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Le complexe annulaire alcalin de Combeynot ( Massifs cristallins externes, Alpes françaises), témoin d'un magmatisme en régime distensif. Pétrogéochimie et signification géodynamique.

Abstract : The Combeynot massif, located on the north-eastern edge of the Haut-Dauphiné massif (external cristalline massifs, French Alps) is basically composed of two units : (1) a metamorphic and mylonitic basement including a migmatitic group and an ortho-augengneiss ; this basement is related to the formations of the core of the Haut-Dauphiné massif, (2) an intrusive subvolcanic ring complex, consisting of volcanic and volcano-detritic formations, of a dense microgranitic and rhyolitic vein pattern, of two concentrically arranged granitic units and of late doleritic veins which end the magmatic cycle. A comparative study of the petrography, the structure, the zircon typology, the geochemistry of major, trace (Y, Nb, Zr, Rb, Sr, U, Th, Hf, Sc, Cs and Ta), and rare earth elements, of the Combeynot complex made it possible to review the magmatic history of the cycle and to test his geodynamic implication. The magmatism of Combeynot is of alkaline within-plate nature and reflects a distensive geotectonic environment. It originates from the mantle where several subcontemporaneous magmas appear under the effect of various degres of partial melting and lead to acid units by crystal fractionation. Their subsurface setting in a fluid-rich orogenic region,wieh is still unconsolidated and the activity of the juvenile fluid phase and/or the meteoric water control the petrographie nature - acidic, oversaturated and subsolvus of the granitic units of the complexe and the postand tardi-magmatic hydrothermal alteration processes.
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Submitted on : Wednesday, February 13, 2013 - 11:51:53 AM
Last modification on : Friday, November 6, 2020 - 3:52:04 AM

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  • HAL Id : tel-00539879, version 2

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CNRS | UGA

Citation

René Costarella. Le complexe annulaire alcalin de Combeynot ( Massifs cristallins externes, Alpes françaises), témoin d'un magmatisme en régime distensif. Pétrogéochimie et signification géodynamique.. Géologie appliquée. Université Scientifique et Médicale de Grenoble, 1987. Français. ⟨tel-00539879v2⟩

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