Electron microscopy, magnetoclimatology, archaeomagnetic secular variation

电子显微镜、磁气候学、古地磁长期变化

• 批准号: 8697-2007
• 负责人: Evans, Michael(Ted)
• 金额: $ 1.62万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2011
• 资助国家: 加拿大
• 起止时间: 2011-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=474429
• 关键词: Electron; microscopy; magnetoclimatology; archaeomagnetic; secular

For fifty years, the magnetic properties of geological and archaeological materials have proven to be a rich source of information concerning our planet's history and dynamics. The switching of the north and south magnetic poles (geomagnetic polarity reversals), the creation and destruction of the ocean floor and the resulting drift of the continents (plate tectonics), the waxing and waning of the great ice sheets (past global warming -- and cooling) are prime examples that spring to mind. And yet there remain serious shortcomings in our understanding of the basic physical mechanisms that lead to the capture of these signals. One of the knotty problems involved is that of interactions between the individual magnetic crystals in the various natural archives in question. These complicate the magnetic properties so much that in his classic papers Louis Néel (Nobel Prize in Physics 1970) wisely avoided this problem by considering a dilute assemblage of tiny non-interacting magnetic particles. Unfortunately, the minerals of interest (iron-titanium oxides) often occur as nanometre-scale intergrowths in which magnetic regions lie in close proximity to one another. Three recent developments make it possible to undertake a renewed attack on this problem. First, electron microscopy is now able to provide detailed images of the magnetic field pattern inside samples of interest. Second, vastly increased computing power now makes it possible to calculate the behaviour of arrays of interacting magnetic particles. Third, the development of new laboratory techniques provides a direct experimental measure of the strength of the interactions. In addition to these mineral physics studies, palaeoclimatic and archaeomagnetic investigations will also be carried out. The former will involve samples already collected from several sites around the world and will attempt to elucidate the mechanisms by which climatic information is magnetically encoded in natural sedimentary archives. The latter will involve new samples collected from archaeological structures in Iberia and Egypt in order to extend the geographic coverage of earlier campaigns in Greece and Italy.

五十年来，地质和考古材料的磁性已被证明是有关我们星球历史和动力学的丰富信息来源。北磁极和南磁极的转换（地磁极性反转）、海底的产生和毁灭以及由此产生的大陆漂移（板块构造）、大冰原的消长（过去的全球变暖和变冷）都是最好的例子。然而，我们对捕获这些信号的基本物理机制的理解仍然存在严重缺陷。其中一个棘手的问题是，在各种自然档案中，各个磁性晶体之间的相互作用。这些使磁性变得如此复杂，以至于路易斯·内尔（Louis Néel，1970年诺贝尔物理学奖得主）在他的经典论文中通过考虑微小的非相互作用磁性粒子的稀组合明智地避免了这个问题。不幸的是，感兴趣的矿物质（铁-钛氧化物）通常以纳米级共生体的形式存在，其中磁性区域彼此非常接近。最近的三项进展使我们有可能对这个问题进行新的攻击。首先，电子显微镜现在能够提供感兴趣的样品内部磁场图案的详细图像。其次，计算能力的大幅提高使得计算相互作用的磁性粒子阵列的行为成为可能。第三，新的实验室技术的发展提供了一个直接的实验测量的相互作用的强度。除了这些矿物物理学研究外，还将进行古气候和古地磁调查。前者将涉及已从世界各地若干地点收集的样本，并将试图阐明气候信息在自然沉积档案中磁性编码的机制。后者将涉及从伊比利亚和埃及的考古结构中收集的新样本，以扩大早期在希腊和意大利开展的活动的地理覆盖范围。