Gravity inversion, AMS and geochronological investigations of syntectonic granitic plutons in the southern part of the Variscan French Massif Central

Aurore Joly (1) , Michel Faure (2) , Guillaume Martelet (3) , Yan Chen (2)

1 Centre for Exploration Targeting
2 ISTO - Institut des Sciences de la Terre d'Orléans
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Magnetic fabric analyses, gravity inversion associated with chemical U-Th-Pb dating and structural observations are carried out to elucidate relationships between faulting and magmatic processes. This multidisciplinary study has been undertaken on Late Carboniferous plutons, situated in the southern part of the Variscan French Massif Central (FMC). The Glénat, Omps and Boisset plutons crop out on both sides of the crustal-scale Sillon Houiller Fault (SHF). The Anisotropy of Magnetic Susceptibility (AMS) measurements and structural observations show that (i) the plutons acquired their final structure during the magma crystallization and record a NW-SE maximum stretching trend; (ii) in the Boisset pluton, post magmatic fabrics predominate with a NNW-SSE trending lineation. The structural pattern deduced from the AMS study is thus consistent with the NW-SE late orogenic extensional tectonic regime that has been documented in other parts of the FMC during Late Carboniferous. The 3D geological modelling refined by 3D gravity inversion does not show any evidence of rooting of the granites along the SHF. Therefore, despite the apparent cartographic relationship between the SHF and the three plutons, our study does not support a genetic link between fault and plutons. It also questions the existence of the SHF in this part of the Massif Central at the time of pluton emplacement, and emphasises the dominant role of the regional tectonic framework rather than local faulting as a factor controlling pluton emplacement.

Mots clés: Sillon Houiller Fault; granite fabrics; monazite chemical U-Th-Pb dating; Anisotropy of Magnetic Susceptibility (AMS); gravity investigations and inversion; 3D modelling; Variscan Belt; Sillon Houiller Fault.

Domaines: Tectonique; Milieux et Changements globaux

Aurore Joly, Michel Faure, Guillaume Martelet, Yan Chen. Gravity inversion, AMS and geochronological investigations of syntectonic granitic plutons in the southern part of the Variscan French Massif Central. Journal of Structural Geology, 2009, 31 (4), pp.421-443. ⟨10.1016/j.jsg.2009.01.004⟩. ⟨insu-00352868⟩