Volcanism of the monts dore (French Massif Central)

Abstract

Pavin volcano is located both in the southern part of Chaîne des Puys and in the Monts Dore volcanic area. According to the very young age of Pavin volcano (about 7000 y BP), Pavin volcanic area is considered to belong to the Chaîne des Puys, while the activity of the Monts Dore stratovolcano ended about 200 ka ago. The Monts Dore composite volcano (maximum elevation: 1886 m) has a surface of 500 km2 and a volume of about 200 km3. It is composed of two distinct volcanic stratovolcanoes: - The Monts Dore s.s. is 3.09-1.46 Ma old. Its activity began with a caldera collapse resulting from the eruption of a rhyolitic ash-and-pumice flow. In the vicinity of the caldera, domes (and associated nuée ardente deposits) and lava flows were emplaced. They are rhyolitic, trachytic, trachyandesitic, basaltic, tephritic and phonolitic in composition. The Sancy stratovolcano is younger, 1.1-0.23 Ma old. It is centred on a small caldera related to a trachytic ash-and-pumice flow eruption, formed about 720 ka ago. Predominant trachyandesites (75 % in volume) occur as domes, pyroclastic deposits, lava flows and dykes. Basaltic lava flows are located on the distal part of this volcano. The petrology of the two volcanoes is almost identical and involves the coexistence of two types of alkaline series, which evolved towards either silica-oversaturated (rhyolitic) or silica-undersaturated (phonolitic) residual liquids. The main magmatic processes controlling this evolution are fractional crystallization, magma mixing and crustal contamination. Pavin volcano is located within the Sancy area. Therefore, the products of the volcanic activity of Pavin may include xenoliths derived from the Sancy volcano, e.g. trachyandesite, basalt, trachyte, and scarce phonolite. According to its young age, Pavin is best regarded as a satellite of the Chaîne des Puys. But the Pavin volcano was built on the south-east flank of Sancy stratovolcano, which itself was located SE of the previous Monts Dore s.s. Thus, the Pavin could also be interpreted as witnessing the first activity of a future stratovolcano.