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Mafic granulite-facies xenoliths in alkali basalts from Chantaburi province represent the only known lower-crustal material in Thailand. Most xenoliths contain garnet (or its secondary product—kelyphite), plagioclase, and clinopyroxene, ± traces of corundum, and are grouped into garnet-rich and clinopyroxene-rich granulites (Groups 2 and 3, respectively). One sample is classified as olivine-garnet clinopyroxenite (Group 1), reflecting the presence of olivine and spinel and the absence of plagioclase. Whole-rock chemistry suggests that the protoliths of these granulite xenoliths have high normative olivine, plagioclase, and diopside, and, in most cases, low abundances and generally flat REE profiles with positive Eu anomalies. These characteristics indicate that the protoliths originated as basaltic cumulates, similar to troctolite and olivine-gabbro. On cooling, cumulate protoliths transformed to granulite-facies assemblages, mainly by the reaction: Pl + Ol = Gt + Cpx. Interestingly, some granulite xenoli...

In mantle xenoliths, metasomatism is recorded by compositional variations within and between minerals, and by the introduction of secondary minerals. However, metasomatism has not been quantitatively evaluated as a process with respect to the fluid composition involved. Diamondiferous eclogites from the Udachnaya kimberlite provide a unique suite of samples that allow a semiquantitative estimation of metasomatic fluid composition. The basis of our analysis involves comparison of reconstructed whole-rock compositions with measured whole-rock analyses. Primary minerals in these samples are relatively homogeneous, and permit the use of modal analyses and mineral chemistry for reconstruction of “pristine” whole-rock compositions. The metasomatic overprint, which is similiar in all samples studied, has produced depletions in SiO2, Na2O, and FeO and enrichments in TiO2, K2O, MgO, and LREE. Secondary minerals from the samples are interpreted as the direct result of metasomatism (i.e., typical metasomatic mineral...

Thirteen new breccia clasts of highland lithologies are described from the Apollo 17 site. The clasts were extracted from three breccias: two from sample 73215 (aphanitic impact melt breccia), six from 73216 (impact melt breccia), and five from 77035 (micropoikilitic impact melt breccia). Breccias 73215 and 73216 were collected from the rim of a 10 m crater at Station 3 and breccia 77035 was collected at Station 7 at the base of the North Massif. The clasts are subdivided into melt-free and melt-rich groups. The melt-free clasts include pristine and brecciated lithologies, with one pristine gabbronoritic anorthosite containing 15 ppb Ir. The melt-rich clasts have compositions that are similar to LKFM, rather than to Apollo 17 KREEP basalts described as clasts from breccia 72275 by Salpas et al. (1987). Three main conclusions are drawn from this study: (1) the presence of 15 ppb Ir in a pristine gabbronoritic anorthosite further demonstrates the complexities associated with estimating the highly siderophil...

In order to better understand the origin and character of late-Archean mantle beneath the Baltic Shield, we have analyzed mafic-ultramafic rocks from one of the best-preserved, least-metamorphosed regions of Karelia, Russia. Trace-element data for samples from the ultramafic and gabbronorite zones of the large (700 km2) Burakovsky layered intrusion (BLI) are presented. Samples from the ultramafic zone are LREE enriched, indicating that they formed from a LREE-enriched parental magma. Indeed, a calculated parental magma for the ultramafic zone has a (Ce/Yb)n ratio of 2.6, a (Nd/Sm)n ratio of 1.1, and a (Dy/Yb)n ratio of 1.6. The LREE enrichment in the parental magma suggests either that the source region was LREE enriched or that the melt was contaminated by crust en route to the BLI magma chamber. Samples from the gabbronorite zone also are LREE enriched and indicate two distinct parental magmas. Group-I magmas, from the lower part of the gabbronorite zone, have (Ce/Yb)n ratios of 6.9 to 13.9, whereas Gro...