Osmium isotopes in Ivory Coast tektites: Confirmation of a meteoritic component and rhenium depletion

The sensitive negative thermal ionization mass spectrometry method was used for the measurement of concentrations and isotopic ratios of osmium and rhenium in four Ivory Coast tektites. These tektites have crustal major and trace element composition, as well as large negative epsilon(sub Nd)(-20) and positive epsilon(sub Sr)(+260 to +300) which are characteristic for old continental crust. Os concentrations ranging from 0.09 to 0.30 ppb were found, clearly much higher than average crustal values, Os-187/Os-186 ratios of about 1.2-1.7, and low Re-187/Os-186 ratios. These results show unambiguously the existence of a meteoritic component (on the order of 0.06%) in the Ivory Coast tektites. Low Re abundances are the result of fractionation of Re during the impact

Regional study of the Archean to Proterozoic crust at the Sudbury Neutrino Observatory (SNO+), Ontario: Predicting the geoneutrino flux

The SNO+ detector, a new kiloton scale liquid scintillator detector capable of recording geoneutrino events, will define the strength of the Earth radiogenic heat. A detailed 3-D model of the regional crust, centered at SNO+ and based on compiled geological, geophysical and geochemical information, was used to characterize the physical and chemical attributes of crust and assign uncertainties to its structure. Monte Carlo simulations were used to predict the U and Th abundances and uncertainties in crustal lithologies and to model the regional crustal geoneutrino signal originating from the at SNO+

Comment on “Discovery of davemaoite, CaSiO₃-perovskite, as a mineral from the lower mantle”

Tschauner et al. (Reports, 11 November 2021, p. 891) present evidence that diamond GRR-1507 formed in the lower mantle. Instead, the data support a much shallower origin in cold, subcratonic lithospheric mantle. X-ray diffraction data are well matched to phases common in microinclusion-bearing lithospheric diamonds. The calculated bulk inclusion composition is too imprecise to uniquely confirm CaSiO₃ stoichiometry and is equally consistent with inclusions observed in other lithospheric diamonds

Regional patterns in the paragenesis and age of inclusions in diamond, diamond composition, and the lithospheric seismic structure of Southern Africa

Abstract The Archean lithospheric mantle beneath the Kaapvaal -Zimbabwe craton of Southern Africa shows F 1% variations in seismic P-wave velocity at depths within the diamond stability field (150 -250 km) that correlate regionally with differences in the composition of diamonds and their syngenetic inclusions. Seismically slower mantle trends from the mantle below Swaziland to that below southeastern Botswana, roughly following the surface outcrop pattern of the Bushveld-Molopo Farms Complex. Seismically slower mantle also is evident under the southwestern side of the Zimbabwe craton below crust metamorphosed around 2 Ga. 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 Proterozoic and show little correspondence with these lithospheric variations. However, silicate inclusions in diamonds and their host diamond compositions for the above kimberlites, Finsch, Jagersfontein, Roberts Victor, Premier, Venetia, and Letlhakane do show some regional relationship to the seismic velocity of the lithosphere. Mantle lithosphere with slower P-wave velocity 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 whereas the converse is true for diamonds from higher velocity mantle. The oldest formation ages of diamonds indicate that the mantle keels which became continental nuclei were created by middle Archean (3.2 -3.3 Ga) mantle depletion events with high degrees of melting and early harzburgite formation. The predominance of sulfide inclusions that are eclogitic in the 2.9 Ga age population links late Archean (2.9 Ga) subduction-accretion events involving an oceanic lithosphere component to craton stabilization. These events resulted in a widely distributed younger Archean generation of eclogitic diamonds in the lithospheric mantle. Subsequent Proterozoic tectonic and magmatic event

Evaluation of the impact of hematocrit and other interference on the accuracy of hospital-based glucose meters,”

ABSTRACT Background: Most glucose meter comparisons to date have focused on performance specifications likely to impact subcutaneous dosing of insulin. We evaluated four hospital-based glucose meter technologies for accuracy, precision, and analytical interferences likely to be encountered in critically ill patients, with the goal of identifying and discriminating glucose meter performance specifications likely to impact intensive intravenous insulin dosing. Methods: Precision, both within-run and day-to-day, was evaluated on all four glucose meters. Accuracy (bias) of the meters and analytical interference were evaluated by comparing results obtained on whole blood specimens to plasma samples obtained from these whole blood specimens run on a hexokinase reference method. Results: Precision was acceptable and differed little between meters. There were significant differences in the degree to which the meters correlated with the reference hexokinase method. Ascorbic acid showed significant interference with three of the four meters. Hematocrit also affected the correlation between whole blood and plasma hexokinase glucose on three of the four glucose meters tested, with the magnitude of this interference also varying by glucose meter technology. Conclusions: Correlation to plasma hexokinase values and hematocrit interference are the main variables that differentiate glucose meters. Meters that correlate with plasma glucose measured by a reference method over a wide range of glucose concentrations and minimize the effects of hematocrit will allow better glycemic control for critically ill patients

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

Age, paragenesis and composition of diamonds and evolution of the Precambrian mantle lithosphere of southern Africa

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 ~2.9 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 (~3.3 to ~3.2 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 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