The La Croix-Valmer garnet-spinel peridotite (Central Maures): A cumulate of oceanic affinity involved in Early-Variscan subduction

A garnet-spinel metaperidotite body has been found in the lebtyno-amphibolitic complex of the central part of the Maures Massif (Hercynian Belt, south eastern France). Based on bulk rock and mineral chemistry, a mantle tectonite origin can be ruled out for this rock. Instead, it appears to be an igneous cumulate that crystallized at low P, in the olivine-plagioclase stability field, and was later brought down to mantle depths (P = 16-18 kbar, T = 850-860 degrees C). Although Sm-Nd isotopes preclude a strictly comagmatic origin, the clear oceanic affinity of neighbouring metagabbros (epsilon(Nd500) +7.7 and +8.7) suggests a very evolved extensional tectonic setting, having led to the break-up of the continental lithosphere and the formation of a rifted margin. The high pressure metamorphic overprint recorded by the peridotite is interpreted as reflecting the subduction of a passive margin, at the final stage of consumption of an oceanic domain. This event probably occurred in Early Hercynian times, as documented elsewhere in the west european Hercynides. (C) Academie des sciences/Elsevier, Paris.