Résumé
The Moa-Baracoa and Mayari-Cristal massifs (E Cuba) are two ophiolitic complexes mainly constituted by harzburgite tectonites and minor dunites, cut by gabbroic dykes. The Moa-Baracoa massif exhibits a well-developed Moho transition zone and an incomplete crustal section made up of layered gabbros and tectonically emplaced pillow basalts. A plutonic crustal section is absent in the Mayari-Cristal massif and mantle tectonites are in tectonic contact with arc-related volcanic rocks. Mantle peridotites are very refractory in terms of modal composition, whole rock major element and HREE contents implying that Moa-Baracoa and Mayari-Cristal harzburgites are residues after high degrees (20-30%) of partial melting. The relative enrichment of Th, Nb, Ta and LREE in peridotites is due to re-equilibration of melting residues with percolating melts. Peridotites lost on average 6 wt% of relative MgO by intense seafloor weathering. REE contents and Mg# of melts in equilibrium with cumulate gabbros from the Moho transition zone and crustal section of the Moa-Baracoa massif coincide with those of the spatially-related pillow basalts. On the other hand, no geochemical relation has been inferred between melt in equilibrium with Mayari-Cristal segregate and the spatially-related arc volcanics. Results indicate that the Mayari-Baracoa Ophiolitic Belt formed at an original back-arc spreading centre.