A new kinematic model for Iberia; further palaeomagnetic and isotopic age evidence

Abstract

Palaeomagnetic results and KAr age data from the Algarve Igneous Province have uncovered three ancient relative field components. It is inferred that the principal magnetization of the Monchique Complex, with a mean direction of D = −42°, I = 181°, ( α 95 = 4.5°), was acquired at around the time of the pluton's emplacement some 72 ± 2 Ma ago. A second magmatic pulse affected the region at 68 ± 2 Ma, leaving behind a relative field component of D = 42°, I = 341°, ( α 95 = 1.7°). Furthermore, an overprinted magnetization, characterized by shallow inclination and somewhat smeared northwesterly-southeasterly declination, most likely originates from the Lower Tertiary. The new palaeomagnetic data are seen in conjunction with previously published Upper Cretaceous results from the Sintra and Sines intrusive complexes. The resulting database gives entirely new perspectives for evaluating the plate tectonic history of the Peninsula in Upper Cretaceous-Lower Tertiary time. A two-phase rotation of the Iberian micro-plate, an anticlockwise one of ∼ 40° followed by a clockwise one of ∼ 70°, is clearly in evidence. The net clockwise rotation provided a major impetus for the compressive deformation in the Pyrenees and the Bay of Biscay, and led to extensive remagnetization of older rock formations in the northern regions of Iberia. Previous palaeomagnetic conclusions, in favour of a single anticlockwise rotation of ∼ 35°, supposed to be directly connected with the formation of the Bay of Biscay, appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame.