大陆岩石圈导电性的研究方法

随着地球科学的进展 ,大陆岩石圈导电性结构的研究越来越引起人们的重视 ,而超宽频带大地电磁测深则是目前用于探测岩石圈导电性最有效的地球物理先进技术。它把现代性能优良的宽频带大地电磁系统 (MT 2 4NS或V5 2 0 0 0 )与长周期智能化大地电磁系统 (LIMS)配套使用 ,采集地面上频率范围为n× 10 -4～n× 10 2 Hz的天然电磁场信号 ,并通过一系列数据处理和反演计算 ,获得深达下地壳和上地幔的地下导电性结构模型。此模型不仅可以提供有关岩石圈地质构造轮廓的信息 ,更重要的是可以间接反映现今地下深部的热结构特征和物质状态分布特点。多年来 ,应用超宽频带大地电磁测深对青藏高原岩石圈导电性结构的研究表明 ,高原的中、下地壳确实是良导电性的 ;它可能说明西藏地壳中普遍存在岩石的局部熔融 ,或地热流体。沿着应县—商河剖面的大地电磁测深研究结果从电性的角度证明了太行山山前断裂为一组向东倾斜的深断裂 ,华北地区岩石圈以其为界划分为东、西两区 ;东区为低阻区 ,与构造活动区的岩石圈导电性特征相符 ;西区为高阻区 ,表现出稳定大陆区岩石圈导电性结构的特点。

METHODS TO STUDY ELECTRICAL CONDUCTIVITY OF CONTINENTAL LITHOSPHERE

With the development of geosciences, more and more attention is focused on the study of electrical conductivity of continental lithosphere. And the super wide band MT sounding, which combines the broad bound MT system(MT 24NS or V5 2000) and long period intelligent MT system (LIMS), is by far the most effective and advanced method to detect the conductivity of continental lithosphere. Using the method, the data of the natural electromagnetic field, frequency ranging from n ×10 -4 to n ×10 2 Hz, can be acquired, processed and inversed. Thus, the electrical structure model of lower crust and upper mantle are inferred. Not only can it provide the information about the geologic structure of the lithosphere, the model also suggests the thermal and mass distribution character in lower curst. For many years, the study of electrical conductivity in the Tibetan plateau, using the super wide band MT sounding, has shown that high electrical conductivity ranging from the middle to lower crust. Such pervasive high conductance suggests that partial melt or aqueous fluids is widespread within the Tibetan crust. The study of profiling from Yingxian to Shanghe, using the super wide band MT sounding, represents that the Taihang Mountain fault is a deep fault descending eastward. The fault divides North China lithosphere into eastern and western parts. The former is low conductivity region, which agrees with the electrical character of active tectonic region of lithosphere. In contrast, the latter is high conductivity, showing the electrical character of stable continental regions.