A remnant of the Palaeotethys break-up: The Variscan Chamrousse ophiolite (Western Alps)
Abstract
Understanding the origin and evolution of Variscan ophiolitic sequences is crucial for reconstructing the palaeogeography of the Variscan belt. The Chamrousse ophiolite (External Crystalline Massif, Western Alps) dated by U -Pb zircon presents a Late Devonian-Early Mississippian age (355-345 Ma), which coincides with the beginning of the Palaeotethysian Cycle. By characterising the melt source of this ophiolite through new zircon chemical investigations, we propose a geodynamic opening model in a pull-apart setting during the Palaeotethysian break-up. Through low U/Yb, Nb/Yb and Th/Yb ratios coupled with highly radiogenic initial Hf isotopes (ca. +12), the Chamrousse ophiolite demonstrates an oceanic origin from a chemically depleted mantle source. Its architecture illustrates the structure of magma-poor oceanic ridges and rifted margins suggesting that the Chamrousse ocean basin opened likely in a transtensional pull-apart setting. This oceanic basin is preserved between its two conjugate margins. To the west, the bimodal Séchilienne unit reflects the Cambro-Ordovician continental rifting of the North-Gondwana margin. To the east, the Late Devonian-Early Mississippian Rioupéroux-Livet-Gavet formation is made of a bimodal magmatic and volcanosedimentary association. The Rioupéroux meta-trondhjemite (ca. 367 Ma) could record the earliest stage of rifting, that may have led to the continental break-up and the Chamrousse opening. This geodynamic scenario can be integrated into the broader triangular Palaeotethysian break-up, where the Chamrousse marginal oceanic basin and other extensional volcano-sedimentary continental basins located in the Moroccan Meseta and Bohemian Massif, are triggered by the westward propagation of the Palaeotethys Ocean, prior to the final assembly of Pangea.
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BibTeX
@article{gunia2026remnant,
title = {{A remnant of the Palaeotethys break-up: The Variscan Chamrousse ophiolite (Western Alps)}},
author = {Maureen Gunia and Adrien Vezinet and Carole Cordier and Emilie Janots and Anna Duhoux and Stéphane Guillot and Alexis Plunder and Alexander V Sobolev},
journal = {Lithos},
year = {2026},
month = sep,
doi = {10.1016/j.lithos.2026.108749},
url = {https://brgm.hal.science/hal-05734026v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A remnant of the Palaeotethys break-up: The Variscan Chamrousse ophiolite (Western Alps)
AU - Maureen Gunia
AU - Adrien Vezinet
AU - Carole Cordier
AU - Emilie Janots
AU - Anna Duhoux
AU - Stéphane Guillot
AU - Alexis Plunder
AU - Alexander V Sobolev
PY - 2026
DA - 2026/09/01
JO - Lithos
DO - 10.1016/j.lithos.2026.108749
UR - https://brgm.hal.science/hal-05734026v1
AB - Understanding the origin and evolution of Variscan ophiolitic sequences is crucial for reconstructing the palaeogeography of the Variscan belt. The Chamrousse ophiolite (External Crystalline Massif, Western Alps) dated by U -Pb zircon presents a Late Devonian-Early Mississippian age (355-345 Ma), which coincides with the beginning of the Palaeotethysian Cycle. By characterising the melt source of this ophiolite through new zircon chemical investigations, we propose a geodynamic opening model in a pull-apart setting during the Palaeotethysian break-up. Through low U/Yb, Nb/Yb and Th/Yb ratios coupled with highly radiogenic initial Hf isotopes (ca. +12), the Chamrousse ophiolite demonstrates an oceanic origin from a chemically depleted mantle source. Its architecture illustrates the structure of magma-poor oceanic ridges and rifted margins suggesting that the Chamrousse ocean basin opened likely in a transtensional pull-apart setting. This oceanic basin is preserved between its two conjugate margins. To the west, the bimodal Séchilienne unit reflects the Cambro-Ordovician continental rifting of the North-Gondwana margin. To the east, the Late Devonian-Early Mississippian Rioupéroux-Livet-Gavet formation is made of a bimodal magmatic and volcanosedimentary association. The Rioupéroux meta-trondhjemite (ca. 367 Ma) could record the earliest stage of rifting, that may have led to the continental break-up and the Chamrousse opening. This geodynamic scenario can be integrated into the broader triangular Palaeotethysian break-up, where the Chamrousse marginal oceanic basin and other extensional volcano-sedimentary continental basins located in the Moroccan Meseta and Bohemian Massif, are triggered by the westward propagation of the Palaeotethys Ocean, prior to the final assembly of Pangea.
SN - 0024-4937
SN - 1872-6143
ER -