Formation of unusual yellow Orapa diamonds

Twenty eclogitic diamonds from Orapa Mine (Botswana) with an unusual yellow colour are characterised for their growth structure, N systematics, and C isotope composition, and the major element composition of their silicate inclusions. The diamonds show complex luminescence with green, blue and non-luminescent zones and occasional sector zonation. All parts of the diamonds have low total N concentrations (<50 at.ppm, with one exception of <125 at.ppm) and a limited range in C isotope composition (−5.7 to −10.6‰). Fourier Transform Infrared spectra show bands at 1334, 1332, 1282, and 1240 cm−1 typical for Ib-IaA diamonds. Relict unaggregated N defects (Ns o and Ns +) are present and the preservation is likely caused by the low N concentrations and possible low mantle residence temperatures rather than young diamond formation (inclusion ages of 140, 1096, 1699 Ma; Timmerman et al. Earth Planet Sc Lett 463:178–188, 2017). Garnet and clinopyroxene inclusions extracted from 14 diamonds have an eclogitic composition with relatively low Ca contents and based on all characteristics, these diamonds form a distinct population from Orapa

Noble gas geochemistry of fluid inclusions in South African diamonds: implications for the origin of diamond-forming fluids

Fibrous diamond growth zones often contain abundant high-density fluid (HDF) inclusions and these provide the most direct information on diamond-forming fluids. Noble gases are incompatible elements and particularly useful in evaluating large-scale mantle processes. This study further constrains the evolution and origin of the HDFs by combining noble gas systematics with δ13C, N concentrations, and fluid inclusion compositions for 21 individual growth zones in 13 diamonds from the Finsch (n = 3), DeBeers Pool (n = 7), and Koffiefontein (n = 3) mines on the Kaapvaal Craton. C isotope compositions range from −2.8 to −8.6‰ and N contents vary between 268 and 867 at.ppm, except for one diamond with contents of &#60;30 at.ppm N. Nine of the thirteen studied diamonds contained saline HDF inclusions, but the other four diamonds had carbonatitic or silicic HDF inclusions. Carbonatitic and silicic HDFs yielded low He concentrations, R/Ra (3He/4Hesample/3He/4Heair) values of 3.2–6.7, and low 40Ar/36Ar ratios of 390–1940. Noble gas characteristics of carbonatitic-silicic HDFs appear consistent with a subducted sediment origin and interaction with eclogite. Saline HDFs are characterised by high He concentrations, with R/Ra mostly between 3.9 and 5.7, and a wide range in 40Ar/36Ar ratios (389–30,200). The saline HDFs likely originated from subducted oceanic crust with low He but moderate Ar contents. Subsequent interaction of these saline HDFs with mantle peridotite could explain the increase in He concentrations and mantle-like He isotope composition, with the range in low to high 40Ar/36Ar ratios dependent on the initial 36Ar content and extent of lithosphere interaction. The observed negative correlation between 4He contents and R/Ra values in saline HDFs indicates significant in situ radiogenic 4He production

Impacts of High-Protein Oral Nutritional Supplements Among Malnourished Men and Women with Sarcopenia: A Multicenter, Randomized, Double-Blinded, Controlled Trial.

BACKGROUND: Recent evidence suggests that nutritional interventions may improve muscle outcomes in malnutrition and sarcopenia. OBJECTIVES: We evaluated the effects of 2 high-quality oral nutritional supplements (ONS) differing in amount and type of key nutrients in older adult men and women. DESIGN: A multicenter, randomized, double-blinded, controlled clinical trial. PARTICIPANTS: Malnourished and sarcopenic men and women, 65 years and older (n = 330). INTERVENTION: A 24-week intervention period with 2 energy-rich (330 kcal) ONS treatment groups: Control ONS (CONS, 14 g protein; 147 IU vitamin D3) versus Experimental ONS (EONS, 20 g protein; 499 IU vitamin D3; 1.5 g CaHMB) taken twice daily. Both ONS also contained other vitamins, minerals, and nutrients in varying amounts. MEASUREMENTS: Isokinetic peak torque (PT, Nm) leg strength, grip strength (kg), and gait speed (m·s-1) were assessed at baseline and 12 and 24 weeks. Left and right leg muscle mass (LMM, kg) were assessed by dual-energy x-ray absorptiometry (DXA). Muscle quality (MQ) was leg strength expressed relative to the tested LMM (Nm·kg-1). Subgroup analyses were performed: severe sarcopenia (low skeletal mass index, low grip strength [ CONS, P = .032) in those with normal grip strength. There were no treatment differences based on sarcopenic severity for either grip strength or gait speed. CONCLUSION: ONS improved strength outcomes in malnourished older adults with sarcopenia. In those with mild-moderate sarcopenia, but not severe sarcopenia, consumption of the EONS improved leg muscle strength and quality compared with the standard CONS

Sublithospheric diamond ages and the supercontinent cycle.

Subduction related to the ancient supercontinent cycle is poorly constrained by mantle samples. Sublithospheric diamond crystallization records the release of melts from subducting oceanic lithosphere at 300-700 km depths1,2 and is especially suited to tracking the timing and effects of deep mantle processes on supercontinents. Here we show that four isotope systems (Rb-Sr, Sm-Nd, U-Pb and Re-Os) applied to Fe-sulfide and CaSiO3 inclusions within 13 sublithospheric diamonds from Juína (Brazil) and Kankan (Guinea) give broadly overlapping crystallization ages from around 450 to 650 million years ago. The intracratonic location of the diamond deposits on Gondwana and the ages, initial isotopic ratios, and trace element content of the inclusions indicate formation from a peri-Gondwanan subduction system. Preservation of these Neoproterozoic-Palaeozoic sublithospheric diamonds beneath Gondwana until its Cretaceous breakup, coupled with majorite geobarometry3,4, suggests that they accreted to and were retained in the lithospheric keel for more than 300 Myr during supercontinent migration. We propose that this process of lithosphere growth-with diamonds attached to the supercontinent keel by the diapiric uprise of depleted buoyant material and pieces of slab crust-could have enhanced supercontinent stability

Diamonds - Time capsules of volatiles and the key to dynamic Earth evolution

Noble gas analyses of basalts indicate that the present-day structure of the Earth comprises a slightly degassed lower mantle and highly degassed upper mantle. The extent and timing of mantle in and out-gassing and sources of volatiles are, however, not well-constrained and require quantification. The objective of this thesis is to address these questions through a study of the noble gas composition of diamonds as diamonds, being chemically inert, can preserve information on the fluid and mantle composition at the time of diamond formation. Specific objectives are to explore the potential of U-Th/He systematics for dating fibrous diamonds, the influence of volatile subduction on the heterogeneity in the sub-continental lithospheric mantle (SCLM), and how noble gas compositions have evolved over time in the SCLM. High-density fluid (HDF) inclusions with different major element compositions found in South African fibrous diamonds have different noble gas compositions that show these fluids originated from subducted sediments and oceanic crust and had either limited interaction with the SCLM (silicic-low Mg carbonatitic fluids) or significant interaction with the SCLM (saline fluids). A positive correlation between 3He/4He and d13C values in monocrystalline lithospheric diamonds from Argyle (Australia), together with low 40Ar/36Ar and He/Ne isotopic compositions, demonstrates a subduction influence caused by high U-Th/3He ratios and thus low 3He/4He ratios in subducted organic material. A noble gas depth profile based on N systematics of these diamonds shows fluid-rock interaction over scales of at least 15 kilometres above the accreted subducted material. Sub-lithospheric diamonds from Brazil, in contrast, show a negative correlation between 3He/4He and d13C values, but 3He/4He ratios are decoupled from trace elements and Pb-Sr isotope systematics that have characteristics of subducted material. This indicates that the subducted sediments have been deprived of U-Th-He and a high 3He/4He source, located in the deep mantle, is dominating the helium budget. Fibrous diamonds are generally assumed to have formed shortly before kimberlite eruption but there is currently no way to date these diamonds. The U-Th-Sm/He systematics of fibrous Congo and Jwaneng diamonds showed that in most cases U-Th/He ratios are sufficiently high to produce significant radiogenic 4He to provide age constraints and some fibrous diamonds are up to several 100 Myr older than the kimberlite eruption age. Previously dated monocrystalline diamonds (with multiple ages ranging from 0.07 to ~3.4 Ga) were analysed for trace elements and He-Ar isotopic compositions and showed similar trace element patterns for all diamonds but a correlation between the age and 4He-40Ar*-3He/4He values. After correcting for radiogenic ingrowth since diamond formation a large variation remains in 3He/4He values at ~1.0 Ga in eclogitic diamonds that can be explained by mixing between mantle and subducted components. Given the preservation of heterogeneities, it is difficult to develop a simple noble gas evolution curve for the SCLM. From examination of fibrous and monocrystalline diamonds from different formation depths, formation ages, and geographic locations this study showed the large influence of subduction at the base of the lithosphere and a more SCLM-like noble gas composition at shallower depths

Diamond-forming media through time - Trace element and noble gas systematics of diamonds formed over 3 billion years of Earth's history

Ten individual gem-quality monocrystalline diamonds of known peridotite/eclogite paragenesis from Southern Africa (Koffiefontein, Letlhakane, Orapa) were studied for trace element concentrations and He and Ar abundances and isotopic compositions. In addition, two samples, consisting of pooled fragments of gem-quality peridotitic diamonds from Finsch and DeBeers Pool respectively, were analysed for noble gases. Previous studies (Richardson et al., 1984; Pearson et al., 1998; Gress et al., 2017; Timmerman et al., 2017) provided age constraints of 0.09, 1.0–1.1, 1.7, 2.3, and 3.2–3.4 Ga on mineral inclusions in the studied diamonds, allowing us to study trace elements and noble gases over 3 Gyr of geological time. Concentrations of trace elements in the diamonds are very low – a few hundred ppt to several tens of ppbs – and are likely dependent on the amount of sub-micron inclusions present. Trace element patterns and trace element/3He ratios of the studied monocrystalline diamonds are similar to those in fibrous diamonds, suggesting that trace elements and stable noble gas isotopes reside within the same locations in diamond and track the same processes that are reflected in the trace element patterns. We cannot discern any temporal differences in these geochemical tracers, suggesting that the processes generating them have been occurring over at least the past 2.3 Ga. 3He/4He ratios decrease and 4He and 40Ar* contents increase with increasing age of peridotitic and some eclogitic diamonds, showing the importance of in-situ radiogenic 4He and 40Ar ingrowth by the decay of U-Th-Sm and K respectively. For most gem-quality monocrystalline diamonds, uncertainties in the 3He/4He evolution of the continental lithospheric mantle combined with large analytical uncertainties and possible spatial variability in U-Th-Sm concentrations limit our ability to provide estimates of diamond formation ages using 4He ingrowth. However, the limited observed 4He ingrowth (low U + Th/3He) together with a R/Ra value of 5.3 for peridotitic diamond K306 is comparable to the present-day sub-continental lithospheric mantle value and supports the young diamond formation age found by Re-Os dating of sulphides in the same diamond by Pearson et al. (1998). After correction for in-situ radiogenic 4He produced since diamond formation a large variation in 3He/4He remains in ∼1 Ga old eclogitic diamonds that is suggested to result from the variable influence of subducted altered oceanic crust that has low 3He/4He. Hence, the 3He/4He isotope tracer supports an origin of the diamond-forming fluids from recycled oceanic crust for eclogitic diamonds, as indicated by other geochemical proxies.This work was supported by AGRTP and Ringwood scholarships to ST, and funded by a CERC grant to GP, and an Australian Research Council grant (DP140101976) to MH

Subcretion of altered oceanic crust beneath the SW São Francisco Craton, Brazil – A stable isotope study on diamonds and their inclusions

The presence of diamonds of lherzolitic, eclogitic and websteritic paragenesis in proximal alluvial deposits on the southwestern edge of the São Francisco Craton documents the incorporation of subducted oceanic crust and associated metasomatism through slab dehydration fluids affecting the local SCLM. To better constrain the subduction-association of diamond substrates and metasomatic events, we conducted a combined study of the δ13C-δ15N-[N] characteristics of 81 diamonds and the δ18O values of four of their eclogitic garnet inclusions. Diamond carbon isotope compositions range from −25.5 to +0.5‰, with 13C-depleted diamonds (≤ −7‰) being exclusively of eclogitic/websteritic paragenesis while the 13C-enriched (≥ −2‰) tail of the distribution is related to diamonds with lherzolitic inclusions. Nitrogen isotope values range from −14.2 to +25.5‰, with about half of the values being positive. A general absence of coherent trends in δ13C-δ15N-[N] across growth zones implies that diamond formation did not occur under fluid-limited conditions. Instead, the observed heterogeneity in carbon and nitrogen isotope compositions reflects contributions of distinct source reservoirs hosted in both altered oceanic crust and Earth's mantle. Nitrogen contents peak around a δ15N value of −3.5‰, indicating that more N-rich fluids, presumably representing a primitive endmember composition, have a mantle-like δ15N signature. While positive and negative δ15N values occur equally near the δ13C mantle value (−5 ± 2‰), 13C-depleted diamonds have nitrogen isotope compositions skewed towards positive values. 13C depletion and 15N enrichment is a signature of biogenic carbonates/organic matter and low-T clays in uppermost, basaltic sections of oceanic crust that experienced low-temperature seawater alteration prior to subduction. Correspondingly, the oxygen isotope compositions of eclogitic garnet inclusions fall in a restricted range between +5.5‰ to +7.0‰. For three of the four samples, the stable isotope signatures of inclusions and host diamonds display perfect agreement, with the intensity of seawater alteration signatures, in the form of garnet inclusion 18O enrichment and host diamond 13C depletion and 15N enrichment, increasing together. For the fourth sample, the δ18O signature of the garnet inclusion (+5.5‰) and δ13C-δ15N signatures of the diamond host (−25 and + 19‰, respectively) are decoupled. While the mantle-like δ18O signature indicates a diamond substrate derived from deeper levels in oceanic crust (e.g., deep sheeted dikes), the diamond-forming fluids must have originated from sources that originally resided near the sea water interface. A viable mode of mixing such disparate isotopic signatures is the interaction of diamond-forming fluids derived from shallow oceanic crust altered at low-temperatures with eclogitized substrates originally formed in deeper levels of oceanic crust. This process likely occurred during diamond formation in a tectonic subduction mélange, which juxtaposes deeper and shallower levels of oceanic crust. In the lithospheric mantle above the subcreted oceanic slab, the elevated carbon isotope and highly variable nitrogen isotope compositions of diamonds formed in lherzolitic substrates likely relate to devolatilization and/or melting of principally oceanic sediments containing marine carbonates and clays and subsequent mixing with mantle-derived volatile components. In combination, our diamond and inclusion stable isotope data provide insight into multiple processes that promote diamond formation both inside subducted slabs accreted to the São Francisco cratonic keel and in adjacent subcontinental lithospheric mantle

Contrasting noble gas compositions of peridotitic and eclogitic monocrystalline diamonds from the Argyle lamproite, Western Australia

He-Ne-Ar compositions were determined in diamonds from the Argyle lamproite, Western Australia, to assess whether subducted material affects the noble gas budget and composition of stable old sub-continental lithospheric mantle (SCLM). Twenty diamonds (both peridotitic and eclogitic) were characterized for their carbon isotopic compositions and N abundance and aggregation from which 10 eclogitic growth zones and 5 peridotitic growth zones were analysed for their He-Ne-Ar compositions. The eclogitic diamonds have δ13C values of −4.7 to −16.6 ‰. indicating a subduction signature, whereas the peridotitic diamonds have mantle-like compositions of −4.0 to −7.8 ‰. Mantle residence temperatures based on N-in-diamond thermometry showed that the eclogitic diamonds were mainly formed at 1260-1270 C or above 1300 C near the base of the lithosphere, whereas the peridotitic diamonds generally formed at lower temperatures (mostly 1135-1230 C). A noble gas subduction signature is present to various extents in the eclogitic diamonds and is inferred from a hyperbolic mixing relationship between R/Ra and 4He and δ13C values concentrations with a predominance of low R/Ra values (<0.5; R/Ra = 3He/4Hesample/3He/4Heair). In addition, low 40Ar/4He and 40Ar/36Ar ratios, high nucleogenic 21Ne/4He and low 3He/22Ne ratios are characteristic of subducted material and were found in the eclogitic diamonds. The peridotitic diamonds show generally higher R/Ra values (median 1.1 +- 1.1) and lower 4He/40Ar ratios compared to eclogitic diamonds (median 0.1 +- 0.8 R/Ra; with 7/10 samples having an average of 0.13 +- 0.14 R/Ra). The studied peridotitic diamond growth zones showed a negative correlation between R/Ra and 4He concentrations over 2 orders of magnitude and limited variation in 3He, that can be largely explained by radiogenic 4He ingrowth. At low 4He concentrations the R/Ra value is around 2.8 for both paragenesis of diamonds and is significantly lower than present-day SCLM values, suggesting (1) a more radiogenic helium isotope composition beneath the Halls Creek Orogen than those for typical SCLM from other cratons and/or (2) that the peridotitic diamonds are formed from fluids that also had a subduction input. The high mantle residence temperature and low R/Ra value in the core and low temperature and higher R/Ra value in the rim of a single peridotitic diamond indicate multiple growth events and that part of the lherzolitic diamond population may be genetically related to the eclogitic diamonds. Combining the diamond mantle residence temperatures with noble gas compositions shows that noble gas subduction signatures are present at the base of the lithosphere below 180 km depth beneath Argyle and that fluid migration and interaction with the SCLM occurred over scales of at least 15 km, between 180 and 165 km depth.This research was supported by AGRTP and Ringwood scholarships to ST and funded by an ARC grant (DP140101976) to MH and ALJ