Diamonds form in the upper mantle during episodic events and have been transported to the Earth's surface from at least the Archean to the Phanerozoic. Small diamonds occur as inclusions in robust minerals in tectonically activated, ultrahigh-pressure metamorphosed crustal rock, establishing an association with subduction processes and recycled carbon but providing no economic deposits. Diamonds in economic deposits are estimated to be mainly (99%) derived from subcontinental lithospheric mantle and rarely (approx. 1%) from the asthenosphere. Harzburgite and eclogite are of roughly equal importance as source rocks, followed by lherzolite and websterite. Diamonds which provide evidence of extensive residence time in the mantle are, with minimal exceptions, smooth-surfaced crystalline diamonds (SCD) with potential commercial value. The oldest prolific SCD formation event documented on the world's major diamond producing cratons occurs in Archean lithospheric mantle harzburgite, metasomatized by likely subduction-related potassic carbonatitic fluids.

Sulphide-bearing diamonds recovered from the similar to 20 Ma Ellendale 4 and 9 lamproite pipes in north-western Australia were investigated to determine the nitrogen aggregation state of the diamonds and Re Os isotope geochemistry of the sulphide inclusions. The majority of diamond studies have been based on diamonds formed in the sub-continental lithospheric mantle (SCLM) below stable cratons, whereas the Ellendale lamproites intrude the King Leopold Orogen, south of the Kimberley craton. The sulphide inclusions consist of pyrrhotite pentlandite chalcopyrite assemblages, and can be divided into peridotitic and eclogitic parageneses on the basis of their Ni and Os contents. A lherzolitic paragenesis for the high-Ni sulphide inclusions is suggested from their Re and Os concentrations. Regression analysis of the Re Os isotope data for the lherzolitic sulphides yields an age of 1426 130 Ma, with an initial Os-187/Os-188 ratio of 0.1042 +/- 0.0034. The upper limit of the uncertainty on the Os-187/Os-188 initial ratio gives a Re depletion age of 2.96 Ga, indicating the presence of SCLM beneath Ellendale since at least the Mesoarchaean, with the lherzolitic diamond-forming event much younger and unrelated to the craton keel stabilisation. The nitrogen aggregation state of the diamonds and calculated mantle residence temperatures suggest an origin and storage of the Ellendale diamonds in a stable cratonic SCLM, consistent with the King Leopold Orogen being cratonised by about 1.8 Ga. The diamonds do not show evidence for pervasive deformation or platelet degradation, which suggests that the diamonds had a relatively undisturbed 1.4 billion year mantle storage history. (C) 2010 Elsevier Ltd. All rights reserved.

Niches are local tissue microenvironments that maintain and regulate stem cells. Long-predicted from mammalian studies, these structures have recently been characterized within several invertebrate tissues using methods that reliably identify individual stem cells and their functional requirements. Although similar single-cell resolution has usually not been achieved in mammalian tissues, principles likely to govern the behavior of niches in diverse organisms are emerging. Considerable progress has been made in elucidating how the microenvironment promotes stem cell maintenance. Mechanisms of stem cell maintenance are key to the regulation of homeostasis and likely contribute to aging and tumorigenesis when altered during adulthood.

A mineral chemistry and whole-rock major element, platinum group element (PGE), and Re-Os isotope dataset is presented for a large suite of mantle xenoliths from 13 kimberlites that erupted through the Proterozoic mobile belts surrounding the Archean Kaapvaal craton of South Africa. The peridotites have compositions that are unusually infertile compared with post-Archean lithosphere outside southern Africa (e.g. mean olivine Mg-number = 91 center dot 4; mean whole-rock Al2O3 = 1 center dot 3 wt %) but are similar to xenoliths from the Gibeon kimberlites of southern Namibia, which also erupted through Proterozoic lithosphere. Rhenium depletion model ages (T-RD) determined from 58 Os isotope compositions of peridotites span a range from 2 center dot 6 to 0 center dot 6 Ga, with an average of 1 center dot 67 Ga. Latest Archean T-RD model ages were determined for three samples from different localities, but whether these indicate the off-craton presence of reworked Archean lithosphere or are simply artifacts of heterogeneity in the convecting mantle is unclear. Low and relatively restricted Al2O3 contents combined with variable Os-187/Os-188(i) in the peridotites are most consistent with a two-stage melt extraction history for southern African off-craton lithosphere, with initial formation in the earliest Proterozoic by widely varying (but, on average, moderate) degrees of melting, followed by a second melt extraction episode associated with the Namaquan orogeny at 1 center dot 3-1 center dot 0 Ga. Extensive metasomatism in the lithosphere beneath East Griqualand, SE of the craton, resulted in extreme clinopyroxene enrichment and addition of ilmenite along with disturbance of PGE abundances in many samples. This is probably due to percolation of melts similar to those parental to the Cr-poor megacryst suite, and related pyroxenites, which are abundant in East Griqualand kimberlites. In other regions, there is evidence for less extensive clinopyroxene addition and cryptic metasomatism. Southern African off-craton mantle xenoliths record evidence of a Mesozoic heating episode probably brought about by mantle upwelling linked to continental break-up and/or Karoo flood basalt magmatism. Prior to this, the thermal state, and hence the thickness, of southern African off-craton and cratonic lithosphere were probably roughly similar. The mantle upwelling responsible for lithospheric heating also appears to have caused moderate (approximate to 30 km) thermal erosion of the off-craton portions of the southern African lithosphere.

Peridotitic sulphide inclusions in diamonds from the central Slave craton constrain the age and origin of their subcontinental lithospheric mantle (SCLM) sources. These sulphides align with either a ca. 3.5 Ga (shallow SCLM) or a ca. 3.3 Ga isochron (deep SCLM) on a Re-Os ischron diagram, with variably enriched initial Os-187/Os-188. Since some Archaean to recent plume-derived melts carry a subducted crust (eclogite) signature and some cratonic SCLM may have been generated in plumes by extraction of komatiitic liquids, we explain these data by subduction of evolved lithospheric material (shallow SCLM) and melting in a hybrid mantle plume that contains domains of recycled eclogite (deep SCLM), respectively. In upwelling hybrid mantle, eclogite-derived melts react with olivine in surrounding peridotites to form aluminous orthopyroxene, convert peridotite to pyroxenite and confer their crustal isotope signatures. We suggest that it is subsequent to orthopyroxene enrichment of peridotite in an upwelling plume that partial melting of this Al- and Si- enriched source generated komatiites and complementary ultradepleted cratonic mantle residues. Although subduction is needed to explain some cratonic features, melting of a hybrid plume source satisfies several key observations: (1) suprachondritic initial Os-187/Os-188 in subsets of lithospheric mantle samples and in some coeval Archaean komatiites; (2) variable enrichment of cratonic mantle by high-temperature aluminous orthopyroxene; (3) high Mg# combined with high orthopyroxene content in cratonic mantle due to higher melt productivity of an Al- and Si-richer source; (4) variable orthopyroxene enrichment possibly linked to varying mantle potential temperatures (Tp), plume buoyancy and resultant eclogite load and/or variable availability of subducted material in the source; and (5) absence of younger analogues due to a secular decrease in Tp. Most importantly, this model also alleviates a mass balance problem, because it predicts a hybrid mantle source with variably higher SiO2 and Al2O3 than primitive mantle, and, contrary to a primitive mantle source, is able to reconcile compositions of komatiites and complementary cratonic mantle residues.

Mineral inclusions encapsulated in diamonds are the oldest, deepest, and most pristine samples of Earth's mantle. They provide age and chemical information over a period of 3.5 billion years-a span that includes continental crustal growth, atmospheric evolution, and the initiation of plate tectonics. We compiled isotopic and bulk chemical data of silicate and sulfide inclusions and found that a compositional change occurred 3.0 billion years ago (Ga). Before 3.2 Ga, only diamonds with peridotitic compositions formed, whereas after 3.0 Ga, eclogitic diamonds became prevalent. We suggest that this resulted from the capture of eclogite and diamond-forming fluids in subcontinental mantle via subduction and continental collision, marking the onset of the Wilson cycle of plate tectonics.

The Eagle Cu-Ni-(PGE) deposit is hosted by mafic to ultramafic intrusive rocks associated with the Marquette-Baraga dike swarm in northern Michigan. Sulfide mineralization formed in a conduit system during early stages in the development of the similar to 1.1 Ga Midcontinent Rift System. The conduit environment represents a prime location for melt-rock interaction. In order to better assess the extent of country rock contamination in the Eagle system, a combined trace element, Nd, Os, O and S isotope study of country rocks, sulfide-bearing igneous rocks and massive sulfide was undertaken.