Carbonatite and Alkaline Magmatism in Taourirt (Morocco): Petrological, Geochemical and Sr-Nd Isotope Characteristics

Alkaline lamprophyre dykes from Taourirt (North Morocco) containnumerous xenoliths, ranging from alkaline pyroxenites, kaersutitites,gabbros and nepheline syenites to a calcite carbonatite. Thesilicate xenoliths and the host rocks consist of Al- and Ti-richdiopside–salite, mica or kaersutitite, ± nepheline,± plagioclase and K-feldspar, and ubiquitous apatite.Both the xenoliths and the lamprophyres are enriched in incompatibleelements. The chemical composition of the lamprophyres cannotbe accounted for by fractional crystallization alone. Moreover,the clinopyroxenes exhibit complex zoning, which requires repeatedmixing of pulses of more or less fractionated melts. The carbonatiteis a sövite cumulate with Sr-rich calcite, pyrochlore,fluorapatite, and rare salite. The Sr–Nd isotopic compositionsof the Taourirt rocks indicate a depleted mantle source, thecarbonatite having the most depleted composition, and definea linear trend similar to that of the East African carbonatites.The different rocks thus represent unrelated magmas, and thetrend is interpreted as mixing between two components with HIMUand EM1 mantle end-member signatures. An EM2 mantle componentcould also be involved for a few samples; it may correspondto hydrous metasomatized mantle of the PP–PKP (phlogopiteand phlogopite K-richterite peridotite) and MARID (mica, amphibole,rutile, ilmenite and diopside) type. KEY WORDS: alkaline magmatism; carbonatite; Morocco; REE; Sr–Nd isotopes