Articles | Volume 35, issue 4
https://doi.org/10.5194/ejm-35-589-2023
© Author(s) 2023. 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-35-589-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
02 Aug 2023
Research article |
| 02 Aug 2023
| 02 Aug 2023
Petrological study of an eclogite-facies metagranite from the Champtoceaux Complex (La Picherais, Armorican Massif, France)
Université de Rennes, CNRS, Géosciences Rennes UMR 6118,
35000 Rennes, France
Philippe Yamato
Université de Rennes, CNRS, Géosciences Rennes UMR 6118,
35000 Rennes, France
Institut Universitaire de France, 75000 Paris, France
Gaston Godard
Université Paris Cité, Institut de Physique du Globe de Paris, 75005 Paris, France
Related authors
Pierre Dietrich, François Guillocheau, Guilhem A. Douillet, Neil P. Griffis, Guillaume Baby, Daniel P. Le Héron, Laurie Barrier, Maximilien Mathian, Isabel P. Montañez, Cécile Robin, Thomas Gyomlai, Christoph Kettler, and Axel Hofmann
Earth Surf. Dynam., 13, 495–529, https://doi.org/10.5194/esurf-13-495-2025, https://doi.org/10.5194/esurf-13-495-2025, 2025
Short summary
Short summary
At the evocation of icy landscapes, Africa is not the first place that comes to mind. The modern relief of Southern Africa is generally considered to be a result of uplift and counteracting erosion. We show that some of the modern relief of this region is due to fossil glacial landscapes – striated pavements, valleys, and fjords – tied to an ice age that occurred ca. 300 Myr ago. We focus on how these landscapes have escaped being erased for hundreds of millions of years.
Thomas Geffroy, Philippe Yamato, Philippe Steer, Benjamin Guillaume, and Thibault Duretz
Solid Earth, 16, 1289–1306, https://doi.org/10.5194/se-16-1289-2025, https://doi.org/10.5194/se-16-1289-2025, 2025
Short summary
Short summary
While erosion's role in mountain building is well known, deformation from valley incision in inactive regions is less understood. Using our numerical models, we show that incision alone can cause significant crustal deformation and drive lower crust exhumation. This is favored in areas with thick crust, weak lower crust, and high plateaux. Our results show surface processes can reshape Earth's surface over time.
Pierre Dietrich, François Guillocheau, Guilhem A. Douillet, Neil P. Griffis, Guillaume Baby, Daniel P. Le Héron, Laurie Barrier, Maximilien Mathian, Isabel P. Montañez, Cécile Robin, Thomas Gyomlai, Christoph Kettler, and Axel Hofmann
Earth Surf. Dynam., 13, 495–529, https://doi.org/10.5194/esurf-13-495-2025, https://doi.org/10.5194/esurf-13-495-2025, 2025
Short summary
Short summary
At the evocation of icy landscapes, Africa is not the first place that comes to mind. The modern relief of Southern Africa is generally considered to be a result of uplift and counteracting erosion. We show that some of the modern relief of this region is due to fossil glacial landscapes – striated pavements, valleys, and fjords – tied to an ice age that occurred ca. 300 Myr ago. We focus on how these landscapes have escaped being erased for hundreds of millions of years.
Gaston Godard, David C. Smith, Damien Jaujard, and Sidali Doukkari
Eur. J. Mineral., 36, 99–122, https://doi.org/10.5194/ejm-36-99-2024, https://doi.org/10.5194/ejm-36-99-2024, 2024
Short summary
Short summary
Petrological and mineralogical studies of mica schists, orthogneisses and glaucophane eclogites from Dumet Island (Armorican Massif, NW France) indicate that this occurrence, which has undergone high-pressure metamorphism up to 16 kbar and 620 °C, is similar to that of Groix Island. There are about 10 similar occurrences within the Ibero-Armorican Arc, forming a discontinuous high-pressure belt, but most of them have remained unnoticed due to a high degree of retrogression.
Cited articles
Abati, J., Gerdes, A., Fernandez Suarez, J., Arenas, R., Whitehouse, M. J.,
and Diez Fernandez, R: Magmatism and early-Variscan continental subduction
in the northern Gondwana margin recorded in zircons from the basal units of
Galicia, NW Spain, GSA Bulletin, 122, 219–235, https://doi.org/10.1130/B26572.1, 2010.
Abers, G. A. and Hacker, B. R.: A MATLAB toolbox and Excel workbook for
calculating the densities, seismic wave speeds, and major element
composition of minerals and rocks at pressure and temperature, Geochem.
Geophy. Geosy., 17, 616–624, https://doi.org/10.1002/2015GC006171, 2016.
Adjerid, Z., Godard, G., and Ouzegane, K.: High-pressure whiteschists from
the Ti-N-Eggoleh area (Central Hoggar, Algeria): A record of Pan-African
oceanic subduction, Lithos, 226, 201–216, https://doi.org/10.1016/j.lithos.2015.02.013, 2015.
Angiboust, S. and Harlov, D.: Ilmenite breakdown and rutile-titanite
stability in metagranitoids: Natural observations and experimental results,
Am. Mineral., 102,
1696–1708, https://doi.org/10.2138/am-2017-6064, 2017.
Austrheim, H.: Eclogitization of lower crustal granulites by fluid migration
through shear zones, Earth Planet. Sc. Lett., 81, 221–232,
https://doi.org/10.1016/0012-821X(87)90158-0, 1987.
Autran, A. and Peterlongo, J. M.: Massif Central, Revue des Sciences
Naturelles d'Auvergne, 45, 5–123, 1973.
Baïsset, M., Labrousse, L., Yamato, P., and Schubnel, A.: Twinning and
partial melting as early weakening processes in plagioclase at high
pressure: insights from Holsnøy (Scandinavian Caledonides, Norway),
Contrib. Mineral. Petrol., 178, 19, https://doi.org/10.1007/s00410-023-01998-x, 2023.
Baldwin, J., Powell, R., White, R., and Štípská, P.: Using
calculated chemical potential relationships to account for replacement of
kyanite by symplectite in high pressure granulites, J. Metamorph.
Geol., 33, 311–330, https://doi.org/10.1111/jmg.12122, 2015.
Ballèvre, M. and Marchand, J.: Zonation du métamorphisme
éclogitique dans la nappe de Champtoceaux (Massif armoricain, France),
C. R. Acad. Sci. II, 312, 705–711,
1991.
Ballèvre, M., Marchand, J., Godard, G., Goujou, J.-C., Christian, J.,
and Wyns, R.: Eo-Hercynian events in the Armorican massif, in: Pre-Mesozoic
geology in France and related areas, Springer, 183–194, https://doi.org/10.1007/978-3-642-84915-2_19, 1994.
Ballèvre, M., Capdevila, R., Guerrot, C., and Peucat, J.-J.: Discovery
of an alkaline orthogneiss in the eclogite-bearing Cellier unit
(Champtoceaux complex, Armorican massif): a new witness of the Ordovician
rifting, C. R. Géosci., 334, 303–311, https://doi.org/10.1016/S1631-0713(02)01760-1, 2002.
Ballèvre, M., Bosse, V., Ducassou, C., and Pitra, P.: Palaeozoic history
of the Armorican Massif: models for the tectonic evolution of the suture
zones, C. R. Géosci., 341, 174–201, https://doi.org/10.1016/j.crte.2008.11.009, 2009.
Ballèvre, M., Martínez Catalán, J.R., López-Carmona, A.,
Pitra, P., Abati, J., Díez Fernández, R., Ducassou, C., Arenas, R.,
Bosse, V., Castiñeiras, P., Fernández-Suárez, J., Barreiro, J. G., Paquette, J.-L., Peucat, J.-J., Poujol, M., Ruffet, G., and Martínez, S. S.: Correlation of the nappe stack in the Ibero-Armorican arc across the
Bay of Biscay: a joint French–Spanish project, in: The Variscan Orogeny:
Extent, timescale and the formation of the European crust, Geol.
Soc. Spec. Publ., 405, 77–113, https://doi.org/10.1144/SP405.13, 2014.
Bauville, A. and Yamato, P.: Pressure-to-depth conversion models for
metamorphic rocks: derivation and applications, Geochem. Geophy.
Geosy., 22, e2020GC009280, https://doi.org/10.1029/2020GC009280, 2021.
Bernard-Griffiths, J. and Cornichet, J.: Origin of eclogites from South
Brittany, France: A Sm-Nd isotopic and REE study, Chem. Geol., 52, 185–201, https://doi.org/10.1016/0168-9622(85)90017-X, 1985.
Bidgood, A. K., Waters, D. J., Dyck, B. J., and Roberts, N. M.: The
emplacement, alteration, subduction and metamorphism of metagranites from
the Tso Morari Complex, Ladakh Himalaya, Mineral. Mag., 87,
40–59, https://doi.org/10.1180/mgm.2022.121, 2023.
Biino, G. G. and Compagnoni, R.: Very-high pressure metamorphism of the
Brossasco coronite metagranite, southern Dora-Maira Massif, Western Alps,
Schweiz. Mineral. Petrog. Mitt., 72,
347–363, 1992.
Bosse, V., Feraud, G., Ruffet, G., Ballèvre, M., Peucat, J.-J., and De
Jong, K.: Late Devonian subduction and early-orogenic exhumation of
eclogite-facies rocks from the Champtoceaux Complex (Variscan belt, France),
Geol. J., 35, 297–325, https://doi/10.1002/gj.864, 2000.
Bras, E., Baïsset, M., Yamato, P., and Labrousse, L.: Transient
weakening during the granulite to eclogite transformation within hydrous
shear zones (Holsnøy, Norway), Tectonophysics, 819, 229026, https://doi.org/10.1016/j.tecto.2021.229026, 2021.
Brière, Y.: Les éclogites françaises, Leur composition
minéralogique et chimique. Leur origine, Bulletin de la Société
française de Minéralogie, 43, 72–222, https://doi.org/10.3406/bulmi.1920.3743, 1920.
Brun, J.-P. and Burg, J.-P.: Combined thrusting and wrenching in the
Ibero-Armorican arc: a corner effect during continental collision, Earth
Planet. Sc. Lett., 61, 319–332, https://doi.org/10.1016/0012-821X(82)90063-2, 1982.
Bruno, M. and Rubbo, M.: The metamorphic history of Monte Mucrone
metagranodiorite constrained by garnet growth modelling, Period.
Mineral., 75, 3–22, 2006.
Bruno, M., Compagnoni, R., and Rubbo, M.: The ultra-high pressure coronitic
and pseudomorphous reactions in a metagranodiorite from the Brossasco-Isasca
Unit, Dora-Maira Massif, western Italian Alps: a petrographic study and
equilibrium thermodynamic modelling, J. Metamorph. Geol., 19,
33–43, https://doi.org/10.1046/j.1525-1314.2001.00291.x, 2001.
Catalán, J. M., Arenas, R., García, F. D., Cuadra, P. G.,
Gómez-Barreiro, J., Abati, J., Castiñeiras, P.,
Fernández-Suárez, J., Martínez, S. S., Andonaegui, P., Clavijo, E. G., Montes, A. D., Pascual, F. J. R., and Aguado, B. V.:
Space and time in the tectonic evolution of the northwestern Iberian Massif:
Implications for the Variscan belt, in: 4-D framework of continental crust,
Vol. 200, Geological Society of America Memoir Boulder,
Colorado, 403–423, https://doi.org/10.1130/2007.1200(21), 2007.
Cavet, P., Marchand, J., Gruet, M., Lardeux, H., Rivière, L. M., and
Arnaud, A.: Carte géologique de la France (1:50 000), feuille Ancenis
(452); notice explicative par Cavet, P., Arnaud, A., Blaise, J., Gruet, M., Lardeux, H., Marchand, J., Nicolas, A., Rivière, L. M., and Rossignol, J. C., 56 pp.,
BRGM, Orléans, 1987.
Chopin, C., Henry, C., and Michard, A.: Geology and petrology of the
coesite-bearing terrain, Dora Maira massif, Western Alps, Eur. J. Mineral., 3, 263–291, https://doi.org/10.1127/ejm/3/2/0263, 1991.
Coggon, R. and Holland, T.: Mixing properties of phengitic micas and
revised garnet phengite thermobarometers, J. Metamorph. Geol.,
20, 683–696, https://doi.org/10.1046/j.1525-1314.2002.00395.x, 2002.
Cogné, J.: Une “nappe” cadomienne de style pennique: la série
cristallophyllienne de Champtoceaux en bordure méridionale du Synclinal
d'Ancenis (Bretagne-Anjou), Bulletin du Service de la carte géologique
d'Alsace et de Lorraine, 19, 107–136, https://doi.org/10.3406/sgeol.1966.1300, 1966.
Compagnoni, R. and Maffeo, B.: Jadeite-bearing metagranites L.S. and
related rocks in the Mount Mucrone area (Sesia-Lanzo zone, western Italian
Alps), Schweizerische Miner. Petrog.,
53, 355–378, 1973.
Connolly, J. A.: Multivariable phase diagrams; an algorithm based on
generalized thermodynamics, Am. J. Sci., 290, 666–718,
1990.
Connolly, J. A.: Computation of phase equilibria by linear programming: a
tool for geodynamic modeling and its application to subduction zone
decarbonation, Earth Planet. Sc. Lett., 236, 524–541, https://doi.org/10.1016/j.epsl.2005.04.033,
2005.
Diener, J., Powell, R., White, R., and Holland, T.: A new thermodynamic
model for clino-and orthoamphiboles in the system
Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O, J. Metamorph. Geol.,
25, 631–656, https://doi.org/10.1111/j.1525-1314.2007.00720.x, 2007.
Doukkari, S. A., Diener, J. F., Ouzegane, K., and Kiénast, J.-R.:
Mineral equilibrium modelling and calculated chemical potential relations of
reaction textures in the ultrahigh temperature In Ouzzal terrane (In Hihaou
area, Western Hoggar, Algeria), J. Metamorph. Geol., 36,
1175–1198, https://doi.org/10.1111/jmg.12441, 2018.
Dubuisson, F. R. A.: Catalogue de la collection minéralogique,
géognostique et minéralurgique du département de la
Loire-Inférieure, appartenant à la mairie de Nantes, Mellinet,
Nantes, 319 pp., 1830.
Engvik, A. K., Austrheim, H., and Andersen, T. B.: Structural, mineralogical
and petrophysical effects on deep crustal rocks of fluid-limited
polymetamorphism, Western Gneiss Region, Norway, J. Geol.
Soc., 157, 121–134, https://doi.org/10.1144/jgs.157.1.121, 2000.
Ferrando, S., Frezzotti, M., Petrelli, M., and Compagnoni, R.: Metasomatism
of continental crust during subduction: the UHP whiteschists from the
Southern Dora-Maira Massif (Italian Western Alps), J. Metamorph. Geol., 27, 739–756, https://doi.org/10.1111/j.1525-1314.2009.00837.x, 2009.
Gil Ibarguchi, J. I.: Petrology of jadeite metagranite and associated
orthogneiss from the Malpica-Tuy allochthon (Northwest Spain), Eur. J. Mineral., 7, 403–416, https://doi.org/10.1127/ejm/7/2/0403, 1995.
Godard, G.: Petrology of some eclogites in the Hercynides: the eclogites
from the southern Armorican massif, France, in: Eclogites and
eclogites-facies rocks, Elsevier, 451–519, 1988.
Godard, G.: The Les Essarts eclogite-bearing metamorphic Complex
(Vendée, Southern Armorican Massif, France), Géologie de la France,
2001, 19–51, 2001.
Godard, G.: Two orogenic cycles recorded in eclogite-facies gneiss from the
southern Armorican Massif (France), Europ. J. Mineral., 21,
1173–1190, https://doi.org/10.1127/0935-1221/2009/0021-1984, 2009.
Godard, G., Kiénast, J.-R., and Lasnier, B.: Retrogressive development
of glaucophane in some eclogites from “Massif Armoricain” (east of Nantes,
France), Contrib. Mineral. Petrol., 78, 126–135, https://doi.org/10.1007/BF00373774, 1981.
Gosso, G., Messiga, B., Rebay, G., and Spalla, M. I.: Interplay between
deformation and metamorphism during eclogitization of amphibolites in the
Sesia–Lanzo Zone of the Western Alps, Int. Geol. Rev.,
52, 1193–1219, https://doi.org/10.1080/00206810903529646, 2010.
Green, E., Holland, T., and Powell, R.: An order-disorder model for
omphacitic pyroxenes in the system jadeite-diopside-hedenbergite-acmite,
with applications to eclogitic rocks, Am. Mineral., 92,
1181–1189, 2007.
Guiraud, M., Powell, R., and Rebay, G.: H2O in metamorphism and unexpected
behaviour in the preservation of metamorphic mineral assemblages, J. Metamorph. Geol., 19, 445–454, https://doi.org/10.1046/j.0263-4929.2001.00320.x, 2001.
Hacker, B. R., Andersen, T. B., Johnston, S., Kylander-Clark, A. R.,
Peterman, E. M., Walsh, E. O., and Young, D.: High-temperature deformation
during continental-margin subduction and exhumation: The ultrahigh-pressure
Western Gneiss Region of Norway, Tectonophysics, 480, 149–171, https://doi.org/10.1016/j.tecto.2009.08.012, 2010.
Hawthorne, F. C., Oberti, R., Harlow, G. E., Maresch, W. V., Martin, R. F.,
Schumacher, J. C., and Welch, M. D.: Nomenclature of the amphibole
supergroup, Am. Mineral., 97, 2031–2048, https://doi.org/10.2138/am.2012.4276, 2012.
Heinrich, C. A.: Kyanite-eclogite to amphibolite facies evolution of hydrous
mafic and pelitic rocks, Adula nappe, Central Alps, Contrib.
Mineral. Petrol., 81, 30–38, https://doi.org/10.1007/BF00371156, 1982.
Hobbs, B. E., Ord, A., Spalla, M. I., Gosso, G., and Zucali, M.: The
interaction of deformation and metamorphic reactions, Geol. Soc.,
Lond. Spec. Publ., 332, 189–223, https://doi.org/10.1144/SP332.12, 2010.
Holland, T. and Powell, R.: An internally consistent thermodynamic data set
for phases of petrological interest, J. Metamorph. Geol., 16,
309–343, https://doi.org/10.1111/j.1525-1314.1998.00140.x, 1998.
Holland, T. and Powell, R.: Activity–composition relations for phases in
petrological calculations: an asymmetric multicomponent formulation,
Contrib. Mineral. Petrol., 145, 492–501, https://doi.org/10.1007/s00410-003-0464-z, 2003.
Holland, T., Baker, J., and Powell, R.: Mixing properties and
activity-composition relationships of chlorites in the system
MgO-FeO-Al2O3-SiO2-H2O, Eur. J. Mineral., 10, 395–406,
https://doi.org/10.1127/ejm/10/3/0395, 1998.
Holyoke, C. W. and Tullis, J.: The interaction between reaction and
deformation: an experimental study using a biotite + plagioclase + quartz
gneiss, J. Metamorph. Geol., 24, 743–762, https://doi.org/10.1111/j.1525-1314.2006.00666.x, 2006.
Kohn, M. J.: A refined zirconium-in-rutile thermometer, Am.
Mineral., 105, 963–971, https://doi.org/10.2138/am-2020-7091, 2020.
Krabbendam, M., Wain, A., and Andersen, T. B.: Pre-Caledonian granulite and
gabbro enclaves in the Western Gneiss Region, Norway: indications of
incomplete transition at high pressure, Geol. Mag., 137,
235–255, 2000.
Kretz, R.: Symbols for rock-forming minerals, Am. Mineral.,
68, 277–279, 1983.
Lacroix, A.: Etude pétrographique des éclogites de la
Loire-Inférieure, Bulletin de la Société des Sciences naturelles
de l'Ouest de la France, I, 81–114, 1891.
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.
Lasnier, B., Leyreloup, A., and Marchand, J.: Découverte d'un granite
charnockitique au sein de gneiss œillés; perspectives nouvelles sur
l'origine de certaines leptynites du massif armoricain méridional
(France), Contrib. Mineral. Petrol., 41, 131–144, https://doi.org/10.1007/BF00375038, 1973.
Le Bas, M. J., Maitre, R. L., Streckeisen, A., Zanettin, B., and IUGS
Subcommission on the Systematics of Igneous Rocks: A chemical classification
of volcanic rocks based on the total alkali-silica diagram, J.
Petrol., 27, 745–750, https://doi.org/10.1093/petrology/27.3.745, 1986.
Li, D.-Y., Xiao, Y., Li, W.-Y., Zhu, X., Williams, H., and Li, Y.-L.: Iron
isotopic systematics of UHP eclogites respond to oxidizing fluid during
exhumation, J. Metamorph. Geol., 34, 987–997, https://doi.org/10.1111/jmg.12217, 2016.
Lotout, C.: Âge, durée et enregistrement du
métamorphisme de haute pression dans le massif Central, Doctoral
dissertation, Université Rennes 1, 2017.
Luisier, C., Baumgartner, L., Schmalholz, S. M., Siron, G., and Vennemann,
T.: Metamorphic pressure variation in a coherent Alpine nappe challenges
lithostatic pressure paradigm, Nat. Commun., 10, 1–11, https://doi.org/10.1186/s00015-021-00397-3, 2019.
Marchand, J., Sellier, D., Bossière, G., Carlier, G., Deniel, C., and
Lasnier, B.: Carte géologique de la France (
Martínez Catalán, J. R., Arenas, R., Díaz García, F.,
Rubio Pascual, F. J., Abati, J., and Marquínez, J.: Variscan exhumation
of a subducted Paleozoic continental margin: the basal units of the Ordenes
Complex, Galicia, NW Spain, Tectonics, 15, 106–121, https://doi.org/10.1029/95TC02617, 1996.
Matte, P.: Accretionary history and crustal evolution of the Variscan belt
in Western Europe, Tectonophysics, 196, 309–337, https://doi.org/10.1016/0040-1951(91)90328-P, 1991.
Moulas, E., Burg, J. P., and Podladchikov, Y.: Stress field associated with
elliptical inclusions in a deforming matrix: Mathematical model and
implications for tectonic overpressure in the lithosphere, Tectonophysics,
631, 37–49, https://doi.org/10.1016/j.tecto.2014.05.004, 2014.
Palin, R. M., Reuber, G. S., White, R. W., Kaus, B. J., and Weller, O. M.:
Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari
massif: an integrated geodynamic and petrological modelling approach, Earth
Planet. Sc. Lett., 467, 108–119, https://doi.org/10.1016/j.epsl.2017.03.029, 2017.
Paquette, J.-L., Marchand, J., and Peucat, J.: Absence de tectonique
cadomienne dans le complexe de Champtoceaux (Bretagne méridionale)?
Comparaison des systèmes Rb-Sr et U-Pb d'un métagranite, Bull.
Soc. Geol. France, 26,
907–912, https://doi.org/10.2113/gssgfbull.S7-XXVI.5.907, 1984.
Pearce, J. A.: Geochemical fingerprinting of oceanic basalts with
applications to ophiolite classification and the search for Archean oceanic
crust, Lithos, 100, 14–48, https://doi.org/10.1016/j.lithos.2007.06.016, 2008.
Peterman, E. M., Hacker, B. R., and Baxter, E. F.: Phase transformations of
continental crust during subduction and exhumation: Western Gneiss Region,
Norway, Eur. J. Mineral., 21, 1097–1118, https://doi.org/10.1127/0935-1221/2009/0021-1988, 2009.
Pitra, P., Ballèvre, M., and Ruffet, G.: Inverted metamorphic field
gradient towards a Variscan suture zone (Champtoceaux Complex, Armorican
Massif, France), J. Metamorph. Geol., 28, 183–208, https://doi.org/10.1111/j.1525-1314.2009.00862.x, 2010.
Pouchou, J.-L. and Pichoir, F.: Quantitative analysis of homogeneous or
stratified microvolumes applying the model “PAP”, in: Electron probe
quantitation, Springer, 31–75, https://doi.org/10.1007/978-1-4899-2617-3_4, 1991.
Powell, R. and Holland, T.: Relating formulations of the thermodynamics of
mineral solid solutions; activity modeling of pyroxenes, amphiboles, and
micas, Am. Mineral., 84, 1–14, https://doi.org/10.2138/am-1999-1-201, 1999.
Proyer, A.: The preservation of high-pressure rocks during exhumation:
metagranites and metapelites, Lithos, 70, 183–194, https://doi.org/10.1016/S0024-4937(03)00098-7, 2003.
Ribeiro, A., Pereira, E., Dias, R., Gil Ibarguchi, J., and Arenas, R.:
Allochthonous sequences, in: Pre-Mesozoic Geology of Iberia,
Springer, 220–246, https://doi.org/10.1007/978-3-642-83980-1_15, 1990.
Roda, M., Spalla, M. I., and Marotta, A. M.: Integration of natural data
within a numerical model of ablative subduction: a possible interpretation
for the Alpine dynamics of the Austroalpine crust, J. Metamorph. Geol., 30, 973–996, https://doi.org/10.1111/jmg.12000, 2012.
Rodríguez, J., Cosca, M., Gil Ibarguchi, J. I., and Dallmeyer, R.: Strain
partitioning and preservation of 40Ar
Rubbo, M., Borghi, A., and Compagnoni, R.: Thermodynamic analysis of garnet
growth zoning in eclogite facies granodiorite from M. Mucrone, Sesia Zone,
Western Italian Alps, Contrib. Mineral. Petrol., 137,
289–303, https://doi.org/10.1007/s004100050551, 1999.
Rubie, D. C.: Role of kinetics in the formation and preservation of
eclogites, Eclogite Facies Rocks, 111–140, 1990.
Rubie, D. C.: Disequilibrium during metamorphism: the role of nucleation
kinetics, Geol. Soc. Lond. Spec. Publ., 138,
199–214, https://doi.org/10.1144/GSL.SP.1996.138.01.12, 1998.
Rumble, D.: Stable isotope geochemistry of ultrahigh-pressure rocks, in: When
continents collide: Geodynamics and geochemistry of ultrahigh-pressure
rocks, Springer, 241–259, https://doi.org/10.1007/978-94-015-9050-1_9, 1998.
Schorn, S.: Self-induced incipient “eclogitization” of metagranitoids at
closed-system conditions, J. Metamorph. Geol., 40, 1271–1290,
https://doi.org/10.1111/jmg.12665, 2022.
Schorn, S., Diener, J. F., Sorger, D., and Clark, C.: The contribution of
charnockite magmatism to achieve near-ultrahigh temperatures in the
Namaqua–Natal Metamorphic Province, South Africa, Lithos, 368, 105585,
https://doi.org/10.1016/j.lithos.2020.105585, 2020.
Shand, S. J.: The Eruptive Rocks, 2nd edition, John Wiley, 444 pp., New York,
1943.
Spencer, K., Hacker, B., Kylander-Clark, A., Andersen, T., Cottle, J.,
Stearns, M., Poletti, J., and Seward, G.: Campaign-style titanite U–Pb
dating by laser-ablation ICP: Implications for crustal flow, phase
transformations and titanite closure, Chem. Geol., 341, 84–101, https://doi.org/10.1016/j.chemgeo.2012.11.012, 2013.
Streckeisen, A.: To each plutonic rock its proper name, Earth-Sci.
Rev., 12, 1–33, https://doi.org/10.1016/0012-8252(76)90052-0, 1976.
Tropper, P., Essene, E. J., Sharp, Z. D., and Hunziker, J. C.: Application
of K-feldspar–jadeite–quartz barometry to eclogite facies metagranites and
metapelites in the Sesia Lanzo Zone (Western Alps, Italy), J. Metamorph. Geol., 17, 195–209, 1999.
Velde, B.: Les éclogites de la région nantaise (de Campbon au
Cellier, Loire Atlantique), Bull. Mineral., 93, 370–385, https://doi.org/10.3406/bulmi.1970.6479, 1970.
Vernon, R. H.: Rapakivi granite problems: plagioclase mantles and ovoid
megacrysts, Austr. J. Earth Sci., 63, 675–700, https://doi.org/10.1080/08120099.2016.1241953, 2016.
Vidal, P., Peucat, J., and Lasnier, B.: Dating of granulites involved in the
Hercynian Fold-belt of Europe: an example taken from the granulite-facies
orthogneisses at La Picherais, Southern Armorican Massif, France,
Contrib. Mineral. Petrol., 72, 283–289, https://doi.org/10.1007/BF00376146, 1980.
Vrabec, M., Janák, M., Froitzheim, N., and De Hoog, J. C.: Phase
relations during peak metamorphism and decompression of the UHP kyanite
eclogites, Pohorje Mountains (Eastern Alps, Slovenia), Lithos, 144, 40–55,
https://doi.org/10.1016/j.lithos.2012.04.004, 2012.
Wain, A., Waters, D., and Austrheim, H.: Metastability of granulites and
processes of eclogitisation in the UHP region of western Norway, J. Metamorph. Geol., 19, 609–625, https://doi.org/10.1046/j.0263-4929.2001.00333.x, 2001.
White, R. and Powell, R.: On the interpretation of retrograde reaction
textures in granulite facies rocks, J. Metamorph. Geol., 29,
131–149, https://doi.org/10.1111/j.1525-1314.2010.00905.x, 2011.
Young, D. and Kylander-Clark, A.: Does continental crust transform during
eclogite facies metamorphism?, J. Metamorph. Geol., 33,
331–357, https://doi.org/10.1111/jmg.12123, 2015.
Young, D. J., Hacker, B. R., Andersen, T. B., and Corfu, F.: Prograde
amphibolite facies to ultrahigh-pressure transition along Nordfjord, western
Norway: Implications for exhumation tectonics, Tectonics, 26, 15 pp., https://doi.org/10.1029/2004TC001781, 2007.
Zhao, Z.-F., Zheng, Y.-F., Gao, T.-S., Wu, Y.-B., Chen, B., Chen, F.-K., and
Wu, F.-Y.: Isotopic constraints on age and duration of fluid-assisted
high-pressure eclogite facies recrystallization during exhumation of deeply
subducted continental crust in the Sulu orogen, J. Metamorph. Geol., 24, 687–702, https://doi.org/10.1111/j.1525-1314.2006.00662.x, 2006.
Short summary
The La Picherais metagranite is a key example of undeformed high-pressure quartzofeldspathic rock from the Armorican Massif. Through petrological observations and thermodynamic modelling, this study determines that the metagranite was pressured above 1.7 GPa and the associated mafic lenses at ~ 2.1 GPa. This metagranite provides an opportunity to study the degree of transformation of quartzofeldspathic rocks at high pressure, which may have a significant impact on the dynamics of subduction.
The La Picherais metagranite is a key example of undeformed high-pressure quartzofeldspathic...
