Iberia in the Cretaceous: new paleomagnetic results from Portugal

摘要

From the Lusitanian-basin and from Algarve, Toarcian through Cenomanian sediments (16 localities, 170 samples) and upper Cretaceous igneous rocks (4 localities, 31 samples) were subjected to paleomagnetic analysis. Sedimentary localities yielded well-defined characteristic magnetizations, with north-westerly declinations, both before and after tilt correction. Igneous rocks exhibited both north-westerly and north-easterly declinations. The paleomagnetic directions of the sediments, when evaluated together with earlier published paleomagnetic results from the Jurassic-Cretaceous sediments of the Lusitanian basin and Algarve, suggest that Iberia rotated about 26° counterclockwise, with respect to stable Europe, after Cenomanian, and before the emplacement of the Lisbon volcanics (around 70 Ma). In the Cretaceous paleomagnetic data set, increased by the results of the present study, there is no evidence for earlier and additional counterclockwise rotation during Cretaceous. While the net post-Permian and post-Cenomanian counterclockwise rotations of Iberia with respect to present north are practically of the same angle, they are different with respect to stable Europe. The difference implies clockwise rotation of stable Europe with respect to Iberia, before Cretaceous. The results of this study from igneous rocks are relevant to the late Cretaceous-early Tertiary movements of Iberia. We suggest that the two igneous bodies with north-westerly declinations (one belonging to the Lisbon volcanics, the other a "Salema intrusion") were intruded before the post-Cenomanian counterclockwise rotation of Iberia; the north-easterly declinations exhibited by two syenite sites and three cross-cutting dykes from the Monchique intrusion are indicative of a small clockwise rotation, probably connected to the Pyrenean mountain building process.