Les dépôts d'avalanches de débris du Cantal (France) : témoins de la construction du plus grand strato­volcan européen d'âge miocène / The debris-avalanche deposits of the Cantal (France): witnesses of the construction of the largest perialpine stratovolcano

摘要

Abstract The Cantal stratovolcano, one of the largest European stratovolcanoes (at present 70 km in diameter, 2500 km2 and 400 km3) was emplaced between 13 and 2 Ma on an uplifted Hercynian basement associated with Oligocène sedimentary basins. The main activity between 8.5 and 7 Ma led to the construction of a high trachyandesitic stratovolcano and its associated laharic piedmont. This edifice collapsed several times, producing gigantic debris-avalanche deposits (total volume 245 km3) that are widespread in the Cantal and as far as 40 km from its center. Abundant isotopic Ar-Ar and K-Ar data indicates the existence of a minimum of four debris avalanches, respectively older than 7.4 Ma (to the east and north), between 7.4 and 7.2 Ma (to the west) and less than 7.2 Ma (to the south and the south-west). The length covered by the debris avalanches implies that the volcanoes reached altitudes higher than 3000 m above sea level.