The cadmium and zinc isotope compositions of the silicate Earth – implications for terrestrial volatile accretionOPEN ACCESS 

· by · in ,

Harvey Pickard, Emeliana Palk, Maria Schönbächler, Rebekah E.T. Moore, Barry J. Coles, Katharina Kreissig, Katrina Nilsson-Kerr, Samantha J. Hammond, Eiichi Takazawa, Christophe Hémond, Peter Tropper, Dan N. Barfod, Mark Rehkämper

Geochimica et Cosmochimica Acta
Available online 6 October 2022

LINK (OPEN ACCESS)

“Zinc and Cd isotope compositions are presented for a comprehensive suite of terrestrial rocks to constrain the extent of Zn and Cd isotope fractionation during igneous processes and better define the δ66Zn and δ114Cd values of the silicate Earth (the δ values denote per mille deviations of 66Zn/64Zn from JMC Lyon Zn and of 114Cd/110Cd from NIST SRM 3108 Cd). Analyses of spinel lherzolites provide a bulk silicate Earth (BSE) δ114CdBSE value of –0.06 ± 0.03‰ (2SD). For Zn, the peridotite data of the current and previous studies define a mean δ66ZnBSE = 0.20 ± 0.05‰ (2SD). Komatiite analyses of this and published investigations yield similar mean values, which suggests that the Zn and Cd isotope compositions of the mantle remained fairly constant since the Archean. Data for loess provide upper continental crust compositions of δ114Cd = 0.03 ± 0.10‰ and δ66Zn = 0.23 ± 0.07‰. The Zn isotope and abundance data for peridotites and oceanic basalts are in accord with the previous observation of a mantle array, with basalts having higher Zn concentrations and δ66Zn values than the peridotites. To a first order, this reflects slightly incompatible behaviour of Zn during mantle melting and melt differentiation with associated enrichment of heavy Zn isotopes in the melt phase. Cadmium is marginally more incompatible than Zn during igneous processes and the oceanic basalts also display a minor enrichment of heavy Cd isotopes relative to peridotites. However, secondary processes produce significant Cd isotope variability in both mantle melts and peridotites, obscuring the primary igneous array. The δ66ZnBSE estimates of this and previous studies resemble the Zn isotope compositions of CV and CO carbonaceous and some enstatite chondrites. In contrast, the BSE has a lower δ114CdBSE value than enstatite and carbonaceous chondrites. This implies that the Cd isotope composition of the BSE was either fractionated during accretion or that Earth’s Cd inventory was not exclusively acquired from material related to carbonaceous and enstatite chondrites. Importantly, delivery of Zn and Cd to the BSE solely by CI and CM chondrites is not in accord with the meteorite and terrestrial stable isotope data of these elements.”

Related posts (automatically generated):

  1. Zinc isotope anomalies in primitive meteorites identify the outer solar system as an important source of Earth’s volatile inventoryOPEN ACCESS 
  2. Nucleosynthetic zinc isotope anomalies reveal a dual origin of terrestrial volatilesOPEN ACCESS 
  3. Tellurium isotope cosmochemistry: Implications for volatile fractionation in chondrite parent bodies and origin of the late veneer
  4. Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impactOPEN ACCESS 
  5. Numerous chondritic impactors and oxidized magma ocean set Earth’s volatile depletionOPEN ACCESS 
  6. Bulk chondrite variability in mass independent magnesium isotope compositions – Implications for initial solar system 26Al/27Al and the timing of terrestrial accretion
  7. Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth’s volatiles
  8. Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretionOPEN ACCESS 
  9. Tungsten stable isotope compositions of terrestrial samples and meteorites determined by double spike MC-ICPMS
  10. The effect of collisional erosion on the composition of Earth-analog planets in Grand Tack models: Implications for the formation of the Earth
Tags: , , ,