Résumé
The Neogene-Quaternary Middle Atlas province is the largest and youngest volcanic field of Morocco, bringing up a large variety of mantle xenoliths. The eighteen xenoliths are mainly lherzolites, but also include harzburgite, wherlite and pyroxenite. A major, trace elements & Sr-Nd-Pb-Hf isotopes study was conducted on CPX and host-rocks (WR) coupled petrographic constraints. Lherzolites show flat REE patterns with variable enrichment in LREE ie. various degrees of metasomatism. Harzburgites present a significant MREE enrichment. Sr isotopes of both WR and CPX show low ratios and define a limited range of variation (0.7023< (super 87) Sr/ (super 86) Sr<0.7035). Reported on the Nd-Sr diagram, they define a field extending between the DMM and HIMU compositions. Pb isotopic ratios are high and range, for (super 208) Pb/ (super 204) Pb, between 38.87 and 40.54, for (super 207) Pb/ (super 204) Pb from 15.59 to 15.64, and for (super 206) Pb/ (super 204) Pb from 19.08 to 20.29. Two Sm/Nd internal isochrons have been calculated for two different volcanic sites and yield Pan-African and Alpine indicative ages. Together, these constraints allow us to propose that Middle-Atlas mantle experienced several lithosphere asthenosphere interaction processses. Such an HIMU signature is common in the european subcontinental mantle sampled by cenozoic volcanism. At last, this study demonstrates that even in geodynamical complex zones experiencing various thinning episodes, preserved old lithospheric mantle can be present in continental lithosphere.