High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy)

Fassmer, Kathrin; Obermüller, Gerrit; Nagel, T.; Kirst, Frederik; Froitzheim, Nikolaus; Sandmann, Sascha; Miladinova, Irena; Fonseca, Raúl O. C.; Münker, Carsten

doi:10.1016/j.lithos.2016.02.019

Cited by 24 publications

(27 citation statements)

References 81 publications

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“…Therefore, this evidence may suggest that the LMO represents a depositional setting located in the oceanward part of an ocean-continent transition setting, protected by the deposition of continental derived material, or an embryonic oceanic basin far from the continental margins. Although it is not within the scope of this work, the latter interpretation seems to better agree with (1) the geochemical and isotopic data from this region (e.g., see Cartwright and Barnicoat, 1999;Widmer et al, 2000;Martin et al, 2008), (2) the recent interpretation of the contact between ZSOs and continental units (i.e., Etirol-Levaz slice) as a product of the Alpine tectonics (e.g., Fassmer et al, 2016), and (3) the lack of any kind of continental-derived material within the CCU.…”

Section: Lmo and The Jurassic Ligurian-piedmont Seafloorsupporting

confidence: 79%

“…However, the local occurrence and mixing and/or juxtaposition of oceanic-and continent-derived material and units allowed the different interpretation of the ZSO as either the remnant of an hyperextended continental margin in an ocean-continent transition zone (e.g., see Beltrando et al, 2014, and references therein) or the result of the Alpine tectonic juxtaposition between oceanic and continental margin units (e.g., Fassmer et al, 2016, and references therein).…”

Section: Regional Geologymentioning

confidence: 99%

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Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

et al. 2017

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The eclogite facies Zermatt-Saas ophiolite in the Western Alps includes a composite chaotic unit exposed in the Lake Miserin area, in the southern Aosta Valley region. The chaotic unit is characterized by a block-in-matrix texture consisting of ultramafic clasts and blocks embedded within a carbonate matrix. This unit overlies massive serpentinite and ophicarbonate rocks and is unconformably overlain by layered calcschist. Despite the effects of subduction and collision-related deformation and metamorphism, the internal stratigraphy and architecture of the chaotic unit are recognizable and are attributed to different types of mass transport processes in the Jurassic Ligurian-Piedmont Ocean. This finding represents an exceptional record of the preorogenic history of the Alpine ophiolites, marked by different pulses of extensional tectonics responsible for the rough seafloor topography characterized by structural highs exposed to submarine erosion. The Jurassic tectonostratigraphic setting envisioned is comparable to that observed in present-day magma-poor slow-and ultraslow-spreading ridges, characterized by mantle exposure along fault scarps that trigger mass transport deposits and turbiditic sedimentation. Our preorogenic reconstruction is significant in an eclogitized collisional orogenic belt in which chaotic rock units may be confused with the exclusive product of subduction-related tectonics, thus obscuring the record of an important preorogenic history. LITHOSPHERE

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Section: Lmo and The Jurassic Ligurian-piedmont Seafloorsupporting

confidence: 79%

Section: Regional Geologymentioning

confidence: 99%

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

et al. 2017

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“…Recent discoveries suggest that the hangingwall of the ZSU may represent a composite domain juxtaposing sub‐km‐scale tectonic slices with differing P–T–t histories [e.g. Lago di Cignana unit: Reinecke, ; Groppo et al ., ; Etirol‐Levaz Unit (ELU): Fassmer et al ., and references therein]. A few slices of continental affinity have been reported along this shear zone [ELU, Theodul Glacier Unit (TGU): Weber & Bucher, ; ChU, Chatillon Unit (ChU): Rolfo et al ., ; see also Ballèvre et al ., ; Fig.…”

Section: Geological Settingmentioning

confidence: 89%

“…]. Recent geochronological investigations revealed Alpine peak metamorphic ages (Lu–Hf: 60–50 Ma; Weber et al ., ; Fassmer et al ., ; Fig. ) c .…”

Section: Geological Settingmentioning

confidence: 99%

Fluid pathways and high‐P metasomatism in a subducted continental slice (Mt. Emilius klippe, W. Alps)

Angiboust

Yamato

Hertgen

et al. 2017

Journal Metamorphic Geology

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The Mt. Emilius klippe (Western Alps, Italy) corresponds to a segment of the stretched Adriatic continental margin metamorphosed at granulite facies during Permian. This slice was subducted during the early Cenozoic Alpine subduction with the underlying eclogite facies remnants of the Tethyan seafloor (Zermatt‐Saas zone). Near the base of the Mt. Emilius massif, there is a shear zone with eclogite facies hydrofracture systems associated with deformation‐induced re‐equilibration of granulites during high‐P metamorphism. In the basal part of the massif, a pluri‐hectometre domain of sheared mafic boudins is hosted in the granulitic paragneiss. In these mafic boudins, there are garnetites, garnet veins and clinopyroxenites, as well as clinozoisite and calcite veins. These features record multiple events of fracture opening, brecciation, boudinage and parallelization of structures coevally with fluid–rock interaction, metasomatism and volume change. This integrated petrological, micro‐textural and geochemical investigation illustrates the multiplicity and the chemical variability of fluid sources during prograde to peak metamorphic evolution in the lawsonite–eclogite‐facies field (at ~2.15–2.4 GPa, 500–550 °C) during subduction of the Mt. Emilius slice. The calcite veins crosscutting the garnetites have relatively low δ18OVSMOW values (∼+6.5‰) near those for marble layers (and nearby calcsilicates) embedded within the metasomatized granulites (+8 to +10‰). It is proposed that infiltration of externally‐derived H2O‐rich fluids derived from the plate interface flushed the marbles, promoting decarbonation followed by short‐distance transport and re‐precipitation along garnetite fractures. This study highlights the importance of inherited structural heterogeneities (such as mafic bodies or sills) in localizing deformation, draining fluids from the downgoing plate and creating long‐lasting mechanical instabilities during subduction zone deformation.

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“…These structurally lower basement slices predominantly crop out south of the Aosta Valley (Mt. Emilius, Glacier Rafray, Santanel, Tour Ponton, and Acque Rosse; Argand, ; Ballèvre et al, ; Battiston et al, ; Dal Piaz, ; Dal Piaz & Nervo, ; Dal Piaz, Nervo, & Polino, ; Dal Piaz et al, ; Nervo & Polino, ; Paganelli, Compagnoni, Nervo, & Tallone, ; Pennacchioni, , ) whereas few occurrences are located to the north (Etirol–Levaz unit: Ballèvre et al, ; Fassmer et al, ; Kienast, ; Theodul Glacier unit: Weber & Bucher, ; Weber et al, ). Other minor basement slivers are found along the Late Oligocene–Neogene Aosta–Ranzola fault system (Chatillon and Grun; Biino & Compagnoni, ; Dal Piaz, ; Dal Piaz & Martin, ).…”

Section: The Axial Belt Of the Western Alps: Geological Frameworkmentioning

confidence: 99%

Nappe stack of Piemonte–Ligurian units south of Aosta Valley: New evidence from Urtier Valley (Western Alps)

Ellero

Loprieno²

2017

Geological Journal

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New results of structural and lithostratigraphic investigations performed in the Urtier Valley, located south of Aosta Valley at the northern flank of the Gran Paradiso Massif, shed new light on the nappe stack architecture of the Western Alps. Two distinct Piemonte–Ligurian units were recognized in the area: (a) the blueschist facies Broillot unit, with a well‐preserved lithostratigraphic succession that includes ophiolites and their metasedimentary cover and (2) the eclogitic Bardonney unit with clasts and/or slices of ophiolites embedded in a carbonate/quarzitic and/or metabasic matrix. Three major deformation stages have been recognized (D1, D2, and D3). D1 phase occurred during the peak metamorphic conditions (i.e., eclogite or blueschist facies). D2 and D3 phases are related to multistage exhumation processes, from early stacking to late refolding of former nappe contacts. Despite the intensity of deformation and metamorphism, the original lithostratigraphic succession of the Broillot unit allowed us to use a lithostratigraphic approach to reconstruct the structures in the study area. For the first time, differences in the nappe stack exposed south and north of the Aosta Valley are reported. In fact, contrary to what is observed in the north, the eclogitic units exposed in the Urtier Valley lay above and not below the blueschist units. A new model for the tectonic evolution, which ranges from stages of subduction to large‐scale nappe refolding, is proposed. It is able to explain the difference in the architecture of the north and south of the Aosta Valley.

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High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy)

Cited by 24 publications

References 81 publications

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

Fluid pathways and high‐P metasomatism in a subducted continental slice (Mt. Emilius klippe, W. Alps)

Nappe stack of Piemonte–Ligurian units south of Aosta Valley: New evidence from Urtier Valley (Western Alps)

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