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

众所周知，地磁场是由地核中的流体运动产生的，在过去的地质历史中曾多次反转过极性，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方转向指向南方(或相反)，仅用了几千年的时间。极性反转的一个特别有趣的方面是磁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，古老的领域每天变化的速度高达6度，这一速度很难与对几个关键地球深部属性的标准估计相一致。这项研究的目标是批判性地测试对新数据的解释，新数据只是地质记录中快速过渡领域变化的第二个例子。这项研究的重点是暴露在Sheep Creek山脉(内华达州中北部)的1520万年前的熔岩流，这些熔岩流碰巧喷发、冷却，并在反转到正常的极性转换期间与地球磁场平行地永久磁化。一股来自高空的气流具有不同寻常的复合磁化作用，记录了两个相隔50度的地磁场方向。我们将这种复合磁化解释为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，更好地约束磁场变化的速度，并更充分地了解其地磁背景，我们正在研究这一流动的综合磁化如何横向变化，并将确定在快速方向变化间隔之前、期间和之后的地磁场强度。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，并让我们得以一窥当地球磁场下一次反转时，子孙后代将经历的环境。除了该项目的科学目标外，该研究还支持本科生的培训，并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群体的参与，并为西方大学的研究基础设施做出贡献。该研究得到了EAR地球物理计划和EAR教育和人力资源计划的支持。

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.