TY - JOUR A1 - Loprieno, Andrea A1 - Bousquet, Romain A1 - Bucher, Stefan A1 - Ceriani, Stefano A1 - Dalla Torre, Florian H. A1 - Fügenschuh, Bernhard A1 - Schmid, Stefan M. T1 - The valais units in Savoy (France) a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps JF - International journal of earth sciences N2 - The Valais units in Savoy (Zone des BrSches 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 Brian double dagger onnais 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 MoA >> tiers unit and the Quermoz unit. Ongoing top-N D2-thrusting and folding substantially modified this nappe stack. Post 35 Ma 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. KW - Alpine geology KW - Valais ocean KW - Palaeogeography KW - Structural geology KW - Tectonics KW - Metamorphism Y1 - 2011 U6 - https://doi.org/10.1007/s00531-010-0595-1 SN - 1437-3254 VL - 100 IS - 5 SP - 963 EP - 992 PB - Springer CY - New York ER - TY - JOUR A1 - Wiederkehr, Michael A1 - Bousquet, Romain A1 - Ziemann, Martin Andreas A1 - Berger, Alfons A1 - Schmid, Stefan M. T1 - 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) JF - International journal of earth sciences N2 - 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 Bundnerschiefer) 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 Bundnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene time. KW - HP-metamorphism KW - Barrovian metamorphism KW - Graphitization KW - Metasediments KW - Micro-Raman spectroscopy KW - Central Alps Y1 - 2011 U6 - https://doi.org/10.1007/s00531-010-0622-2 SN - 1437-3254 VL - 100 IS - 5 SP - 1029 EP - 1063 PB - Springer CY - New York ER - TY - JOUR A1 - Berger, Alfons A1 - Schmid, Stefan M. A1 - Engi, Martin A1 - Bousquet, Romain A1 - Wiederkehr, Michael T1 - Mechanisms of mass and heat transport during Barrovian metamorphism: A discussion based on field evidence from the Central Alps (Switzerland/northern Italy) JF - Tectonics N2 - Tectonic and metamorphic data for the Central Alps (Switzerland/Italy) are used to discuss this classic example of a Barrovian metamorphic terrain, notably the evolution of its thermal structure in space and time. Available P-T-t data indicate variable contributions of advective and conductive heat transport during collision and subsequent cooling and exhumation. Some areas experienced a prolonged period of partial melting while other areas, at the same time, show but moderate heating. The Barrow-type metamorphic field gradient observed in the final orogen is the result of two distinct tectonic processes, with their related advective and conductive heat transport processes. The two tectonic processes are (1) accretion of material within a subduction channel related to decompression and emplacement of high-pressure units in the middle crust and (2) wedging and related nappe formation in the continental lower plate. The second process postdates the first one. Wedging and underthrusting of continental lower plate material produces heat input into lower crustal levels, and this process is responsible for predominantly conductive heat transport in the overlying units. The interacting processes lead to different maximum temperatures at different times, producing the final Barrovian metamorphic field gradient. The south experienced rapid cooling, whereas the north shows moderate cooling rates. This discrepancy principally reflects differences in the temperature distribution in the deeper crust prior to cooling. Differences in the local thermal gradient that prevailed before the cooling also determined the relationships between cooling rate and exhumation rate in the different areas. Citation: Berger, A., S. M. Schmid, M. Engi, R. Bousquet, and M. Wiederkehr (2011), Mechanisms of mass and heat transport during Barrovian metamorphism: A discussion based on field evidence from the Central Alps (Switzerland/northern Italy), Tectonics, 30, TC1007, doi:10.1029/2009TC002622. Y1 - 2011 U6 - https://doi.org/10.1029/2009TC002622 SN - 0278-7407 VL - 30 IS - 2 PB - American Geophysical Union CY - Washington ER -