Fluid–rock interactions along detachment faults during continental rifting and mantle exhumation: the case of the Urdach lherzolite body (North Pyrenees)

The North Pyrenean Zone corresponds to the palaeopassive margin of Iberia plate, at foot which subcontinental mantle was exhumed during Albian times. Rare bodies rocks associated with strongly sheared lenses continental crust are scattered among metasediments. Significant fluid flow occurred along a major décollement basement–Trias interface in Urdach massif (Chaînons Béarnais). Fluids broad range salinity (10–38 wt.% NaCl equiv.), indicative mixing between brines and more dilute waters, produced strong silicification breccias. circulated c. 240–280°C under lithostatic pressures 6 ± 1 km depth. fluids became increasingly saline towards final stages. syndeposition Cenomano-Turonian flysch layers then progressively isolated lower aquifers close where Triassic were predominant. release migration significant volumes stretching squeezing evaporites played crucial part mineralogical rheological transformations that Cretaceous rifting event.