摘要
大洋中脊玄武岩磁性研究是了解洋脊磁异常机理和洋壳圈层结构等基础科学问题的重要手段,但由于深海样品采集难度较大,岩浆后期氧化和热液蚀变如何改变岩石磁性至今仍然是研究的瓶颈.本文从磁性矿物类型、岩石磁性能和磁性颗粒特征等方面概述了大洋中脊玄武岩的岩石磁性特征,其主要的磁性矿物是钛磁铁矿,平均居里温度274℃,具有较高的Q比.这表明在磁法勘探正演与资料解释过程中,不能忽视岩石剩余磁化和感应磁化的共同作用.通过重点对比分析超慢速扩张西南印度洋中脊的玄武岩磁性特征,认为该区的岩石磁性研究将为磁法勘探提供约束条件,同时有望基于岩石磁性研究,在热液蚀变过程定量化研究,与超慢速扩张洋中脊下地壳演化模型等研究方面取得突破.
Researches on the magnetic characters of mid-ocean ridge basalts(MORBs) provide unique insight into the mechanism of magnetic anomaly on mid-ocean ridge and the structure of oceanic crust. However, how the deuteric oxidation and hydrothermal alteration change the magnetic properties of rocks remains unclear due to the difficulty of deep-sea sampling. Here, we outline the rock magnetic characteristics of MORBs from the perspectives of magnetic minerals, rock magnetic properties and magnetic particles, the main magnetic mineral of titanomagnetite, hydrothermal alteration will cause the gradual dissolution of titanomagnetite, which will reduce magnetisation of MORBs, and the alteration will also affect the joint change of density and magnetic susceptibility of MORBs. The average Curie temperature of MORBs is 274 ℃, with high Q-ratio, M;/M;is usually 0.35~0.65, so the main magnetic particles are dominated by SD particles and contain a large number of MD particles and possibly PSD particles, and hydrothermal alteration leads to higher M;/M;ratio. The combined effect of multiple factors(cooling rate, deuteric oxidation, hydrothermal alteration, etc.) causes the change of magnetisation, which further affects the amplitude change of oceanic magnetic anomaly. The higher Q-ratio shows that the combined effect of remanence magnetization and induced magnetization of rocks should not be ignored in the process of forward modeling, inversion and interpretation. The Southwest Indian Ridge(SWIR) is a hotspot for geoscientific research, and the wide range and diversity of sample coverage here are not only beneficial to the magnetic study of MORBs, but also have fundamental geological significance. Therefore, by comparative analysis of the magnetic properties of the basalt on the ultraslow spreading Southwest Indian Ridge, we found that the study of rock magnetism in the research area can provide the constraints(needed in forward modeling and inversion) for magnetic exploration. And this study could be the breakthrough in quantif
作者
刘隆
周建平
吴涛
陶春辉
李倩宇
陈明
LIU Long;ZHOU JianPing;WU Tao;TAO ChunHui;LI QianYu;CHEN Ming(Second Institute Of Oceanography,MNR,Key Lab of Submarine Geosciences,Hangzhou 310012,China;Institute of Geophysics and Geomatics,China University Of Geosciences(Wuhan),Wuhan 430074,China;School of Oceanography,Shanghai Jiao Tong University,Shanghai 200030,China)
出处
《地球物理学进展》
CSCD
北大核心
2021年第5期1880-1890,共11页
Progress in Geophysics
基金
国家自然科学基金(41906065)
国际海域资源调查与开发“十三五”课题(DY135-S1-01-06)联合资助。
