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.

国际地球势研究十年是一项全球计划，专注于卫星观测的重力和磁力数据，其最雄心勃勃的计划即将结束。 SWARM是三颗测量磁场的卫星，定于2011年发射，将收集前所未有的磁场数据。 该使命的目标之一是调查地壳的磁性，在卫星飞行任务的下地壳模型与我们从航空磁力调查获得的知识之间架起一座桥梁。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作用的厚大陆地壳来复制观测场的模型。 对由于变形而隆起并暴露在地表的下地壳岩石的研究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。 位于加拿大北方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区之一，它为我们提供了一个很好的研究这些深层岩石磁性特征的第一手资料。 该地区的航磁异常图显示了复杂多样的模式，有许多阳性和阴性区域;从该地区收集岩石样本将使我们能够研究材料的磁性和历史。研究结果将有助于调查地球磁场的历史，并揭示我们星球的地质历史。 在加拿大北方阿萨巴斯卡麻粒岩地体的地表暴露的下地壳岩石的磁性性质的性质将有助于回答“下地壳中的磁性是什么”的问题。早期对地表暴露的下地壳岩石的研究未能提供足够的磁化强度来模拟从卫星数据中观察到的磁性异常。 我们的目标是提供一个详细的解释下地壳岩石在一个地区，航磁研究表明有许多不同的异常，并将其与卫星观测和下地壳模型。 据推测，reversium磁化，可能是由于层状磁化发现在血红素钛铁矿岩石，必须是所观察到的磁化的一个组成部分。 方法将包括地面磁性和磁化率测量原位，收集岩石从关键领域的位置确定使用航磁异常，和实验室测量的许多磁性。测量磁滞、磁化率和沿着高温和低温下磁化行为，并对已识别的下地壳岩石进行光学和SEM显微镜研究，将提供有关导致所观察到异常的材料的磁性特征、行为和矿物学的详细信息。 所有的磁性研究都将与正在进行的地形地质和变质研究相结合，提供额外的限制、信息和解释，以帮助回答这个问题。