Geochronological and thermometric evidence of unusually hot fluids in an Alpine fissure of Lauzière granite (Belledonne, Western Alps)

Abstract : A multi-method investigation into Lauziere granite, located in the external Belledonne massif of the French Alps, reveals unusually hot hydrothermal conditions in vertical open fractures (Alpine-type clefts). The host-rock granite shows sub-vertical mylonitic microstructures and partial retrogression at temperatures of <400 degrees C during Alpine tectonometamorphism. Novel zircon fission-track (ZFT) data in the granite give ages at 16.3 +/- 1.9 and 14.3 +/- 1.6 Ma, confirming that Alpine metamorphism was high enough to reset the pre-Alpine cooling ages and that the Lauziere granite had already cooled below 240-280 degrees C and was exhumed to < 10 km at that time. Novel microthermometric data and chemical compositions of fluid inclusions obtained on millimetric monazite and on quartz crystals from the same cleft indicate early precipitation of monazite from a hot fluid at T > 410 degrees C, followed by a main stage of quartz growth at 300-320 degrees C and 1.5-2.2 kbar. Previous Th-Pb dating of cleft monazite at 12.4 +/- 0.1 Ma clearly indicates that this hot fluid infiltration took place significantly later than the peak of the Alpine metamorphism. Advective heating due to the hot fluid flow caused resetting of fission tracks in zircon in the cleft hanging wall, with a ZFT age at 10.3 +/- 1.0 Ma. The results attest to the highly dynamic fluid pathways, allowing the circulation of deep mid-crustal fluids, 150-250 degrees C hotter than the host rock, which affect the thermal regime only at the wall rock of the Alpine-type cleft. Such advective heating may impact the ZFT data and represent a pitfall for exhumation rate reconstructions in areas affected by hydrothermal fluid flow.
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Contributeur : Christine Maury Referent Hal Edytem <>
Soumis le : lundi 11 février 2019 - 15:38:54
Dernière modification le : mercredi 13 février 2019 - 01:05:06


  • HAL Id : hal-02014379, version 1

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Emilie Janots, Alexis Grand'Homme, Matthias Bernet, Damien Guillaume, Edwin Gnos, et al.. Geochronological and thermometric evidence of unusually hot fluids in an Alpine fissure of Lauzière granite (Belledonne, Western Alps). Solid Earth, European Geosciences Union, 2019, 10 (1), pp. 211-223. 〈hal-02014379〉



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