpreted as an electrical reflection of the thrust fault at the northern edge of the Dabashan arc zone. In the resistivity model, the high-resistiviy anomalies(R2, R3, and R4) in the Yangtze block slopes northward to the Qinling orogenic belt. But the high-resistivity anomaly(R5 and R6) in the northern Ordos block slopes southward to the Qinling orogenic belt. The high-resistivity anomalies ca

关 键 词：大地电磁测深 秦岭造山带 华北(鄂尔多斯)地块 扬子地块 双向俯冲 物质逃逸 

分 类 号：P631.325[天文地球—地质矿产勘探]