A new type of isotopic anomaly in shergottite sulfides

Abstract

The isotopic composition and abundance of sulfur in extraterrestrial materials are of interest for constraining models of both planetary and solar system evolution. A previous study that included phase‐specific extraction of sulfur from 27 shergottites found the sulfur isotopic composition of the Martian mantle to be similar to that of terrestrial mid‐ocean ridge basalts, the Moon, and nonmagmatic iron meteorites. However, the presence of positive Δ33S anomalies in igneous sulfides from several shergottites, indicating incorporation of atmospherically processed sulfur into the subsurface, complicated this interpretation. The current study expands upon the previous work through analyses of 20 additional shergottites, enabling tighter constraints on the isotopic composition of juvenile Martian sulfur. The updated composition (δ34S = −0.24 ± 0.05‰, Δ33S = 0.0015 ± 0.0016‰, and Δ36S = 0.039 ± 0.054‰, 2 s.e.m.), representing the weighted mean for all shergottites within the combined population of 47 without significant Δ33S anomalies, strengthens our earlier result. The presence of sulfur isotopic anomalies in igneous sulfides of some meteorites suggests that their parent magmas may have assimilated crustal material. We observed small negative Δ33S anomalies in sulfides from two meteorites, NWA 7635 and NWA 11300. Although negative Δ33S anomalies have been observed in nakhlites and ALH 84001, previous anomalies in shergottites have all shown positive values of Δ33S. Because NWA 7635 has formation age of 2.4 Ga and is much more ancient than shergottites analyzed previously, this finding expands our perspective on the continuity of Martian atmospheric sulfur photochemistry over geologic time.

Earth-like Habitable Environments in the Subsurface of Mars

“…(e) Radionuclide abundances in martian meteorites (Meyer, 2016) and GRS data from 60°S to 60°N, where near-surface ice does not contaminate measurements (Boynton et al, 2007;Tarnas et al, 2018 Assume density of 5000 kg/m 3 for sulfide and 3000 kg/m 3 for host rock to convert from vol % to wt %. The data of Franz et al (2014Franz et al ( , 2019 and Wang and Becker (2017) were calculated from whole-rock S contents assuming 38 wt % S for pyrrhotite and 54 wt % for pyrite. Other sulfide abundances are from image analyses on polished thick sections.…”

“…Sulfide concentrations range from <0.01-1.0 wt %. The assumed sulfide concentration ranges in the model are derived based on these sulfide concentrations found in martian meteorites (Greenwood et al, 2000b(Greenwood et al, , 2000aRochette et al, 2001Rochette et al, , 2005Lorand et al, 2005Lorand et al, , 2015Lorand et al, , 2018aLorand et al, , 2018bChevrier et al, 2011;Franz et al, 2014Franz et al, , 2019Baumgartner et al, 2017;Hewins et al, 2017Hewins et al, , 2020Wang and Becker, 2017) (Fig. 1f; Table 1).…”

Can Isotopologues Be Used as Biosignature Gases in Exoplanet Atmospheres?

“…As such, sulfur isotopes may prove to be a valuable biosignature for solar system bodies such as Mars and Europa where in situ and sample return measurements will be possible [30]. δ 34 S has already been measured on Mars as −0.24 ± 0.05‰ [32] and sulfur has been detected on the surface of Europa [33]. Chela-Flores [34] posit that sulfur isotope fractionation of −70‰ or more is caused by a metabolic process and could be used as evidence for life on solar system bodies.…”