Résumé
Clinopyroxene-rich, poorly metasomatised spinel lherzolites are rare worldwide but predominate among xenoliths in five Quaternary basaltic eruption centres in Tariat, central Mongolia. High-precision analyses of the most fertile Tariat lherzolites are used to evaluate estimates of primitive mantle compositions; they indicate Mg#(PM) = 0.890 while lower Mg# in the mantle are likely related to metasomatic enrichments in iron. Within a 10 x 20 km area, and between similar to 45 and 60 km depth, the sampled xenoliths suggest that the Tariat mantle does not show km-scale chemical heterogeneities and mainly consists of residues after low-degree melt extraction at 1-3 GPa. However, accessory (< 1%) amphibole and phlogopite are unevenly distributed beneath the eruption centres. Ca abundances in olivine are controlled by temperature whereas Al and Cr abundances also depend on Cr/Al in coexisting spinel. Comparisons of conventional and high-precision analyses obtained for 30 xenoliths show that high-quality data, in particular for whole-rocks and olivines, are essential to constrain the origin of mantle peridotites.