The ruthenium isotopic composition of the oceanic mantle

Abstract

The approximately chondritic relative, and comparatively high absolute m antle abundances of the highly siderophile elem ents (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ~0.5 to 1% of "late accretion" to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosm ochem ical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic m antle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ 100 Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, mem bers of the Main Group and sLL subgroup of the lAB iron meteorite complex which have a collective CRE corrected μ 100 Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these m eteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

New insights into Mo and Ru isotope variation in the nebula and terrestrial planet accretionary genetics

“…The reported data were reduced using one of two different reduction protocols. One protocol utilized an assumed oxygen isotopic composition (obtained from Nier, 1950) for oxide interference corrections, while the other protocol relied on the direct measurement of the oxygen isotopic composition ("Nier reduction method" and "measured oxygen reduction method", respectively; Walker, 2012; Bermingham et al, 2016;Worsham et al, 2016b;Bermingham and Walker, 2017). The latter reduction scheme became available approximately mid-way through the course of this study with the addition of 10 12 ohm and 10 13 ohm resistor amplifiers to the Triton Plus.…”

“…To assess the Ru isotope composition of the Earth's mantle, Fischer-Gödde et al 2015reported the Ru isotope composition of a terrestrial chromitite from the Shetland Ophiolite Complex. Subsequently, Bermingham and Walker (2017) reported an estimate of the Ru isotopic composition of the oceanic mantle, which is likely representative of the BSE, from measurements of thirteen different ophiolite chromitites and Os-Ir-Ru alloy grains which sample eight different, mainly Phanerozoic, mantle domains ( Table SM1b). The isotopic compositions of these materials were found to be identical, within analytical uncertainties, to a reference material solution used as a standard in studies of meteoritic Ru.…”

Chemical Separation of Tungsten and Other Trace Elements for TIMS Isotope Ratio Measurements Using Organic Acids

“…, Rizo et al . , Bermingham and Walker , Dickson , Mundl et al . ) and extra‐terrestrial (e.g., Akram and Schönbächler , Hunt et al .…”

The late Earth's accretion: Processes and materials

“…The relative abundances of NM seen in Figure 1b imply enstatite-like chondrites to be carriers of these species and thus a principal component of the late veneer. Study of the nucleosynthetic isotope anomalies showed a minimal difference between these meteorites and terrestrial rocks: the late veneer was derived from the inner Solar system material with a slightly higher contribution of the s-process nuclides compared with E-chondrites [Bermingham and Walker, 2017;Burkhardt et al, 2016;Fischer-Gödde and Kleine, 2017]. Ruthenium presents a clear isotopic evidence for an inner Solar System origin of the late veneer (Figure 2).…”