Casquet Martín, CésarGalindo Francisco, María Del CarmenGonzález Casado, José ManuelAlonso Millán, Ángela2023-06-202023-06-2019920213-683Xhttps://hdl.handle.net/20.500.14352/56924A 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 (Weald facies). Physical conditions at the thermal peak are estimated at abo 1 Kb (PL) and 326± 13°C (i.e. very low grade metamorphism). Fluids were largely water brines with minor amounts of gases, CO2 and CH4• f02 and f52 were close to the graphite and Po-Py buffers respectively. This metamorphism is spatially associated with a deformation band (5-6 km. ín wídth) wíth schístosíty ín the pelitíc beds and promínent tensíonal, quartz ínfílled veíns in the more samítíc ones. K-Ar dating on authígeníc illites has gíven ages from 108 to 86 M.a., i.e. Míddle Cretaceous, and thus younger than the basín fílling (Urbíón Group+Enciso F.+Olívan F.). Metamorphism migth be related wíth the circulatíon of hot mígratory fluíds (i.e. tectoníc brínes), along the deformation bando The tectonic sígníficance of this deformation band is slill uncertain.spajournal articlehttp://www.sociedadgeologica.es/publicaciones_geogaceta.htmlopen access552.4(234.1)Cameros BasinVery Low grade metamorphismGeochronologyK/Ar datingPetrología