Orthogneiss, mylonite and non coaxial deformation of granites: the example of the South Armorican Shear Zone

Berthe, D.; Cartigny, Pierre; Jegouzo, P.

doi:10.1016/0191-8141(79)90019-1

Cited by 1,148 publications

(364 citation statements)

References 13 publications

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“…[14] In the SE region (i.e., regions II and III, Figure 2a), the Monte Leone unit (Figure 1) shows a strong penetrative mylonitic foliation (Figure 2b, regions II and III) with well developed and unequivocal shear criteria indicating a dextral sense (e.g., sheared and boudinaged quartz veins rotated into the foliation plane ( Figure 3a) and shear band or C′ structures [Berthé et al, 1979]). In region II, the foliation strike has an E-W orientation and swings into a WSW-ENE orientation in region III (Figure 2b), where the foliation dips steeply to the SSE (∼60°toward 155°, Figure 2c) and forms part of the Southern Steep Belt [Milnes, 1974].…”

Section: Se Prolongation Of the Simplon Fault Zonementioning

confidence: 99%

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

et al. 2010

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[1] Major low-angle normal faults juxtapose different structural levels of the crust that record both brittle and ductile deformation. Field relationships alone cannot establish whether these different responses to deformation represent (1) parts of a single process of exhumation along the detachment or (2) two separate events, with the later, more discrete brittle detachment exhuming a fossil ductile shear zone from depth. These two general models are critically assessed for the lowangle normal Simplon Fault Zone (SFZ) in the central Alps. The SFZ shows a spatial transition from a broad ductile mylonitic shear zone to a discrete brittle detachment with identical kinematics. The age of the ductile shear zone and ductile-brittle transition is controversial. We present a detailed geochronological study based on fission track, 40 Ar/ 39 Ar, and Rb/Sr microsampling dating, coupled with structural, petrological, and chemical analyses that provides tight constraints on SFZ timing. Discontinuous mineral cooling ages over a broad range of temperatures across the fault zone argue for fault activity between 20 and 3 Ma. On the basis of synkinematic white mica in low-temperature shear zones and necks of foliation boudinage, the brittle-ductile transition in the footwall could be dated at ∼14.5-10 Ma. Overall, the data presented here are consistent with a continuous transition from ductile shearing to a more localized zone of brittle deformation within the same geological framework, over a period of ∼15 Ma. The SFZ is therefore an example of a telescoped crustal section within a single major lowangle fault, involving a continuous period of exhumation rather than a two-stage structure.

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Section: Se Prolongation Of the Simplon Fault Zonementioning

confidence: 99%

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

et al. 2010

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“…This subvertical shear zone has approximately WSW-ENE strike and consists of several branches spreading over hundreds of kilometers from westernmost Brittany to Vendée-Poitou region. The SASZ bears subhorizontal lineation, records right-lateral movement and is associated with development of S-C fabrics (Berthé et al 1979). …”

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

Pressure solution in rocks: focused ion beam/transmission electron microscopy study on orthogneiss from South Armorican Shear Zone, France

Bukovská

Wirth

Morales

2015

Contrib Mineral Petrol

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In order to characterize the µm-to-nm structures related to operation of pressure solution on phase boundaries in naturally deformed rocks, we have performed a detailed focused ion beam/transmission electron microscopy study in ultramylonite samples from South Armorican Shear Zone (France) that focused on grain boundary scale. We have studied phase boundaries between quartz, K-feldspar and white mica both in 2 and 3D and compare our evidences with theoretical dissolution-precipitation models in the current literature. The dissolution (re)precipitation processes lead to the development of different features at different phase boundaries. In both quartz-white mica and quartz-K-feldspar phase boundaries, voids were ubiquitously observed. These voids have different shapes and the development of some of them is crystallographically controlled. In addition, part of these voids might be filled with vermiculite.Amorphous leached layers with kaolinite composition were observed at the boundaries of Kfeldspar-quartz and K-feldspar-white mica. The development of different features along the phase boundaries is mainly controlled by the crystallography of the phases sharing a common interface, together with the presence of fluids that either leaches or directly dissolve the mineral phases. In addition, the local dislocation density in quartz may play an important role during pressure solution.We suggest that the nano-scale observations of the quartz -white mica phase boundaries show direct evidence for operation of island-and-channel model as described in Wassmann and Stöckhert (2013), while K-feldspar -quartz phase boundaries represents amorphous layers formed via interface-coupled dissolution-reprecipitation as described by Hellmann et al. (2012).

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“…On observe aussi une schistosité entraînée le long de micro-cisaillements qui forment une fabrique de type « C-S » compatible avec un mouvement apparent dextre. Dans de telles fabriques, la schistosité « S » se positionne de façon orthogonale à la contrainte principale (ai) et les terminaisons subissent une rotation asymptotique le long des plans de cisaillement « C » dû à la déformation progressive (Berthé et al 1979). La déformation cassante s'exprime par de petites failles fragiles orientées approximativement E-0 qui recoupent des veines sigmoïdales de quartz encaissées dans la bande cisaillée (Figure 2.21b).…”

Section: Cadre Structuralunclassified

Contrôles structuraux de la minéralisation aurifère de la veine Consuelo, Pataz, La Libertad, Pérou /

Tremblay¹

2012

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Orthogneiss, mylonite and non coaxial deformation of granites: the example of the South Armorican Shear Zone

Cited by 1,148 publications

References 13 publications

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

Pressure solution in rocks: focused ion beam/transmission electron microscopy study on orthogneiss from South Armorican Shear Zone, France

Contrôles structuraux de la minéralisation aurifère de la veine Consuelo, Pataz, La Libertad, Pérou /

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