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,

摘要

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 to better understand the place of the late orogenic magmatism in Variscan orogeny. Through a methodological approach, the close spatial association of the pluton with the lithospheric SHF is investigated in order to clarify the relationships between faulting and magmatic processes during the Late Carboniferous. Therefore a multidisciplinary study has been carried out on the Montmarault massif. Combining geochronology, field and laboratory 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 the following conclusions: (1) The Montmarault pluton, dated by the chemical U-Th-Pb method on monazite at 321 ± 2 Ma, was emplaced in a NW-SE maximum stretching trend which is consistent with the regional extensional tectonic regime; (2) the Montmarault pluton is rooted in its eastern part along the SHF with a laccolite-like shape in its western part; (3) at circa 320 Ma, the “Proto-SHF” acted probably as a normal fault considered as the feeding channel for the magma emplacement; and (4) Late Carboniferous NE-SW extensional tectonics reworked the Montmarault pluton in a brittle postsolidus stage.