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

众所周知，由地核流体运动产生的地磁场，在地质历史上曾多次发生极性逆转，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），只需要几千年的时间就会发生。极性反转的一个特别有趣的方面是在事件发生期间磁场可以改变方向的速度。从俄勒冈州1600万年前的火山岩中发现的有争议的证据表明，古代地界的变化速度高达每天6度，这一速度很难与对几个关键地球深部特性的标准估计相吻合。这项研究的目的是对新数据的解释进行批判性的测试，这些新数据代表了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绵羊溪山脉（内华达州中北部）暴露的1520万年前的熔岩流堆栈，这些熔岩流碰巧爆发，冷却，并在反向到正常的极性转换过程中与地球磁场平行永久磁化。一股来自高层叠的气流具有不同寻常的复合磁化强度，记录了两个地磁场方向相差超过50度。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）以产生两种磁化成分。为了证实我们的解释，更好地约束磁场变化的速度，并更全面地了解其地磁背景，我们正在研究该流的复合磁化如何横向变化，并将确定快速方向变化间隔之前，期间和之后的地磁场强度。这项研究的结果将增强我们对地球深部过程和特性的理解，并提供对地球磁场下一次极性反转时后代将经历的环境的一瞥。除了该项目的科学目标之外，这项研究还支持本科生的培训，并为他们开展研究项目提供机会，有助于扩大地球科学领域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EAR地球物理计划和EAR教育与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.