磁各向异性的地磁异常响应及反演研究

The magnetic anisotropy of crustal rocks provide important evidences for studying the geological processes such as mineralization, magmatic emplacement and deep crustal stress, as it is closely related to directional recrystallization, directional alignment and stress-strain of magnetic minerals caused by sedimentation, magmatic activity, tectonic stress and metamorphism. Magnetic structure information is the physical basis for the change of magnetic field. This magnetic anisotropic information would generate corresponding magnetic field response that is included in the observed multi-scale magnetic data. In this project, based on the main line of relationship between magnetic anisotropy and magnetic field responses and using numerical simulations, physical models construction and field data, we firstly study the magnetic field response regularities of total field, vector and gradient tensor components under the magnetic anisotropy condition. The magnetic anisotropic mathematical–physical–geological model of typical geological process and target body is constructed. Based on the prior information constraints such as geology, rock magnetism and geophysics, we carry out the inversion of magnetic data under magnetic anisotropy condition, and further extract magnetic anisotropy information from inversion results. We study the influence of magnetic observation ways to the inversion accuracy. Finally, some laboratory physical models and field data are used to test and to apply for the methods. The study of this project will expand the basic theory and technology of magnetic exploration, and also will provide technical support for studying deep geological processes and mineral resource that is related to the magnetic anisotropy.

地壳岩石的磁各向异性与沉积作用、岩浆活动、构造应力、变质过程引起的磁性矿物定向重结晶、定向排列、应力应变密切相关，是研究成矿作用、岩浆侵位及地壳深部应力状态等地质过程的重要依据。磁性结构信息是磁场变化的物性基础，这些磁各向异性信息将产生对应的磁场响应，并隐含在观测的多尺度磁测数据中。本项目以磁各向异性与磁场响应关系为主线，通过数值模拟、构建物理模型和实际数据相结合的途径：研究磁各向异性条件下总场、矢量及梯度张量的磁场响应规律，构建代表性地质过程和目标体磁各向异性数学-物理-地质模型；基于地质、岩石磁学及地球物理等先验信息约束，进行磁各向异性条件下磁场反演，提取磁各向异性信息，研究磁场观测方式对反演精度影响；进行实验室物理模型及实际数据的检验与应用研究。本项目研究将拓展磁力探测的基础理论与方法技术，为研究磁各向异性相关的深部地质过程及矿产资源提供技术支撑。

地壳岩石的磁各向异性与沉积作用、岩浆活动、构造应力、变质过程引起的磁性矿物定向重结晶、定向排列、应力应变密切相关，是研究成矿作用、岩浆侵位及地壳深部应力状态等地质过程的重要依据。总磁化强度矢量是连接磁各向异性结构与地磁异常的桥梁，本项目以三维磁化强度矢量反演为基础，开展磁各向异性条件下的磁异常反演研究，取得了如下成果。1）揭示了磁化率各向异性与退磁形状各向异性对磁场的响应机制。数值模拟计算表明，磁化率各向异性时，磁化方向变化将导致总磁异常的幅值和形态发生变化，且各向异性度越大，形态和幅值变化也越大。强磁性体的退磁形状各向异性使异常幅值变小、形态畸变，磁性体内部磁化强度大小、表面磁荷密度分布不均匀，磁化强度方向往磁性体长轴方向偏转。2）提出了磁各向异性复杂条件下地磁异常磁化强度矢量反演技术。与磁场观测数据有直接联系的物理量是总磁化强度矢量，总磁化强度矢量是解决退磁各向异性与磁化率各向异性等复杂问题的中间变量或桥梁，建立了磁各向异性表征参数，实现各种磁各向异性的数学表达，构建了磁各向异性的数学-物理-地质模型，提出了基于稀疏约束的磁化强度矢量精细反演技术，提取剩余磁化强度与磁化率信息。3）发展了基于互相关和多重相关的高精度磁化强度方向估计方法。改进了基于维纳滤波的化极算子，提高了MAX-MIN方法磁化方向及化极异常的计算精度，提出了基于多重相关理论的磁异常总磁化方向估计方法，发现了磁势总梯度的包络特征，开发了与RTP场相关性估计总磁化方向方法，为高精度磁化强度矢量反演奠定了基础。4）研究成果在JGR、Geophysics、IEEE-TGRS等国际权威期刊发表SCI论文14篇，撰写中文专著1部，获批/申请专利2项，参加国际/国内学术会议10余人次，培养中青年学术带头人1人，培养博士后、硕士与博士研究生10人，项目负责人获傅承义青年科技奖及中国地球物理学会科技进步奖二等奖（R3）。