Two decades of diamond research in southern Africa allow the age and average composition (C isotope and N abundance) of diamonds and the dominant paragenesis (peridotitic versus eclogitic) of their syngenetic silicate and sulfide inclusions to be reviewed on a cratonwide scale. Individual eclogitic sulfide inclusions in diamonds from the Kimberley area kimberlites, Koffiefontein, Orapa and Jwaneng have Re-Os isotopic ages that range from similar to2.9 Ga to the Proterozoic and display little correspondence with the prominent variations in the P-wave velocity (+/-1%) that the mantle lithosphere shows at depths within the diamond stability field (150 to 225km). Silicate inclusions in diamonds and their host diamond compositions for the above kimberlites, Finsch, Jagersfontein, Roberts Victor, Premier, Venetia and Letlhakane show a regional relationship to the seismic velocity of the lithosphere. Mantle lithosphere with slower P-wave velocity relative to the craton average correlates with a greater proportion of eclogitic versus peridotitic silicate inclusions in diamond, a greater incidence of younger Sm-Nd ages of silicate inclusions, a greater proportion of diamonds with lighter C isotopic composition, and a lower percentage of low-N diamonds. The converse is true for diamonds from higher velocity mantle. The oldest formation ages of diamonds support a model whereby mantle that became part of the keel of the oldest continental nuclei was created by middle Archean (similar to3.3 to similar to3.2 Ga or older) mantle depletion events with high degrees of melting and early harzburgite formation. The predominance of eclogitic sulfide inclusions in the similar to2.9 Ga age population links late Archean subduction-accretion events involving an oceanic lithosphere component to craton stabilization. These events resulted in a widely-distributed, late Archean generation of eclogitic diamonds in an amalgamated craton. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the already extensive Archean diamond suite.

Initial Os-187/Os-188 (350 Ma) of cumulate garnet pyroxenites enclosed in high-temperature peridotite massifs from a Paleozoic convergent plate margin (lower Austria) is slightly suprachondritic to highly radiogenic (Os-187/Os-188(i) up to 0.686). The main factor controlling Os-187/Os-188 appears to be the extent of Os exchange of the parent melts with the host peridotites. The radiogenic Os-187/Os-188; of the least reacted parent melts is most easily explained by an Os flux from the slab, although low Os concentrations suggest that the magnitude of this flux may be rather small. Sediment-like Sr-Nd-Pb isotopic compositions and negative Eu anomalies in plagioclase-free pyroxenites indicate that the Os was derived from the sediment section in the slab. Osmium abundances in the pyroxenites correlate well with Ni and Cr, indicating compatible behavior during pyroxene and garnet fractionation, likely because of coprecipitating sulfide. Rhenium abundances in the pyroxenites do not correlate with mildly incompatible elements such as Yb and are obviously not controlled by silicate phases. Except for two samples with high Re. Re appears to have partitioned preferentially into the melt, which, judging from low sulfur and scarce sulfides in most pyroxenites, may have been undersaturated in sulfur.

Major element and Re-Os isotope analysis of single sulfide inclusions in diamonds from the 240 Ma Jwaneng kimberlite has revealed the presence of at least two generations of eclogitic diamonds at this locality, one Proterozoic (ca. 1.5 Ga) and the other late Archean (ca. 2.9 Ga). The former generation is considered to be the same as that of eclogitic garnet and clinopyroxene inclusion bearing diamonds from Jwaneng with a Sm-Nd isochron age of 1.54 Ga. The latter is coeval with the 2.89 Ga subduction-related generation of eclogitic sulfide inclusion bearing diamonds from Kimberley formed during amalgamation of the western and eastern Kaapvaal craton near the Colesberg magnetic lineament.

Two decades of diamond research in southern Africa allow the age, average N content and carbon composition of diamonds, and the dominant paragenesis of their syngenetic silicate and sulfide inclusions to be integrated on a cratonwide scale with a model of craton formation. Individual eclogitic sulfide inclusions in diamonds from the Kimberley area kimberlites, Koffiefontein, Orapa and Jwaneng have Re-Os isotopic ages that range from circa 2.9 Ga to the mid-Proterozoic and display little correspondence with the prominent variations in the P-wave velocity (+/-1%) that the mantle lithosphere shows at depths within the diamond stability field (150-225 km). Silicate inclusions in diamonds and their host diamond compositions for the above kimberlites, Finsch, Jagersfontein, Roberts Victor, Premier, Venetia, and Letlhakane show a regional relationship to the seismic velocity of the lithosphere. Mantle lithosphere with slower P-wave velocity relative to the craton average correlates with a greater proportion of eclogitic vs. peridotitic silicate inclusions in diamond, a greater incidence of younger Sm-Nd ages of silicate inclusions, a greater proportion of diamonds with lighter C isotopic composition, and a lower percentage of low-N diamonds. The oldest formation ages of diamonds support a model whereby mantle that became part of the continental keel of cratonic nuclei first was created by middle Archean (3.2-3.3 Ga or older) mantle depletion events with high degrees of melting and early harzburgite formation. The predominance of eclogitic sulfide inclusions in the 2.9 Ga age population links late Archean (2.9 Ga) subduction-accretion events to craton stabilization. These events resulted in a widely distributed, late Archean generation of eclogitic diamonds in an amalgamated craton. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the already extensive Archean diamond suite. Similar age/paragenesis systematics are seen for the more limited data sets from the Slave and Siberian cratons. (C) 2004 Elsevier B.V. All rights reserved.

Os-Hf-Sr-Nd isotopes and PGE were determined in peridotite xenoliths carried to the surface by Quaternary alkali basaltic magmas in the Tokinsky Stanovik Range on the Aldan shield. These data constrain the timing and nature of partial melting and metasomatism in the lithospheric mantle beneath SE Siberian craton. The xenoliths range from the rare fertile spinel lherzolites to the more abundant, strongly metasomatised olivine-rich (70-84%) rocks. Hf-Sr-Nd isotope compositions of the xenoliths are mainly within the fields of oceanic basalts. Most metasomatised xenoliths have lower Nd-143/Nd-144 and Hf-116/Hf-177 and higher Sr-117/Sr-86 than the host basalts indicating that the metasomatism is older and has distinct sources. A few xenoliths have elevated Hf-176/Hf-177 (up to 0.2838) and plot above the Hf-Nd mantle array defined by oceanic basalts.