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Mineralogical Magazine; April 2006; v. 70; no. 2; p. 175-185; DOI: 10.1180/0026461067020322
© 2006 Mineralogical Society of Great Britain and Ireland
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A Variscan slow-spreading ridge (MOR-LHOT) in Limousin (French Massif Central): magmatic evolution and tectonic setting inferred from mineral chemistry

J. Berger1,2,*, O. Féménias2, J.-C. C. Mercier3 and D. Demaiffe2

1 Section de Géologie Isotopique, Africa Museum, Leuvensteenweg 13, B-3080 Tervuren, Belgium
2 Laboratoire de Géochimie Isotopique et Géodynamique Chimique, DSTE, Université Libre de Bruxelles (CP 160/02), 50 Avenue Roosevelt, B-1050 Brussels, Belgium
3 CLDG, Université de La Rochelle, av. Crépeau, F-17402 La Rochelle cedex 1, France ABSTRACT

* E-mail: julien.berger{at}africamuseum.be

The Limousin ophiolite (French Massif Central) occurs as elongate bodies forming a (nearly) continuous suture zone between two major lithotectonic units of the French Variscan belt. The mantle section of the ophiolite is made of diopside-bearing harzburgite, harzburgite and dunite characteristic of a lherzolite-harzburgite ophiolite type (LHOT). The plutonic section is essentially composed of troctolites, wehrlites and gabbros locally intruded by ilmenite-rich mafic dykes. All the rocks were strongly affected by an ocean-floor hydrothermal metamorphism. The composition and evolution of primary magmatic phases (olivine, clinopyroxene, plagioclase and spinel) throughout the lowermost magmatic sequence correspond to those described in oceanic cumulates (ODP data). The Limousin ophiolite is thus of MOR type instead of SSZ type. The whole lithological section, the mineral chemistry, the extensive hydrothermal oceanic alteration and the relatively thin crustal section are typical of a slow-spreading ridge ocean (i.e. Mid-Atlantic ridge). Comparison of the Limousin ophiolite with other ophiolites from European Variscides suggests that the oceanic domain was actively spreading during the Late Palaeozoic and extended from the Armorican massif to the Polish Sudetes.

KEYWORDS: LHOT, MOR, slow-spreading ridge, Variscan, Limousin, France






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