Paleomagnetic evidence for the rotation of the Iberian Peninsula

Abstract

The results of a paleomagnetic investigation on igneous and sedimentary rocks from Portugal and Spain are presented. The age of the formations investigated varies from Ordovician to Eocene. Apart from geologic studies the Natural Remanent Magnetizations (N.R.M.) were analyzed with the aid of a.c. magnetic field and thermal demagnetization techniques. In the case of three folded formations the characteristic remanent magnetizations could be proved to be acquired before the subsequent folding took place. These formations are the Upper Silurian Almadén volcanics, the Upper Carboniferous-Lower Permian Buçaco Formation of Portugal and the Eocene basalts of the Lisbon region. All three other Upper CarboniferousLower Permian sample groups of Spain yield similar directions of magnetization. Several groups of Paleozoic and Triassic samples revealed only secondary magnetizations.

Together with previous results from the Spanish Meseta and the Spanish Pyrenees, the data are compared with results from Africa and from other European countries. The comparison is satisfactory only for the Upper Carboniferous-Lower Permian results: it indicates that the Iberian Peninsula has rotated relative to that part of Europe north of the Alpine fold belts. This rotation has been counterclockwise over approximately 35°. It is argued that a plausible ancient configuration can be realised by rotating the Iberian Peninsula back to its Permian position, while closing the Bay of Biscay at the 2,000-mdepth line. The pivot point of this rotation lies in the western Pyrenees, as previously suggested by Carey (1958).