Multiple sulfur isotopic composition of main group pallasites support genetic links to IIIAB iron meteorites

The group IIF iron meteorites and Eagle Station pallasites (PES) have highly siderophile element abundances (HSE; Re, Os, Ir, Ru, Pt, and Pd) of metal that are consistent with formation in planetesimal cores by fractional crystallization with minor to major solid metal-liquid metal mixing. Modeling of HSE abundances of the IIF irons indicates a complex formation history that included the mixing of primitive and evolved solid and liquid metals. By contrast, modeling of HSE abundances of PES metal suggests these meteorites formed mainly as equilibrium solids from a common liquid. Abundances of some of the siderophile elements in the IIF irons and PES are permissive of a common core origin; however, the abundances of W and Ni indicate the PES ultimately formed on a more oxidized body. The PES most likely formed by the injection of olivine present at the core-mantle boundary into a metallic core liquid as a result of impact. The core then crystallized inward, trapping the olivine.

Section: Introductionmentioning

confidence: 95%

“…2011; Dottin et al. 2018). However, differences in the measured cooling rates of PMG metal (2.5–18 K Myr −1 ) and IIIAB irons (50–350 K Myr −1 ) are difficult to explain in a common core scenario, and have been interpreted by some to suggest that the PMG and IIIAB irons ultimately formed on separate bodies (Yang et al.…”

Section: Introductionmentioning

confidence: 99%

Crystallization histories of the group IIF iron meteorites and Eagle Station pallasites

Hilton

Ash

Walker

2020

“…; Dottin et al. ). It also remains plausible that the crustal remnants of the Main‐group parent body were transported to the inner solar system through the same mechanisms that delivered the pallasites and IIIABs, and are thus represented somewhere in the meteorite collection.…”

Section: Introductionmentioning

confidence: 98%

“…Because thermal conduction establishes that the core responsible for the IIIAB iron meteorites should have cooled more slowly than the surrounding CMB, it is surprising that metallographic cooling rates yield the opposite: the IIIAB irons appear to have cooled more rapidly at 50-350 K Myr À1 . Studies based on metallographic cooling rates and siderophile trace elements have questioned the genetic relationship between Main-group pallasites and IIIABs (Wasson and Choi 2003;Yang and Goldstein 2006;Yang et al 2010), though recent oxygen and sulfur isotope measurements continue to support formation in the same parent body (Franchi et al 2013;Dottin et al 2018). It also remains plausible that the crustal remnants of the Main-group parent body were transported to the inner solar system through the same mechanisms that delivered the pallasites and IIIABs, and are thus represented somewhere in the meteorite collection.…”

Section: Introductionmentioning

confidence: 99%

The Fukang pallasite: Characterization and implications for the history of the Main‐group parent body

DellaGiustina

Habib

Domanik

et al. 2019

We report the results of a study of the Fukang pallasite that includes measurements of bulk composition, mineral chemistry, mineral structure, and petrology. Fukang is a Main‐group pallasite that consists of semiangular olivine grains (Fo 86.3) embedded in an Fe‐Ni matrix with 9–10 wt% Ni and low‐Ir (45 ppb). Olivine grains sometimes occur in large clusters up to 11 cm across. The Fe‐Ni phase is primarily kamacite with accessory taenite and plessite. Minor phases include schreibersite, chromite, merrillite, troilite, and low‐Ca pyroxene. We describe a variety of silicate inclusions enclosed in olivine that contain phases rarely or not previously reported in Main‐group pallasites, including clinopyroxene (augite), tridymite, K‐rich felsic glass, and an unknown Ca‐Cr silicate. Pressure constraints determined from tridymite (<0.4 GPa), two‐pyroxene barometry (0.39 ± 0.07 GPa), and geophysical calculations that assume pallasite formation at the core–mantle boundary (CMB), provide an upper estimate on the size of the Main‐group parent body from which Fukang originated. We conclude that Fukang originated at the CMB of a large differentiated planetesimal 400–680 km in radius.

“…A growing body of work involving meteorites and lunar samples has suggested homogeneity in the D 33 S of the Earth, Moon, and Mars, which match that of Cañon Diablo Troilite (CDT) within error (AE0.008&, 1r; Peters et al 2010;Labidi et al 2013;Antonelli et al 2014;Franz et al 2014;Wing and Farquhar 2015). However, small-magnitude mass-independent signatures have been observed in some achondrite groups (Farquhar et al 2000a;Rai et al 2005), in magmatic iron meteorites (Antonelli et al 2014), pallasites (Dottin et al 2018), and in some chondrites (Rai and Thiemens 2007;Labidi et al 2017). These findings suggest homogeneity for sulfur delivered to the Earth, Moon, Mars, and nonmagmatic iron meteorites, but also the presence of low-level sulfur isotopic heterogeneity in other protoplanetary materials.…”

Section: Introductionmentioning

confidence: 99%

A new type of isotopic anomaly in shergottite sulfides

Franz

Farquhar

et al. 2019

Self Cite

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.