Articles | Volume 37, issue 6
https://doi.org/10.5194/ejm-37-927-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/ejm-37-927-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Coesite in garnet-quartzite of Orco Valley (Western Alps): an additional UHP unit in the records of deeply subducted meta-ophiolites
Earth Sciences Department, University of Torino, via Valperga Caluso 35, 10125 Torino, Italy
Stefano Ghignone
Earth Sciences Department, University of Torino, via Valperga Caluso 35, 10125 Torino, Italy
Mattia Gilio
Earth and Environmental Sciences Department, University of Pavia, via Ferrata 1, 27100 Pavia, Italy
Alessia Borghini
Faculty of Geology, Geophysics and Environmental Protection, AGH University of Kraków, Aleja Mickiewicza 30, 30-059 Kraków, Poland
Emanuele Scaramuzzo
Department of Science and High Technology, University of Insubria, via Valleggio 11, 22100 Como, Italy
Ivano Gasco
TYLin Italy, via V. Amedeo II 6, 10121 Torino, Italy
Marco Bruno
Earth Sciences Department, University of Torino, via Valperga Caluso 35, 10125 Torino, Italy
NIS, Center for Nanostructured Interfaces and Surfaces, University of Torino, via G. Quarello 15/a, 10135, Torino, Italy
Related authors
No articles found.
Emanuele Scaramuzzo, Franz A. Livio, Maria Giuditta Fellin, and Colin Maden
Solid Earth, 16, 619–640, https://doi.org/10.5194/se-16-619-2025, https://doi.org/10.5194/se-16-619-2025, 2025
Short summary
Short summary
We address the transition between the Paleozoic Variscan and Alpine Mesozoic–Cenozoic cycles using tectono-stratigraphy and thermochronology. This transition unfolds through a multi-phase rifting history. An initial rifting stage occurred in the early Permian, followed in the early–middle Permian by a phase of transcurrent tectonics. This was succeeded by a period of erosion/non-deposition in the middle Permian. Crustal stretching in the Middle Triassic marked the onset of the Alpine cycle.
Franz A. Livio, Anna M. Blumetti, Valerio Comerci, Francesca Ferrario, Gilberto Binda, Marco Caciagli, Michela Colombo, Pio Di Manna, Fernando Ferri, Fiorenzo Fumanti, Roberto Gambillara, Maurizio Guerra, Luca Guerrieri, Paolo Lorenzoni, Valerio Materni, Francesco Miscione, Rosa Nappi, Rosella Nave, Kathleen Nicoll, Alba Peiro, Marco Pizza, Roberto Pompili, Luca M. Puzzilli, Mauro Roma, Aurora Rossi, Valerio Ruscito, Vincenzo Sapia, Argelia Silva Fragoso, Emanuele Scaramuzzo, Frank Thomas, Giorgio Tringali, Stefano Urbini, Andrea Zerboni, and Alessandro M. Michetti
EGUsphere, https://doi.org/10.5194/egusphere-2025-2531, https://doi.org/10.5194/egusphere-2025-2531, 2025
Short summary
Short summary
The Rieti Basin in Central Italy, though surrounded by active faults, has been largely overlooked in earthquake studies. To better understand its seismic past, we dug 17 trenches and discovered evidence of 15 ancient earthquakes over the past ca. 20,000 years. The findings show that earthquakes in this area tend to cluster in time, likely due to stress shifting between nearby faults, and can reach a magnitude of 6.5.
Alessia Borghini, Silvio Ferrero, Patrick J. O'Brien, Bernd Wunder, Peter Tollan, Jarosław Majka, Rico Fuchs, and Kerstin Gresky
Eur. J. Mineral., 36, 279–300, https://doi.org/10.5194/ejm-36-279-2024, https://doi.org/10.5194/ejm-36-279-2024, 2024
Short summary
Short summary
We studied primary granitic and halogen-rich melt inclusions trapped in mantle rocks in the Bohemian Massif (Germany) in order to retrieve important information about the nature of the melt and the source rock. The melt was produced by the partial melting of metasediments during the deepest stages of subduction and interacted with the mantle. This work is an excellent example of transfer of crustal material, volatiles in particular, in the mantle during the subduction of the continental crust.
Silvio Ferrero, Alessia Borghini, Laurent Remusat, Gautier Nicoli, Bernd Wunder, and Roberto Braga
Eur. J. Mineral., 35, 1031–1049, https://doi.org/10.5194/ejm-35-1031-2023, https://doi.org/10.5194/ejm-35-1031-2023, 2023
Short summary
Short summary
Garnet often entraps small droplets of deep melts generated during mountain building processes. Using high-resolution techniques, we studied these droplets in order to provide hard numbers for the quantification of volatile budgets during crustal evolution, show how even melts formed at >1000°C contain water, and clarify how water behaves during metamorphism and melting at the microscale. Moreover, we provide the very first data on chlorine in natural melts from crustal reworking.
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.
Angiboust, S., Pettke, T., De Hoog, J. C. M., Caron, B., and Oncken, O.: Channelized Fluid Flow and Eclogite – Facies Metasomatism Along the Subduction Shear Zone, J. Petrol., 55, 883–916, https://doi.org/10.1093/petrology/egu010, 2014.
Baldwin, S. L., Schönig, J., Gonzalez, J. P., Davies, H., and von Eynatten, H.: Garnet sand reveals rock recycling processes in the youngest exhumed high- and ultrahigh-pressure terrane on Earth, P. Natl. Acad. Sci. USA, 118, e2017231118, https://doi.org/10.1073/pnas.2017231118, 2021.
Ballèvre, M., Camonin, A., Manzotti, P., and Poujol, M.: A step towards unraveling the paleogeographic attribution of pre-Mesozoic basement complexes in the Western Alps based on U-Pb geochronology of Permian magmatism, Swiss J. Geosci., 113, https://doi.org/10.1186/s00015-020-00367-1, 2020.
Beltrando, M., Rubatto, D., and Manatschal, G.: From passive margins to orogens: The link between ocean-continent transition zones and (ultra) high-pressure metamorphism, Geology, 38, 559–562, https://doi.org/10.1130/G30768.1, 2010.
Boyer, H., Smith, D. C., Chopin, C., and Lasnier, B.: Raman microprobe (RMP) determinations of natural and synthetic coesite, Phys. Chem. Miner., 12, 45–48, https://doi.org/10.1007/BF00348746, 1985.
Bucher, K. and Grapes, R.: The Eclogite-facies Allalin Gabbro of the Zermatt-Saas Ophiolite, Western Alps: a Record of Subduction Zone Hydration, J. Petrol., 50, 1405–1442, https://doi.org/10.1093/petrology/egp035, 2009.
Campomenosi, N., Mazzucchelli, M. L., Mihailova, B., Scambelluri, M., Angel, R. J., Nestola, F., Reali, A., and Alvaro, M.: How geometry and anisotropy affect residual strain in host-inclusion systems: coupling experimental and numerical approaches, Am. Mineral., 103, 2032–2035, https://doi.org/10.2138/am-2018-6700CCBY, 2018.
Carswell, D. A. and Compagnoni, R. (Eds.): Ultrahigh Pressure Metamorphism. EMU Notes in Mineralogy, 5, 508 pp., ISBN 963 463 6462, 2003.
Chopin, C.: Coesite and pure pyrope in high-grade blueschists of the western Alps: A first record and some consequences, Contrib. Mineral. Petrol., 86, 107–118, https://doi.org/10.1007/BF00381838, 1984.
Compagnoni, R., Gilio, M., Ghignone, S., Scaramuzzo, E., Borghini, A., and Bruno, M.: Comment on “first finding of continental deep subduction in the Sesia Zone of Western Alps and implications for subduction dynamics”, Nat. Sci. Rev., nwae454, https://doi.org/10.1093/nsr/nwae454, 2024.
Cossio, R., Ghignone, S., Borghi, A., Corno, A., and Vaggelli, G.: A supervised machine learning procedure for EPMA classification and plotting of mineral groups, Appl. Comput. Geosci., 23, 100186, https://doi.org/10.1016/j.acags.2024.100186, 2024.
Dewey, J. F., Holdsworth, R. E., and Strachan, R. A.: Transpression and transtension zones, in: Continental Transpressional and Transtensional Tectonics, edited by: Holdsworth, R. E., Strachan, R. A., and Dewey, J. F., Geol. Soc., London, Spec. Publ. 135, 1–14, 1998.
Dragovic, B., Angiboust, S., and Tappa, M. J.: Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps), Earth Planet. Sc. Lett., 547, 116446, https://doi.org/10.1016/j.epsl.2020.116446, 2020.
Ferrero, S. and Angel, R. J.: Micropetrology: Are Inclusions Grains of Truth?, J. Petrol., 59, 1671–1700, https://doi.org/10.1093/petrology/egy075, 2018.
Gasco, I. and Gattiglio, M.: Geological map of the middle Orco Valley, Western Italian Alps, Journal of Maps, 7, 463–477, https://doi.org/10.4113/jom.2010.1121, 2011.
Gasco, I., Gattiglio, M., and Borghi, A.: Structural evolution of different tectonic units across the AustroAlpine-Penninic boundary in the middle Orco Valley (Western Italian Alps), J. Struct. Geol., 31, 301–314, https://doi.org/10.1016/j.jsg.2008.11.007, 2009.
Ghignone, S., Balestro, G., Gattiglio, M., and Borghi, A.: Structural evolution along the Susa Shear Zone: the role of a first-order shear zone in the exhumation of meta-ophiolite units (Western Alps), Swiss J. Geosci., 113, 17, https://doi.org/10.1186/s00015-020-00370-6, 2020.
Ghignone, S., Borghi, A., Balestro, G., Castelli, D., Gattiglio, M., and Groppo, C.: HP-tectonometamorphic evolution of the Internal Piedmont Zone in Susa Valley (Western Alps): New petrologic insight from garnet + chloritoid-bearing micaschists and Fe-Ti metagabbro, J. Metamorph. Geol., 39, 391–416, https://doi.org/10.1111/jmg.12574, 2021.
Ghignone, S., Scaramuzzo, E., Bruno, M., and Livio, F.: A new UHP unit in the Western Alps: first occurrence of coesite from the Monviso Massif (Italy), Am. Mineral., 108, 1368-1375, https://doi.org/10.2138/am-2022-8621, 2023.
Ghignone, S., Gilio, M., Borghini, A., Boero, F., Bruno, M., and Scaramuzzo, E.: Mineralogical and petrological constraints and tectonic implications of a new coesite-bearing unit from the Alpine Tethys oceanic slab (Susa Valley, Western Alps), Lithos, 472/473, 107575, https://doi.org/10.1016/j.lithos.2024.107575, 2024.
Gilotti, J. A.: The realm of ultrahigh-pressure metamorphism, Elements, 9, 255–260, https://doi.org/10.2113/gselements.9.4.255, 2013.
Groppo, C. and Castelli, D.: Prograde P-T evolution of a lawsonite eclogite from the Monviso meta-ophiolite (Western Alps): dehydration and redox reactions during subduction of oceanic FeTi-oxide gabbro, J. Petrol., 51, 2489–2514, https://doi.org/10.1093/petrology/egq065, 2010.
Groppo, C., Beltrando, M., and Compagnoni, R.: The P-T path of the ultra-high pressure Lago Di Cignana and adjoining high-pressure meta-ophiolitic units: insights into the evolution of the subducting Tethyan slab, J. Metamorph. Geol., 27, 207–231, https://doi.org/10.1111/j.1525-1314.2009.00814.x, 2009.
Groppo, C., Ferrando, S., Castelli, D., Elia, D., Meirano, V., and Facchinetti, L.: A possible new UHP unit in the Western Alps as revealed by ancient Roman quern-stones from Costigliole Saluzzo, Italy, Eur. J. Mineral., 28, 1215–1232, https://doi.org/10.1127/ejm/2016/0028-2531, 2016.
Groppo, C., Ferrando, S., Tursi, F., and Rolfo, F.: A New UHP-HP Tectono-Metamorphic Architecture for the Southern Dora-Maira Massif Nappe Stack (Western Alps) Based on Petrological and Microstructural Evidence, J. Metamorph. Geol., 43, 359–383, https://doi.org/10.1111/jmg.12812, 2025.
Handy, M. R., Schmid, S. M., Bousquet, R., Kissling, E., and Bernoulli, D.: Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological–geophysical record of spreading and subduction in the Alps, Earth-Sci. Rev., 102, 121–158, https://doi.org/10.1016/j.earscirev.2010.06.002, 2010.
Herviou, C., Agard, P., Plunder, A., Mendes, K., Verlaguet, A., Deldicque, D., and Cubas, N.: Subducted fragments of the Liguro-Piemont ocean, Western Alps: Spatial correlations and offscraping mechanisms during subduction, Tectonophysics, 827, 229267, https://doi.org/10.1016/j.tecto.2022.229267, 2022.
Jolivet, L., Faccenna, C., Goffe, B., Burov, E., and Agard, P.: Subduction tectonics and exhumation of high-pressure metamorphic rocks in the Mediterranean orogens, Am. J. Sci., 303, 353–409, https://doi.org/10.2475/ajs.303.5.353, 2003.
Krogh, E. J.: Metamorphic evolution of Norwegian country-rock eclogites, as deduced from mineral inclusions and compositional zoning in garnets, Lithos, 15, 305–321, https://doi.org/10.1016/0024-4937(82)90021-4, 1982.
Lanari, P., Vidal, O., De Andrade, V., Dubacq, B., Lewin, E., Grosch, E. G., and Schwartz, S.: XMapTools: A MATLAB©-based program for electron microprobe X-ray image processing and geothermobarometry, Comput. Geosci., 62, 227–240, https://doi.org/10.1016/j.cageo.2013.08.010, 2014.
Lanari, P., Vho, A., Bovay, T., Airaghi, L., and Centrella, S.: Quantitative compositional mapping of mineral phases by electron probe micro-analyser, Geological Society Special Publication, 478, 39–63, https://doi.org/10.1144/SP478.4, 2019.
Lardeaux, J. M.: Metamorphism and linked deformation in understanding tectonic processes at varied scales, Comptes Rendus, Géoscience, Geodynamics of Continents and Oceans – A tribute to Jean Aubouin, 356/S2, 525–550, https://doi.org/10.5802/crgeos.204, 2024.
Locatelli, M., Verlaguet, A., Agard, P., Federico, L., and Angiboust, S.: Intermediate-Depth Brecciation Along the Subduction Plate Interface (Monviso Eclogite, W. Alps), Lithos, 320/321, 378–402, https://doi.org/10.1016/j.lithos.2018.09.028, 2018.
Maffeis, A., Petroccia, A., Nerone, S., Caso, F., Corno, A., Bonazzi, M., Boero, F., Corvò, S., Ghignone, S., and Groppo, C.: Filling the gap in the UHP metamorphic record of the Liguro-Piemont Lower unit: insights on fluid-mediated formation of atoll garnets, Lithos, 498–499, 107981, https://doi.org/10.1016/j.lithos.2025.107981, 2025.
Malusà, M. G., Faccenna, C., Garzanti, E., and Polino, R.: Divergence in subduction zones and exhumation of high pressure rocks (Eocene Western Alps), Earth Planet. Sc. Lett., 310, 21–32, https://doi.org/10.1016/j.epsl.2011.08.002, 2011.
Malusà, M. G., Faccenna, C., Baldwin, S. L., Fitzgerald, P. G., Rossetti, F., Balestrieri, M. L., Danišík, M., Ellero, A., Ottria, G., and Piromallo, C.: Contrasting styles of (U) HP rock exhumation along the Cenozoic Adria-Europe plate boundary (Western Alps, Calabria, Corsica), Geochem. Geophy. Geosy., 16, 1786–1824, https://doi.org/10.1002/2015GC005767, 2015.
Malusà, M. G., Guillot, S., Zhao, L., Paul, A., Solarino, S., Dumont, T., Schwartz, S., Aubert, C., Baccheschi, P., Eva, E., Lu, Y., Lyu, C., Pondrelli, S., Salimbeni, S., Sun, W., and Yuan, H.: The deep structure of the Alps based on the CIFALPS seismic experiment: A synthesis, Geochem. Geophy. Geosy., 22, e2020GC009466, https://doi.org/10.1029/2020GC009466, 2021.
Manzotti, P., Bosse, V., Pitra, P., Robyr, M., Schiavi, F., and Ballèvre, M.: Exhumation rates in the Gran Paradiso Massif (Western Alps) constrained by in situ U–Th–Pb dating of accessory phases (monazite, allanite and xenotime), Contrib. Mineral. Petrol., 173, https://doi.org/10.1007/s00410-018-1452-7, 2018.
Manzotti, P., Schiavi, F., Nosenzo, F., Pitra, P., and Ballèvre, M.: A journey towards the forbidden zone: a new, cold, UHP unit in the Dora-Maira Massif (Western Alps), Contrib. Mineral. Petrol., 177, 59, https://doi.org/10.1007/s00410-022-01923-8, 2022.
Marthaler, M. and Stampfli, G. M.: Les Schistes lustrés à ophiolites de la nappe du Tsaté: Un ancien prisme d'accrétion issu de la marge active apulienne?, Schweizerische mineralogische und petrographische Mitteilungen, 69, 211–216, 1989.
Mazzucchelli, M. L., Burnley, P., Angel, R. J., Morganti, S., Domeneghetti, M. C., Nestola, F., and Alvaro, M.: Elastic geothermobarometry: corrections for the geometry of the host-inclusion system, Geology, 46, 231–234, https://doi.org/10.1130/G39807.1, 2018.
Michard, A., Goffé, B., Chopin, C., and Henry, C.: Did the Western Alps develop through an Oman-type stage? The geotectonic setting of high-pressure metamorphism in two contrasting Tethyan transects, Eclogae Geol. Helv., 89, 43–80, 1996.
Platt, J. P.: Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks, Geol. Soc. Am. Bull., 97, 1037–1053, https://doi.org/10.1130/0016-7606(1986)97<1037:DOOWAT>2.0.CO;2, 1986.
Reinecke, T.: Very-high-pressure metamorphism and uplift of coesite-bearing metasediments from the Zermatt-Saas zone, Western Alps. Eur. J. Mineral., 3, 7–17, https://doi.org/10.1127/ejm/3/1/0007, 1991.
Rosenbaum, G. and Lister, G. S.: The Western Alps from the Jurassic to Oligocene: Spatiotemporal Constraints and Evolutionary Reconstructions, Earth Sci. Rev., 69, 281–306, https://doi.org/10.1016/j.earscirev.2004.10.001, 2005.
Scaramuzzo, E., Livio, F. A., Granado, P., Di Capua, A., and Bitonte, R.: Anatomy and kinematic evolution of an ancient passive margin involved into an orogenic wedge (Western Southern Alps, Varese area, Italy and Switzerland), Swiss J. Geosci., 115, 4, https://doi.org/10.1186/s00015-021-00404-7, 2022.
Schmid, S. M., Fügenschuh, B., Kissling, E., and Schuster, R.: Tectonic map and overall architecture of the Alpine orogen, Eclogae Geol. Helv., 97, 93–117, https://doi.org/10.1007/s00015-004-1113-x, 2004.
Schmid, S. M., Kissling, E., Diehl, T., van Hinsbergen, D. J. J., and Molli, G.: Ivrea mantle wedge, arc of the Western Alps, and kinematic evolution of the Alps–Apennines orogenic system, Swiss J. Geosci, 110, 581–612, https://doi.org/10.1007/s00015-016-0237-0, 2017.
Schönig, J., von Eynatten, H., Meinhold, G., and Lünsdorf, N. K.: Diamond and coesite inclusions in detrital garnet of the Saxonian Erzgebirge, Germany, Geology, 47, 715–18, https://doi.org/10.1130/G46253.1, 2019. Schönig, J., von Eynatten, H., Meinhold, G., and Lünsdorf, N. K.: Life-cycle analysis of coesite-bearing garnet, Geological Magazine, 158, 1421–1440, https://doi.org/10.1017/S0016756821000017, 2021.
Smith, D.: Coesite in clinopyroxene in the Caledonides and its implications for geodynamics, Nature, 310, 641–644, https://doi.org/10.1038/310641a0, 1984.
Taguchi, T., Kouketsu, Y., Igami, Y., Kobayashi, T., and Miyake, A.: Hidden intact coesite in deeply subducted rocks, Earth Planet. Sc. Lett., 558, 116763, https://doi.org/10.1016/j.epsl.2021.116763, 2021.
Thompson, A. B., Tracy, R. J., Lyttle, P., and Thompson Jr., J. B.: Prograde reaction histories deduced from compositional zonation and mineral inclusions in garnet from the Gassetts schists, Vermont, Am. J. Sci., 277, 1152–1167, https://doi.org/10.2475/ajs.277.9.1152, 1977.
Warr, L. N.: IMA-CNMNC approved mineral symbols, Mineral. Mag., 85, 291–320, https://doi.org/10.1180/mgm.2021.43, 2021.
Zhang, L., Ellis, D. J., and Jiang, W.: Ultrahigh-pressure metamorphism in western Tianshan, China: part I. Evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites, Am. Mineral., 87, 853–860, https://doi.org/10.2138/am-2002-0707, 2002.
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.
We report a new ultra-high-pressure (UHP) locality in the western Alps (Italy). Micro-Raman...