剩磁和退磁条件下磁化强度矢量反演研究

Geomagnetic anomaly contains rich geological information from surface to deep Earth, which provides an important basis for exploring solid mineral resources and investigating Earth’s interior structures. However, the remanence and the high-susceptibility self-demagnetization change the shapes and amplitudes of geomagnetic-field reduced anomaly, hence misleading the interpretation of magnetic anomaly. The physical mechanisms of remanence and self-demagnetization are totally different, but they have the same responses that both alter the magnitude and direction of total magnetization vector. Based on this common features, we use the magnetization vector as a basic parameter to study the three-dimensional inversion of magnetic anomaly which is affected by remanence and self-demagnetization, respectively. We firstly propose a sequential inversion method of successively recovering the distributions of magnetization magnitude and direction by use of the magnetic magnitude transforms that are weak sensitive to the magnetization direction. Then the recovered magnetization vector distributions are used to qualitatively evaluate the influences of remanence and self-demagnetization. Based on the measured magnetic properties, we study the relationships among magnetization vector and remanence and self-demagnetization when the remanence and self-demagnetization are present, respectively. Then the distributions of magnetic sources are obtained and the information on remanence and self-demagnetization is extracted from the recovered magnetization vector. Finally, this research will improve the inversion theory of magnetic field data, which will realize the accurate interpretation of magnetic anomaly and the precise recovery of magnetic sources in the presence of remanence and self-demagnetization. This study also will offer a technological support for mineral resources prospecting and crustal structure investigation.

地磁异常蕴含着从地表到地球深部丰富的地质信息，为寻找固体矿产资源和研究地球内部结构提供重要依据。地磁异常解释中，剩磁和高磁化率体的退磁作用会导致感磁作用下的磁异常形态和幅值发生变化，从而影响磁异常的准确评判。尽管剩磁和退磁产生的物理机制不同，但它们具有相同的表现形式——改变了磁性体内部总磁化强度矢量的大小和方向。本项目以磁化强度矢量为切入点，研究剩磁和退磁分别存在条件下的磁异常三维反演：基于磁异常转换模量弱敏感于磁化方向的特点，进行磁化强度大小和方向顺序反演，获取磁化强度矢量分布；用磁化强度矢量定性评估剩磁与退磁影响，结合物性测量信息，分别考虑剩磁和退磁影响情况，研究磁化强度矢量与剩磁和退磁的关系，获取磁性体分布并从磁化强度矢量中提取剩磁与退磁信息。本研究将完善磁场反演理论，实现剩磁和退磁影响下的磁异常准确解译和磁性体精确定位，为矿产资源探测与地壳结构研究提供技术支撑。

地磁异常蕴含着从地表到地球深部非常丰富的地质信息，为寻找固体矿产资源和研究地球内部结构提供重要依据。地磁异常解释中，剩磁和高磁化率体的退磁作用会导致感磁作用下的磁异常形态和幅值发生变化，从而影响磁异常的准确评判。本项目以磁化强度矢量为切入点，开展剩磁和退磁条件下的磁异常三维反演研究。1）发展了磁数据三维反演技术，提高磁数据反演的分辨能力和计算效率。进行多井、多分量磁测数据联合反演，地面磁测与井中磁测联合反演，降低多解性，提高分辨率；提出基于生物群智能的粒子群算法，进行磁数据非线性反演，避免直接求解大型矩阵方程，提高了反演效率；提出了改进的DEXP磁数据成像方法，相比正则化反演，成像方法更有效地节省存储空间和提高反演速率。2）发展了剩磁与退磁影响下的地磁异常反演技术，提出了通过地磁异常提取剩磁信息方法，为地磁异常研究深部地质过程提供新的应用研究方向。系统总结和发展了磁化强度矢量反演技术；基于Köenigsberger比值先验信息约束，提出通过磁异常直接反演磁化率和剩磁矢量方法，获取剩磁大小和方向信息；通过厘清剩磁与感磁的相互耦合关系，提出根据磁异常提取剩磁强度和方向信息的方法；当剩磁、退磁、感磁三者相互耦合时，根据总磁化强速、剩磁和退磁相互关系及先验信息，提取剩磁方向和强度信息，为地质演化研究提供了地球物理证据。3）提出的系列方法技术应用于我国重点矿集区深部结构及矿产资源探测，实现了深部矿体、岩体和构造的精细定位成像。在湖北大冶铁矿区，考虑剩磁与退磁作用的地磁异常反演获得更准确的铁资源储量；地磁异常反演结果揭示了南京冶山地区新生代玄武岩的深部结构特征，发现玄武岩为地磁场倒转时期侵入；在大冶老矿区，地表人文干扰严重，井中地磁异常反演发现旁侧隐伏矿体；井地联合反演更准确反映了新疆蒙库铁矿区深部矿体的埋深和形态特征。4）在JGR、GJI、Geophysics等重要国际期刊发表SCI论文10篇，发表中文专著1部，英文专著章节1部。