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3D MODELING OF MULTISCALE MAGNETIC ANOMALIES |
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Pastore, Z. (1), McEnroe, S. (1), Fichler, C. (1), ter Maat, G. (1), Church, N. (1), Michels, A. (1), Oda H. (2), Larsen, R. (1) |
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(1) Norwegian University of Science and Technology (NTNU), Department of Geoscience and Petroleum, Trondheim, Norway. (2) Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST). |
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Magnetic anomalies are observed on multiple scales, from the planetary to the submillimeter scale. Investigations of these anomalies can lead to information on the nature of their sources and the processes that generate them. The resolvable size of the source causing the anomaly strongly depends on the magnetic survey design, which varies with the target. Here we used 3D magnetic modeling to investigate the sources of the magnetic anomalies on three distinct scales. In the first study aeromagnetic and gravity data are modelled revealing the deep crustal structure and the magnetization of the rocks forming the Seiland Igneous Province (SIP), the largest complex of mafic and ultramafic rocks in northern Norway, and one of the few examples in the world of a well preserved deep-seated magmatic plumbing system. In the second study ground and helicopter-borne magnetic data are used in combination with gravity data to explore one of the major ultramafic complexes of the SIP, the Reinfjord Ultramafic complex. Here, the magnetic anomalies do not match the mapped lithological boundaries, but are correlated with changes in magnetic properties and densities. In particular, the deviating densities and magnetic susceptibilities at the northern side of the complex are interpreted to be due to serpentinization. This alteration can significantly enhance the rock magnetic properties and therefore change the nature of the magnetic anomaly. The third study investigates the magnetic anomalies at a submillimeter scale combining scanning magnetic microscopy with other microscopy techniques, rock magnetic methods and magnetic modeling. Three thin sections magnetic scans, of a pristine dunite sample and of two serpentinized samples from the Reinfjord Ultramafic Complex are investigated. We apply a forward and inverse modeling approaches on the magnetic anomaly maps acquired over the thin sections to characterize the natural remanent magnetization of discrete magnetic minerals within the samples in terms of intensities and direction. The application of magnetic modeling in the three studies gave different degree of information on the magnetic petrology of the sources, and helped refining the geological interpretation. |
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