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Chevauchements et décrochements alpins aux limites du massif du Mont Blanc (Alpes occidentales)

Abstract : Compared study of structures at aIl scales in the ante-triasic basement and the mesozoïc cover has been carried out on each side of the Mont-Blanc massif, firstly on his north-western front, secondly on the east of the eastern side of the Mont-Blanc, in the Grand Saint Bernard zone. At the Mont-Blanc, Aiguilles Rouges, Belledonne junction, this study allowed us to conclude to an alpine regional deformation of the external crystalline massives. The alpine deformation combines gravitational motion for superficial dauphinois nappes and crustal shortening for the basement. This complex process leads to a regional strain pattern which is the result of superposed deformations. Nevertheless , incremental strain studies have alowed to state precisely the directions of these deformations and have shown a generalized left hand rotation during the tertiary time. These data alow to propose a tectonic history for the alpine deformation in this external zone. The direction of crustal shor tening and gravitational displacement has been firstly northward and secondly west ward. This change occurs progressively and is recorded by the ductile and heterogeneous tertiary deformation in both the basement and the caver. In the Col du Grand Saint Bernard area, this compared study of basement and triasic cover, has shown that the north - south structures of this part of the Grand Saint Bernard zone, are associated to a combined thrusting and sinistral wrenching regional deformation, accompaning a displacement in the NNW direction. This deformation corresponds to an intermediate stage in the history of the regional deformation which seems to begin with an early tangential shearing (in the NNW direction ) and to end with an north-south flattening combined to a sinistral wrenching . This frontal part of the Grand Saint Bernard zone can be inter preted as a lateral ramp which has limited the displacement of the Grand Saint Bernard nappe, exposed in the northern part of the Grand Saint Bernard zone .
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Contributor : Pascale Talour <>
Submitted on : Wednesday, November 23, 2011 - 4:46:02 PM
Last modification on : Monday, December 14, 2020 - 9:42:24 AM
Long-term archiving on: : Monday, December 5, 2016 - 5:56:18 AM

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  • HAL Id : tel-00644149, version 1

Citation

Pierre Gourlay. Chevauchements et décrochements alpins aux limites du massif du Mont Blanc (Alpes occidentales). Tectonique. Université Pierre et Marie Curie - Paris VI, 1986. Français. ⟨tel-00644149⟩

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