Deformation history of a subducted continental crust (Gran Paradiso, Western Alps): continuing crustal shortening during exhumation

Bayon, Benjamin Le; Ballèvre, Michel

doi:10.1016/j.jsg.2006.02.009

Cited by 61 publications

(43 citation statements)

References 64 publications

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“…Last, in the continent‐derived internal crystalline massifs, RSCM T is ∼540 °C in the Pinerolo unit, which is very similar to peak T estimated in the equivalent Money unit to the N in the Grand Paradis massif (Le Bayon and Ballèvre, 2006). Pristine graphite is observed in the Brossasco ultra‐high pressure unit, implying a peak metamorphic T higher than 650 °C (Beyssac et al.…”

Section: Resultssupporting

confidence: 70%

Thermal structure of a fossil subduction wedge in the Western Alps

et al. 2009

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New peak metamorphic temperatures are obtained by Raman spectroscopy of Carbonaceous Material to document the thermal structure of the central Western Alps with high sampling resolution. We show that peak metamorphic T gradually increases eastward from <330 to 350 °C (ultra‐Dauphinois to subbriançonnais units), ∼350 to more than 400 °C (Briançonnais domain including the Zone Houillère where metamorphic index minerals are rare) and from 350 to more than 500 °C (Liguro–Piemontese domain). Combined with other constraints on the metamorphic evolution, this dataset reveals a good preservation of the overall thermal structure of the fossil subduction wedge, with no particular thermal overprint during collision. However, local confrontation with P–T estimates and radiometric ages reveals more subtle variations within tectonic units and across the main contacts that are linked to the past activity of the major thrusts and extensional shear zones during subduction and exhumation.

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Section: Resultssupporting

confidence: 70%

Thermal structure of a fossil subduction wedge in the Western Alps

et al. 2009

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“…In the part of the Penninic Zone comprising the former Briançonnais microcontinent, a pre‐Triassic basement is present (i) in the external (frontal) part (Zone Houillère) (Figure ), where Carboniferous and Permian sediments are unconformably covered by the Triassic to Eocene sediments (Lemoine et al, ), (ii) as basement slices in more internal units (Acceglio, Ambin, Vanoise, and Grand Saint‐Bernard) having suffered a blueschist‐facies deformation of Eocene age (Ganne et al, ), and (iii) as folded basement nappes (Monte Rosa, Gran Paradiso, and Dora‐Maira) having suffered an early eclogite‐facies deformation, and thrusted at a later stage onto lower‐pressure units, exposed in the Money and Pinerolo windows (Figure ) (Le Bayon & Ballèvre, ; Manzotti, Poujol, & Ballèvre, , Manzotti et al, ). Due to the pervasive and polyphased Alpine deformation, undeformed volumes are relatively modest in size and allow only limited deductions about the large‐scale structure of the Paleozoic basement.…”

Section: Geological Settingmentioning

confidence: 99%

Pre‐Alpine (Variscan) Inheritance: A Key for the Location of the Future Valaisan Basin (Western Alps)

2018

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The boundary between the Helvetic and the Penninic (=Briançonnais) Zones has long been recognized as a major fault (“Penninic Front”) in the Western Alps. A narrow oceanic domain has been postulated at least along part of this boundary (the Valaisan Basin). However, the information provided by the pre‐Triassic basement has not been fully exploited and will be discussed here in detail. The igneous and metamorphic history of the pre‐Triassic basement shows significant differences between the External Massifs from the Helvetic Zone, with abundant Late Carboniferous granites, and the basement of the Briançonnais Zone, including the Internal Massifs (Dora‐Maira, Gran Paradiso, and Monte Rosa), devoid of Carboniferous granites. A major coal‐bearing basin, the “Zone Houillère,” opened along this boundary. This limnic intramontane basin has never been properly investigated. The Zone Houillère is not comparable with the external, paralic, flexural, basins on both sides of the Variscan belt but shows similarities with the Saar‐Saale Basin. Like the latter, we interpret the Zone Houillère as a transtensional basin opened along a major, crustal‐scale, fault zone, namely, the East Variscan Shear Zone. The Permian magmatism and sedimentation displays contrasting distributions, being absent or very localized in the Helvetic Zone, and widespread in the Penninic Zone. The above data indicate that the structural inheritance from the Variscan belt plays a major role in defining the future location of the Valaisan Basin, that is, the boundary between the European paleomargin and the Briançonnais microcontinent.

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“…Farther south, greenschist‐facies top‐to‐W extension is documented on top of the eclogitic ophiolites exposed west of the Dora‐Maira unit [ Agard et al ., ], and in the Queyras calcschists on top of the Viso ophiolites [ Ballèvre et al ., ; Schwartz et al ., ]. Extension in the Eclogite belt is associated with a regular pattern of stretching lineations perpendicular to the orogen trend, observed within extensional shear zones both in the Internal Massifs [ Wheeler , ; Brouwer et al ., ; Pleuger et al ., ; Le Bayon and Ballèvre , ] and in their ophiolitic envelopes [ Philippot , ; Inger and Ramsbotham , ; Reddy et al ., ; Gasco et al ., , ], which is fully consistent with the trend observed in the overlying Cretaceous wedge [ Gasco et al ., ]. On the northern tip of the Eclogite belt, close to the Lepontine dome, late tectonic shortening overprinted extensional shearing after (U)HP exhumation, thus shaping regional‐scale Adria‐vergent folds such as the Vanzone antiform, located NE of the Monte Rosa Massif [ Keller et al ., ].…”

Section: Exhumation Triggered By Motion Of the Upper Plate: The Westementioning

confidence: 99%

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Malusà

Faccenna

Baldwin

et al. 2015

Geochem Geophys Geosyst

118

145

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Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary.

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Deformation history of a subducted continental crust (Gran Paradiso, Western Alps): continuing crustal shortening during exhumation

Cited by 61 publications

References 64 publications

Thermal structure of a fossil subduction wedge in the Western Alps

Thermal structure of a fossil subduction wedge in the Western Alps

Pre‐Alpine (Variscan) Inheritance: A Key for the Location of the Future Valaisan Basin (Western Alps)

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

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