A multidisciplinary study of a syntectonic pluton close to a major lithospheric-scale fault : Relationships between the Montmarault granitic massif and the Sillon Houiller Fault in the Variscan French Massif Central : 1. Geochronology, mineral fabrics and tectonic implications

[1] Because of its location along one of the major faults, the Sillon Houiller Fault (SHF)of the French Massif Central (FMC), the Montmarault granitic pluton is well suited tobetter understand the place of the late orogenic magmatism in Variscan orogeny. Through amethodological approach, the close spatial association of the pluton with thelithospheric SHF is investigated in order to clarify the relationships between faulting andmagmatic processes during the Late Carboniferous. Therefore a multidisciplinary studyhas been carried out on the Montmarault massif. Combining geochronology, field andlaboratory microstructural observations, and anisotropy of magnetic susceptibility(AMS) methods presented in this paper and gravity and aeromagnetic modeling (part 2),as well as similar studies from other plutons in the FMC, allows us to draw thefollowing conclusions: (1) The Montmarault pluton, dated by the chemical U-Th-Pbmethod on monazite at 321 ± 2 Ma, was emplaced in a NW-SE maximum stretching trendwhich is consistent with the regional extensional tectonic regime; (2) the Montmaraultpluton is rooted in its eastern part along the SHF with a laccolite-like shape in itswestern part; (3) at circa 320 Ma, the ‘‘Proto-SHF’’ acted probably as a normalfault considered as the feeding channel for the magma emplacement; and (4) LateCarboniferous NE-SW extensional tectonics reworked the Montmarault pluton in a brittlepostsolidus stage.