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Genèse et évolution des magmas primitifs de la chaine des Puys (Massif Central): une approche par l'étude des inclusions magmatiques

Abstract : The Chaîne des Puys is the last magmatic province of the French Massif Central and comprises eighty young well-preserved volcanoes. Erupted basaltic lavas display differenciated compositions. Therefore, the primary feature of the magmas of these volcanoes remains largely unknown and the nature of their mantle source is still a matter of debate. Minute melts preserved as quenched glass inclusions inside early-formed olivine crystal can provide direct constraints about these primary characteristics. Melt inclusions trapped in Mg-rich olivines (Fo84-86) from several volcanoes of the Chaîne des Puys display basanite and alkali-basalt compositions. Their variation in trace-element composition is larger than that of the basaltic lavas and reflects variable degrees of partial melting of a mantle source containing amphibole as a residual phase. The restricted P-T stability field of this mineral requires that the partial melting event occurs in a metasomatised lithospheric mantle. The primitive trapped melts display significant amount of dissolved water, which could explain the early crystallization of amphibole in the Chaîne des Puys magmatic serie and is likely to play an important role in its evolution towards SiO2-saturated compositions. Finally melts trapped as inclusions in olivine porphyroclasts of spinel peridotite nodules extruded from a single volcano of the Chaîne des Puys exhibit alkali and silica rich compositions drastically different from those of olivine-hosted melt inclusions in basalts. These melts are in equilibrium with their host olivines and could represent trapped aliquots of near-solidus partial melts of spinel peridotite around 1 GPa. However they do not show clear genetic link with both the melts trapped in olivine phenocrysts and the erupted lavas.
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Submitted on : Friday, March 30, 2012 - 2:33:30 PM
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  • HAL Id : tel-00684061, version 1

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Séverine Jannot. Genèse et évolution des magmas primitifs de la chaine des Puys (Massif Central): une approche par l'étude des inclusions magmatiques. Géologie appliquée. Université Blaise Pascal - Clermont-Ferrand II, 2005. Français. ⟨NNT : 2005CLF21619⟩. ⟨tel-00684061⟩

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