KINEMATICS OF THE IBERIAN PLATE

For a quarter of century, it as been recognized that the opening of th e Atlantic ocean, the opening of the Bay oi Biscay and the evolution o f the Pyrenees are part of the same question. Understanding the three series of events thus requires a global approach. Yet from a mass of e ver better constrained date and opinions have arisen more misunderstan ding and more contradictions than has coherent synthesis. The reason f or this lies in an excess of fragmentary or one-sided conclusions.From an analysis of geological and geophysical data and a review of publis hed kinematical reconstructions, this study aims at having an in-depth look at presently conceivable solutions. First are considered the con cepts oi plate, blocks, intra-plate deformation, first and second orde r plate boundaries, kinematical models and kinematical phases; and the n how to estimate the precision of the reconstructions is discussed. T he evolution oi the Iberian plate is in the larger context of the main plates that surround it - Eurasia, North America and Africa - as well as of the smaller ones which play a role in the opening of the North Atlantic and in the evolution oi the Arctic : Greenland, Rockall, Sval bard. This evolution includes that of the present ocean floor checked by analysis of the magnetic anormal record and also an estimation of t he intra-continental deformation, linked either to formation intra-con tinental bassins and continental margins, or to peri-Atlantic mountain building, Furthermore, the reconstructions concern the evolution of t he whole area since as early as th Late Hercynian age. The conclusions are presented with respect to three separate questions : 1. the origi n of the Pyrenean area. In terms si two widely accepted hypothesis -(a ) the attenuation of the continental crust beneath the bassins and mar gins would results exclusively from a stretching process and (b) the d eep peri-Iberian bassins (the Tagus abyssal plain, the Armorican bassi n, etc.) would have opened in Jurassic and Cretaceous time - we propos e a detailed solution (reconciling the movements oi a detain of plates or blocks) which is coherent with these from a kinematical point oi v iew. But we lay stress on the numerous difficulties or impossibilities for such a solution from a geological point of view, which render que stionable the initial hypotheses, 2. the evolution of the Pyrenean are a during the opening of the Bay of Biscay.We show that it is possible to model the evolution of the Pyrenean area between chrons MO and 34 i n two phases : opening between 120 and 107 Ma and strike-slip between 107 and 90 Ma. This model is compatible with both the Atlantic kinemat ical data and the pyrenean geological data, 3. the Pyrenean evolution during the compressional phases. We show that the total compressional movement between the Iberian meseta and Europa cannot be smaller than 150 km.