Magma ¯ow directions of shallow dykes from the East Greenland volcanic margin inferred from magnetic fabric studies J.-P. Callot a,1, * , L. Geoffroy a,2 , C. Aubourg b , J.P. Pozzi a , D. Mege c a Laboratoire de Ge Âologie, Ecole Normale Supe Ârieure, UMR 8538, 24 rue Lhomond, 75231, Paris, France b De Âpartement des Sciences de la Terre, Universite  de Cergy-Pontoise, ESA 7072, 8 Le Campus, 95031 France c Laboratoire de Tectonique quantitative, Institut P. and M. Curie, Paris VI, 6 place Jussieu, 75005 Paris, France Received 10 July 2000; accepted 21 February 2001 Abstract The role played by plume-generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma ¯ow directions in shallow intrusives from the East Greenland volcanic margin. We investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic af®nity belonging to a dyke swarm associated with the Tertiary opening of the North Atlantic Ocean. The thickness of the sampled dykes ranges from 3 to 37 m. The dykes are of doleritic texture and contain up to 12% of opaque minerals and 35% of plagioclase laths. Dykes showing a magnetic foliation plane within the dyke plane, i.e. a magnetic fabric usually attributed to magmatic processes, represent 40% of the samples from the studied swarm. These dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate. Inverse magnetic fabrics, where the maximum principal susceptibility axis lies near the pole to the dyke account for 60% of the data. We interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy. The ¯ow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation. Analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations. The inferred ¯ow directions are predominantly horizontal, throwing a new light on volcanic margin development. q 2001 Elsevier Science B.V. All rights reserved. Keywords: volcanic margin; dyke; basalt; AMS; magnetic fabric; magma ¯ow 1. Introduction Volcanic margins belong to Large Igneous Provinces which includes continental ¯ood basalts, volcanic margins, oceanic plateaus and ocean basin ¯ood basalts see a review in Cof®n and Eldholm, 1994). Large Igneous Provinces consist of massive emplacements of ma®c extrusive and intrusive rocks, emplaced in a short period of time White and McKenzie, 1989; Richards et al., 1989; Cof®n and Eldholm, 1994). Volcanic margins may be related to lithospheric break-up over a mantle plume Eldholm et al., 1995) when they are clearly asso- ciated with abnormally thick adjacent oceanic crust and a hot-spot track and tail. Volcanic margins differ in several ways from non- volcanic passive margins. Classic volcanic passive margins present the following features: 1) thick Tectonophysics 335 2001) 313±329 0040-1951/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0040-195101)00060-9 www.elsevier.com/locate/tecto * Corresponding author. E-mail address: callot@geologie.ens.fr J.-P. Callot). 1 Also at: Laboratoire de Ge Âologie, Universite  du Maine, Faculte  des Sciences, avenue O. Messiaen, 72085, Le Mans, cedex 09, France. 2 Now at: Laboratoire de Ge Âologie, Universite  du Maine, Faculte  des Sciences, avenue O. Messiaen, 72085, Le Mans, cedex 09, France.