“…There is negligible sulfur isotopic fractionation between the melt and the residual for the case where all sulfur is present as sulfide in both materials, based on the isotope composition of coexisting silicate and sulfide in natural samples ( 34 α = 1.0000 ± 0.0003; Labidi & Cartigny, 2016; Labidi et al., 2014; Mandeville et al., 2009). Some studies suggest that the mantle may be split into an upper and lower mantle (Spencer, Katz, Hewitt, May, & Keszthelyi, 2020), which we include as an option with an inter‐mantle flux of sulfur between them. Our model assumes that mantle melts are either intruded into the crust as plutons or erupted at the surface and degassed; based on Spencer, Katz, and Hewitt (2020), we assume 80% is intruded (Section S2.2 in Supporting Information ).…”