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Peridotite xenoliths from the Cascade arc in the United States and in the Japan arc have neodymium and osmium isotopic compositions that are consistent with addition of 5 to 15 percent of subducted material to the present-day depleted mantle. These observations suggest that osmium can be partitioned into oxidized and chlorine-rich slab-derived fluids or melts. These results place new constraints on the behavior of osmium (and possibly other platinum group elements) during subduction of oceanic crust by showing that osmium can be transported into the mantle wedge., Studies of the isotopic compositions and large-ion lithophile and light element abundances of arc lavas (1-3) have shown the importance of recycled subducted material in the genesis of arc magmas. [...]

Calculations with data for asteroidal cores indicate that Earth's outer core may have a rhenium/osmium ratio at least 20 percent greater than that of the chondritic upper mantle, potentially leading [...]

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately ± 31 millioon years for meteorites 4500 million years old. Although an absolute rheniumosmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of [sup.187.Re], an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represents by these iron groups may have cooled significantly later than the parent body of the IIA irons., IRON METEORITES ARE DIVIDED INTO groups on the basis of their internal structures and chemical compositions. In most instances, irons of the same group were likely derived from the same [...]

Iridosmine grains from placer deposits associated with peridotite-bearing ophiolites in the Klamath mountains have extremely radiogenic [sup.186]Os/[sup.188]Os ratios and old Re-Os minimum ages, from 256 to 2644 million years. This indicates the existence of an ancient platinum group element reservoir with a supra-chondritic Pt/Os ratio. Such a ratio may be produced in the outer core as a result of inner core crystallization that fractionates Os from Pt. However, if the iridosmine Os isotopic compositions are a signature of the outer core, then the inner core must have formed very early, within several hundred million years after the accretion of Earth., Osmium has two radiogenic isotopes, [sup.186]Os and [sup.187]Os. [sup.190]Pt decays to [sup.186]Os with a half-life of ~449.4 billion years (Gy) (1), and [sup.187]Re decays to [sup.187]Os with a half-life of [...]

Two depth profiles of the osmium concentration and the [sup.187]OS/[sup.186]OS isotopic ratio in the Indian Ocean showed that the osmium concentration seems to be unaltered by chemical or biological processes occuring in seawater; accordingly, osmium is conservative. These data were obtained from an experimental method that eliminated the problems related to osmium preconcentration. This method led to a new evaluation of the concentration of osmium in seawater; the mean concentration of osmium and the [sup.187]Os/ [sup.186]Os ratio are equal to 10.86 ± 0.07 picograms per kilogram and 8.80 ± 0.07, respectively. The results suggest the existence of an organocomplex that dominates the speciation of osmium in seawater., The [sup.187]Os/[sup.186]Os ratios in marine sediments are considered to indicate the relative variations of continental, mantle, and meteoritic input to seawater and to provide a record of continental weathering. However, [...]

Given a new tool similar to a hammer, a carpenter will quickly learn how to use it. Learning to use an unfamiliar new tool, on the other hand, takes some [...]