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Insights in the ductile history of the northern Sillon Houiller Fault via a multidisciplinary study of the Late Variscan Montmarault pluton (French Massif Central).

Abstract : In order to better understand the role of the lithosphere-scale Sillon Houiller Fault (SHF) during the Late Variscan evolution of the Massif Central, a multidisciplinary study has been carried out on the Montmarault massif: petrology, geochronology, Anisotropy of Magnetic Susceptibility (AMS), gravity as well as interpretation of aeromagnetic survey. Based on rock density and magnetic susceptibility measurements, a direct 2D joint gravity and magnetic modelling has been performed along several cross sections. Then, the new geophysical, field and AMS structural information, have been integrated into a 3D geological model which highlights the geometry, the emplacement of Montmarault pluton and its posterior deformations. These results allow us to draw the following conclusions. The Montmarault pluton exhibits a magnetic foliation dipping at high angle towards to the SHF for those sites close to the fault and flat lying or gently dipping for other sites. The majority of sampled sites shows a consistently NW-SE trending magnetic lineation, perpendicular to the SHF. From East to West, the Montmarault granitic pluton is a kilometre thick laccolith that roots in the SHF and intrudes the metamorphic series. These geometric and kinematic features complemented by the new chemical dating of Montmarault pluton at 321± 2 Ma imply that the early SHF behaved as a normal fault during Namurian times. These results comply well with the overall late-orogenic regional extensional pattern at the scale of the whole Variscan French Massif Central. During the Late Carboniferous (Stephanian), the Montmarault pluton is deformed by NE dipping listric normal faults that control the opening of half-grabens coal basins. In the same time, the SHF acted as a sinistral brittle wrench fault.
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https://hal-insu.archives-ouvertes.fr/hal-00106996
Contributor : Nathalie Pothier <>
Submitted on : Tuesday, October 17, 2006 - 9:11:34 AM
Last modification on : Thursday, August 6, 2020 - 3:35:09 PM

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Aurore Joly, Yan Chen, Michel Faure, Guillaume Martelet. Insights in the ductile history of the northern Sillon Houiller Fault via a multidisciplinary study of the Late Variscan Montmarault pluton (French Massif Central).. 21e Réunion des Sciences de la Terre, Dec 2006, Dijon, France. 1p. ⟨hal-00106996⟩

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