Fig. 3: Martian magma ocean (MMO) evolutionary signatures during devolatilization and crystallization.

a Copper and potassium isotope systematics reveal distinct fractionation extents. Potassium isotopes (δ⁴¹K) exhibit greater fractionation than Cu isotopes (δ⁶⁵Cu) at equivalent volatile loss fraction. Rayleigh fractionation modeling (fractionation factors α from Sossi et al. ⁵⁴; Supplementary Method 2) indicates ~35% K depletion. Assuming analogous Cu volatility, δ⁶⁵Cu increases by 0.09‰. Value for δ⁴¹K_BSMa follows Tian et al. ⁵⁷, δ⁶⁵Cu and δ⁴¹K of bulk Mars derive from mass balance calculations (Supplementary Method 1). b The alphaMELTS 1.9 simulations (0.2 GPa step size) reveal that the basal liquidus temperatures (in K) and the sulfur content at sulfide saturation (SCSS; in wt.%) decrease with MMO crystallization. Polynomial fits through discrete steps (black crosses) illustrate relationships between crystallization progress and residual melt properties. Predicted S contents (in wt.%) are calculated by mass balance, assuming full S retention in silicate melt until sulfide saturation. SCSS parameterization follows Blanchard et al. ²¹.