Constraining compositional proxies for Earth’s accretion and core formation through high pressure and high temperature Zn and S metal-silicate partitioning

Investigating Earth's Formation History Through Copper and Sulfur Metal‐Silicate Partitioning During Core‐Mantle Differentiation

“…Errors for all EPMA measurements of DAC experiments are reported as 1SD (σ). Errors for piston cylinder experiments are reported as 2SE to account for integration of local heterogeneities, as previously discussed (Chabot et al, ; Mahan et al, ; Mahan, Siebert, et al, ; Siebert et al, ).…”

“…The following models have focused on chondrule‐rich accretion scenarios, which is by and large an iteration of pebble accretion, or the accretion of planetary materials from centimeter‐ to meter‐sized objects. Such accretion mechanisms are of specific interest as they may have played an important role in terrestrial planet formation (e.g., Bollard et al, ; Cuzzi et al, ; Jacobsen & Walsh, ; Johansen et al, ; Levison et al, ), since chondrule‐rich accretion can potentially explain volatile and moderately volatile element abundances in the BSE and BE (e.g., Amsellem et al, ; Hewins & Herzberg, ; Mahan, Siebert, et al, ; Righter et al, ), especially in the absence of appreciable volatile loss from Earth and other terrestrial bodies during accretion (e.g., Canup et al, ; Stewart et al, ). Moreover, chondrules likely provide a reliable record of the conditional and compositional evolution of the solar system during the planet‐forming epoch (Libourel & Portail, ; Mahan, Moynier, et al, ).…”

“…Furthermore, they are exceptionally depleted in S both in the bulk and in their chondrules (Lodders & Fegley Jr, ; Bischoff et al, , respectively). Given the likely suppressed siderophile behavior of S at HP‐HT during Earth's formation (Suer et al, ), this marked S depletion in Earth's initial source material in order to generate present‐day S contents in the BSE (e.g., Mahan, Siebert, et al, ). With all this in mind, bulk CH chondrites may provide a viable model precursor material—but probably not actual precursor material—for Earth and other terrestrial planets.…”

Reply to Comment by Jennings et al. on “Investigating Earth's Formation History Through Copper and Sulfur Metal‐Silicate Partitioning During Core‐Mantle Differentiation”

“…The resultant contribution of secondary X‐ray fluorescence from Cu grids as outlined in Jennings et al (), ~70% for both metal and silicate phases, is substantially larger than that observed in the current work, at ~50% in both phases. Although a detailed exploration into where this ~20% difference arises is far outside the scope of the current work, it is likely the cumulative result of multiple contributing factors, such as: The approach taken by Jennings, Wade, and Llovet () to investigate the potential effects of secondary X‐ray fluorescence from Cu grids, which is largely based on Monte Carlo simulations in which idealized compositions are used (pure Fe for metal, CFMAS for silicate), and therefore does not fully encapsulate the experimental compositions of Mahan, Siebert, Blanchard, Badro, et al (). The sample lamella simulated, at 20 x 12 x 3 μm, are less than half the size of those typically found in Mahan, Siebert, Blanchard, Badro, et al () (approximately 20 x 30 x 3 μm), which may focus and/or enhance the effects of secondary X‐ray fluorescence. The simulations of Jennings, Wade, and Llovet () differ from typical DAC experimental run products as they assume that all silicate has melted to become basaltic glass, which is not the case (see Figures and S1; Mahan, Siebert, Blanchard, Borensztajn, et al, ; Mahan, Siebert, Blanchard, Badro, et al, ), and thus these simulations also cannot account for the size, structure, and/or geometry of this reaction zone. The simulations of Jennings, Wade, and Llovet () furthermore do not account for the Pt welding, gaps between the metal and silicate phases (from differential thermal expansion/contraction), surface topography, TEM grid orientation relative to samples, or any other morphological features and variables that are typical of actual DAC experiments. …”

“…3. The simulations of Jennings, Wade, and Llovet (2019) differ from typical DAC experimental run products as they assume that all silicate has melted to become basaltic glass, which is not the case (see Figures 1 and S1; Mahan, Siebert, Blanchard, Borensztajn, et al, 2018;, and thus these simulations also cannot account for the size, structure, and/or geometry of this reaction zone. 4.…”