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Articles de revues sur le sujet « Zermatt-Saas Zone »

Auteur : Grafiati
Publié le 9 mars 2023

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1

REBAY, GISELLA, DAVIDE ZANONI, ANTONIO LANGONE, PIETRO LUONI, MASSIMO TIEPOLO et MARIA IOLE SPALLA. « Dating of ultramafic rocks from the Western Alps ophiolites discloses Late Cretaceous subduction ages in the Zermatt-Saas Zone ». Geological Magazine 155, no 2 (3 mai 2017) : 298–315. http://dx.doi.org/10.1017/s0016756817000334.

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AbstractThe Zermatt-Saas Zone was part of the Middle to Late Jurassic Tethyan lithosphere that underwent oceanic metamorphism during Mesozoic time and subduction during Eocene time (HP to UHP metamorphism). In upper Valtournanche, serpentinite, metarodingite and eclogite record a dominant S2 foliation that developed under 2.5±0.3 GPa and 600±20°C during Alpine subduction. Serpentinites contain clinopyroxene and rare zircon porphyroclasts. Clinopyroxene porphyroclasts show fringes within S2 with similar compositions to that of grains defining S2. Zircon cores show zoning typical of magmatic growth and thin fringes parallel to the S2 foliation. These features indicate crystallization of clinopyroxene and zircon fringes during HP syn-D2 metamorphism, related to the Alpine subduction. The U–Pb zircon dates for cores and fringes reveal crystallization at 165±3.2 Ma and 65.5±5.6 Ma, respectively. The Middle Jurassic dates are in agreement with the known ages for the oceanic accretion of the Tethyan lithosphere. The Late Cretaceaous - Paleocene dates suggest that the Zermatt-Saas Zone experienced high-pressure to ultra-high-pressure (HP–UHP) metamorphism at c. 16 Ma earlier than previously reported. This result is in agreement with the evidence that in the Western Alps the continental Sesia-Lanzo Zone reached the subduction climax at least from 70 Ma and was exhumed during ongoing oceanic subduction. Our results are further evidence that the Zermatt-Saas ophiolites diachronically recorded heterogeneous HP–UHP metamorphism.
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BARNICOAT, A. C., et N. FRY. « High-pressure metamorphism of the Zermatt-Saas ophiolite zone, Switzerland ». Journal of the Geological Society 143, no 4 (juillet 1986) : 607–18. http://dx.doi.org/10.1144/gsjgs.143.4.0607.

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Barnicoat, A. C. « Zoned high-pressure assemblages in pillow lavas of the Zermatt-Saas ophiolite zone, Switzerland ». Lithos 21, no 3 (mars 1988) : 227–36. http://dx.doi.org/10.1016/0024-4937(88)90011-4.

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Reinecke, Thomas. « Very-high-pressure metamorphism and uplift of coesite-bearing metasediments from the Zermatt-Saas zone, Western Alps ». European Journal of Mineralogy 3, no 1 (21 février 1991) : 7–18. http://dx.doi.org/10.1127/ejm/3/1/0007.

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Widmer, T. « Local origin of high pressure vein material in eclogite facies rocks of the Zermatt-Saas-Zone, Switzerland ». American Journal of Science 301, no 7 (1 septembre 2001) : 627–56. http://dx.doi.org/10.2475/ajs.301.7.627.

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McNamara, D. D., J. Wheeler, M. Pearce et D. J. Prior. « Fabrics produced mimetically during static metamorphism in retrogressed eclogites from the Zermatt-Saas zone, Western Italian Alps ». Journal of Structural Geology 44 (novembre 2012) : 167–78. http://dx.doi.org/10.1016/j.jsg.2012.08.006.

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Gilio, Mattia, Marco Scambelluri, Samuele Agostini, Marguerite Godard, Daniel Peters et Thomas Pettke. « Petrology and Geochemistry of Serpentinites Associated with the Ultra-High Pressure Lago di Cignana Unit (Italian Western Alps) ». Journal of Petrology 60, no 6 (30 mai 2019) : 1229–62. http://dx.doi.org/10.1093/petrology/egz030.

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AbstractIn the Western Alps, the ophiolitic Zermatt–Saas Zone (ZSZ) and the Lago di Cignana Unit (LCU) record oceanic lithosphere subduction to high (540°C, 2·3GPa) and ultra-high pressure (600°C, 3·2GPa), respectively. The top of the Zermatt–Saas Zone in contact with the Lago di Cignana Unit consists of olivine + Ti-clinohumite-bearing serpentinites (the Cignana serpentinite) hosting olivine + Ti-clinohumite veins and dykelets of olivine + Ti-chondrodite + Ti-clinohumite. The composition of this serpentinite reveals a refertilized oceanic mantle peridotite protolith that became subsequently enriched in fluid-mobile elements (FME) during oceanic serpentinization. The olivine + Ti-clinohumite veins in the Cignana serpentinite display Rare Earth Element (REE) and FME compositions quite similar to the host-rock, which suggests closed-system dehydration of this serpentinite during subduction. The Ti-chondrodite-bearing dykelets are richer in REE and FME than the host-rock and the dehydration olivine + Ti-clinohumite veins: their Nd composition points to a mafic protolith, successively overprinted by oceanic metasomatism and by subduction zone recrystallization. These dykelets are comparable in composition to eclogites within the ultra-high pressure LCU that derive from subducted oceanic mafic crust. Different from the LCU, serpentinites from the core domains of the ZSZ display REE compositions indicating a depleted mantle protolith. The oceanic serpentinization of these rocks led to an increase in FME and to seawater-like Sr isotope compositions. The serpentinites sampled at increasing distance from the ultra-high pressure LCU reveal different mantle protoliths, still preserve an oceanic geochemical imprint and contain mafic dykelets affected by oceanic metasomatism. The subduction zone history of these rocks thus occurred under relatively closed system conditions, the only possible change during subduction being an enrichment in As and Sb recorded by the serpentinites closer to the crustal LCU. The ZSZ and Cignana serpentinites thus likely evolved in a slab setting and were weakly exposed to interaction with slab-derived fluids characteristic of plate interface settings. Our data suggest two possible scenarios for the evolution of the studied ZSZ and Cignana serpentinites. They are either part of a coherent ophiolite unit whose initial lithospheric mantle was variably affected by depletion and re-fertilization processes, or they belong to separate tectonic slices derived from two different oceanic mantle sections. In the Cignana serpentinite atop the ZSZ, the presence of Ti-chondrodite dykelets similar in composition to the LCU eclogites suggests these two domains were closely associated in the oceanic lithosphere and shared the same evolution to ultra-high pressure conditions during Alpine subduction.
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Bucher, K., et R. Grapes. « The Eclogite-facies Allalin Gabbro of the Zermatt-Saas Ophiolite, Western Alps : a Record of Subduction Zone Hydration ». Journal of Petrology 50, no 8 (7 juillet 2009) : 1405–42. http://dx.doi.org/10.1093/petrology/egp035.

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Reinecke, T. « Prograde high- to ultrahigh-pressure metamorphism and exhumation of oceanic sediments at Lago di Cignana, Zermatt-Saas Zone, western Alps ». Lithos 42, no 3-4 (mars 1998) : 147–89. http://dx.doi.org/10.1016/s0024-4937(97)00041-8.

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Pleuger, Jan, Sybille Roller, Jens M. Walter, Ekkehard Jansen et Nikolaus Froitzheim. « Structural evolution of the contact between two Penninic nappes (Zermatt-Saas zone and Combin zone, Western Alps) and implications for the exhumation mechanism and palaeogeography ». International Journal of Earth Sciences 96, no 2 (12 juillet 2006) : 229–52. http://dx.doi.org/10.1007/s00531-006-0106-6.

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Pleuger, Jan, Sybille Roller, Jens M. Walter, Ekkehard Jansen et Nikolaus Froitzheim. « Structural evolution of the contact between two Penninic nappes (Zermatt-Saas zone and Combin zone, Western Alps) and implications for the exhumation mechanism and palaeogeography ». International Journal of Earth Sciences 96, no 6 (5 juillet 2007) : 1211–12. http://dx.doi.org/10.1007/s00531-007-0197-8.

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Weber, Sebastian, Sascha Sandmann, Irena Miladinova, Raúl O. C. Fonseca, Nikolaus Froitzheim, Carsten Münker et Kurt Bucher. « Dating the initiation of Piemonte-Liguria Ocean subduction : Lu–Hf garnet chronometry of eclogites from the Theodul Glacier Unit (Zermatt-Saas zone, Switzerland) ». Swiss Journal of Geosciences 108, no 2-3 (28 mars 2015) : 183–99. http://dx.doi.org/10.1007/s00015-015-0180-5.

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Angiboust, S., P. Agard, L. Jolivet et O. Beyssac. « The Zermatt-Saas ophiolite : the largest (60-km wide) and deepest (c.70-80 km) continuous slice of oceanic lithosphere detached from a subduction zone ? » Terra Nova 21, no 3 (juin 2009) : 171–80. http://dx.doi.org/10.1111/j.1365-3121.2009.00870.x.

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Cartwright, I., et A. C. Barnicoat. « Petrology, geochronology, and tectonics of shear zones in the Zermatt-Saas and Combin zones of the Western Alps ». Journal of Metamorphic Geology 20, no 2 (12 février 2002) : 263–81. http://dx.doi.org/10.1046/j.0263-4929.2001.00366.x.

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Stoffel, M. « Impacts of climate change on natural hazards and land use in the Saas and Zermatt Valleys (Switzerland) ». Geographica Helvetica 54, no 4 (31 décembre 1999) : 224–28. http://dx.doi.org/10.5194/gh-54-224-1999.

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Abstract. The aim of Swiss land use planning is to guarantee an expedient and economical use ofthe land and an orderly development of the country. Therefore. land use planning has to designate areas suitable for optimal economic development. The possiblility of climate change poses a special challenge for land use planners. This paper examines the implications of environmental change resulting from climate change and anticipates new zones of conflict between existing and future land uses in the Saas and Zermatt Valleys (Valais. Switzerland). Differences between the «reul-time» decisions of planners and the possible development of nsks and changes predicted by scientists are key factors examined in this paper. Furthermore, this paper investigates the legal implications of land use planning under conditions of climatic uncertainty. Particular emphasis is given lo the various ways natural dangers can be taken into account at the levels of the «cantonal» general plan, communal zoning plan and the issueing of building permits. Finally, this paper recommends the establishmenl of «buller areas» or zones of potential high risk as precautionary measures and Highlights the fundamental necessit) of risk communication for natural hazard control.
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Kirst, Frederik, et Bernd Leiss. « Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy) : constraints on the exhumation of Zermatt–Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust ». International Journal of Earth Sciences 106, no 1 (21 mars 2016) : 215–36. http://dx.doi.org/10.1007/s00531-016-1316-1.

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Bucher, Kurt, et Ingrid Stober. « Metamorphic gabbro and basalt in ophiolitic and continental nappes of the Zermatt region (Western Alps) ». Swiss Journal of Geosciences 114, no 1 (12 avril 2021). http://dx.doi.org/10.1186/s00015-021-00390-w.

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AbstractThe composition of meta-gabbro and meta-basalt occurring abundant and widespread in all nappes of the nappe stack exposed in the Zermatt region of the Western Alp shows distinct patterns related to the geodynamic origin of metamorphic basic rocks. Eclogitic meta-basalts of the ophiolitic Zermatt-Saas Unit (ZSU) show enriched MORB signatures. The meta-basalts (eclogites) of the continental fragment of the Theodul Glacier Unit (TGU) derive from pre-Alpine metamorphic continental intraplate basalts. Meta-basalts (eclogites) from the continental basement of the Siviez-Mischabel nappe (SMN) derive from MORB thus a genetic relation to the TGU eclogites can be excluded. All basic igneous rocks experienced post-magmatic alteration by fluid-rock interaction ranging from processes at the seafloor, in the shallow crust, during subduction zone hydration, in the exhumation channel and late Alpine regional metamorphisms. The consequences of these alteration processes can be identified at various levels in the rock composition data. It was found that the REE data are little affected by fluid-rock alteration. Some trace elements, notably Cs, Rb, and Ba are typically massively altered relative to igneous compositions in all three groups of meta-basalts. Generally, meta-basalts from the TGU and the SMN preserved the features of the original composition whilst the ZSU meta-volcanic rocks experienced massive alteration. For the ZSU meta-volcanic rocks it is evident that Zr was gained and Y lost during high-pressure fluid-rock interaction indicating a mobile behavior of the two elements during HP-metamorphism in contrast to their behavior in hydrothermal near-surface fluid-rock interaction.
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Zanoni, Davide, Gisella Rebay, Jacopo Bernardoni et Maria Iole Spalla. « Using multiscale structural analysis to infer high-/ultrahigh-pressure assemblages in subducted rodingites of the Zermatt-Saas Zone at Valtournanche, Italy ». Journal of the Virtual Explorer 41 (2012). http://dx.doi.org/10.3809/jvirtex.2011.00290.

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Bovay, Thomas, Daniela Rubatto et Pierre Lanari. « Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet ». Contributions to Mineralogy and Petrology 176, no 7 (24 juin 2021). http://dx.doi.org/10.1007/s00410-021-01806-4.

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AbstractDehydration reactions in the subducting slab liberate fluids causing major changes in rock density, volume and permeability. Although it is well known that the fluids can migrate and interact with the surrounding rocks, fluid pathways remain challenging to track and the consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive fluid-rock interaction in a sequence of schists and mafic felses exposed in the Theodul Glacier Unit (TGU), Western Alps. This unit is embedded within metaophiolites of the Zermatt-Saas Zone and reached eclogite-facies conditions during Alpine convergence. Chemical mapping and in situ oxygen isotope analyses of garnet from the schists reveal a sharp chemical zoning between a xenomorphic core and a euhedral rim, associated to a drop of ~ 8‰ in δ18O. Thermodynamic and δ18O models show that the large amount of low δ18O H2O required to change the reactive bulk δ18O composition cannot be produced by dehydration of the mafic fels from the TGU only, and requires a large contribution of the surrounding serpentinites. The calculated time-integrated fluid flux across the TGU rocks is 1.1 × 105 cm3/cm2, which is above the open-system behaviour threshold and argues for pervasive fluid flow at kilometre-scale under high-pressure conditions. The transient rock volume variations caused by lawsonite breakdown is identified as a possible trigger for the pervasive fluid influx. The calculated schist permeability at eclogite-facies conditions (~ 2 × 10–20 m2) is comparable to the permeability determined experimentally for blueschist and serpentinites.
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Bouilhol, P., B. Debret, E. C. Inglis, M. Warembourg, T. Grocolas, T. Rigaudier, J. Villeneuve et K. W. Burton. « Decoupling of inorganic and organic carbon during slab mantle devolatilisation ». Nature Communications 13, no 1 (14 janvier 2022). http://dx.doi.org/10.1038/s41467-022-27970-0.

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AbstractSerpentinites are an important sink for both inorganic and organic carbon, and their behavior during subduction is thought to play a fundamental role in the global cycling of carbon. Here we show that fluid-derived veins are preserved within the Zermatt-Saas ultra-high pressure serpentinites providing key evidence for carbonate mobility during serpentinite devolatilisation. We show through the O, C, and Sr isotope analyses of vein minerals and the host serpentinites that about 90% of the meta-serpentinite inorganic carbon is remobilized during slab devolatilisation. In contrast, graphite-like carbonaceous compounds remain trapped within the host rock as inclusions within metamorphic olivine while the bulk elemental and isotope composition of organic carbon remains relatively unchanged during the subduction process. This shows a decoupling behavior of carbon during serpentinite dehydration in subduction zones. This process will therefore facilitate the transfer of inorganic carbon to the mantle wedge and the preferential slab sequestration of organic carbon en route to the deep mantle.
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Kempf, Elias D., Jörg Hermann, Eric Reusser, Lukas P. Baumgartner et Pierre Lanari. « The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland) ». Swiss Journal of Geosciences 113, no 1 (26 octobre 2020). http://dx.doi.org/10.1186/s00015-020-00368-0.

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AbstractMetamorphic olivine formed by the reaction of antigorite + brucite is widespread in serpentinites that crop out in glacier-polished outcrops at the Unterer Theodulglacier, Zermatt. Olivine overgrows a relic magnetite mesh texture formed during ocean floor serpentinization. Serpentinization is associated with rodingitisation of mafic dykes. Metamorphic olivine coexists with magnetite, shows high Mg# of 94–97 and low trace element contents. A notable exception is 4 µg/g Boron (> 10 times primitive mantle), introduced during seafloor alteration and retained in metamorphic olivine. Olivine incorporated 100–140 µg/g H2O in Si-vacancies, providing evidence for low SiO2-activity imposed by brucite during olivine growth. No signs for hydrogen loss or major and minor element diffusional equilibration are observed. The occurrence of olivine in patches within the serpentinite mimics the former heterogeneous distribution of brucite, whereas the network of olivine-bearing veins and shear zones document the pathways of the escaping fluid produced by the olivine forming reaction. Relic Cr-spinels have a high Cr# of 0.5 and the serpentinites display little or no clinopyroxene, indicating that they derive from hydrated harzburgitic mantle that underwent significant melt depletion. The enrichment of Mg and depletion of Si results in the formation of brucite during seafloor alteration, a pre-requisite for later subduction-related olivine formation and fluid liberation. The comparison of calculated bulk rock brucite contents in the Zermatt-Saas with average IODP serpentinites suggests a large variation in fluid release during olivine formation. Between 3.4 and 7.2 wt% H2O is released depending on the magnetite content in fully serpentinized harzburgites (average oceanic serpentinites). Thermodynamic modelling indicates that the fluid release in Zermatt occurred between 480 °C and 550 °C at 2–2.5 GPa with the Mg# of olivine varying from 68 to 95. However, the majority of the fluid released from this reaction was produced within a narrow temperature field of < 30 °C, at higher pressures 2.5 GPa and temperatures 550–600 °C than commonly thought. Fluids derived from the antigorite + brucite reaction might thus trigger eclogite facies equilibration in associated metabasalts, meta-gabbros, meta-rodingites and meta-sediments in the area. This focused fluid release has the potential to trigger intermediate depths earthquakes at 60–80 km in subducted oceanic lithosphere.
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