Kinematics of subduction in the Ibero-Armorican arc constrained by 3D microstructural analysis of garnet and pseudomorphed lawsonite porphyroblasts from Île de Groix (Variscan belt) Aerden, Domingo Gerard Ruiz Fuentes, Alejandro Sayab, Mohammad Forde, Aidan The research was supported by Spanish government project CGL2016-80687-R AEI/FEDER and projects RNM148, P18-RT-3275 and B-RNM-301-UGR18 of the Andalusia Autonomous Government. The first author wishes to thank José Ramón Martínez Catalán for his guidance and friendship during a postdoc in Salamanca (1996–1999). We thank Michel Ballèvre for helping us obtain permission from the Préfecture du Morbihan to collect samples on Île de Groix and for suggesting we include the Pouldu schists in our study. Île de Groix national park guide Catherine Robert (and her dog) provided Domingo Aerden with helpful information and pleasant company during fieldwork. We thank Fátima Linares-Ordoñez for X-ray scanning our samples and Bernhardt Schulz for clarifying various aspects about the petrology of the study area. The authors are very grateful to the two anonymous reviewers, who provided constructive comments, and the handling editors of Solid Earth, Ícaro Dias da Silva and Federico Rossetti. The small island of Groix in southern Brittany, France, is well known for exceptionally well-preserved outcrops of Variscan blueschists, eclogites, and garnetiferous mica schists that mark a Late Devonian suture between Gondwana and Armorica. The kinematics of polyphase deformation in these rocks is reconstructed based on 3D microstructural analysis of inclusion trails within garnet and pseudomorphed lawsonite porphyroblasts using differently oriented thin sections and X-ray tomography. Three sets of inclusion trails striking NE-SW, NNW-SSE, and WNW-ESE are recognized and interpreted to witness a succession of different crustal shortening directions orthogonal to these strikes. The curvature sense of sigmoidal and spiral-shaped inclusion trails of the youngest set is shown to be consistent with northwest and northward subduction of Gondwana under Armorica, provided that these microstructures developed by overgrowth of actively forming crenulations without much porphyroblast rotation. Strongly non-cylindrical folds locally found on the island are reinterpreted as fold-interference structures instead of having formed by progressive shearing and fold-axis reorientation. Six samples of a lower-grade footwall unit of the Groix ophiolitic nappe (Pouldu schists) were also studied. Inclusion trails in these rocks strike E-W, similar to the youngest set recognized on Groix island. They record Carboniferous N-S shortening during continental collision. These new microstructural data from southern Brittany bear a strong resemblance to earlier measured in inclusion-trail orientations in the northwestern Iberia Massif. A best fit between both regions suggests not more than about 15 degrees anticlockwise rotation of Iberia during the Cretaceous opening of the Gulf of Biscay. 2021-05-28T12:11:24Z 2021-05-28T12:11:24Z 2021-04-26 info:eu-repo/semantics/article Aerden, D. G. A. M., Ruiz-Fuentes, A., Sayab, M., and Forde, A.: Kinematics of subduction in the Ibero-Armorican arc constrained by 3D microstructural analysis of garnet and pseudomorphed lawsonite porphyroblasts from Île de Groix (Variscan belt), Solid Earth, 12, 971–992, [https://doi.org/10.5194/se-12-971-2021], 2021 http://hdl.handle.net/10481/68860 10.5194/se-12-971-2021 eng http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Copernicus GmbH