REMANENT MAGNETIZATION IN CRUSTAL ROCKS Suzanne A. McEnroe (1) , Karl Fabian (1) , Peter Robinson (1) and Laurie Brown (2) (1) Geological Survey of Norway, N-7491 Trondheim, Norway, Email: suzanne.mcenroe@ngu.no; karl.fabian@ngu.no; peter.robinson@ngu.no (2) Department of Geoscience, University of Massachusetts, Amherst, MA, 01003, USA, Email lbrown@geo.umass.edu ABSTRACT The current CHAMP and the upcoming SWARM missions provide high-resolution magnetic data which for the first time, allow study of remanent crustal magnetization directly from space. SWARM promises nearly to close the resolution gap to aeromagnetic surveys, thereby opening new doors for validation of level 2 data products. By combining aeromagnetic data with mineralogical investigations on old crustal shields, we study the primary sources of large scale-remanent anomalies in continental crust. We observe that an important contribution in strong anomalies in old oxidized crust arises from lamellar magnetism. The mineralogic and magnetic investigation of this newly discovered remanence source on length scales from nanometer to aeromagnetic will help to understand and validate the crustal magnetic data inferred from the SWARM mission. INTRODUCTION Geomagnetic-field research currently is in a period of extraordinary growth. The accomplishments of previous and upcoming satellite missions mark the increased interest in understanding the details of the Earth's magnetic field. In 2011 the European SWARM satellite mission will start acquiring high-resolution magnetic signals from the Earth’s lithosphere at a level never achieved before on a global scale. In combination with high-resolution aeromagnetic data, the new SWARM data may also provide a cost-effective means for large-scale surveying of unexplored areas, especially where the necessary infrastructure for seismic studies is lacking. The potential to identify geological structures related to mineral deposits, oil and gas reservoirs and other natural resources is large. Accompanying the dramatic improvements in data acquisition and processing in the last decade, a critical need will develop for a better understanding of the relationships between large-scale magnetic signatures and the iron-oxide minerals which dominate rock responses, and thus delineate geological structures magnetically. Numerous large economic ore deposits have distinct negative anomalies associated with them, due to a large contribution to the total magnetization of the remanent magnetic vector, where it is at a steep angle to the inducing field. In the last decade we have studied numerous localities spanning three continents which have remanence-controlled anomalies [2-13] showing that remanent anomalies are more common that previously thought. Potential-field data, though extremely valuable, are not sufficient to constrain models to a unique distribution of magnetic sources. To make the maximum use of magnetic data obtained from satellites and high-resolution aeromagnetic surveys (Fig. 1), petrophysical data from well characterized samples and well documented geologic settings are necessary. Detailed study, combining oxide mineralogy with petrophysical measurements, and relating the resulting data to the magnetic anomalies measured by fixed-wing and high-resolution helicopter aeromagnetic surveys, and ground-magnetic surveys, will provide a wealth of knowledge about the magnetic response of different rock types and geological conditions that will aid in the interpretation of the SWARM satellite data. REMANENT AND INDUCED MAGNETIZATION To advance interpretation of local and global magnetic anomalies, it is essential to include the signals arising from magnetic remanence in contrast to induced magnetization, which is mainly considered today. Induced magnetization is the magnetization imposed on a rock body by today’s external magnetic field. Todays approach to anomaly interpretation mainly relies on the assumption that the natural remanent magnetization (NRM) is small in comparison to the magnetic susceptibility χ times the external geomagnetic field H. These two quantities are compared by the Koenigsberger ratio: Figure 1. Combined aeromagnetic and satellite map of Norway, Sweden and north Atlantic. Modified from [1] courtesy of M. Purucker.