Linking Rock Magnetic Properties to the Performance of Paleointensity Techniques

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。地球磁场的方向和强度在时间和空间上都是不同的。随着火山岩冷却下来，它们记录下了磁场的快照，通过仔细的实验室实验，地球在大约45亿年的历史中磁场的演变可以被解开。确定地球在关键时期的磁场将有助于更好地理解地球液态外核中的对流、固体内核的生长、地球外核和固体地幔之间的相互作用，以及板块构造速率和穿过核-地幔边界的热流之间的关系。虽然磁场的方向是由实验直接确定的，但它的大小（也称为古强度）却更有问题。没有精确的古强度测量，地球磁场就不能被完全定义，上面概述的重要过程也永远不能被完全理解。尽管对古强度的理论认识和用于获得更精确结果的方法已经取得了进展，但还没有一个全面的研究将古强度实验的成功与所研究材料的特定磁性联系起来。本提案中概述的研究旨在确定岩石的磁性特征，当与特定的古强度程序相结合时，将导致对地球磁场强度的更准确估计。大多数古强度技术都是时间和劳动密集型的，成功率很低（25%到35%）。少数创新研究提出了筛选样品的方法，以提高使用特定古强度技术确定的估计的准确性。我们的目标是在这种方法的基础上，充分表征样品的岩石磁性，然后用最适合的古强度技术来匹配它们的特性。将用于解决这些问题的样本是来自佛得角福戈火山岛的熔岩，这些熔岩是在过去60年里从天文台数据中得知地磁场强度时喷发的。样品将使用一套细致的岩石磁性分析和穆斯堡尔光谱学来检查。电子显微镜将用于矿物学显微结构成像和确定元素组成。将评估多种古强度方法，包括最常用技术的变化以及需要进一步验证的新方法。以前没有研究将这种古强度技术应用于特征如此充分的样品上。本研究结果将指导未来的工作人员根据样品的岩石磁性选择最合适的古强度技术，提高效率和准确性。这项研究最终将有利于地球物理学家和行星科学家调查和模拟地球深部过程。除了该项目的研究目标之外，该奖项还支持三名早期职业研究人员，扩大代表性不足的群体在地球科学领域的参与，并为本科生提供培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The direction and intensity of the Earth's magnetic field varies in both time and space. As volcanic rocks cool they record a snapshot of the field and through careful laboratory experiments the evolution of the magnetic field during Earth's approximately 4.5 billion year history can be unravelled. Determining the Earth's magnetic field across critical periods of time will allow a greater understanding of convection in the Earth's liquid outer core, the growth of the solid inner core, interactions between the Earth's outer core and solid mantle, and the relationship between the rate of plate-tectonics and heat flow across the core-mantle boundary. Although the direction of the magnetic field is straightforwardly determined experimentally, its magnitude (also called paleointensity) is more problematic. Without accurate paleointensity measurements the Earth's magnetic field cannot be defined fully and the important processes outlined above will never be fully understood.Although progress has been made in the theoretical understanding of paleointensity and the methodologies used to obtain more accurate results, there has not been a comprehensive study linking the success of paleointensity experiments to the specific magnetic properties of the materials being studied. The research outlined in this proposal aims to identify rock magnetic characteristics that when combined with specific paleointensity procedures will lead to more accurate estimates of the strength of the Earth's magnetic field. Most paleointensity techniques are time and labor intensive and have low success rates (25 to 35%). A small number of innovative studies have proposed methods for screening samples to improve the accuracy of the estimates determined using a specific paleointensity technique. We aim to build on this approach by fully characterizing the rock magnetic properties of our samples and then matching their properties with the best suited paleointensity technique. The samples that will be used to address these problems are lavas from the volcanic island of Fogo, Cape Verde, and were erupted during the last sixty years when the intensity of the geomagnetic field is known from observatory data. Samples will be examined using a meticulous suite of rock magnetic analyses and Mossbauer spectroscopy. Electron microscopes will be used to image mineralogic microstructures and determine elemental compositions. Multiple paleointensity methods will be assessed, including variations on the most commonly used techniques as well as newer approaches needing further validation. No previous study has applied this variety of paleointensity techniques on such well-characterized samples. Results of this research will guide future workers in choosing the most appropriate paleointensity technique based on a sample's rock magnetic properties, increasing efficiency and accuracy. This research will ultimately benefit geophysicists and planetary scientists investigating and modeling deep Earth processes. In addition to the research goals of this project, the award is supporting three early career researchers, is broadening the participation of underrepresented groups in the earth sciences, and is providing training for undergraduate students.