Variscan volcanism of Central and Western Europe

Abstract

The type of volcanism in Central and Western Europe clearly reflects the tectonic conditions of the time of its manifestation. Two main types of Variscan volcanism can be distinguished: (1) spilitokeratophyre (pre-orogenic); and (2) postorogenic calc-alkaline. The spilito-keratophyre associations are widespread in space and time and form belts related to regional faults, intraplate rifts and grabens. This reflects a tectonic regime of tension. Spilito-keratophyre sequences are connected with the initial stages of the individualisation of new basins (Devonian, Carboniferous). They can appear several times in one region. It seems possible that the spilitic belts mark the boundaries of small plates or blocks. The source of magma was the upper mantle. The tectonic conditions during the time of eruption of postorogenic volcanics is quite different. They are characterised by folding, vertical movements, compression arid anatectic melting in the sialic crust. Two associations can be distinguished: (1) a late-orogenic one of monotonous acid (rhyolites, dacite) composition, forming magmatic structures of the central type related to cauldron subsidence; and 2) a postorogenic or final one of bimodal composition on (trachybasalts- rhyolites) marking the beginning of a new period of tension related to the uplift of the region.