What is Magnetic in the Lower Crust? Studies from the Athabasca Granulite Terrane, Canada

下地壳中的磁性是什么？

• 批准号: 1045515
• 负责人: Laurie Brown
• 金额: $ 28.95万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2016-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1045515&HistoricalAwards=false
• 关键词: What; Magnetic; Lower; Crust; Studies

The International Decade of Geopotential Research, a global program concentrated on gravity and magnetic data from satellite observations, is drawing to a close with its most ambitious program. SWARM, a trio of satellites to measure magnetic fields, is due to launch in 2011 and will collect an unprecedented amount of field data. One of the goals of the mission is to investigate the magnetism of the Earth's crust, providing a bridge between models for the lower crust from satellite missions to our knowledge from aeromagnetic surveys. Previous studies of satellite data on crustal magnetism have led to models requiring high susceptibility and thick continental crust with strong magnetizations to duplicate the observed fields. Investigations of lower crustal rocks, now uplifted and exposed at the surface due to deformation, do not reveal similarly high susceptibilities, causing us to question magnetic processes in lower crustal rocks. One of the world's largest exposed sections of lower crustal rocks, the Athabasca Granulite Terrain in northern Canada, provides us an excellent place to study first hand the magnetic character of these deep-seated rocks. Aeromagnetic anomaly maps of the region reveal a complex and varied pattern with numerous positive and negative areas; the collection of rock samples from the area will allow us to study the magnetic nature and history of the materials. Results will aid in investigating the history of the Earth's magnetic field, and in unraveling the geologic history of our planet. The nature of the magnetic properties of lower crustal rocks, now exposed at the surface in the Athabasca Granulite Terrain, northern Canada, will aide in answering the question "What is magnetic in the lower crust" Earlier studies of lower crustal rocks exposed at the surface have failed to provide sufficient magnetization to model observed magnetic anomalies from satellite data. Our goal is to provide a detailed interpretation of lower crustal rocks in an area where aeromagnetic studies indicate there are numerous distinct anomalies and link this to satellite observations and models of the lower crust. It is hypothesized that remanent magnetization, possibly due to lamellar magnetization found in hemo-ilmenite rocks, must be a component of the observed magnetizations. Methods will include ground magnetic and susceptibility measurements in situ, collections of rocks from key field locations identified using aeromagnetic anomalies, and laboratory measurements of numerous magnetic properties. Measurements of hysteresis, susceptibility, and magnetization behavior at high and low temperatures along with microscopy studies, both optical and SEM, of well-identified lower crustal rocks will provide detailed information on the magnetic signature, behavior, and mineralogy of the materials responsible for the observed anomalies. All magnetic studies will be keyed to on-going geologic and metamorphic research in the terrain, providing additional constraints, information, and interpretations for aid in answering this question.

国际地球势能研究十年是一个专注于来自卫星观测的重磁数据的全球计划，其最雄心勃勃的计划即将结束。这三颗测量磁场的卫星将于2011年发射，并将收集史无前例的大量现场数据。这次飞行任务的目标之一是调查地壳的磁性，在卫星飞行任务中的下地壳模型和我们从航空磁学调查中获得的知识之间提供一座桥梁。以前对地壳磁性卫星数据的研究导致了需要高磁化率和具有强磁化的厚大陆地壳的模型，以复制观测到的磁场。对下地壳岩石的调查，现在由于变形而在地表隆起和暴露，并没有发现类似的高磁化率，这使我们对下地壳岩石中的磁性过程产生了疑问。加拿大北部的阿萨巴斯卡麻粒岩地体是世界上最大的下地壳岩石裸露部分之一，它为我们提供了一个第一手研究这些深部岩石的磁性的绝佳场所。该地区的航磁异常图显示了一个复杂多样的模式，有许多正负区域；从该地区收集岩石样品将使我们能够研究这些物质的磁性和历史。这些结果将有助于研究地球磁场的历史，并有助于揭开我们星球的地质史。现已暴露在加拿大北部阿萨巴斯卡麻粒岩地形地表的下地壳岩石磁性的性质，将有助于回答“下地壳什么是磁性”的问题。我们的目标是在航磁研究表明存在许多明显异常的地区提供对下地壳岩石的详细解释，并将其与卫星观测和下地壳模型联系起来。推测剩余磁化作用，可能是由于在赤钛铁矿岩石中发现的片层磁化作用，一定是观测到的磁化作用的一个组成部分。方法将包括现场地磁和磁化率测量、利用航磁异常确定的关键野外地点的岩石收集，以及对多种磁性的实验室测量。在高温和低温下测量磁滞、磁化率和磁化行为，以及光学和扫描电子显微镜研究，将提供有关导致观察到的异常的物质的磁性特征、行为和矿物学的详细信息。所有的磁学研究将以地形中正在进行的地质和变质研究为重点，提供额外的约束、信息和解释，以帮助回答这个问题。