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Mineral magnetism of shocked ferrimagnetic minerals

冲击亚铁磁性矿物的矿物磁性

基本信息

批准号：
236619798
负责人：
Privatdozentin Dr. Agnes Kontny
金额：
--
依托单位：
Abteilung Strukturgeologie und Tektonophysik
依托单位国家：
德国
项目类别：
Priority Programmes
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/236619798?language=en
关键词：
Mineral magnetism shocked ferrimagnetic minerals

项目摘要

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.

亚铁磁性矿物的磁性取决于其晶格、各向异性、化学成分和粒度。后者参数强烈地受显微结构的控制，这对于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抑制（例如磁黄铁矿中的34 K转变，磁铁矿中的Verwey转变）。特别是为了充分研究铁磁矿物中的冲击诱导改性，因此，显微结构和磁性测量的结合是必不可少的。该项目集中在极端条件下的两个重要方面-冲击波对地球上的天然物质和铁陨石中外来磁性矿物的磁性矿物学的影响。为了获得变形结构和磁性之间的一般相关性，将把海洋目标（Lockne和切萨皮克湾）中两个撞击结构的样品的特定磁性和载体以及微观结构与撞击坑外（Lockne）以及撞击坑内（切萨皮克湾）未变形巨块的冲击磁铁矿和含磁铁矿目标岩性进行比较。我们将测试的假设，如果冲击相关的微观结构和相关的磁性可以显着叠加由震后热液蚀变。我们特别希望关注Verwey过渡（TV），因为较低的TV被描述为冲击岩性。因此，本研究的主要重点在于磁矿物学的调查，结合联合收割机低，高温磁化率和饱和等温剩磁与矿物学和显微结构的调查。同样的方法也将用于铁陨石的研究，铁陨石的磁性除了金属相外，还常常受到外来磁性矿物如硬硅钙石、钙铝榴石和钠铝榴石的控制。这些阶段的磁转变温度是很少记录在其化学成分，以及他们的结晶和微观结构配置。然而，为了对地外和地球物质中与冲击相关的磁化过程有一个普遍的了解，获得初始“未冲击”状态与随后的冲击和蚀变相关叠加之间的一般相关性至关重要。