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    • Plusieurs versions

    Metamorphic heterogeneities within a single HP unit: Overprint effect or metamorphic mix?

    Bousquet, Romain
    LITHOS, 2008, Vol.103(1), pp.46-69 [Revue évaluée par les pairs]

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    Anorogenic plateau formation: The importance of density changes in the lithosphere

    Duesterhoeft, Erik, Bousquet, Romain, Wichura, Henry, Oberhänsli, Roland
    Journal of Geophysical Research: Solid Earth, July 2012, Vol.117(B7), pp.n/a-n/a [Revue évaluée par les pairs]

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    3-D assessment of peak-metamorphic conditions by Raman spectroscopy of carbonaceous material: an example from the margin of the Lepontine dome (Swiss Central Alps)

    Wiederkehr, Michael
    Bousquet, Romain, Ziemann, Martin, Berger, Alfons, Schmid, Stefan
    International Journal of Earth Sciences. - 2011/100/5/1029-1063
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    Titre: 3-D assessment of peak-metamorphic conditions by Raman spectroscopy of carbonaceous material: an example from the margin of the Lepontine dome (Swiss Central Alps)
    Auteur: Wiederkehr, Michael
    Contributeur: Bousquet, Romain; Ziemann, Martin; Berger, Alfons; Schmid, Stefan
    Sujet: HP-metamorphism - Barrovian metamorphism - Graphitization - Metasediments - Micro-Raman spectroscopy - Central Alps
    Description: This study monitors regional changes in the crystallinity of carbonaceous matter (CM) by applying Micro-Raman spectroscopy to a total of 214 metasediment samples (largely so-called Bündnerschiefer) dominantly metamorphosed under blueschist- to amphibolite-facies conditions. They were collected within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across refolded nappe contacts, both along and across strike within the northeastern margin of the Lepontine dome and adjacent areas. Further to the northeast, the isotemperature contours reflect temperatures reached during the Late Eocene subduction-related blueschist-facies event and/or during subsequent near-isothermal decompression; these contours appear folded by younger, large-scale post-nappe-stacking folds. A substantial jump in the recorded maximum temperatures across the tectonic contact between the frontal Adula nappe complex and surrounding metasediments indicates that this contact accommodated differential tectonic movement of the Adula nappe with respect to the enveloping Bündnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene time
    Publication en relation: International Journal of Earth Sciences. - 2011/100/5/1029-1063
    Document hôte: International Journal of Earth Sciences
    Identifiant: 10.1007/s00531-010-0622-2 (DOI)

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    Titre: From subduction to collision: Thermal overprint of HP/LT meta-sediments in the north-eastern Lepontine Dome (Swiss Alps) and consequences regarding the tectono-metamorphic evolution of the Alpine orogenic wedge
    Auteur: Wiederkehr, Michael
    Contributeur: Bousquet, Romain; Schmid, Stefan; Berger, Alfons
    Sujet: Lepontine dome - meta-sediments - Fe-Mg carpholite - Barrovian metamorphism - high-pressure metamorphism - Alpine tectonics
    Description: The Cenozoic-age metamorphic structure of the Alps consists of a throughgoing pressure-dominated belt (blueschists and eclogites) that strikes parallel to the orogen and was later truncated by two thermal domes characterised by Barrow-type metamorphism (Lepontine dome and Tauern window). This study documents for the first time that relics of Fe-Mg carpholite occur also within meta-sedimentary units that are part of the north-eastern Lepontine structural and metamorphic dome, where so far exclusively Barrovian assemblages were found. They occur in meta-sediments of both Valais Oceanderived Lower Penninic Bündnerschiefer and structurally lower Europe-derived Sub-Penninic cover nappes and slices. These high-pressure units were subsequently overprinted by a thermal event, as is documented by the growth of new minerals typical for Barrovian metamorphism. We present evidence for a two-stage metamorphic evolution in the northern part of the Lepontine dome: (1) Early subduction-related syn-D1 (Safien phase) HP/LT metamorphism under blueschist facies conditions (350-400°C and 1.2-1.4 GPa) was immediately followed by "cold” isothermal (or cooling) decompression during D2 nappe-stacking (Ferrera phase). (2) Collisionrelated Barrovian overprint (500-570°C and 0.5-0.8 GPa) postdates the D3 nappe-refolding event (Domleschg phase) and represents a late heating pulse, separated by D2 and D3 from the D1 high-pressure event. It occurred before and/or during the initial stages of D4 (Chiéra phase) representing a second nappe-refolding event. In discussing possible heat sources for the late Barrow-type heating pulse it is argued that heat release from radioactive decay of accreted material may play an important role in contributing much to heat production. Based on the field evidence, we conclude that heat transfer was essentially conductive during these latest stages of the thermal evolution
    Publication en relation: Swiss Journal of Geosciences. - 2008/101//127-155
    Document hôte: Swiss Journal of Geosciences
    Identifiant: 10.1007/s00015-008-1289-6 (DOI)

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    Dating Polygenetic Metamorphic Assemblages along a Transect across the Western Alps

    Villa, Igor M
    Bucher, Stefan, Bousquet, Romain, Kleinhanns, Ilka C, Schmid, Stefan M
    Journal of Petrology. - 2014/55/4/803-830
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    Titre: Dating Polygenetic Metamorphic Assemblages along a Transect across the Western Alps
    Auteur: Villa, Igor M
    Contributeur: Bucher, Stefan; Bousquet, Romain; Kleinhanns, Ilka C; Schmid, Stefan M
    Sujet: Original Papers - 39Ar-40Ar geochronology - Ar diffusion - eclogite dating - retrograde reaction dating - Western Alps
    Description: Multichronometric analyses were performed on samples from a transect in the French-Italian Western Alps crossing nappes derived from the Briançonnais terrane and the Piemonte-Liguria Ocean, in an endeavour to date both high-pressure (HP) metamorphism and retrogression history. Twelve samples of white mica were analysed by 39Ar-40Ar stepwise heating, complemented by two samples from the Monte Rosa nappe 100 km to the NE and also attributed to the Briançonnais terrane. One Sm-Nd and three Lu-Hf garnet ages from eclogites were also obtained. White mica ages decrease from c. 300 Ma in the westernmost samples (Zone Houillère), reaching c. 300°C during Alpine metamorphism, to 6·45 atoms per formula unit increases eastward. Across the whole traverse, phengitic mica grown during HP metamorphism defines the D1 foliation. Syn-D2 mica is more Si-poor and associated with nappe stacking, exhumation, and hydrous retrogression under greenschist-facies conditions. Syn-D1 phengite is very often corroded, overgrown by, or intergrown with, syn-D2 muscovite. Most importantly, syn-D2 recrystallization is not limited to S2 schistosity domains; micrometre-scale chemical fingerprinting reveals muscovite pseudomorphs after phengite crystals, which could be mistaken for syn-D1 mica based on microstructural arguments alone. The Cl/K ratio in white mica is a useful discriminator, as D2 retrogression was associated with a less saline fluid than eclogitization. As petrology exerts the main control on the isotope record, constraining the petrological and microstructural framework is necessary to correctly interpret the geochronological data, described in both the present study and the literature. Our approach, which ties geochronology to detailed geochemical, petrological and microstructural investigations, identifies 47-48 Ma as the age of HP formation of syn-D1 mica along the studied transect and in the Monte Rosa area. Cretaceous apparent mica ages, which were proposed to date eclogitization by earlier studies based on conventional ‘thermochronology', are due to Ar inheritance in incompletely recrystallized detrital mica grains. The inferred age of the probably locally diachronous, greenschist-facies, low-Si, syn-D2 mica ranges from 39 to 43 Ma. Coexistence of D1 and D2 ages, and the constancy of non-reset D1 ages along the entire transect, provides strong evidence that the D1 white mica ages closely approximate formation ages. Volume diffusion of Ar in white mica (activation energy E = 250 kJ mol−1; pressure-adjusted diffusion coefficient D'0 < 0·03 cm2 s−1) has a subordinate effect on mineral ages compared with both prograde and retrograde recrystallization in most samples
    Publication en relation: Journal of Petrology. - 2014/55/4/803-830
    Document hôte: Journal of Petrology
    Identifiant: 10.1093/petrology/egu007 (DOI)

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    Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps

    Negro, François
    Bousquet, Romain, Vils, Flurin, Pellet, Clara-Marine, Hänggi-Schaub, Jeanette
    Swiss Journal of Geosciences. - 2013/106/1/63-78
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    Titre: Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps
    Auteur: Negro, François
    Contributeur: Bousquet, Romain; Vils, Flurin; Pellet, Clara-Marine; Hänggi-Schaub, Jeanette
    Sujet: RSCM thermometry - Zermatt-Saas - Combin - Cignana - HP and UHP metamorphism
    Description: In the Western Alps, the Piemont-Ligurian oceanic domain records blueschist to eclogite metamorphic conditions during the Alpine orogeny. This domain is classically divided into two "zones” (Combin and Zermatt-Saas), with contrasting metamorphic evolution, and separated tectonically by the Combin fault. This study presents new metamorphic and temperature (RSCM thermometry) data obtained in Piemont-Ligurian metasediments and proposes a reevaluation of the P-T evolution of this domain. In the upper unit (or "Combin zone”) temperatures are in the range of 420-530°C, with an increase of temperature from upper to lower structural levels. Petrological evidences show that these temperatures are related to the retrograde path and to deformation at greenschist metamorphic conditions. This highlights heating during exhumation of HP metamorphic rocks. In the lower unit (or "Zermatt-Saas zone”), temperatures are very homogeneous in the range of 500-540°C. This shows almost continuous downward temperature increase in the Piemont-Ligurian domain. The observed thermal structure is interpreted as the result of the upper and lower unit juxtaposition along shear zones at a temperature of ~500°C during the Middle Eocene. This juxtaposition probably occurred at shallow crustal levels (~15-20km) within a subduction channel. We finally propose that the Piemont-Ligurian Domain should not be viewed as two distinct "zones”, but rather as a stack of several tectonic slices
    Publication en relation: Swiss Journal of Geosciences. - 2013/106/1/63-78
    Document hôte: Swiss Journal of Geosciences
    Identifiant: 10.1007/s00015-013-0119-7 (DOI)

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    Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps

    Negro, François
    Bousquet, Romain, Vils, Flurin, Pellet, Clara-Marine, Hänggi-Schaub, Jeanette
    Swiss Journal of Geosciences. - 2013/106/1/63-78
    Disponible
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    Titre: Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps
    Auteur: Negro, François
    Contributeur: Bousquet, Romain; Vils, Flurin; Pellet, Clara-Marine; Hänggi-Schaub, Jeanette
    Sujet: RSCM thermometry - Zermatt-Saas - Combin - Cignana - HP and UHP metamorphism
    Description: In the Western Alps, the Piemont-Ligurian oceanic domain records blueschist to eclogite metamorphic conditions during the Alpine orogeny. This domain is classically divided into two “zones” (Combin and Zermatt-Saas), with contrasting metamorphic evolution, and separated tectonically by the Combin fault. This study presents new metamorphic and temperature (RSCM thermometry) data obtained in Piemont-Ligurian metasediments and proposes a reevaluation of the P–T evolution of this domain. In the upper unit (or “Combin zone”) temperatures are in the range of 420–530 °C, with an increase of temperature from upper to lower structural levels. Petrological evidences show that these temperatures are related to the retrograde path and to deformation at greenschist metamorphic conditions. This highlights heating during exhumation of HP metamorphic rocks. In the lower unit (or “Zermatt-Saas zone”), temperatures are very homogeneous in the range of 500–540 °C. This shows almost continuous downward temperature increase in the Piemont-Ligurian domain. The observed thermal structure is interpreted as the result of the upper and lower unit juxtaposition along shear zones at a temperature of ~500 °C during the Middle Eocene. This juxtaposition probably occurred at shallow crustal levels (~15–20 km) within a subduction channel. We finally propose that the Piemont-Ligurian Domain should not be viewed as two distinct “zones”, but rather as a stack of several tectonic slices.
    Publication en relation: Swiss Journal of Geosciences. - 2013/106/1/63-78
    Document hôte: Swiss Journal of Geosciences
    Identifiant: 10.1007/s00015-013-0119-7 (DOI)

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    The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps

    Loprieno, Andrea
    Bousquet, Romain, Bucher, Stefan, Ceriani, Stefano, Dalla Torre, Florian, Fügenschuh, Bernhard, Schmid, Stefan
    International Journal of Earth Sciences. - 2011/100/5/963-992
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    Titre: The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps
    Auteur: Loprieno, Andrea
    Contributeur: Bousquet, Romain; Bucher, Stefan; Ceriani, Stefano; Dalla Torre, Florian; Fügenschuh, Bernhard; Schmid, Stefan
    Sujet: Alpine geology - Valais ocean - Palaeogeography - Structural geology - Tectonics - Metamorphism
    Description: The Valais units in Savoy (Zone des Brèches de Tarentaise) have been re-mapped in great detail and are subject of combined stratigraphic, structural and petrological investigations summarized in this contribution. The sediments and rare relics of basement, together with Cretaceous age mafic and ultramafic rocks of the Valais palaeogeographical domain, represent the heavily deformed relics of the former distal European margin (External Valais units) and an ocean-continent transition (Internal Valais unit or Versoyen unit) that formed during rifting. This rifting led to the opening of the Valais ocean, a northern branch of the Alpine Tethys. Post-rift sediments referred to as "Valais trilogy” stratigraphically overlie both External and Internal Valais successions above an angular unconformity formed in Barremian to Aptian times, providing robust evidence for the timing of the opening of the Valais ocean. The Valais units in Savoy are part of a second and more external mid-Eocene high-pressure belt in the Alps that sutured the Briançonnais microcontinent to Europe. Top-N D1-deformation led to the formation of a nappe stack that emplaced the largely eclogite-facies Internal Valais unit (Versoyen) onto blueschist-facies External Valais units. The latter originally consisted of, from internal to external, the Petit St. Bernard unit, the Roc de l'Enfer unit, the Moûtiers unit and the Quermoz unit. Ongoing top-N D2-thrusting and folding substantially modified this nappe stack. Post 35Ma D3 folding led to relatively minor modifications of the nappe stack within the Valais units but was associated with substantial top-WNW thrusting of the Valais units over the Dauphinois units along the Roselend thrust during W-directed indentation of the Adria block contributing to the formation of the arc of the Western Alps
    Publication en relation: International Journal of Earth Sciences. - 2011/100/5/963-992
    Document hôte: International Journal of Earth Sciences
    Identifiant: 10.1007/s00531-010-0595-1 (DOI)

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    Géosciences : la dynamique du système Terre

    Robert, Christian, 1947-
    Bousquet, Romain
    Paris : Belin
    2013
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    Titre: Géosciences : la dynamique du système Terre / Christian Robert, Romain Bousquet
    Auteur: Robert, Christian, 1947-
    Contributeur: Bousquet, Romain
    Editeur: Paris : Belin
    Date: 2013
    Collation: 1159 p. : ill.
    Sujet RERO: Sciences de la Terre - Géologie - Géophysique - Pétrologie - Sédimentologie - Cosmologie - Tectonique
    Classification: LC QE26.2
    Identifiant: 9782701138169 (ISBN); http://catalogue.bnf.fr/ark:/12148/cb43644075m (URN)
    No RERO: R007344183
    Permalien:
    http://data.rero.ch/01-R007344183/html?view=FR_V1

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    Emplacement of the mid-Miocene Yatta lava flow, Kenya: Implications for modelling long channelled lava flows

    Wichura, Henry, Bousquet, Romain, Oberhänsli, Roland
    Journal of Volcanology and Geothermal Research, 12/2010, Vol.198(3-4), pp.325-338 [Revue évaluée par les pairs]
    Elsevier (via CrossRef)
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    Titre: Emplacement of the mid-Miocene Yatta lava flow, Kenya: Implications for modelling long channelled lava flows
    Auteur: Wichura, Henry; Bousquet, Romain; Oberhänsli, Roland
    Sujet: Modelling Long Channelled Lava Flows;
    Description: The emplacement of the 13.51 m.y. old Yatta lava flow in Kenya has been investigated using evidence from field observations combined with a novel method of modelling length-dominated lava flows along channels. The Yatta lava erupted as an individual flow from a single vent on the eastern rim of the present-day East African Plateau during the extensive volcanism that occurred in mid-Miocene times. It then followed an old river valley for nearly 300 km, thus forming one of the longest phonolitic lava flows on Earth. For our modelling we combined a composition and temperature dependent viscosity equation with empirical cooling and morphological relationships. By using an average channel width and the known length of the Yatta lava flow but varying the mean thickness and underlying topography, we have improved flow rate calculations for the internal part of the lava, close to the front of the lava flow. Within this zone the lava's motion was treated as steady, uniform, and laminar, following a stepwise cooling from the eruption temperature to the temperature at the cessation of flow. Comparison of eight different compositions ranging from basaltic to rhyolitic has revealed that the length-dominated Yatta lava flow emplacement was rapid (~ 7 days), approximately isothermal (cooling at 0.71 °C/km), and the result of high effusion rates (~ 7900 m 3/s). This study shows that morphology of a lava flow, and in particular its length, is not a simple function of rheological properties and effusion rate, but is also affected by many other parameters. Small changes in H 2O compounds in the lava chemistry can affect melt viscosity significantly and thus lava flow morphology. Therefore H 2O content, together with slope angle and the mean lava flow thickness, ultimately control the length of a lava flow within a channel. Research Highlights ► Deriving lava flow morphology from rheology and vice versa. ► Modelling lava flow viscosities and velocities as a function of T and X. ► High effusion rates facilitate the formation of long channelled lava flows. ► Laminar flow and isothermal conditions enable rapid lava flow emplacement.
    Fait partie de: Journal of Volcanology and Geothermal Research, 12/2010, Vol.198(3-4), pp.325-338
    Identifiant: 03770273 (ISSN); http (DOI)