Early Cretaceous motion of Flemish Cap with respect to North America: implications on the formation of Orphan Basin and SE Flemish Cap–Galicia Bank conjugate margins

Abstract

AbstractBouguer gravity anomalies together with deep seismic reflection and magnetic data on both sides of the North Atlantic are used to locate the hinge zones of the Flemish Cap and Galicia Bank within the Iberian and North American plates, regions across which there were abrupt changes in lithospheric extension. The characteristic shape and alignment of these hinge zones suggest that they were conjugate features generated during chrons M25–M0 (Late Jurassic–Early Aptian) around a distally located Euler pole of rotation. Rifting between Iberia and North America involved these two larger plates and the two smaller microplates – the Flemish Cap and Galicia Bank microplates. The motion of the microplates, which were adjacent to Eurasia, was much more complex than those of the larger plates. The motion between the microplates from chron M25 or older to chron M0 was complicated by the fact that they remained attached to each other for most of the time when regions to the south were rifting apart. As a result, continental regions landward of these segments were subjected to extension that created the Orphan and Flemish Pass basins on the North American side and the Galicia Interior Basin on the Iberian side. By comparing the hinge zones delineated off Galicia Bank and Flemish Cap using the Bouguer anomalies, we were able to infer that Flemish Cap rotated approximately 43° relative to Galicia Bank and Iberia, and moved 200–300 km SE with respect to North America.Such motions of Flemish Cap and Galicia Bank agree remarkably well with extensional episodes deduced from industry multichannel seismic reflection data acquired in the Orphan Basin. Normal fault orientations identified in the West Orphan Basin trend N020° and are approximately perpendicular to the flow lines of our proposed Flemish Cap–North American motion during the M25–M0 period, which provides an independent constraint on our proposed kinematic model. Therefore, extensional events affected not only the Galicia Bank–Flemish Cap conjugate margins but also the Galicia Interior and Orphan Basins, and need to be taken into account in any assessment of the geological development of the Iberian and North American continental margins.