Ocean-floor hydrothermal metamorphism in the Limousin ophiolites (western French Massif Central): evidence of a rare preserved Variscan oceanic marker |
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| Authors: | J BERGER O FEMENIAS J C C MERCIER D DEMAIFFE |
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| Institution: | Département de Géologie, Section de Géologie Isotopique, Africa Museum, B-3080 Tervuren, Belgium (); Laboratoire de Géochimie Isotopique et Géodynamique Chimique, DSTE, UniversitéLibre de Bruxelles (CP 160/02), 50 Avenue Roosevelt, B-1050 Brussels, Belgium; CLDG, Universitéde La Rochelle, av. M. Crépeau, 17042 La Rochelle Cedex 1, France |
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| Abstract: | The Limousin ophiolite is located at the suture zone between two major thrust sheets in the western French Massif Central. This ophiolitic section comprises mantle‐harzburgite, mantle‐dunite, wehrlites, troctolites and layered gabbros. It has recorded a static metamorphic event transforming the gabbros into undeformed amphibolites and the magmatic ultramafites into serpentinites and/or pargasite‐bearing chloritites. With various thermobarometric methods, it is possible to show that the different varieties of amphibole have registered low‐P (c. 0.2 GPa) conditions with temperature ranging from high‐T, late‐magmatic conditions to greenschist–zeolite metamorphic facies. The abundance of undeformed metamorphic rocks (which is typical of the lower oceanic crust), the occurrence of Ca–Al (–Mg) metasomatism illustrated by the growth of Ca–Al silicates in veins or replacing the primary magmatic minerals, the P–T conditions of the metamorphism and the numerous similarities with oceanic crustal rocks from Ocean Drilling Program and worldwide ophiolites are the main arguments for an ocean‐floor hydrothermal metamorphism in the vicinity of a palaeo‐ridge. Among the West‐European Variscan ophiolites, the Limousin ophiolites constitute an extremely rare occurrence that has not been involved in any HP (subduction‐related) or MP (orogenic) metamorphism as observed in other ophiolite occurrences (i.e. France, Spain and Germany). |
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| Keywords: | gabbros hydrothermal metamorphism ophiolite thermobarometry Variscan |
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