Nature and origin of the J-magnetic anomaly offshore Iberia-Newfoundland: implications for plate reconstructions

The nature and origin of the J-magnetic anomaly along the Iberia-Newfoundland margins are controversial and its validity for plate kinematic reconstructions questioned. At present, it is interpreted as either an oceanic isochron or an edge effect of oceanic crust corresponding to lithosphere breakup. Both interpretations result in restorations that are in conflict with the current knowledge from Pyrenean and North Atlantic geology. We combine seismic interpretations and dating of magmatic additions with magnetic data to examine the nature and formation process of this anomaly and discuss its value for plate restorations. We show that the J-anomaly is the result of polygenic and multiple magmatic events occurring during and after the formation of the first oceanic crust. Therefore, we conclude that the J-anomaly cannot be used for plate kinematic studies and, more generally, we question the validity of using ill-defined magnetic anomalies outside unequivocal oceanic domains for plate reconstructions.