Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

Herviou, Clément; Verlaguet, Anne; Agard, Philippe; Locatelli, Michele; Raimbourg, Hugues; Lefeuvre, Benjamin; Dubacq, Benoît

doi:10.1016/j.lithos.2021.106168

Cited by 15 publications

(35 citation statements)

References 190 publications

(327 reference statements)

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“…12 kbar, 330 °C (low-T blueschist) in the western (uppermost) unit towards ca. 18-20 kbar, 450-470 °C (blueschist-eclogite facies transition) found in the most internal (lowest) unit, which overlies the Monviso eclogitic complex (Agard et al, 2001;Herviou et al, 2021;Lefeuvre et al, 2020;Schwartz et al, 2013). Quartz-eclogite to coesite-eclogite facies conditions of metamorphism are well-known in the Dora-Maira units beneath the MGA, as reported above (chapter 3.2).…”

Section: Meso-and Microstructuresmentioning

confidence: 55%

“…13) compare with those obtained further to the north by Schwartz et al (2013) in their Medium Temperature Blueschist (MT-BS) unit that overlies the Acceglio-Longet Band, and in their High Temperature Blueschist (HT-BS) unit 2) overlying the Monviso Complex, respectively. These temperature values are equivalent within uncertainty to the peak metamorphic temperatures inferred by Lefeuvre et al (2020) and Herviou et al (2021) for their LPU2 and LPM units, which correspond to the MT-BS and HT-BS units of Schwartz et al (2013), respectively. The Monviso Complex contrasts with the Queyras units by its higher, eclogite-facies grade of metamorphism, bordering the coesite stability field (550 °C, 26-27 kbar) in the Lago Superiore subunit but reaching lower peak P-T conditions in the Monviso subunit (500 °C, 22-24 kbar;Angiboust et al, 2012;Schwartz et al, 2013).…”

Section: Metamorphismmentioning

confidence: 67%

“…The Maira-Sampeyre and Val Grana Allochthons are obliquely overlain by two lithologically different tectonic units derived from the Piemonte-Liguria Ocean: (i) the Monviso (MV) ophiolitic complex, consisting of eclogitic units that dominantly expose metagabbros and metabasites with subordinate oceanic metasediments (breccias, marbles, calcschists), underlain by a thick basal sole of serpentinites (Lombardo et al, 1978;Deville et al, 1992;Schwartz et al, 2000bSchwartz et al, , 2013Agard et al, 2001;Angiboust et al, 2012;Castelli et al, 2014;Angiboust and Glodny, 2020), and, (ii) the ophiolite-bearing Queyras nappe (QN), consisting of three units (not separated in Fig. 3) of blueschist-facies oceanic metasediments hosting boudinaged kilometric meta-ophiolite bodies (Lagabrielle and , 1988;Deville et al, 1992;Schwartz et al, 2000a, b;Tricart and Schwartz, 2006;Herviou et al, 2021). Between the Upper Po and Varaita valleys (Figs.…”

Section: Tectonic Units and Their Mutual Relationshipsmentioning

confidence: 99%

“…The P-T conditions of metamorphism of the Piemonte-Liguria nappes have been thoroughly analyzed north of our study area (Agard et al, 2001(Agard et al, , 2009Schwartz et al, 2013;Lefeuvre et al, 2020;Herviou et al, 2021). Our T RSCM results for the Queyras Schistes lustrés samples #39-40 and #13-16 (Fig.…”

Section: Metamorphismmentioning

confidence: 99%

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The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): review and new data on the tectonometamorphic evolution of the Briançonnais distal margin

et al. 2022

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Here we describe the structure, the high-pressure, low-temperature (HP-LT) metamorphism and tectonic evolution of the Briançonnais distal margin units from the south Western Alps. The studied area extends southwest of the Dora-Maira (U)HP basement units and east-southeast of the classical Briançonnais nappes. A new structural map accompanied by geological profiles shows the thrusting of the oceanic nappes (Monviso and Queyras units) onto the distal Briançonnais units (D1 and D2 late Eocene deformation phases) under blueschist-facies conditions. Subsequent deformation during the Early Oligocene (D3 deformation phase) took place under greenschist-facies conditions and was associated with back-folding and -thrusting in the units overlying the Dora-Maira massif and with exhumation related to normal reactivation of former thrusts within the latter massif. Two large cover units, detached from their former distal Briançonnais basement, are redefined as the Maira-Sampeyre and Val Grana Allochthons (shortly: Maira-Grana Allochthons = MGA) including, (i) the Val Maira-Sampeyre unit involving Lower and Middle Triassic formations, seemingly detached from the Dora-Maira units during the subduction process, and (ii) the Val Grana unit with Middle-Upper Triassic and Early-Middle Jurassic formations, which was probably detached from the Maira-Sampeyre unit and correlates with the “Prepiemonte units” known from the Ligurian Alps to the Swiss Prealps. Three major shear zones involving tectonic mélanges of oceanic and continental rocks at the base of the Val Grana, Maira-Sampeyre and Dronero units testify to an early phase of exhumation within the subduction channel in front of the Adria plate. We present a new metamorphic map based on published and new petrological data, including new thermometric data obtained by Raman spectroscopy of carbonaceous material (RSCM). The TRSCM values range from ~ 400 °C to > 500 °C, going from the most external Val Grana unit and overlying Queyras schists to the uppermost Dora-Maira unit. During the Late Triassic, the width of the Briançonnais s.l. domain can be restored at ~ 100 km, whereas it reached ~ 150 km after the Jurassic rifting. A significant, second rifting event affected the Briançonnais domain during the Late Cretaceous-Paleocene, forming the Longet-Alpet chaotic breccias, which deserve further investigations.

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Section: Meso-and Microstructuresmentioning

confidence: 55%

Section: Metamorphismmentioning

confidence: 67%

Section: Tectonic Units and Their Mutual Relationshipsmentioning

confidence: 99%

Section: Metamorphismmentioning

confidence: 99%

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The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): review and new data on the tectonometamorphic evolution of the Briançonnais distal margin

et al. 2022

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“…They further argued that the hottest fluids were exsolved during the HT event related to magma crystallization at or after 17 Ma. The link between distinguishable Cl concentrations in the circulating metamorphic fluids and phengite-muscovite retrogression was independently observed in the Western Alps (Herviou et al, 2021;Villa et al, 2014), establishing the Cl/K ratio as a very valuable diagnostic tool to unravel petrological mixtures. If, in addition to phengite and muscovite, paragonite is also present, its contribution can be proxied by 37 Ar (Allaz et al, 2011).…”

Section: Chemical Correlation Diagramsmentioning

confidence: 99%

Petrochronology of polygenetic white micas (Naxos, Greece)

Villa

Glodny

Peillod

et al. 2022

Journal Metamorphic Geology

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Naxos in the Greek Cyclades preserves a type example of polymetamorphism. The southern and northern parts of the island record different Tertiary P–T histories between Eocene and Miocene times, including a blueschist facies event, one or more amphibolite/greenschist facies overprint(s) and contact metamorphism. Age attributions for these events are inconsistent in the literature. Here, we propose a new approach that combines electron probe microanalyzer (EPMA) characterization of the white mica (WM) with 39Ar‐40Ar–Rb‐Sr multichronometry. Textural–petrographic–compositional observations reveal that the polygenetic WM consists of five different generations: pre‐Eocene relicts, paragonite, high‐Si phengite, low‐Si phengite and muscovite. EPMA mapping of four WM samples, previously analysed by Rb‐Sr, reveals major element compositions heterogeneous down to the μm scale. Each WM consists of chemically distinct generations, documenting submicron‐scale retrogression of high‐pressure (HP) phengite grains to muscovite. Four WM samples from a N‐S traverse across the island were analysed by 39Ar‐40Ar stepheating, comparing coarse and fine sieve size fractions to obtain overdetermined K‐Ar systematics. Fine sieve fractions are richer in Cl than coarse ones. Linear arrays in Cl/K‐age isotope correlation diagrams show two predominant WM generations (one Cl‐poor at ca. 38 Ma and one Cl‐rich at <20 Ma). A lower‐grade sample from southern Naxos was less pervasively recrystallized, provides older ages and preserves at least three WM generations, including a relict WM with a pre‐Palaeocene K‐Ar age, consistent with the high Ar retentivity of WM in the absence of complete recrystallization. The age of the Cl‐poor end‐member WM approximates the age of the HP event, 38 Ma. Ar inheritance in Cretaceous mica relicts is heterogeneous at the single‐grain scale. Comparing the degassing rates of the WM fractions rules out ‘multidomain’ diffusion. As no sample is monomineralic, the degassing rate of each polygenetic mica is instead controlled by the mass balanced sum of the unrelated rate constants of its constituent minerals. Given the commonness of zoned and composite micas, the approach detailed here is potentially useful for reconstructing polyphase metamorphic histories worldwide.

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Oceanic Subduction in the Alps

AGARD

2024

Geodynamics of the Alps 2

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Along-dip variations of subduction fluids: The 30–80 km depth traverse of the Schistes Lustrés complex (Queyras-Monviso, W. Alps)

Cited by 15 publications

References 190 publications

The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): review and new data on the tectonometamorphic evolution of the Briançonnais distal margin

The Maira-Sampeyre and Val Grana Allochthons (south Western Alps): review and new data on the tectonometamorphic evolution of the Briançonnais distal margin

Petrochronology of polygenetic white micas (Naxos, Greece)

Oceanic Subduction in the Alps

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