Abstract
In the Basque-Cantabrian Basin, an important submarine volcanic activity of alkaline character was developed during the upper Cretaceous. This vulcanism was related to a rift and/or transform fault in the continental crust associated to the opening of the North Atlantic ocean. Pillow lava flows are noteworthy among the other volcanic materials by their volume and excellent preservation state. The lava flows are formed by the pile up of small flow-and cooling units, i.e. tubes or lava tubes, characterized by: i) coarse cylindrical morphology with abundant constrictions, ii) diameter less than 1 meter in a transversal section, iii) smooth or striated surface, iv) concentric and/or radial internal structure, and iv) the branches and direction changes during the outflow. Lava flows/tubes shape and surface characteristics depend on the viscosity, effusion rate and the thickness of quenched crust during growth. The Tubes are moted directly on feeder dykes or are connected in tabular flows. The expanding and advancement of the tubes was the result of stretching or breaking of the quenched surface crust and spreading of the molten lava from the interior. Stretching features and cracks appear mainly at the flow front, but lobes of lava developed from the top and the flanks of the tubes are not uncommon. Only scarce pillowed lavas are truly isolated magma sacks separated from their sources. Related to the tabular flows and the biggest pillow lavas, some breccias were occasionally formed by the gravitational collapse of the roof of the draining tunnels.
Highlights
In the Basque-Cantabrian Basin, an important submarine volcanic activity of alkaline character was developed during the upper Cretaceous
Related to the tabular flows and the biggest pillow lavas, sorne breccias were occasionally formed by the gravitacional collapse of the roof of the draining tunnels
Estas coladas son abundantes en los cinturones de rocas verdes precámbricos, en una buena parte de los complejos ofiolíticos, en formaciones subacuosas someras de diferentes edades, y, sobre todo, en los fondos oceánicos actuales, incluyendo fundamentalmente a los productos generados a nivel de las dorsales mediooceánicas, pero también a los formados en relación con montes submarinos y con islas volcánicas, especialmente en su etapa de crecimiento subacuoso (e.g. Moore, 1965; Jones, 1969; Cann, 1970; Dimroth et al, 1978; Wells et al, 1979; Robson y Caan, 1982; Juteau, 1993; Embley y Chadwich, 1994; Chadwich y Embley, 1994; Kennish y Lutz, 1998)
Summary
Fig. l.-Mapa Geológico y de situación de la Cordillera Vasco-Cantábrica (basado en Sangüesa, 1998). Por el sur está limitada por los depósitos terciarios de antepaís de las depresiones del Duero y del Ebro y por el norte se sumerge bajo el Mar Cantábrico, en el golfo de Vizcaya (Feuillée y Rat, 1971; Rat, 1988; Boillot, 1984; EVE, 1995). La evolución deposicional y tectónica en la Cuenca está controlada por los movimientos diferenciales de la placa Ibérica respecto a la Europea, en el marco de la expansión del Atlántico Norte y la apertura del Golfo de Vizcaya El Arco Vasco corresponde a una zona profunda situada entre las placas Ibérica y Europea, con pliegues y cabalgamientos vergentes al norte que no afectan al basamento hercínico, mientras que los tres Bloques, separados por importantes fallas transversales, pertenecen a una zona distal dentro de la placa Ibérica, relativamente tranquila en cuanto a su tectónica, poco deformada y en algunos casos notablemente horizontalizada. Características generales del vulcanismo de edad cretácica en la Cordillera Vasco-Cantábrica
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