摘要：A multi-method investigation into Lauzière granite, located in the external Belledonnemassif of the French Alps, reveals unusually hot hydrothermal conditions invertical open fractures (Alpine-type clefts). The host-rock granite showssub-vertical mylonitic microstructures and partial retrogression attemperatures of <400∘C during Alpine tectonometamorphism.Novel zircon fission-track (ZFT) data in the granite give ages at16.3±1.9 and 14.3±1.6Ma, confirming that Alpinemetamorphism was high enough to reset the pre-Alpine cooling ages and thatthe Lauzière granite had already cooled below 240–280∘C andwas exhumed to <10km at that time. Novel microthermometric dataand chemical compositions of fluid inclusions obtained on millimetricmonazite and on quartz crystals from the same cleft indicate earlyprecipitation of monazite from a hot fluid atT>410∘C, followed by a main stage of quartz growthat 300–320∘C and 1.5–2.2kbar. Previous Th-Pb dating of cleftmonazite at 12.4±0.1Ma clearly indicates that this hot fluidinfiltration took place significantly later than the peak of the Alpinemetamorphism. Advective heating due to the hot fluid flow caused resetting offission tracks in zircon in the cleft hanging wall, with a ZFT age at10.3±1.0Ma. The results attest to the highly dynamic fluidpathways, allowing the circulation of deep mid-crustal fluids,150–250∘C hotter than the host rock, which affect the thermal regime only at the wall rock of theAlpine-type cleft. Such advective heating may impact the ZFT data andrepresent a pitfall for exhumation rate reconstructions in areas affected byhydrothermal fluid flow.
