The Fate of Sulfur and Chalcophile Elements During Crystallization of the Lunar Magma Ocean

Abstract

The occurrence and extent of sulfide liquid saturation in silicate melts are governed by the abundance of sulfur (S) and its solubility or S concentration at sulfide liquid saturation (SCSS); S content at sulfide liquid saturation) for a particular melt. The SCSS is a function of both silicate and sulfide liquid composition, pressure (P), temperature (T) and redox state (

Large sulfur isotope fractionation in lunar volcanic glasses reveals the magmatic differentiation and degassing of the Moon

“…Under these conditions, the SCSS for the silicate melt will range from 549- to 611-ppm sulfur, significantly below the estimated ~1220-ppm sulfur of the urKREEP. Our results are consistent with the hypothesis that the late-stage crystallization of the LMO reached sulfide saturation ( 34 ). We estimated a range in the FeS-silicate melt equilibrium isotope fractionation factor α FeS - melt of 1.004 and 1.002 at 1000°C (see table S3) ( 41 , 44 ).…”

“…The model indicates that if the LMO reaches a range in δ 34 S between −1 and −1.5‰ after core segregation, it will result in an LMO sulfur content between 83 and 33 ppm, a core S content of 0.8 and 1.1 wt %, and an equilibrium sulfur isotope fractionation factor α core-mantle of 1.0016 and 1.0007 for batch equilibrium and open system, respectively. All output results are within values previously estimated or experimentally determined ( 34 , 54 – 56 , 60 , 61 ).…”

“…We evaluate the effect that sulfide saturation had on the δ 34 S value of the cumulates formed during the late stages of the LMO crystallization. Most models agree that by the end of the LMO crystallization (≥90%), the residual melt reached sulfide saturation ( 34 ). We use Ding et al .…”

“…In the open-system model, the core is treated as a cumulative product. We considered for our model a core mass fraction in the range of 2 mass % ( 54 – 56 ), an initial bulk Moon sulfur content of 250 ppm, with a chondritic δ 34 S = 0 ‰ ( 34 ), and a metal-silicate melt sulfur partition coefficient of ~100 ( 58 , 59 ). The model indicates that if the LMO reaches a range in δ 34 S between −1 and −1.5‰ after core segregation, it will result in an LMO sulfur content between 83 and 33 ppm, a core S content of 0.8 and 1.1 wt %, and an equilibrium sulfur isotope fractionation factor α core-mantle of 1.0016 and 1.0007 for batch equilibrium and open system, respectively.…”

“…In contrast, the high-Ti volcanic glasses with enriched trace elements and volatile contents, including high initial sulfur content and δ 34 S +0.8 to +1.6‰, point to a component generated during the late-stage crystallization of the LMO. The crystallization of the LMO will generate a late-stage ilmenite and urKREEP components enriched in incompatible elements and volatile contents, including S, which most likely reached sulfide saturation ( 34 ). Therefore, the addition of these late-stage components to the early LMO cumulate pile would increase the sulfur and δ 34 S values, as well as the titanium content, giving rise to the source of the high-Ti lunar magmas ( 1 ).…”