超基性岩热液硫化物矿床磁性物质来源和磁异常特征  

Magnetic source and magnetic anomaly characteristics of sulfide deposits in ultramafic hydrothermal system

作　　者：胡智龙 吴招才 韩喜彬 张家岭 阳凡林[1] 赵宁 HU ZhiLong;WU ZhaoCai;HAN XiBin;ZHANG JiaLing;YANG FanLin;ZHAO Ning(College of Geodesy and Geomatics,Shandong University of Science and Technology,Qingdao 266590,China;The Second Institute of Oceanography,MNR,Key Lab of Submarine Geosciences,MNR,Hangzhou 310012,China;Department of Marine Sciences,Zhejiang University,Zhoushan 316021,China)

机构地区：[1]山东科技大学测绘与空间信息学院,青岛266590 [2]自然资源部第二海洋研究所,自然资源部海底科学重点实验室,杭州310012 [3]浙江大学海洋科学系,舟山316021

出　　处：《地球物理学进展》2022年第4期1405-1413,共9页Progress in Geophysics

基　　金：印度洋靶区地球物理异常及其找矿应用(DY135-S2-104);国家自然科学基金项目(41676037,42076078)联合资助。

摘　　要：围岩为超基性岩的热液硫化物矿床是一种重要的海底热液硫化物矿床类型,相比围岩为玄武岩的热液硫化物矿床,超基性岩热液硫化物矿床研究相对较少,磁性特征也更为复杂.超基性岩热液硫化物矿床在热液蚀变作用下产生磁铁矿和磁黄铁矿等磁性矿物,从而呈现出与玄武岩型热液矿床相反的强烈的正磁异常.在超基性岩热液硫化物矿床发育的初始阶段,高温热液流体与周围超基性岩作用发生蛇纹石化,开始产生磁铁矿等磁性矿物,呈现出强烈的正磁异常;随着热液系统持续活跃,超基性岩蛇纹石化程度逐渐增加,产生的磁性矿物含量也逐渐增加,呈现的正磁异常达到最强;随着热液活动逐渐停止,热液蚀变伴随的蛇纹石化反应逐渐停止,热液系统温度逐渐降低,无法继续维持还原环境,之前产生的磁黄铁矿和磁铁矿会被氧化成非磁性硫化物或氧化物导致其磁性大大降低形成弱的正磁异常.然而,如Lost City这样的低温活跃的超基性岩热液系统也表现为较弱的正磁异常,原因可能为低温环境下超基性岩的热液蚀变与高温流体不同,低温环境下的蛇纹石化过程中铁元素会转移到所生成的非磁性水镁石等岩石中,导致也形成弱的正磁异常.Ultramafic hydrothermal sulfide deposits are an important type of submarine hydrothermal sulfide deposits.Compared with the basalt hydrothermal sulfide deposits,the study of hydrothermal sulfide deposits in ultramafic rocks is relatively Less,the magnetic characteristics are more complex. Ultrabasic hydrothermal sulfide deposits under hydrothermal alteration to produce magnetic minerals such as magnetite and pyrrhotite,which presents a strong positive magnetic anomaly opposite to basalt hydrothermal deposits. At the initial stage of ultramafic hydrothermal sulfide deposit development,serpentinization occurs when the high-temperature hydrothermal fluid reacts with the surrounding ultramafic rocks,and magnetic minerals such as magnetite are produced,presenting strong positive magnetic anomalies. As the hydrothermal system continues to be active,the serpentinization degree of ultramacfic rocks gradually increases,and the content of magnetic minerals also gradually increases,presenting the strongest positive magnetic anomaly. As the hydrothermal activity gradually ceases,the serpentinization reaction accompanying the hydrothermal alteration gradually ceases,and the temperature of the hydrothermal system gradually decreases,and the reducing environment can not be maintained. The magnetite and pyrrhotite previously produced will be oxidized into non-magnetic sulfide or oxide,lead to the magnetization of sulfide deposits is reduced rapidly,forming weak positive magnetic anomaly. However,ultramafic-hosted hydrothermal system with low fluid temperature such as the Lost City is also characterized by weak positive magnetic anomaly,the reason may be that the ultramafic rock hydrothermal alteration in low temperature fluid and high temperature fluid exists different reaction process. Serpentinization in low temperature environment,the iron will be transferred to the generated weak magnetic brucite,also resulting in the formation of weak positive magnetic anomaly.

关 键 词：超基性岩热液系统 硫化物矿床 磁异常 

分 类 号：P318[天文地球—固体地球物理学] P738[天文地球—地球物理学]