Alpine remagnetization and tectonic rotations in the French Pyrenees

A palaeomagnetic study of the 100 to 90 m.y. old alkaline igneous rocks of the French Pyrenees has in part revealed large between-site scatter caused by highly variable declination. Magnetomineralogical evidence suggests that the original titano-magnetite has undergone variable low-temperature oxida tion through martitization and maghemitization processes, suggesting that t he rocks have been remagnetized. When viewed in the context of the Upper Cr etaceous-Lower Tertiary inclination pattern based on Portuguese palaeomagne tic data, it is concluded that the rocks most likely acquired their present magnetization during early Campanian-Maastrichtian time, i.e. 20-30 m.y. a fter their original cooling. On the other hand, this magnetization postdate s a major phase of late Cretaceous compressive deformation. Subsequent stri ke-slip movement along the Pyrenean zone in the Lower Tertiary led to varia ble rotation of cover units along the orogenic belt, producing the inconsis tent palaeomagnetic declination picture presently observed. It is concluded that the geological history of the alkaline rocks of the French Pyrenees, from the magmatic stage to the subsequent events of remagnetization and tec tonic deformation, is strongly associated with the Alpine-age rotational in stability of Iberia. The principal kinematic history of the Peninsula compr ised ca. 40 degrees counterclockwise rotation (relative to Europe) during C enomanian-Turonian time (100-90 m.y. ago) followed by ca. 70 degrees clockw ise rotation in the early Campanian (ca. 75 m.y. ago).