The petrology and geochemistry of shallow continental lithospheric mantle (SCLM) can be studied via (1) tectonically emplaced ultramafic massifs and (2) mantle xenoliths entrained in alkaline magmas. Data from these two separate sources are used to identify processes that have formed and modified the SCLM. In western and central Europe where the continental crust consolidated in Phanerozoic times, both sources of information are available for study. Rock types found in ultramafic massifs in Europe are generally similar to those found in ultramafic xenolith suites. The most frequent lithology is anhydrous spinel lherzolite, grading towards harzburgite. Massifs reveal pyroxenite layering, harzburgite bands and cross-cutting mafic and ultramafic dykes. The Phanerozoic European SCLM xenoliths and massifs show broad mineralogical and chemical similarities to Phanerozoic continental spinel peridotites world-wide. The main process that controls the geochemistry of the SCLM is depletion by removal of basaltic melt. Differences from this norm reflect significantly different processes in the SCLM, such as interaction with melts and fluids. Such processes probably gave rise to hornblendite veins and pyroxenite layers, although the latter have also been interpreted as recycled oceanic crust. Rare earth element data for whole-rock peridotites and their constituent clinopyroxenes show a variety of patterns, including light rare earth element (LREE) depletion as a result of removal of basaltic melt, LREE enrichment caused by metasomatism, and U-shaped REE patterns that are probably due to interaction with carbonatite melts. Extended mantle-normalized incompatible trace element patterns for whole rocks show enrichment in Rb and Ba in peridotites considered to have been subduction-metasomatized, whereas those considered to be carbonate-metasomatized have strong negative anomalies in Zr, Nb and Hf. Mantle amphiboles are strongly enriched in LREE when found in veins, but can be LREE depleted if they are interstitial. Radiogenic isotope ratios for xenoliths and massifs largely overlap, although the xenoliths show a significant clustering around a ‘plume-component’ identical to the Neogene alkaline magmatism of Europe. This component is lacking in the massifs, most of which were emplaced into the crust before the onset of Neogene plume activity. Infiltration of carbonatite melts is observed petrographically in some xenoliths and evidenced by low Ti/Eu ratios in bulk rocks, but is very rare. The effect of passage of hydrous fluids from subducting slabs is also seen in some suites and massifs, being exhibited mainly as unusual Sr and Pb isotope ratios, although enrichment in K, Rb and Ba, and the presence of modal phlogopite, may also point to subduction-metasomatism.

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzburgites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al₂O₃ contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al₂O₃ and TiO₂) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have ¹⁴³Nd/¹⁴⁴Nd values that range from 0·5121 (close to the host minette values) to 0·5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low ¹⁴³Nd/¹⁴⁴Nd values (0·5113) and extremely high ⁸⁷Sr/⁸⁶Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf) as in the host minettes, and their Sr–Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere.

The 650–621 Ma plume which impinged beneath the Siberian craton during the breakup of Rodinia caused the formation of several alkaline carbonatite massifs in craton margins of the Angara rift system. The Beloziminsky alkaline ultramafic carbonatite massif (BZM) in the Urik-Iya graben includes alnöites, phlogopite carbonatites and aillikites. The Yuzhnaya pipe (YuP) ~ 645 Ma and the 640–621 Ma aillikites in BZM, dated by ⁴⁰Ar/³⁹Ar, contain xenoliths of carbonated sulfide-bearing dunites, xenocrysts of olivines, Cr-diopsides, Cr-phlogopites, Cr-spinels (P ~ 4–2 GPa and T ~ 800–1250 °C) and xenocrysts of augites with elevated HFSE, U, Th. Al-augites and kaersutites fractionated from T ~ 1100–700 °C along the 90 mW/m² geotherm. Higher T trend for Al-Ti augite, pargasites, Ti-biotites series (0.4–1.5 GPa) relate to intermediate magma chambers near the Moho and in the crust. Silicate xenocrysts show Zr-Hf, Ta-Nb peaks and correspond to carbonate-rich magma fractionation that possibly supplied the massif. Aillikites contain olivines, rare Cr-diopsides and oxides. The serpentinites are barren, fragments of ore-bearing Phl carbonatites contain perovskites, Ta-niobates, zircons, thorites, polymetallic sulphides and Ta-Mn-Nb-rich magnetites, ilmenites and Ta-Nb oxides. The aillikites are divided by bulk rock and trace elements into seven groups with varying HFSE and LILE due to different incorporation of carbonatites and related rocks. Apatites and perovskites reveal remarkably high LREE levels. Aillikites were generated by 1%–0.5% melting of the highly metasomatized mantle with ilmenite, perovskite apatite, sulfides and mica, enriched by subduction-related melts and fluids rich in LILE and HFSE. Additional silicate crystal fractionation increased the trace element concentrations. The carbonate-silicate P-bearing magmas may have produced the concentration of the ore components and HFSE in the essentially carbonatitic melts after liquid immiscibility in the final stage. The mechanical enrichment of aillikites in ore and trace element-bearing minerals was due to mixture with captured solid carbonatites after intrusion in the massif.