Improving Absolute Paleointensity Experiments through Pressure Cycling

通过压力循环改进绝对古强度实验

基本信息

批准号：
1620582
负责人：
Joshua Feinberg
金额：
$ 24万
依托单位：
University of Minnesota-Twin Cities
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-07-15 至 2021-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1620582&HistoricalAwards=false
关键词：
Improving Absolute Paleointensity Experiments through

项目摘要

The Earth's magnetic field shields the surface of our planet from harmful levels of solar radiation, providing a protective envelope that retains our atmosphere and hydrosphere, establishing the conditions necessary for life, and even safeguarding modern communication satellites from low intensity solar storms. However, our understanding of variability of the strength of the Earth's magnetic field, and any concomitant disruptions these fluctuations might cause, is still in its infancy. Direct measurements of the field from magnetic observatories only extend ~150 years into the past, and while this is significant in human terms, this magnetic record does not include phenomena such as geomagnetic reversals, excursions, or intensity spikes. In order to study these important geomagnetic behaviors scientists rely on the magnetization recorded by rocks, such as lava flows, which record the direction and strength of the Earth's magnetic field as they cool. However, natural materials are not ideal magnetic recorders and efforts to uncover variations in the strength of the ancient magnetic field, or "paleointensity", have been severely hampered by the presence of magnetic minerals whose dimensions are too large to allow them to accurately record the geomagnetic field. This research will aim to overcome this problem and obtain more reliable paleointensity estimates by incorporating pressure treatments into conventional methodologies. Preliminary work has shown that pressure cycling preferentially removes the problematic magnetizations held by larger magnetic grains, while leaving the more reliable magnetizations held by smaller (single domain) grains largely intact. Pressure experiments on volcanic glass (obsidian) have led to significant improvements in our ability to estimate the field responsible for a rock's final magnetization. This research aims to test this new pressure methodology on more commonly used geologic materials, with a special focus on the volcanic rocks of the 1.1 billion year-old Midcontinent Rift in Minnesota. Broader impacts will be achieved through the mentoring of an early career postdoc, the inclusion of undergraduate students in the research, and the creation of a unique, non-magnetic pressure cell that will allow visiting researchers from throughout scientific community to better explore the effects of pressure on the magnetism of natural materials at the Institute for Rock Magnetism.Thermal remanent magnetization processes, e.g., how rocks acquire permanent magnetization, or "remanences" when cooling through their Curie temperature, is fundamental to paleomagnetism. This proposal will examine how thermal remanent magnetizations are influenced by the addition and removal of stress energy. It appears that pressure treatments strongly minimize the types of remanence (PSD and MD) that are detrimental to paleointensity experiments, which are based on single domain magnetic theory. Hence, the PIs think they can overcome a longstanding problem and provide a theoretical understanding of how pressure changes thermal remanence in PSD and MD grains. This new method will potentially increase the success rate of paleointensity experiments, which currently ranges from 10-30%, leading to a significant time savings. The ability to gather paleointensities from pressurized materials is also of special importance to planetary sciences (e.g. meteorite and planetary magnetism). The work proposed here will further our understanding of how pressure influences paleointensities, and can be applied to a variety of different protocols. A continuous monitoring of induced and remanent rock magnetic parameters with increasing pressure will help us understand how magnetic properties change with pressure cycling and will generally improve our understanding of the magnetic behavior of common magnetic minerals.

地球磁场保护地球表面免受有害太阳辐射的影响，提供了保护大气层和水圈的保护层，为生命创造了必要的条件，甚至保护现代通信卫星免受低强度太阳风暴的影响。然而，我们对地球磁场强度变化以及这些波动可能引起的任何伴随干扰的理解仍处于起步阶段。磁观测站对磁场的直接测量只能追溯到过去约 150 年，虽然这对人类来说意义重大，但该磁记录不包括地磁反转、偏移或强度尖峰等现象。为了研究这些重要的地磁行为，科学家们依靠岩石记录的磁化强度，例如熔岩流，这些岩石在冷却时记录了地球磁场的方向和强度。然而，天然材料并不是理想的磁记录器，并且由于磁性矿物的存在而严重阻碍了揭示古代磁场强度或“古强度”变化的努力，因为磁性矿物的尺寸太大，无法准确记录磁场。地磁场。这项研究旨在通过将压力处理纳入传统方法来克服这个问题并获得更可靠的古强度估计。初步工作表明，压力循环优先消除较大磁性颗粒所具有的有问题的磁化强度，同时使较小（单畴）颗粒所具有的更可靠的磁化强度基本完好无损。火山玻璃（黑曜石）的压力实验极大地提高了我们估计岩石最终磁化强度的能力。这项研究旨在在更常用的地质材料上测试这种新的压力方法，特别关注明尼苏达州 11 亿年前大陆中部裂谷的火山岩。通过对早期职业博士后的指导、让本科生参与研究以及创建独特的非磁性压力盒，将实现更广泛的影响，该压力盒将使来自整个科学界的访问研究人员能够更好地探索岩石磁学研究所天然材料磁性的压力。热剩磁过程，例如岩石如何获得永久磁化，或冷却到居里温度时的“剩磁”，是古地磁学的基础。该提案将研究应力能的添加和去除如何影响热剩磁。看来，压力处理极大地减少了剩磁类型（PSD 和 MD），这些类型对基于单畴磁理论的古强度实验是有害的。因此，PI 认为他们可以克服长期存在的问题，并提供关于压力如何改变 PSD 和 MD 晶粒热剩磁的理论理解。这种新方法将有可能提高古强度实验的成功率（目前的成功率范围为 10-30%），从而节省大量时间。从加压材料中收集古强度的能力对于行星科学（例如陨石和行星磁学）也特别重要。这里提出的工作将进一步加深我们对压力如何影响古强度的理解，并且可以应用于各种不同的协议。随着压力的增加，连续监测岩石的感应和剩磁磁性参数将有助于我们了解磁性如何随着压力循环而变化，并且通常会提高我们对常见磁性矿物磁性行为的理解。

项目成果

期刊论文数量（3）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Changes in physical properties of 4C pyrrhotite (Fe7S8) across the 32 K Besnus transition

4C 磁黄铁矿 (Fe7S8) 在 32 K Besnus 转变过程中物理性质的变化

DOI：
10.2138/am-2018-6514
发表时间：
2018-10
期刊：
American Mineralogist
影响因子：
3.1
作者：
Volk, Michael W.R.;McCalla, Eric;Voigt, Bryan;Manno, Michael;Leighton, Chris;Feinberg, Joshua M.
通讯作者：
Feinberg, Joshua M.

Domain State and Temperature Dependence of Pressure Remanent Magnetization in Synthetic Magnetite: Implications for Crustal Remagnetization

合成磁铁矿中压力剩磁的磁畴状态和温度依赖性：对地壳再磁化的影响