The Importance of Rift Inheritance in Understanding the Early Collisional Evolution of the Western Alps

Manatschal, Giänreto; Chenin, Pauline; Haupert, Isabelle; Masini, Emmanuel; Frasca, Gianluca; Decarlis, Alessandro

doi:10.3390/geosciences12120434

Cited by 5 publications

(3 citation statements)

References 148 publications

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“…The CO is a portion of the oceanic lithosphere exhumed at the seafloor of the Alpine Tethys (i.e., the Ligurian‐Piedmont ocean) in the Late Jurassic (Manatschal et al, 2022, and references therein). Studies based on mantle compositions through various units of the Alpine Tethys suggest that the CO could belong to the most ocean‐ward part of the hyper‐extended margin, rather than to a true ocean (Picazo et al, 2016; Rampone & Piccardo, 2000).…”

Section: Discussionmentioning

confidence: 99%

To be or not to be Alpine: New petrological constraints on the metamorphism of the Chenaillet Ophiolite (Western Alps)

Corno

Groppo

Borghi

et al. 2023

Journal Metamorphic Geology

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The Chenaillet Ophiolite represents a very well‐preserved portion of Ligurian‐Piedmont ocean in the Western Alps. It is formed from an oceanic lithospheric succession comprising exhumed mantle, various mafic intrusives (i.e., gabbro sensu lato), and a world‐renowned sequence of pillow basalts. Apart from scarce breccias closely related to oceanic lithosphere, no sedimentary cover is exposed. Historically, the Chenaillet Ophiolite has been known for its very low temperature–low pressure Alpine metamorphism, ascribed to obduction processes. However, studies aimed at constraining the peak pressure–temperature (P–T) conditions of Alpine metamorphism are virtually lacking, the general focus having been so far on its high temperature metamorphism and geochemical features. In this paper, we investigate two kinds of rocks: gabbro and albitite/alkali syenite, whose petrographic features shed light on the complex metamorphic history of the Chenaillet Ophiolite. Detailed analyses of mineral assemblages, blastesis/deformation relationships, and mineral chemical data allow two metamorphic events to be distinguished: an earlier, high temperature event (already reported in the literature) and a second, later low temperature, high pressure event, recognized here for the first time. The low temperature, high pressure event is strikingly testified by the occurrence of lawsonite relicts in the gabbro and of interstitial omphacite in the albitite. Thermodynamic modelling (i.e., via isochemical phase diagrams) performed on a gabbro sample suggests for this unit a minimum of 9 kbar and 300°C and a maximum of 15 kbar and 450°C. Overlapping these P–T conditions with those inferred for the albitite based on the observed mineral assemblage allows the Alpine peak metamorphism to be constrained to 10–11 kbar and 340–360°C. These P–T conditions suggest a thickness of the overlying nappe stack of about 35–40 km, which is incompatible with obduction or burial processes, and instead consistent with subduction processes related to the Alpine orogeny. We argue that, opposite to the common belief that the Chenaillet Ophiolite escaped Alpine metamorphism, our new data strongly support the idea that it experienced low temperature‐blueschist‐facies metamorphism, whose evidence can still be tracked in those (few) rocks that better recorded and preserved it. This finding generates new challenging questions regarding both subduction and exhumation processes in complex orogens such as the Western Alps.

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Section: Discussionmentioning

confidence: 99%

To be or not to be Alpine: New petrological constraints on the metamorphism of the Chenaillet Ophiolite (Western Alps)

Corno

Groppo

Borghi

et al. 2023

Journal Metamorphic Geology

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“…An additional hypothesis, that is also coherent with the upper plate derivation of the NSMC eclogites, is the subduction of tectonic slices derived from the hyperextended continental margin The onset of Neo-Tethys subduction in the Early Jurassic at the ocean-continent transition (Manatschal et al 2022). However, in order to lean towards this hypothesis, remnants of (meta)sedimentary sequences and fossil structures typical of rifted margins (Manatschal & Chenin, 2023) should have been recognized.…”

Section: B Timing and Tectonic Implicationsmentioning

confidence: 96%

The onset of Neo-Tethys subduction in the Early Jurassic: evidence from the eclogites of the North Shahrekord Metamorphic Complex (Sanandaj-Sirjan Zone, W Iran)

Montemagni,

Zanchetta,

Malaspina

et al. 2023

Geol. Mag.

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Geodynamic models implying subduction of continental crust either consider this process happening during collision, when the continental margin of the lower plate attempts subduction, or in pre-collisional stages, when tectonic erosion of the upper plate or subduction of continental extensional allochthons drag continental crust in the subduction channel. In the Zagros orogen (W Iran), high-pressure rocks are known only from the Sanandaj-Sirjan Zone, NE of the Main Zagros Thrust. Here, eclogites of the North Shahrekord Metamorphic Complex suggest subduction of continental crust slices derived from the upper plate (Central Iran) during the onset of the Neo-Tethys subduction along the southern margin of Iran. Eclogites record a clockwise pressure-temperature-time path, with pre-eclogitic epidote-amphibolites-facies phase assemblages preserved in garnet cores, a high-pressure stage, and a subsequent retrogression at amphibolite-facies conditions. By means of forward thermodynamic modelling and 40Ar/39Ar geochronology, the peak metamorphism has been constrained at 1.9-2.1 GPa and 550-600 °C, in the 191-194 Ma time span. The following retrogression during exhumation lasted at least until 144 Ma. Our data suggest that the onset of the Neo-Tethys subduction traces back prior to 190 Ma, involving together with the Neo-Tethys oceanic lithosphere also slices of the upper plate continental crust scraped off by means of tectonic erosion processes.

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“…The segmentation of the continental margins (Fig. 5c) may also explain the arcuate shape, the non-cylindricity and the different timing of continental collision across the orogen (Handy et al 2010;Schmid et al 2017;Manatschal et al 2022b).…”

Section: From Proto-oceanic Domain To Convergencementioning

confidence: 99%

Kinematic reconstruction of the Alpine Tethys and surrounding Mesozoic rifted margins

Frasca,

Manatschal,

Chenin

2024

Int J Earth Sci (Geol Rundsch)

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In plate kinematic reconstructions, the restoration of rifted margins and their fossil equivalents exposed in orogens remains challenging. Tight fit reconstructions rely on the mapping of margins rift domains, their restoration to their pre-rift crustal thickness, and the removal of the oceanic and exhumed mantle domains. At present-day margins, high-resolution wide-angle seismic imaging allows mapping and measurement of rift domains; however, restoring fossil margins is trickier because they are largely overprinted and partially lost during convergence. Here, we present a new kinematic model for the Mesozoic rifting along the Tethys–Atlantic junction, which relies on two assumptions: (1) the width of the fossil Alpine Tethys rift domains was comparable to that of their present-day analogs, and (2) the necking zones of the former tectonic plates can be mapped, dated and used as kinematic markers. This reproducible workflow allows us, for the first time, to restore the rifted margins of the Alpine Tethys. Our reconstruction shows: (1) a westward propagation of extension through the Ionian, Alpine Tethys and Pyrenean rift systems from the Triassic to the Cretaceous, (2) the segmentation of the Mesozoic Tethyan rifted margins by strike-slip corridors, (3) the opening of an oceanic gateway at 165 Ma as mantle was exhumed along the entire Alpine Tethys and (4) the subdivision of the Mesozoic oceanic domain into compartments that were later consumed during subduction. This new model is supported by published data from the Alps, the Ionian Sea, the Pyrenees and the southern North Atlantic. Graphical abstract

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The Importance of Rift Inheritance in Understanding the Early Collisional Evolution of the Western Alps

Cited by 5 publications

References 148 publications

To be or not to be Alpine: New petrological constraints on the metamorphism of the Chenaillet Ophiolite (Western Alps)

To be or not to be Alpine: New petrological constraints on the metamorphism of the Chenaillet Ophiolite (Western Alps)

The onset of Neo-Tethys subduction in the Early Jurassic: evidence from the eclogites of the North Shahrekord Metamorphic Complex (Sanandaj-Sirjan Zone, W Iran)

Kinematic reconstruction of the Alpine Tethys and surrounding Mesozoic rifted margins

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