de Groot Lennart V, Fabian Karl, Béguin Annemarieke, Kosters Martha E, Cortés-Ortuño David, Fu Roger R, Jansen Chloë M L, Harrison Richard J, van Leeuwen Tristan, Barnhoorn Auke
Paleomagnetic laboratory Fort Hoofddijk Faculty of Geosciences Utrecht University Utrecht The Netherlands.
Department of Geoscience and Petroleum Norwegian University of Science and Technology Trondheim Norway.
J Geophys Res Solid Earth. 2021 Oct;126(10):e2021JB022364. doi: 10.1029/2021JB022364. Epub 2021 Oct 13.
Our understanding of the past behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g., (volcanic) rocks. Bulk rock samples, however, often contain magnetic grains that differ in chemistry, size, and shape; some of them record the Earth's magnetic field well, others are unreliable. The presence of a small amount of adverse behaved magnetic grains in a sample may already obscure important information on the past state of the geomagnetic field. Recently it was shown that it is possible to determine magnetizations of individual grains in a sample by combining X-ray computed tomography and magnetic surface scanning measurements. Here we establish this new Micromagnetic Tomography (MMT) technique and make it suitable for use with different magnetic scanning techniques, and for both synthetic and natural samples. We acquired reliable magnetic directions by selecting subsets of grains in a synthetic sample, and we obtained rock-magnetic information of individual grains in a volcanic sample. This illustrates that MMT opens up entirely new venues of paleomagnetic and rock-magnetic research. MMT's unique ability to determine the magnetization of individual grains in a nondestructive way allows for a systematic analysis of how geological materials record and retain information on the past state of the Earth's magnetic field. Moreover, by interpreting only the contributions of known magnetically well-behaved grains in a sample, MMT has the potential to unlock paleomagnetic information from even the most complex, crucial, or valuable recorders that current methods are unable to recover.
我们对过去地磁场行为的理解源于存储在地质材料（如火山岩）中的磁信号。然而，块状岩石样本通常包含化学性质、大小和形状各异的磁性颗粒；其中一些能很好地记录地球磁场，而另一些则不可靠。样本中少量行为异常的磁性颗粒的存在可能已经掩盖了有关地磁场过去状态的重要信息。最近有研究表明，通过结合X射线计算机断层扫描和磁性表面扫描测量，可以确定样本中单个颗粒的磁化强度。在此，我们建立了这种新的微磁断层扫描（MMT）技术，并使其适用于不同的磁性扫描技术以及合成样本和天然样本。我们通过在合成样本中选择颗粒子集获得了可靠的磁方向，并获取了火山样本中单个颗粒的岩石磁性信息。这表明MMT为古地磁和岩石磁性研究开辟了全新的途径。MMT以无损方式确定单个颗粒磁化强度的独特能力，使得对地质材料如何记录和保留有关地球磁场过去状态的信息进行系统分析成为可能。此外，通过仅解释样本中已知磁行为良好颗粒的贡献，MMT有潜力从当前方法无法恢复的最复杂、关键或有价值的记录器中解锁古地磁信息。
