Metal-silicate Partitioning Behavior of Molybdenum, Tungsten, and Nickel: Implications for Core Formation

The interior structure of Earth, particularly the metal core, is responsible for the core dynamo and thus our magnetic field and supplying the mantle with heat to encourage solid state convection and thus decompression melting and hot spot volcanism. Therefore determining how Earth\u27s core formed and if that process was unique to our planet in the solar system is of great scientific interest. Core formation can be studied experimentally by examining the metal-silicate partitioning behavior of siderophile elements and using the results to explain their observed upper mantle depletions relative to bulk Earth abundances. This study investigated the partitioning behavior of the moderately siderophile elements molybdenum and tungsten by conducting experiments using multi-anvil presses and obtaining compositional analyses of the run products using electron probe microanalysis. Molybdenum was found to dissolve as Mo4+ in silicate melts, whereas tungsten dissolved as W6+. The partition coefficients [Di = ci(metal)/ci(silicate)] for both molybdenum and tungsten decrease with increasing pressure; however, DW increases slightly with increasing temperature whereas DMo decreases. Both elements become less siderophile as silicate melt polymerization decreases. The addition of carbon to the metal phase causes DMo and DW to increase, while addition of sulfur causes DMo and DW to decrease. Parameterization of the data from this study and literature data allowed for core formation modeling to determine what conditions could explain Earth\u27s mantle abundances of molybdenum, tungsten, and nickel (the most extensively studied element). The modeling suggests that the abundances of these elements were set by a global magma ocean near the end of accretion with conditions of 35-37 GPa (~1100 km depth) and 2950-3000 K with XC = 0.07, XS = 0.05, and XSi = 0.06. Thus implying that large impacts in the late stages of Earth\u27s accretion were energetic enough to re-equilibrate the already differentiated metal and silicate, leaving the distinct chemical signature of a single equilibration event in the mantle. Applying the parameterizations to other differentiated bodies for which we have compositional data indicates that magma oceans were common occurrences in the early solar system, but each body underwent a unique differentiation history

Supplemental information for: Experimental assessment of EAIRMS normalization methodologies for environmental stable isotopes

<p>This repository contains data for the manuscript "Experimental assessment of EAIRMS normalization methodologies for environmental stable isotopes" by Sawyer Balint, Morgan Schwartz, Drew Fowler, Stella Linnekogel, Sáde Cromratie Clemons, and Laura K. Burkemper.</p&gt

Experimental assessment of elemental analyzer isotope ratio mass spectrometry normalization methodologies for environmental stable isotopes

•Rationale: In stable isotope mass spectrometry, isotope delta values are normalized to internationally recognized reference scales using a combination of certified and in-house isotope reference materials. Numerous techniques exist for performing this normalization, but these methodologies need to be experimentally assessed to compare their effect on reproducibility of isotope results. •Methods: We tested normalization methods by the number of reference materials used, their matrix, their isotope range, and whether normalization required extrapolating beyond the isotope range. We analyzed eight commercially available isotope reference materials on a ThermoFinnigan Delta-V isotope ratio mass spectrometer (IRMS) and an Elementar VisION IRMS for nitrogen and carbon isotope composition via solid combustion with an elemental analyzer and computed every possible isotope normalization (n = 612). Additionally, we assessed how sample matrix affected linearity effects on both instruments using five in-house reference materials. •Results: Normalizations exhibited the best performance when the reference materials spanning an isotope range of at least 20‰ were matrix matched with the samples and did not require extrapolation beyond the calibration curve. When these conditions were not met, the number of reference materials used had a significant effect on accuracy, with normalizations composed of two reference materials exhibiting particularly inconsistent performance at isotope ranges below 20‰. Linearity effects were found to exceed instrument precision by two orders of magnitude irrespective of matrix type and were not predicted by working gas diagnostics. •Conclusions: Interlaboratory comparability of isotope results is improved when operators of elemental analyzer isotope ratio mass spectrometry (EAIRMS) systems select reference materials spanning an isotope range of at least 20‰. Additionally, using three or more isotopic reference materials, avoiding extrapolation beyond the range of the normalization curve, and matching the matrix of the reference materials to the samples improve normalizations

The Mars Science Laboratory APXS calibration target: Comparison of Martian measurements with the terrestrial calibration

The Mars Science Laboratory Curiosity rover carries a basalt calibration target for monitoring the performance of the alpha particle X-ray spectrometer. The spectrum acquired on Sol 34 shows increased contributions from Mg, S, Cl and Fe relative to laboratory spectra recorded before launch. Mars Hand Lens Imager images confirm changes in the appearance of the surface. Spectra taken on Sols 179 and 411 indicate some loss of the deposited material. The observations suggest deposition of a surface film likely consisting of dust mobilized by impingement of the sky crane's terminal descent engine plumes with surface fines during Curiosity's landing. New APXS software has been used to model the thin film that coated the calibration target on landing. The results suggest that a film of about 100 nm thickness, and containing predominantly MgO, Fe 2O3, SO3, Cl and Na2O could give rise to the observed spectral changes. If this film is also present on the alpha particle sources within the APXS, then its effect is negligible and the terrestrial calibration remains appropriate