Can crustal extension be distinguished from thrusting in the internal parts of mountain belts? A case history of the Entrelor shear zone, Western Alps

Butler, Robert W.; Freeman, S. R.

doi:10.1016/0191-8141(96)00005-3

Cited by 38 publications

(37 citation statements)

References 27 publications

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“…Hence this direction could be compatible with the classical postulate of back-thrusting towards the ESE, (i.e. Butler & Freeman 1996). However no stretching lineations or shear zones connected to D3 where observed and large-scale observations, discussed below, do in fact indicate top-WNW transport during D3.…”

Section: Transport Directions Associated With D3supporting

confidence: 67%

“…3d). The transport direction, including that observed along the contact referred to as "Entrelor tectonic contact" or "Entrelor shear zone" (Butler & Freeman 1996), is consistently top-W-NW, as is indicated by shear bands and asymmetric porphyroclasts ( Fig. 7a-f).…”

Section: D2 Structuresmentioning

confidence: 99%

“…This overturned D2-thrust of the P-L oceanic unit over the Internal zone ("Entrelor tectonic contact"; Bucher et al 2003) can be followed along strike to the NW and into the area around the Col d' Entrelor. As discussed in Bucher et al (2003) the observed top-W-NW sense of shear along this overturned thrust excludes back-thrusting along this contact, referred to as "Entrelor shear zone" by Butler & Freeman (1996) and interpreted as a backthrust by these same authors, in spite of clear evidence for top-W-shearing (Caby 1996).…”

Section: Combined Cross Sections D-d'' and E-e'mentioning

confidence: 99%

“…It is classically explained by outward directed displacement, followed by inward directed back-thrusting (Butler & Freeman 1996). However, Caby (1996) already stated that the kinematics along the various tectonic contacts only show evidence for outward directed displacement.…”

Section: Introductionmentioning

confidence: 99%

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Tectonic evolution of the Briançonnais units along a transect (ECORS-CROP) through the Italian-French Western Alps

Bucher¹,

Ulardic

Bousquet³

et al. 2004

Eclogae geol. Helv.

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Based on new structural data from an area in the Italian-French Western Alps, situated between the Petit Saint Bernard pass and the Gran Paradiso massif, the large-scale geometry of the tectonic features is established for the tectonic units derived from the Briançonnais paleogeographic domain. Based on this, and other new data on the metamorphic evolution and geochronology of the area, a consistent model for the tectonic evolution for the Briançonnais domain is proposed. A nappe stack consisting of, from bottom to top, Zone Houillère unit, Ruitor unit, Internal unit and Piemont-Ligurian oceanic unit, was affected by three deformation phases. The third phase of deformation (35-31 Ma), referred to as post-nappe folding, is responsible for the formation of two large-scale folds: the Ruitor and Valsavaranche mega-folds. An overturned nappe stack, characterized by foreland-dipping foliations, is found between the axial planes of these two mega-folds. No evidence was found for back-thrusting, postulated by many previous authors. The individual thrusts between the tectonic units were active during a second phase of deformation (43-35 Ma), characterized by top-NW to -NNW shearing. This D2 is related to nappe stacking and accompanied by substantial exhumation. Thrusting becomes relatively younger towards the external parts of the study area. We emphasize that extension played no significant role in the exhumation of the highpressure units of the Italian-French Alps. The contacts between the tectonic units were already active during the first phase of deformation (50-43 Ma), which is related to subduction and peak pressures.

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Section: Transport Directions Associated With D3supporting

confidence: 67%

Section: D2 Structuresmentioning

confidence: 99%

Section: Combined Cross Sections D-d'' and E-e'mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tectonic evolution of the Briançonnais units along a transect (ECORS-CROP) through the Italian-French Western Alps

Bucher¹,

Ulardic

Bousquet³

et al. 2004

Eclogae geol. Helv.

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“…This was followed by later backfolding and backthrusting at the exhuming nappe front (e.g. Butler and Freeman, 1996) and vertical ductile thinning (Ring and Kassem, 2007) (Figure 11b). The extrusion wedge model has been shown as a viable exhumation mechanism for high-pressure rocks in the Aegean Sea region and the Tauern Window of the Eastern Alps (Ring et al, 2007a;Ring et al, 2007b;Ring and Glodny, 2010).…”

Section: Exhumation Of the Gran Paradiso Massifmentioning

confidence: 99%

Dating deformation in the Gran Paradiso Massif (NW Italian Alps): Implications for the exhumation of high-pressure rocks in a collisional belt

Rosenbaum

Menegon

Glodny

et al. 2012

Lithos

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The Gran Paradiso massif, situated in the internal part of the Western Italian Alps, records a complex tectono-metamorphic history involving high-pressure metamorphism and subsequent exhumation during retrograde metamorphism. The exact timing of deformation and, consequently, the geodynamic evolution of this part of the Western Alps is still debated and is addressed here by the application of Rb/Sr geochronology, 40 Ar/ 39 Ar step heating and 40 Ar/ 39 Ar total fusion dating techniques. forming an extruding wedge. The kinematics associated with this wedge involved topto-W shearing within the Gran Paradiso nappe (e.g. Pont area shear zones) and top-to-E shearing at the top of the extruding wedge (e.g. Orco shear zone). Subsequent deformation (after ~34 Ma) was characterised by coaxial strain involving orogenicscale backfolding and backthrusting.

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The mode of deformation in the orogenic mid‐crust revealed by seismic attribute analysis

Torvela

Moreau

Butler

et al. 2013

Geochem Geophys Geosyst

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[1] The processes and the structures within the middle and the lower crust are intimately related to the evolution of orogenies, but more detailed knowledge is needed of these deep crustal processes. Seismic reflection data, chiefly displayed in amplitude, are commonly used to interpret deep crustal structures. The strongest amplitude events are probably related to lithological changes and do not necessarily correspond to geological structures, tectonic boundaries, or deformation fabrics. Furthermore, the detailed structures and the strain distribution between the interpreted structural boundaries remain obscure. Here, we show an example of how seismic attributes, combined with the seismic facies interpretation technique, can be used to enhance 2D seismic reflection data from the Palaeoproterozoic Svecofennian crust of southern Finland, to reveal unprecedentedly detailed information about the deformation fabrics within the mid-crust of a collisional orogen. The images are plausibly interpreted to show that the extension/lateral flow of the orogenic middle and lower crust was mainly accommodated by kilometer-scale S-C 0 structures. The structures form penetrative deformation fabrics which are correlated with outcrop observations. The successful enhancement of the seismic data confirms the ductile extension affecting hot orogenic crust, and gives new information about the strain distribution of the regional, syn-to late-orogenic deformation. The seismic attribute method and the seismic facies interpretational approach described in this paper should be applicable to other seismic datasets from the crystalline basement.

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Can crustal extension be distinguished from thrusting in the internal parts of mountain belts? A case history of the Entrelor shear zone, Western Alps

Cited by 38 publications

References 27 publications

Tectonic evolution of the Briançonnais units along a transect (ECORS-CROP) through the Italian-French Western Alps

Tectonic evolution of the Briançonnais units along a transect (ECORS-CROP) through the Italian-French Western Alps

Dating deformation in the Gran Paradiso Massif (NW Italian Alps): Implications for the exhumation of high-pressure rocks in a collisional belt

The mode of deformation in the orogenic mid‐crust revealed by seismic attribute analysis

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