| Reference Type | Journal (article/letter/editorial) |
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| Title | Tertiary and Quaternary volcanism in the Massif Central, France |
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| Journal | Geological Society, London, Special Publications |
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| Authors | Downes, Hilary | Author |
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| Year | 1987 (January) | Volume | 30 |
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| Page(s) | 517-530 | Issue | 1 |
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| Publisher | Geological Society of London |
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| URL | |
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| DOI | doi:10.1144/gsl.sp.1987.030.01.25Search in ResearchGate |
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| Classification | Not set | LoC | Not set |
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| Mindat Ref. ID | 425170 | Long-form Identifier | mindat:1:5:425170:9 |
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| GUID | 0 |
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| Full Reference | Downes, Hilary (1987) Tertiary and Quaternary volcanism in the Massif Central, France. Geological Society, London, Special Publications, 30 (1). p.517-530. doi:10.1144/gsl.sp.1987.030.01.25 |
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| Plain Text | Downes, Hilary (1987) Tertiary and Quaternary volcanism in the Massif Central, France. Geological Society, London, Special Publications, 30 (1). p.517-530. doi:10.1144/gsl.sp.1987.030.01.25 |
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| In | Fitton, J. G., Upton, B. G. J. - Eds. (1987) Alkaline Igneous Rocks. Special Publication Vol. 30. Geological Society of London |
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| Abstract/Notes | Summary Continental alkaline volcanics of the French Massif Central range in age from 65 Ma to 3450 years BP and can be divided by geography and age into 20 separate areas. There is no correlation between the age of an area and the geographic locality. Two magma series are present: a silica-undersaturated basanite-tephrite-phonolite series and an alkali basalt-trachyandesite-trachyte-rhyolite series, the evolved members of which are silica-saturated. Rare nephelinites are also found. Primitive magmas of both main series may be derived from 2%–20% partial melting of a mantle enriched with light rare-earth elements with variable amounts of garnet in the residue; nephelinites were formed from a source which was isotopically and chemically distinct. Fractional crystallization of observed phases accounts for the diversity of intermediate and evolved products. Amphibole fractionation in basalts at depth causes the trend towards silica saturation, while alkali feldspar fractionation dominates the final stages of crystallization. Removal of small quantities of sphene and zircon explains trace-element depletions in trachytes, phonolites and rhyolites. Up to 30% crustal contamination has occurred in the evolved magmas but contamination is generally absent from their basaltic parents. Sr, Nd and Pb isotope data indicate that the most probable contaminant is undepleted meta-sedimentary granulite-facies lower crust. Variations in Sr and Nd isotope ratios also constrain petrogenetic hypotheses such as amphibole fractionation and magma mixing. Mineralogical disequilibrium, compositional banding and emulsification textures indicate extensive magma mixing. Some flows are homogeneous hybrid lavas in which only the unusual composition and rare mineral disequilibria indicate the mode of formation. |
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