海洋磁异常条带的磁化强度矢量反演方法研究

Marine magnetic anomaly stripes and their corresponding oceanic lithosphere magnetization structure provide crucial evidence for seafloor spreading, plate tectonics, and geomagnetic polarity reversals. Increasing accumulation of oceanic magnetic data with high resolution and high accuracy, and methods for magnetic vector inversion provide good data and technique basis for constructing the magnetization structure of oceanic lithosphere. Therefore, research on the modeling method for magnetization vector structure of oceanic lithosphere is, certainly, a natural development trend of using advanced approaches in geomagnetism to study solid Earth geophysical problems. However, the recent techniques for magnetization inversion of striped magnetic anomalies just obtain the magnetization intensity below the basic assumptions, such as a constant magnetization depth and a same total magnetization direction with the IGRF. To make more full use of the tectonic and physical information contained in the oceanic striped anomalies, this project will mainly research on the geologically constrained magnetization vector inversion of oceanic striped magnetic data and aims at developing systematic method and technique for constructing the magnetization vector structure of oceanic lithosphere near ridges. Furthermore, the method can be introduced to magnetization vector imaging of global oceanic lithosphere, and the magnetization vector structure as complementary constraint data or information will serve to tectonics and dynamics as well as basic study for global oceanic magnetic modelling.

海洋条带状磁异常及其对应的海洋岩石圈磁性结构提供了洋底扩张、板块构造、地磁场极性倒转等方面的重要证据。日益积累的高质量海洋磁测数据以及磁化强度矢量反演方法与技术的发展，为构建海洋岩石圈磁化强度矢量结构创造了良好的数据和技术条件。但是，目前利用海洋磁异常反演海洋岩石圈磁化强度的方法通常基于磁性层厚度恒定、磁化强度方向与当前地磁场一致等简化假设，并非真正的矢量反演。为了更准确地恢复条带状磁异常中包含的信息，本项目拟开展复杂地质环境下由有效地质和地球物理先验信息约束的磁化强度矢量反演方法研究，以理论研究、模型试验与实际应用为手段，构建海洋洋中脊地区岩石圈磁性矢量结构建模的方法与技术体系。本项目研究将为全球海洋岩石圈磁化强度矢量成像提供方法和技术参考，进一步为板块构造学、地球动力学提供海洋岩石圈三维磁化强度矢量结构方面的约束资料以及作为全球海洋磁场建模的基础研究。

海洋岩石圈的磁化强度分布能为海洋岩石圈演化、区域大地构造、古地磁场幅值变化等研究提供定量解释方面的参考，其幅值和方向均具有重要意义。但是由于其具有正负极性带交接排布、磁化强度方向复杂等特点，同时获取磁化强度幅值和方向具有一定的难度。本项目以海洋岩石圈及其磁异常条带为主要研究对象，摸索并制定了一套适用于磁化强度方向复杂多样条件下的磁化强度矢量反演方法与技术流程。项目组首先构建了海洋岩石圈剩余磁化强度简化模型，该模型能服务于正演计算及分析也能作为先验约束信息。然后通过正演计算磁异常及其多种转换参量，给出了适用于矢量反演的总强度磁异常及其总梯度模和磁异常总模量的数据类型组合。最后采用先给定磁化强度方向、后反演磁化强度幅值的串行方式实现矢量反演，并通过模型试验和实际资料处理对方法的有效性和实用性进行了检验。本项目发展的相关技术，为复杂条件下的磁化强度矢量反演提供了思路，同时在全球岩石圈磁场建模及卫星磁测数据解释等方面也具有一定的应用前景。