Mineral magnetism of shocked ferrimagnetic minerals

铁磁性矿物的磁性取决于它们的晶格、各向异性、化学成分和晶粒尺寸。后一参数受微观结构的强烈控制，这对解释冲击磁性矿物的磁性具有重要意义。断裂和晶格缺陷是导致磁畴尺寸减小的主要原因，并导致矫顽力增加和磁转变（如磁黄铁矿中的34 K转变，磁铁矿中的Verwey转变）的抑制。因此，显微结构和磁测量的结合是必要的，特别是为了充分研究铁磁性矿物中激波引起的修饰。该项目侧重于极端条件的两个重要方面-冲击波对地球上天然物质的影响以及铁陨石中外来磁性矿物的磁矿物学。为了获得变形结构与磁性能之间的一般相关性，本文将从海洋靶区（Lockne和Chesapeake Bay）两个冲击构造中获得的样品的特定磁性能、载流子和微观结构，与撞击坑外（Lockne）和撞击坑内（Chesapeake Bay）未变形的巨块体的冲击磁铁矿矿石和含磁铁矿目标岩性进行比较。我们将测试冲击相关的微观结构和相关的磁性能是否会被冲击后热液蚀变显著地叠加。我们特别想关注Verwey跃迁（TV），因为较低的TV被描述为冲击冲击岩性。因此，本研究的重点是磁矿物学研究，将低温磁化率和饱和等温剩余磁化率与矿物学和微观结构研究相结合。同样的方法将被用于铁陨石的研究，铁陨石的磁性通常是由外来的磁性矿物控制的，如直晶、晶贝石和泥辉石，以及金属相。这些相的磁转变温度与它们的化学成分以及它们的晶体学和微观结构构型有关的文献很少。然而，对于地外和陆地材料中与冲击相关的磁化过程的一般理解，至关重要的是获得初始“非冲击”状态与随后的冲击和变化相关的套印之间的一般相关性。

Magnetic properties of ferrimagnetic minerals depend on their crystal lattice, anisotropy, chemical composition and grain size. The latter parameter is strongly controlled by microstructures, which are significant for the interpretation of the magnetic properties of shocked magnetic minerals. Fracturing and lattice defects are the main causes for magnetic domain size reduction and generate an increase in coercivity and the suppression of magnetic transitions (e.g. 34 K transition in pyrrhotite, Verwey transition in magnetite).Especially for an adequate investigation of shock-induced modifications in ferromagnetic minerals, a combination of microstructural and magnetic measurements is therefore essential.This project focusses on two significant aspects of extreme conditions – the consequence of shock waves on natural material on Earth and on the magnetic mineralogy of exotic magnetic minerals in iron meteorites. In order to obtain general correlations between deformation structures and magnetic properties, the specific magnetic properties and carriers as well as microstructures of samples from two impact structures in marine targets (Lockne and Chesapeake Bay) will be compared with shocked magnetite ore and magnetite-bearing target lithologies from outside the crater (Lockne) as well as from undeformed megablocks within the crater (Chesapeake Bay). We will test the hypothesis if shock-related microstructures and associated magnetic properties can significantly be overprinted by postshock hydrothermal alteration. We especially want to focus on the Verwey transition (TV) as lower TVs are described for shocked impact lithologies. Hence, the main focus of this study lies on magneto-mineralogical investigations which combine low- and high-temperature magnetic susceptibility and saturation isothermal remanent magnetization with mineralogical and microstructural investigations. The same methods will then be used for the investigation of iron meteorites, whose magnetic properties are often controled by exotic magnetic minerals like cohenite, schreibersite and daubreelite in addition to the metal phases. Magnetic transition temperatures of those phases are poorly documented in relation to their chemical composition as well as to their crystallographic and microstructural configuration. For a general understanding of shock-related magnetization processes in extraterrestrial and terrestrial material, however, it is crucial to obtain a general correlation between the initial “unshocked” state and the subsequent shock- and alteration-related overprints.