Articles | Volume 37, issue 6
https://doi.org/10.5194/ejm-37-927-2025
https://doi.org/10.5194/ejm-37-927-2025
Letter
 | 
11 Dec 2025
Letter |  | 11 Dec 2025

Coesite in garnet-quartzite of Orco Valley (Western Alps): an additional UHP unit in the records of deeply subducted meta-ophiolites

Federica Boero, Stefano Ghignone, Mattia Gilio, Alessia Borghini, Emanuele Scaramuzzo, Ivano Gasco, and Marco Bruno

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Cited articles

Agard, P.: Subduction of oceanic lithosphere in the Alps: Selective and archetypal from (slow-spreading) oceans, Earth Sci. Rev., 214, 103517. https://doi.org/10.1016/j.earscirev.2021.103517, 2021. 
Agard, P. and Handy, M. R.: Ocean subduction dynamics in the Alps, Elements, 17, 9–16, https://doi.org/10.2138/gselements.17.1.9, 2021. 
Agard, P., Monie, P., Jolivet, L., and Goffé, B.: Exhumation of the Schistes Lustres Complex: In Situ Laser Probe 40Ar /39Ar Constraints and Implications for the Western Alps, J. Metamorph. Geol., 20, 599–618. https://doi.org/10.1046/j.1525-1314.2002.00391.x, 2002. 
Angel, R. J., Nimis, P., Mazzucchelli, M. L., Alvaro, M., and Nestola, F.: How large are departures from lithostatic pressure? Constraints from host-inclusion elasticity, J. Metamorph. Geol., 33, 801–813, https://doi.org/10.1111/jmg.12138, 2015. 
Angiboust, S., Langdon, R., Agard, P., Waters, D., and Chopin, C.: Eclogitization of the Monviso Ophiolite (W. Alps) and Implications on Subduction Dynamics, J. Metamorph. Geol., 30, 37–61, https://doi.org/10.1111/j.1525-1314.2011.00951.x, 2012. 
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Short summary
We report a new ultra-high-pressure (UHP) locality in the western Alps (Italy). Micro-Raman analyses of garnet-hosted inclusions reveal the metamorphic evolution from the prograde path to exhumation. The finding of coesite in the Internal Piedmont Zone (IPZ) meta-ophiolites of Orco Valley suggests that UHP localities represent remnants of a former level that underwent comparable conditions in the coesite stability field in the oceanic slab, from Lago di Cignana to Monviso Massif.
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