| Popis: |
The Pyrenees display numerous paleomagnetic studies acquired during the past six decades after the pioneer works carried out by the University of Utrecht in the early sixties (Van der Voo, 1969 and references therein). Currently, the Pyrenean Paleomagnetic Database (of IGME) includes nearly 40,000 individual vectors (demagnetizations) from more than 3000 sampling sites and more than 170 magnetostratigraphic profiles (comprising more than 35 kilometres of sections) that are harmonized and synthesized. This implies a significant increase (ca. 20%) with respect to previous versions introduced in the Iberian paleomagnetic meeting in 2017. This outstanding amount of data (considering the rather small size of the Pyrenees) is due to: 1) excellent outcrop conditions of stratigraphic sequences and biostratigraphic calibrations with global interest; 2) the availability of synorogenic materials, allowing for an accurate dating of deformation processes; and 3) the occurrence of well-exposed areas affected by lateral transference of deformation (oblique structures) that have motivated abundant paleomagnetic studies focused on characterizing vertical-axis rotations.In this work we present the state of the art of the Pyrenean Paleomagnetic Database. About 75% of the compiled paleomagnetic data display fisherian means with alfa95 below 15° (84% below 20°) that are in agreement to standard reliability criteria of paleomagnetic data in tectonic studies. Most sites and localities are drilled in Cenozoic (Miocene to Paleocene) and Upper Cretaceous rocks, thus, coeval or younger than the Pyrenean convergence time. Sites in Lower Cretaceous and Jurassic rocks represent pre-orogenic stages and are coeval or older than the rotation of Iberia (Biscay Bay opening). Less than 15% of the paleomagnetic sites come from Triassic and Permian red-beds and display an uneven distribution along the mountain chain. A similar uneven distribution of sites is observed in Paleozoic rocks. Several studies have determined remagnetization processes in the Pyrenees from the Western Basque Palaeozoic massifs to other Palaeozoic rocks of the Axial Zone mostly in relation to burial processes. This is the case of Lower Cretaceous, highly subsiding basins, like Organyá, Mauléon, Cotiella or the Chaînons Béarnais, as well as other Ceno-Mesozoic sequences in the Internal Sierras and related units; Larra-Monte Perdido, Nogueras, Boixols, Cadí, etc. In most cases, the remagnetization ages are Cenozoic when maximum temperatures were acquired at the base of the sequences during the convergence period or, in any case, younger than the rotation of Iberia and the opening of the Biscay Bay. Van der Voo, R. (1969). Paleomagnetic evidence for the rotation of the Iberian Peninsula. Tectonophysics, 7(1), 5-56. |
