Space–time evolution of monogenetic volcanism in the mafic Garrotxa Volcanic Field (NE Iberian Peninsula)

We reconstructed the evolution of the volcanic activity within the central Garrotxa monogenetic Volcanic Field, the youngest volcanic area of the Iberian Peninsula, by investigating the stratigraphy of the volcanic successions and the morphology of the monogenetic eruptive centres. Analysis of this volcanic succession has been conducted following the Unconformity Bounded Stratigraphic Units criteria. The detailed stratigraphy of the volcanic successions shows that the central Garrotxa Volcanic Field (GVF) evolved through four main periods of volcanic activity (Synthems) represented by the eruptive products of the mafic monogenetic volcanoes and associated syn-eruptive reworked deposits (Eruptive Units) and by the inter-eruptive deposits (Epiclastic Units). The distribution and the morphologies of the monogenetic volcanoes suggest that feeder dykes were emplaced under influence of the present stress filed and along pre-existing fractures of the basement. Our facies analysis of the deposits and their distribution shows that migration of volcanism toward the centre of the basin was accompanied by a trend of increasing explosivity. Episodic hydromagmatism in central Garrotxa occurred without a specific geographic locus or obvious temporal correlation. Finally, by integrating field data with the stratigraphy extracted from water wells, we determined the volume of the volcanic deposits. The small average volume of products emitted during each eruptive period, and the long quiescence separating them, allow us to classify the GVF as a low-output rate volcanic field.