Trachyte Phase Relations and Implication for Magma Storage Conditions in the Cha|Πne des

Petrological data have been acquired on natural trachytes from the Cha|Œ ne des Puys, French Massif Central, and on experimental prod-ucts from phase equilibria to (1) constrain the storage conditions of trachytic magmas that lead to explosive eruptions (dome destructions as block-and-ash flows or pumice-and-ash flows) and (2) provide phase relationships and chemical compositions for differentiated alkaline liquids in an intraplate continental context. Phase assem-blages, proportions, and compositions have been determined on six trachytes with SiO2 contents varying from 62 to 69 wt % and alkali contents of 10·5^12·0 wt %. The samples contain up to 30 % of phenocrysts, mainly consisting of feldspar (15^17%; plagioclase and/or alkali-feldspar), biotite (2^6%; except in the most SiO2-poor sample), Fe^Ti oxides (1^3%) amphibole (55%), clinopyroxene (1%). All samples have apatite and zircon as minor phases and titanite was found in one sample