RUI: Rapid geomagnetic change recorded by a partially remagnetized lava flow

RUI：部分重磁化熔岩流记录的快速地磁变化

• 批准号: 1015396
• 负责人: Scott Bogue
• 金额: $ 12.9万
• 依托单位: Occidental College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1015396&HistoricalAwards=false
• 关键词: RUI; Rapid; geomagnetic; change; recorded

It is well established that the geomagnetic field, which is generated by fluid motions in the Earth's core, has reversed polarity many times in the geological past, most recently about 800,000 years ago. The geological record shows that this global-scale change, during which compasses everywhere go from pointing north to pointing south (or visa versa), takes only a few thousand years to occur. An especially interesting aspect of polarity reversals is the speed at which the field can change direction during the event. Controversial evidence from 16 million year old volcanic rocks in Oregon suggests that the ancient field changed as rapidly as 6 degrees per day, a rate that difficult to reconcile with standard estimates of several key deep earth properties. The goal of this study is to critically test an interpretation of new data representing just the second example of rapid transitional field change from the geologic record. This study focuses on stack of 15.2 million year old lava flows exposed in the Sheep Creek Range (North Central Nevada) that happened to erupt, cool, and became permanently magnetized parallel to earth's magnetic field during a reverse-to-normal polarity switch. One flow from high in the stack has an unusual composite magnetization recording two geomagnetic field direction over 50 degrees apart. We interpret this composite magnetization to be the result of a two-stage cooling process during which the geomagnetic field changed rapidly (at least 1 degree/week) to produce the two magnetization components. To confirm our interpretation, better constrain the rate of field change, and more fully understand its geomagnetic context, we are investigating how the composite magnetization of this flow varies laterally and will determine how strong the geomagnetic field was before, during, and after the interval of rapid directional change. The outcome of the study will sharpen our understanding of deep earth processes and properties as well as provide a glimpse of the environment that future generations will experience when the earth's magnetic field next reverses polarity. In addition to the scientific goals of the project, the research is supporting the training of undergraduate students and providing opportunities for them to conduct research projects, is contributing to the broadening of participation for underrepresented groups in the earth sciences, and is contributing to research infrastructure at Occidental University.The research is being supported by the EAR Geophysics Program and the EAR Education and Human Resources Program.

众所周知，由地核中的流体运动产生的地磁场在过去的地质时期曾多次反转极性，最近一次是在大约80万年前。地质记录表明，这种全球范围的变化，在此期间，各地的指南针从指向北到指向南（或相反），只需要几千年就发生了。 极性逆转的一个特别有趣的方面是场在事件期间改变方向的速度。来自俄勒冈州1600万年前火山岩的有争议的证据表明，古代磁场的变化速度高达每天6度，这一速度难以与几个关键的深层地球特性的标准估计相一致。本研究的目的是严格测试新数据的解释，这些新数据仅代表地质记录中快速过渡场变化的第二个例子。 这项研究的重点是在羊溪山脉（内华达州中北部）暴露的1520万年前的熔岩流，这些熔岩流在反向到正常极性切换期间发生喷发，冷却并成为平行于地球磁场的永久磁化。一股来自叠层高处的气流具有不寻常的复合磁化，记录了两个相隔50度的地磁场方向。我们解释这种复合磁化是两阶段冷却过程的结果，在此过程中，地磁场迅速变化（至少1度/周），以产生两个磁化分量。为了证实我们的解释，更好地限制磁场变化的速率，并更充分地了解其地磁背景，我们正在研究这种流动的复合磁化如何横向变化，并将确定地磁场在快速方向变化之前，期间和之后的强度。这项研究的结果将加深我们对地球深部过程和性质的理解，并提供一个环境的一瞥，未来几代人将经历时，地球的磁场下一次极性逆转。除了该项目的科学目标外，该研究还支持本科生的培训，为他们提供开展研究项目的机会，有助于扩大地球科学中代表性不足的群体的参与，并有助于西方大学的研究基础设施。该研究得到了地球物理学计划和地球物理学教育和人力资源计划的支持。