Mechanisms of margin inversion in the external Western Alps: Implications for crustal rheology

Bellahsen, Nicolas; Jolivet, Laurent; Lacombe, Olivier; Bellanger, Mathieu; Boutoux, Alexandre; Garcia, Sébastien; Mouthereau, Frédéric; Pourhiet, Laëtitia Le; Gumiaux, Charles

doi:10.1016/j.tecto.2012.06.022

Cited by 79 publications

(145 citation statements)

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“…[32][33][34] argue that faults within crystalline basement become weak because of reaction softening: phyllosilicate-rich mylonites (phyllonites) form from the mechanical breakdown of feldspars, which is followed by a chemical breakdown in the presence of a fluid, or grain-size reduction allowing grain-boundary sliding. [35] found that the crystalline basement in the external parts of the Western Alps deformed in a brittle-ductile regime with distributed shear within spaced shear zones or shear bands that are up to a few hundred meters thick. The focusing of deformation into distinct shear zones, in which phyllonite formation is observed [35], corresponds to an overall weakening of the basement blocks.…”

Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

“…[35] found that the crystalline basement in the external parts of the Western Alps deformed in a brittle-ductile regime with distributed shear within spaced shear zones or shear bands that are up to a few hundred meters thick. The focusing of deformation into distinct shear zones, in which phyllonite formation is observed [35], corresponds to an overall weakening of the basement blocks. [36] discuss how thrust faults may propagate through crystalline basement by deformation ahead of the propagating fault's tip.…”

Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

“…Thus for Alpine geologists the involvement of crystalline basement in nappe tectonics was never questioned. The thick-and thin-skinned involvement of crystalline basement in Alpine nappe tectonics has been discussed recently by [113], [35,183] and [1,184] and will thus be touched briefly only here. The two examples presented below, the Western and Eastern Alps, were chosen for their particular aspects regarding tectonic style.…”

Section: Western and Eastern Alpsmentioning

confidence: 99%

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Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Pfiffner¹

2017

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This paper gives an overview of the large-scale tectonic styles encountered in orogens worldwide. Thin-skinned and thick-skinned tectonics represents two end member styles recognized in mountain ranges. A thick-skinned tectonic style is typical for margins of continental plates. Thick-skinned style including the entire crust and possibly the lithospheric mantle are associated with intracontinental contraction. Delamination of subducting continental crust and horizontal protrusion of upper plate crust into the opening gap occurs in the terminal stage of continent-continent collision. Continental crust thinned prior to contraction is likely to develop relatively thin thrust sheets of crystalline basement. A true thin-skinned type requires a detachment layer of sufficient thickness. Thickness of the décollement layer as well as the mechanical contrast between décollement layer and detached cover control the style of folding and thrusting within the detached cover units. In subduction related orogens, thin-and thick-skinned deformation may occur several hundreds of kilometers from the plate contact zone. Basin inversion resulting from horizontal contraction may lead to the formation of basement uplifts by the combined reactivation of pre-existing normal faults and initiation of new reverse faults. In composite orogens thick-skinned and thin-skinned structures evolve with a pattern where nappe stacking propagates outward and downward.

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Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

Section: Western and Eastern Alpsmentioning

confidence: 99%

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Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Pfiffner¹

2017

Preprint

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“…[33][34][35][36][37] argue that faults within crystalline basement become weak because of reaction softening: phyllosilicate-rich mylonites (phyllonites) form from the mechanical breakdown of feldspars, which is followed by a chemical breakdown in the presence of a fluid, or grain-size reduction allowing grain-boundary sliding. [38] report that the crystalline basement in the external parts of the Western Alps deformed in a brittle-ductile regime with distributed shear within spaced shear zones or shear bands that are up to a few hundred meters thick. The focusing of deformation into distinct shear zones, in which phyllonite formation is observed [38], corresponds to an overall weakening of the basement blocks.…”

Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

“…[38] report that the crystalline basement in the external parts of the Western Alps deformed in a brittle-ductile regime with distributed shear within spaced shear zones or shear bands that are up to a few hundred meters thick. The focusing of deformation into distinct shear zones, in which phyllonite formation is observed [38], corresponds to an overall weakening of the basement blocks. [39] discuss how thrust faults may propagate through crystalline basement by deformation ahead of a propagating fault tip.…”

Section: Mechanical Aspects Of Thrust Faultsmentioning

confidence: 99%

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Pfiffner¹

2017

Preprint

View full text Add to dashboard Cite

This paper gives an overview of the large-scale tectonic styles encountered in orogens worldwide. Thin-skinned and thick-skinned tectonics represent two end member styles recognized in mountain ranges. Both styles are encountered in former passive margins of continental plates. Thick-skinned style including the entire crust and possibly the lithospheric mantle are associated with intracontinental contraction. Delamination of subducting continental crust and horizontal protrusion of upper plate crust into the opening gap occurs in the terminal stage of continent-continent collision. Continental crust thinned prior to contraction is likely to develop relatively thin thrust sheets of crystalline basement. A true thin-skinned type requires a detachment layer of sufficient thickness. Thickness of the décollement layer as well as the mechanical contrast between décollement layer and detached cover control the style of folding and thrusting within the detached cover units. In subduction-related orogens, thin-and thick-skinned deformation may occur several hundreds of kilometers from the plate contact zone. Basin inversion resulting from horizontal contraction may lead to the formation of basement uplifts by the combined reactivation of pre-existing normal faults and initiation of new reverse faults. In most orogens thick-skinned and thin-skinned structures both occur and evolve with a pattern where nappe stacking propagates outward and downward.

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Basement shear zones development and shortening kinematics in the Ecrins Massif, Western Alps

et al. 2014

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In the Western Alps, Oligocene shortening affected a highly heterogeneous European crust with Liassic half-grabens inherited from the rifting stage and the finite deformation was strongly partitioned between the rigid basement and the weak Jurassic sediments. In the Ecrins Massif (Oisans, external crystalline massifs), where the half-grabens are best exposed and preserved, compressional structures within the basement have to date never been described in details. This massif was shortened under moderate metamorphic conditions (250-350°C and 0.1-0.5 GPa), and the rheological contrast between the basement and the cover is strong. While the sediments are intensely folded, the cover-basement interface presents apparent open folds underlined by the Lower Triassic layers. The basement itself shows a more localized deformation along several brittle-ductile shear zones. We here report new evidences of such brittle-ductile shear zones characterized by anastomosed phyllonitic shear bands rich in phengite and quartz, a low-strength material where strain has localized. New detailed maps of reverse shear zones, faults, schistosity, and stretching lineations in both the cover and the basement are provided. We show that the Oligocene crustal shortening was mainly E-W to ENE-WSW. Local N-S to NW-SE shortening occurred and was limited to the eastern border of the Ecrins Massif, around the Penninic Frontal Thrust, which likely was a sinistral transpressive structure in this area. Finally, new balanced cross sections show that these basement shear zones have accommodated more than 50% of the Oligocene crustal shortening.

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Mechanisms of margin inversion in the external Western Alps: Implications for crustal rheology

Cited by 79 publications

References 75 publications

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective

Basement shear zones development and shortening kinematics in the Ecrins Massif, Western Alps

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