Compositional variations in a fertile mantle domain: peridotite xenoliths from the Tariat region, Mongolia

Continental lithospheric mantle is heterogeneous in terms of modal and chemical composition. There are fundamental differences between cratonic and younger mantle (Boyd et al., 1997), and non-cratonic mantle has broad compositional variations worldwide (McDonough, 1990). Xenoliths of spinel peridotites in alkali basalts are direct samples of lithospheric mantle but it may not be clear whether a single xenolith suite can provide a representative sample of the mantle in a given lithospheric unit. The range and scale of compositional variations in a mantle volume can be established by representative sampling of xenoliths from different eruption centres of a similar age. Questions of particular interest are (i) whether lithospheric mantle in individual tectonic units has limited variation ranges specific to each unit, (ii) the scale of mantle heterogeneity and spatial relationships between rock types, and (iii) the relationship between variations in modal composition (including accessory minerals), major and trace element compositions.