Résumé
Correlations between major and minor transition elements in tectonically-emplaced orogenic peridotites are generally ascribed to variable degrees of melt extraction or igneous refertilization processes superimposed on melting depletion events. In order to elucidate how melt depletion and refertilization are recorded in the subcontinental lithospheric mantle, we analyzed a large geochemical database of peridotites from the four tectonometamorphic domains of the Beni Bousera orogenic massif (Rif Belt, NE Morocco; Fig. 1). From SW to NE these domains are: Garnet and Spinel mylonites; Ariègite subfacies domain; Ariègite-Seiland domain; and Seiland subfacies domain. Our study reveals that variations in major elements and modal compositions of lherzolites, as well as the LREEdepleted patterns of their clinopyroxenes, are the result of different mechanism involving melt-rock reactions of pyroxenite-derived and under-saturated silicate melts with refractory, residual lithospheric mantle. We propose that Beni Bousera lherzolites were formed by refertilization processes after residues of partial melting (harzburgites and depleted lherzolites) that existed previous to the current zonation by domains of the massif. We can distinguish at least two distinct near solidus, melt-rock reactions associated to the development of the domains: (1) pyroxene precipitation at expenses of olivine dissolution, mainly recorded in the Ariègite domain; and (2) dissolution of orthopyroxene at expenses of clinopyroxene, with minor olivine dissolution, affecting mainly the Ariègite-Seiland and Seiland domains. We conclude that the Beni Bousera tectono-metamorphic zoning records different refertilization processes, associated with the thermomechanical erosion and rejuvenation of the subcontinental lithospheric mantle by asthenosphere upwelling in the westernmost Mediterranean.