基于AUV近海底磁法的西南印度洋脊典型热液区磁性结构研究

The study of structural features of hydrothermal sulfide area on mid-ocean ridge (MOR) makes a great significance to associated sulfide mineral resources evaluation, but is still a key and difficult question that need to be urgently solved. High-resolution magnetic exploration is considered as a crucial parameter for locating hydrothermal sites and characterizing their structures, while lacks study of spatial structures and much less combines rock-magnetism to infer the formation mechanism of magnetic minerals. Fortunately, a series high-resolution near-bottom magnetic data were collected by autonomous underwater vehicle (AUV) and many rock samples were obtained by TV grab in typical hydrothermal area on southwest Indian ridge (SWIR). Based on that, the project will measure the magnetic parameters of rock samples to analyze the magnetic formation mechanism of each type rocks and deposits, will map and explain the near-bottom magnetic anomalies by some magnetic processing and conversion methods, and will inverse 3-D geomagnetic structure of study areas by using 3-D focused inversion method with undulating terrain and adding depth-weighting function. Furthermore, the project proposes a new idea that synthetically compare magnetic structure, rock magnetism and petrological microstructure of surrounding and hydrothermal sulfide area (or samples) to study the changing rule of magnetization in the typical hydrothermal areas. The research results can provide support for assessment resources of polymetallic sulfides and evidence for hydrothermal system evolution.

洋脊热液区结构特征研究对其伴生的硫化物矿产资源评价具有重大意义，是目前资源评价的重点与难点。高精度的近底磁探测是推断热液区结构特征的重要手段，但缺乏三维空间结构的划分研究，且很少结合岩石磁性学对磁性响应机理的研究。为此，本项目拟基于自主潜水器（AUV）在西南印度洋超慢速扩张洋脊（SWIR）龙旂与断桥热液区获得的高精度近底磁资料与岩石样品，开展岩石样品的磁化率、剩磁、热磁、频率磁化率等多磁性参数测量，以研究不同类型岩石的磁性响应机理；解译典型热液区近底磁异常特征，改进并利用带地形的深度加权聚焦法进行三维磁性结构反演，以划分热液区空间结构；创新性地将围岩与蚀变区的磁性结构、岩石样品磁参数与岩石学磁性矿物显微特征进行多尺度的综合对比研究，以推断典型热液区热液作用过程中磁性变化规律。研究成果可为海底硫化物矿产资源评价与热液系统演化过程研究提供依据。

高精度的近底磁探测是推断热液区结构特征的重要手段，对其伴生的硫化物矿产资源评价具有重大意义。本项目基于自主潜水器（AUV）在西南印度洋超慢速扩张洋脊（SWIR）龙旂与断桥热液区获得的高精度近底磁资料与岩石样品，开展了岩石样品的多磁性参数测量、近底磁资料的解译、三维磁性结构反演与结构划分等工作，取得如下成果与认识：（1）获得了SWIR硫化物区不同岩石磁性特征集，得到不同类型岩石的磁性响应机理；（2）建立了典型热液区三维磁性结构反演方法，获得典型硫化物区空间结构；（3）获得了典型热液区热液作用过程中磁性变化规律。项目很好的完成了预期目标，并首次基于近底磁识别了短周期的磁条带，依此开展了拆离断层演化研究。研究成果为海底硫化物矿产资源评价与热液系统演化过程研究提供依据，同时为超慢速洋脊岩浆与构造相互作用的洋壳增生过程的研究提供一研究范例。