Correlation between the Palaeozoic structures from West Iberian and Grand Banks margins using inversion of magnetic anomalies

The Ibero-Armorican Arc (IAA) is a huge geological structure of Pre-Cambria n origin, tightened during hercynian times and deeply affected by the openi ng of the Atlantic Ocean and the Bay of Biscay. Its remnants now lie in Ibe ria, north-western France and the Canadian Grand Banks margins. The qualita tive correlation between these three blocks has been attempted by several a uthors (e.g. Lefort, J.P., 1980. Un 'Fit' structural de l'Atlantique Nord: arguments geologiques pour correler les marqueurs geophysiques reconnus sur les deux marges. Mar. Geol. 37, 355-369; Lefort, J.P., 1983. A new geophys ical criterion to correlate the Acadian and Hercynian orogenies of Western Europe and Eastern America. Mem. Geol. Sec. Am. 158, 3-18; Galdeano, A., Mi randa, J.M., Matte, P., Mouge, P., Rossignol, C., 1990. Aeromagnetic data: A tool for studying the Variscan are of Western Europe and its correlation with transatlantic structures. Tectonophysics 177, 293-305) using magnetic anomalies, mainly because they seem to preserve the hercynian zonation, in spite of the strong thermal and mechanical processes that took place during rifting and ocean spreading. In this paper, we present a new contribution to the study of the IAA struct ure based on the processing of a compilation of magnetic data from Iberia a nd Grand Banks margins. To interpret the magnetic signature, a Fourier-doma in-based inversion technique was applied, considering a layer with a consta nt thickness of 10 km, and taking into account only the induced field. The digital terrain model was derived from ETOPO5 (ETOPO5, 1986. Relief map of the earth's surface. EOS 67, 121) and TerrainBase (TerrainBase, 1995. In: R ow III, L.W., Hastings, D.A., Dunbar, P.K. (Eds.), Worldwide Digital Terrai n Data, Documentation Manual, CD-ROM Release 1.0. GEODAS-NGDC Key to Geophy sical Records. Documentation N. 30, April) databases. The pseudo-susceptibi lity distribution obtained was repositioned for the 156.5 Ma epoch, using t he Srivastava and Verhoef [Srivastava, S.P., Verhoef, J., 1992. Evolution o f Mesozoic sedimentary basins around the North Central Atlantic: a prelimin ary plate kinematic solution. In: Parnell, J. (Ed.), Basins on the Atlantic Seaboard: Petroleum Geology Sedimentology and Basin Evolution, Geological Society Special Publication No. 62, pp. 397-420] pole. Using this coherent magnetic framework, we can verify that the continuity b etween adjacent blocks is quite good, in terms of the amplitude, wavenumber and magnetic susceptibility pattern. If we accept that the magnetic proper ties can be taken as a marker of the hercynian zonation, as was verified in previous studies (Miranda, J.M., Galdeano, A., Rossignol, J.C., Mendes-Vic tor, L.A., 1989. Aeromagnetic anomalies in mainland Portugal and their tect onic implications. Earth Planet. Sci. Lett. 95, 161-177; Galdeano, A., Mira nda, J.M., Matte, P., Mouge, P., Rossignol, C., 1990. Aeromagnetic data: A tool for studying the Variscan are of Western Europe and its correlation wi th transatlantic structures. Tectonophysics 177, 293-305; Socias, I., 1994. Estudios de los Elementos del Campo Magnetico en la Espana Peninsular a pa rtir de Dates Aeromagmaneticos. Ph.D. thesis, University of Madrid), we can conclude that (1) the characteristic magnetic signature of Ossa Morena Zon e is absent on the Iberian Margin and west of it; (2) no eastward continuat ion of the Collector Anomaly is found in Iberia; (3) only the inner zones o f the Variscan Belt can be followed towards NW France; (4) there is a major (left lateral ?) strike-slip fault along the northern Portuguese shoreline that cuts the IAA and significantly displaces the once-contiguous variscan units. (C) 2000 Elsevier Science B.V. All rights reserved.