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

“国际地势研究十年”（International Decade of Geopotential Research）是一项专注于从卫星观测中获取重力和磁场数据的全球计划，它最雄心勃勃的计划即将结束。SWARM由三颗测量磁场的卫星组成，将于2011年发射，并将收集前所未有的磁场数据。该任务的目标之一是调查地壳的磁性，在卫星任务的下地壳模型与我们从航空磁调查中获得的知识之间提供一座桥梁。以前对卫星地壳磁性数据的研究导致模型需要高磁化率和厚大陆地壳强磁化才能复制观测到的磁场。对下地壳岩石的研究，现在由于变形而隆起并暴露在地表，并没有显示出类似的高敏感性，这使我们质疑下地壳岩石的磁性过程。加拿大北部的阿萨巴斯卡麻粒岩地形是世界上最大的下地壳岩石暴露剖面之一，为我们提供了第一手研究这些深部岩石磁性特征的绝佳场所。该地区航磁异常图呈现出复杂多变的格局，正、负区众多；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。研究结果将有助于研究地球磁场的历史，并揭示地球的地质历史。加拿大北部阿萨巴斯卡麻粒岩地表暴露的下地壳岩石的磁性性质将有助于回答“下地壳的磁性是什么”这个问题。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异常。我们的目标是在航磁研究表明有许多明显异常的地区提供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。据推测，残余磁化，可能是由于在血红钛铁矿岩石中发现的层状磁化，必须是观察到的磁化的一个组成部分。方法将包括地面磁场和磁化率的原位测量，利用航磁异常识别关键地点的岩石收集，以及大量磁性能的实验室测量。在高温和低温下测量磁滞、磁化率和磁化行为，以及对已确定的下地壳岩石进行光学和扫描电镜研究，将提供有关导致观察到的异常的材料的磁特征、行为和矿物学的详细信息。所有的磁研究都将与正在进行的地形地质和变质研究密切相关，为回答这个问题提供额外的限制、信息和解释。

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.