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Comportement des éléments traces et majeurs dans la série alcaline du Velay ; comparaison avec la chaîne des Puys (Massif Central, France)

1983; Volume: 106; Issue: 4 Linguagem: Inglês

10.3406/bulmi.1983.7726

0180-9210

B. Villemant, M. Treuil,

Geochemistry and Geologic Mapping

The behavior of trace elements (hygromagmaphile elements : Th, U, Hf, Ta, La and transition elements : Cr, Co, Ni, Se) shows that the volcanic suite of Velay Oriental, Massif Central, France) is a fractional crystallization series. A potassium enrichment in the magmatic liquid during fractional crystallization is shown. We propose a model of exchange between a fluid phase and the magma during the differentiation, which permits an estimation of the relative contamination for each element. Post-magmatic alteration disturbs the behaviour mainly of rubidium, but also of some alkali and alkaline earth elements in some basaltic samples. The behavior of trace and major elements distinguishes this series (basalt-phonolite) from the series of Chaîne des Puys (basalt-rhyolite). The initial liquids of both series are generated from mande sources of a same chemical composition and by a same degree of partial melting. The slight composition differences in initial liquids of both series are explained by different primary differentiation processes, or possibly by differences in the mineralogy of the sources. The interaction between the magma and a fluid phase in the magma chamber of the Velay series may explain many of the observed differences in the behavior of the elements.