Micrormagnetic modelling of naturally occurring mineral systems.

天然矿物系统的微磁建模。

• 批准号: EP/F011113/1
• 负责人: Wyn Williams
• 金额: $ 16.7万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF011113%2F1
• 关键词: Micrormagnetic; modelling; naturally; occurring; mineral

Much of the geological history of the Earth and our understanding of the physical process occurring deep within it, have been unravelled by studying the recordings of the geomagnetic field made by rocks that form on the Earth's surface. Without such information we would not be aware, for example, of the fact that the geomagnetic field has reversed, and would have little understanding of the physical and chemical processes that occur within the Earth's core. The mapping of the motions of the continental plates relies almost entirely on the detailed interpretation of rock-magnetic recordings in well dated rocks, whilst compiling the frequency and periods of geomagnetic field reversals through time provides a magneto-stratigraphic dating tool used extensively in the oil industry and in geological research. Unfortunately, magnetic recording properties are highly grain size dependent, and it is only for the smallest grains, with near uniform magnetisations called single-domain (SD) grains, that we fully understand their ability to record a magnetic field. Naturally occurring magnetic materials in rocks are in fact far from ideal magnetic recorders since, in general, they contain a variety of magnetic mineralogies and have a wide range of grains geometries and sizes. Frequently, most of the magnetic information recorded by the rocks will be carried by grains whose magnetisation is inhomogeneous, but nevertheless their contribution to the magnetic remanence (strength or recording) is almost as high as that of SD grains. Such particles are called pseudo-single-domain (PSD) grains. Despite the dominant contribution of these particles to rock-magnetic remanences, their fidelity of magnetic recoding is poorly understood.This project aims to address this problem by building a numerical model that is able to examine the magnetic properties of PSD grains and in particular the magnetisation in specific grain geometries of that are commonly found in natural samples. We will address the two most perplexing problems remaining in rock-magnetism. Firstly we will model magnetic grains that are sufficiently close to each other that they interact, in the same way as closely spaced bar magnetic might interact. Secondly we will examine the ability of PSD grains to hold an accurate recording of the geomagnetic field as a function of time and temperature, over geological timescales.In order to achieve these goals we must have a numerical model that is capable of the high spatial resolutions needed to accurately account for the inhomogeneous domain structures that occur not just in a single grain, but in a cluster of interacting grains. We also need to be able to determine their thermal stability by estimating, for any particular magnetic structure, the energy barrier preventing thermal fluctuations from destroying its magnetic remanence. Such models cannot be run using a single computer processor on any reasonable time frame (weeks of computation for one solution). Instead we must increase computational efficiency by spreading the calculations across many processors, particularly for the magnetostatic (interaction) field that requires the most computation. This project will develop such a parallelised micromagnetic model capable of detailing, for the first time, the magnetic fidelity of geomagnetic recordings in naturally occurring magnetic minerals.

地球的大部分地质历史和我们对地球深处发生的物理过程的理解，都是通过研究地球表面形成的岩石形成的地磁场的记录而揭开的。例如，如果没有这些信息，我们就不会意识到地球磁场已经反转的事实，也不会对地核内发生的物理和化学过程了解很少。大陆板块运动的测绘几乎完全依赖于对测年准确的岩石中的岩石磁性记录的详细解释，而汇编地磁场随时间反转的频率和周期则提供了一种在石油工业和地质研究中广泛使用的磁性地层测年工具。不幸的是，磁记录特性高度依赖于颗粒大小，只有对于最小的颗粒，具有近乎均匀的磁化作用，我们才能完全了解它们记录磁场的能力。岩石中自然产生的磁性材料实际上远不是理想的磁性记录器，因为它们通常含有各种磁性矿物，并具有广泛的颗粒、几何形状和大小。通常，岩石记录的大部分磁信息将由磁化不均匀的颗粒携带，但它们对剩磁的贡献(强度或记录)几乎与SD颗粒一样高。这种颗粒被称为伪单域(PSD)颗粒。尽管这些颗粒对岩石剩磁的贡献很大，但人们对它们的磁记录保真度了解很少。这个项目旨在通过建立一个数值模型来解决这个问题，该模型能够检查PSD颗粒的磁性，特别是在自然样品中常见的特定颗粒几何形状的磁化作用。我们将解决岩石磁学中仍然存在的两个最令人困惑的问题。首先，我们将对彼此足够接近的磁性颗粒进行建模，使它们相互作用，就像紧密间隔的条形磁性可能相互作用一样。其次，我们将考察PSD颗粒在地质时间尺度上准确记录地磁场随时间和温度变化的能力。为了实现这些目标，我们必须有一个能够准确解释不仅出现在单个颗粒中，而且出现在相互作用的颗粒簇中的不均匀磁区结构所需的高空间分辨率的数值模型。我们还需要能够通过对任何特定的磁结构进行估计来确定它们的热稳定性，对于任何特定的磁结构，防止热涨落破坏其剩磁的能垒。这样的模型不能在任何合理的时间框架内使用单个计算机处理器运行(一种解决方案需要数周的计算)。相反，我们必须通过将计算分散到多个处理器来提高计算效率，特别是对于需要最多计算的静磁(相互作用)场。该项目将开发这样一个并行微磁模型，能够首次详细描述自然磁性矿物中地磁记录的磁保真度。

项目成果

Multi-scale three-dimensional characterization of iron particles in dusty olivine: Implications for paleomagnetism of chondritic meteorites

• DOI: 10.2138/am-2016-5738ccby
• 发表时间: 2016-09-01
• 期刊: AMERICAN MINERALOGIST
• 影响因子: 3.1
• 作者: Einsle, Joshua F.;Harrison, Richard J.;Midgley, Paul A.
• 通讯作者: Midgley, Paul A.

Giant magnetofossils and hyperthermal events

• DOI: 10.1016/j.epsl.2012.07.031
• 发表时间: 2012-10-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Chang, Liao;Roberts, Andrew P.;Muxworthy, Adrian R.
• 通讯作者: Muxworthy, Adrian R.

A strong angular dependence of magnetic properties of magnetosome chains: Implications for rock magnetism and paleomagnetism

• DOI: 10.1002/ggge.20228
• 发表时间: 2013-10-01
• 期刊: GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
• 影响因子: 3.5
• 作者: Li, Jinhua;Ge, Kunpeng;Qin, Huafeng
• 通讯作者: Qin, Huafeng

Effects of the core-shell structure on the magnetic properties of partially oxidized magnetite grains: Experimental and micromagnetic investigations

核壳结构对部分氧化磁铁矿颗粒磁性能的影响：实验和微磁研究

• DOI: 10.1002/2014gc005265
• 发表时间: 2014-05-01
• 期刊: GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
• 影响因子: 3.5
• 作者: Ge, Kunpeng;Williams, Wyn;Yu, Yongjae
• 通讯作者: Yu, Yongjae