Casquet Martín, CésarGalindo, CarmenGonzález Casado, J. M.Alonso, ÁngelaMas, RamónRodas, M.García, E.Barrenechea, J. F.2020-05-182020-05-181991http://hdl.handle.net/10272/17982A case of hydrothermal metamorphism is described from the Cameros Basin along the rio Cidacos transect. The highest grade is reached at the base of the Urbión Group, a fluvial sequence Upper Jurassic to Lower Cretaceous in age (Wea/d facies). Physical conditions at the thermal peak are estimated at ab. I Kb (PL) and 326± 130 C (i.e. very Iow grade metamorphism). Fluids were largely water brines with minor amounts of gases, C02 and CH4. f02 and fS2 were close to the graphite and Po-Py buffers respectively. This metamorphism is spatially associated with a deformation band (5-6 km. in width) with schistosity in the pelitic beds and prominent tensional, quartz infilled veins in the more samitic ones. 1<-Ar dating on authigenic illites has given ages from 708 to 86 M.a., i.e. Middle Cretaceous, and thus younger than the basin filling (Urbión GroupÆnciso F.+Olivan F.). Metamorphism migth be related with the circulation of hot migratory fluids (i.e. tectonic brines), along the deformation band. The tectonic significance of this deformation band is still uncertainspaAtribución-NoComercial-SinDerivadas 3.0 Españahttp://creativecommons.org/licenses/by-nc-nd/3.0/es/Cameros BasinVery Low grade metamorphismGeochronologyK/Ar datingjournal articleopen access