断裂岩岩石磁学研究进展

断裂岩的岩石磁学研究可以揭示地震断裂作用的物理和化学环境,对于探讨地震断裂作用机制具有重要作用。本文在断裂岩岩石磁学最新文献的基础上,结合笔者及所在研究团队在龙门山断裂带获得的研究成果,综述了断裂岩的岩石磁学研究进展。大量研究发现断层泥和假玄武玻璃通常具有磁化率值或剩磁强度异常特征。顺磁性矿物在摩擦热或流体作用下形成新的铁磁性矿物是断层泥和假玄武玻璃高磁化率值或高剩磁强度的主要原因;地震断裂摩擦熔融作用中形成的单质铁是假玄武玻璃中高磁化率值或高剩磁强度异常的另一个重要原因。蠕滑断裂和出露于浅地表的断裂带中可见一些具有低磁化率值异常的断层泥,原因可能是流体作用或断裂带未经历高温摩擦热。断裂岩的岩石磁学研究为地震断裂带的应力应变、形成温度、摩擦热效应、流体作用、形成深度和氧化还原特征等提供了重要信息,可用于分析地震断裂的孕震和发震环境。综合岩石磁学测试和微米至纳米尺度的超显微学研究,并辅助地震断裂岩的摩擦实验、高温热模拟实验等研究可以更好地获得断裂岩的岩石磁学信息。

A Review of Rock Magnetism for Fault Rocks

Rock magnetism of fault rocks reveals the physical and chemical characteristics of earthquake fault zone and contributes to the study of seismic faulting mechanism and active behavior. This paper reviews the rock magnetic studies of earthquake fault rocks, based on the newest literature and works related to rock magnetism as well as achievements from the Longmen Shan fault zone. Rock magnetic studies have revealed magnetic highs or lows in fault gouge or pseudotachylyte. The frictional heating high temperatures or fluids induced thermal decomposition of paramagnetic minerals, forming ferromagnetic minerals and contributing to the high magnetic susceptibility values or remanence of fault gouge or pseudotachylyte; pure iron in frictional melting is another important reason for high magnetic susceptibility values or remanence of pseudotachylyte. Some fault gouges in creep fault zone or surface fault zone have lower magnetic susceptibility values than wall rocks, and this might result from the fluid or low frictional heating temperature. Rock magnetism of fault rocks provides important information for stress, strain, temperature, frictional heating, fluid, formation depth and different redox characteristics of earthquake fault zone, which is helpful to analyzing the seismogenic environment. Combined with rock magnetic measurements, the microstructural studies in micron or nanometer and the strengthening of frictional experiments as well as high temperature heating experiments of fault rocks will lead to better obtaining the magnetic information of earthquake fault zone.