Résumé
Fossil and present-day passive margins associated with mantle exhumation at the ocean-continent transition seem to develop under high heat flow conditions. However, these proximal-distal synrift thermal gradients distributed along these hyper-extended margins are difficult to access. In the Pyrenees, the North Pyrenean Zone constitutes a early Cretaceous rifting zone, displaying a HT-LP metamorphism and alkaline magmatism due to an hyper-extension, allowing nowaday to explore the synrift temperature conditions. The Pyrenees orogen results of the closure of these basins and its genesis was entirely controlled by the different stages of aperture of the atlantic ocean. In the western part of the chain, the Mauleon basin appears as the less deformed cretaceous basin and is a suitable environnement for thermal and structural studies. Based on a dense outcrops and borehole samples dataset (156 samples), Raman Spectroscopy of Carbonaceous Material (RSCM) analysis was performed. The obtained data allows us to discuss the distribution of the thermal gradients along a transect across the inverted hyper-thinned Mauleon rift Basin. The paleo thermal gradients estimated in this work differ strongly according to their structural position across the Albian-Cenomanian rift domains along a proximal-distal margin transect. The paleo-thermal gradient increases basinward: -36 degrees C/km on the European proximal margin, approximately 38-47 degrees C/km on the two necking zones and 57-60 degrees C/km on the hyper-extended domain. The high gradient is directly correlated with the positive gravity anomaly localized under the Mauleon Basin hyper-extended domain, interpreted as the presence at low depth of sub-continental mantle, currently at around 10km depth. The European margin is affected by northward thrusting transporting of the paleo isotherms on the proximal margin without any thermal heating of the footwalls. The ante-collisional paleo thermal gradient of both hyper-extended domain and European margin is thus preserved on the northern part of the basin. On the other hand, the Iberian margin (southward of the basin) underwent thermal gradient increase after the collision iberia-Europe. This gradient increase is though to be linked to the Iberian continental crust thickening following the formation of the Axial Zone antiformal crustal stack.