86
1500 1000 1500 1500 1500 1500
NNO
0,25 Ma - Sancy volcano: late stage1 Ma - Sancy volcano: initial stage2 Ma - Northern volcanoes (Banne d’Ordanche and Aiguiller)2,5 Ma - Intra-caldera volcanism3,2 Ma - Pre-caldera alkaline series
Basement
Phonolites
Basalts
Rhyolites
Evolved pyroclastites(mostly ‘Grande Nappe’ ignimbrite)Pyroclastic rocks of trachyteand trachyandesite composition
Sediment
Ordanchites
Trachytes and trachyandesites
0
4 km
Haute Dordogne
caldera
Sancycaldera
SSE
E D C B A
Fig. 4.2
Evolution of the growth and destruction of the Monts Dore massif (After Cantagrel and Baubron
1983
, modifi
ed). Ordanchite is tephrite related to the undersaturated series. A to E cor-
responds to the fi
ve main cycles of activity
A. Gourgaud