Magnetic and plagioclase linear fabric discrepancy in dykes: a new way to define the flow vector using magnetic foliation |
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| Authors: | L Geoffroy J P Callot C Aubourg & M Moreira |
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| Institution: | Laboratoire de Géodynamique des Rifts et des Marges Passives, EA3264, Universitédu Maine, Ave Olivier Messiaen, 72085 Le Mans Cedex 09, France,;Laboratoire de Géologie, Ecole Normale Supérieure, 24, rue Lhomond, 75005 Paris, France,;UMR 7072, Laboratoire de Tectonique, 8, Departement des Sciences de la Terre, Le Campus. Universitéde Cergy-Pontoise, 95031 Cergy-Pontoise Cedex, France,;Centro de Geofisica da Universidade de Lisboa, rua da Ecola Politécnica, 58, 1250 Lisbon, Portugal |
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| Abstract: | In basaltic dykes the magnetic lineation K1 (maximum magnetic susceptibility axis) is generally taken to indicate the flow direction during solidification of the magma. This assumption was tested in Tertiary basaltic dykes from Greenland displaying independent evidence of subhorizontal flow. The digital processing of microphotographs from thin sections cut in (K1, K2) planes yields the preferred linear orientation of plagioclase, which apparently marks the magma flow lineation. In up to 60% of cases, the angular separation between K1 and the assumed flow direction is greater than 45°. This suggests that the uncorroborated use of magnetic lineations in dykes is risky. A simple geometrical method is proposed to infer the flow vector from AMS in dykes based solely on magnetic foliations. |
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