Petrogenesis of olivine-bearing cumulates and associated basalt dykes from Bocca di Tenda (northern Corsica): constraints on post-Variscan mantle sources.

The Early Permian gabbroic sequence of Bocca di Tenda (Northern Corsica) intrudes a plutonic suite made of hornblende-granitoids and is crosscut by basalt dykes with chilled margins. The gabbroic sequence includes olivine-gabbronorite cumulates that consist mainly of euhedral olivine (Fo78-72) and plagioclase (An68-61), and poikilitic clinopyroxene (Mg# = 0.85-0.80), orthopyroxene and Ti-pargasite. Pyroxenes from the olivinegabbronorites have ?18O values of +6.3? to +6.7?, which are evidence for the involvement of a crustal component in the petrogenesis of these rocks. The basalts have Mg# values of 57 to 53 and chondrite-normalised patterns characterised by a steady decrease from LREE to HREE. Relative to modern N-MORB, they show also moderate enrichment of Nb and Ta over Zr and Hf, which are in turn slightly enriched over Y and HREE. The olivine-gabbronorites and basalts show overlapping Nd isotopic compositions (initial ?Nd of +2.4 to +1.4 and of +3.0 to +1.5, respectively) and have clinopyroxenes with nearly parallel incompatible trace element patterns, thus revealing that these two rock types formed by melts with similar compositions. Most likely, the primary melts of Bocca di Tenda gabbroic sequence were slightly enriched in most incompatible elements and Nd isotopic compositions relative to modern N-MORB.