08 Oct 2020

08 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal SE.

Kinematics and extent of the Piemont-Liguria Basin – implications for subduction processes in the Alps

Eline Le Breton1, Sascha Brune2,3, Kamil Ustaszewski4, Sabin Zahirovic5, Maria Seton5, and R. Dietmar Müller5 Eline Le Breton et al.
  • 1Department of Earth Sciences, Freie Universität Berlin, Germany
  • 2Geodynamic Modelling Section, German Research Centre for Geosciences, GFZ Potsdam, Germany
  • 3Institute of Geosciences, University of Potsdam, Potsdam, Germany
  • 4Institute for Geological Sciences, Friedrich-Schiller-Universität Jena, Germany
  • 5EarthByte Group, School of Geosciences, The University of Sydney, NSW 2006, Australia

Abstract. Assessing the size of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont-Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean-Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modelling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e. ages of syn-rift sediments, rift-related fault activity and mafic rocks) and shows that the PL Basin opened in four stages: (1) Rifting of the proximal continental margin in Early Jurassic (200–180 Ma), (2) Hyper-extension of the distal margin in Early-Middle Jurassic (180–165 Ma), (3) Ocean-Continent Transition (OCT) formation with mantle exhumation and MORB-type magmatism in Middle-Late Jurassic (165–154 Ma), (4) Break-up and mature oceanic spreading mostly in Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm/yr, full rate) and decreased to ~ 5 mm/yr after 145 Ma while completely ceasing at about 130 Ma due to motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL Ocean reached a maximum of 250 km along a NW–SE transect between Europe and Adria (Ivrea). In the Cretaceous and Cenozoic, the amount of plate convergence between Adria (Ivrea) and Europe during Alpine subduction (84–35 Ma, 420 km) and collision (35–0 Ma, 260 km) largely exceeded the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys Ophiolites exhumed today derived from OCT zones. Our work highlights the importance of distal rifted continental margins during subduction and exhumation processes and provides quantitative estimates for future geodynamic modelling and a better understanding of the Alpine Orogeny.

Eline Le Breton et al.

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Eline Le Breton et al.

Eline Le Breton et al.


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Short summary
Using plate tectonic reconstructions and geodynamic modelling, we show that the former Piemont-Liguria Ocean, which separated Europe from Africa-Adria in the Jurassic, opened as an arm of the Central Atlantic and reached only 250 km width between Europe and Adria. Moreover, at least 65 % of the lithosphere subducted into the mantle and/or incorporated into the Alpine mountain belt during convergence in Cretaceous and Cenozoic times was highly thinned continental, while only 35 % was truly oceanic.