In situ analysis of platinum group elements in equilibrated ordinary chondrite kamacite and taenite

Abstract

Platinum group element (PGE) concentrations have been determined in situ in ordinary chondrite kamacite and taenite grains via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Results demonstrate that PGE concentrations in ordinary chondrite metal (kamacite and taenite) are similar among the three ordinary chondrite groups, in contrast to previous bulk metal studies in which PGE concentrations vary in the order H < L < LL. PGE concentrations are higher in taenite than kamacite, consistent with preferential PGE partitioning into taenite. PGE concentrations vary between and within metal grains, although average concentrations in kamacite broadly agree with results from bulk studies. The variability of PGE concentrations in metal decreases with increasing petrologic type; however, variability is still evident in most type six ordinary chondrites, suggesting that equilibration of PGEs does not occur between metal grains, but rather within individual metal grains via self-diffusion during metamorphism. The constant average PGE concentrations within metal grains across different ordinary chondrite groups are consistent with the formation of metal via nebular condensation prior to the accretion of ordinary chondrite parent bodies. Post-condensation effects, including heating during chondrule-formation events, may have affected some element ratios, but have not significantly affected average metal PGE concentrations. H chondrites Buzzard*Specimens provided by the Smithsonian National Museum of Natural History. All other specimens are from the University of Alberta Meteorite Collection. Provided with the meteorite name is its classification and specimen number.

Parent body histories recorded in Rumuruti chondrite sulfides: Implications for the onset of oxidized, sulfur‐rich core formation

“…CI normalization is from McDonough and Sun (1995). the primary carrier phases of siderophile elements: pentlandite in R chondrite NWA 11304 (K d pn/po ~2-500) versus both kamacite and taenite in ordinary chondrites (K d T-K ~1-7; Gilmour & Herd, 2020). The high concentrations and interelement proportions of siderophile elements in R chondrite pentlandite are consistent with formation of chondritic sulfides through the sulfidation of nebular Fe,Ni metal (Kerridge, 1976;Lauretta et al, 1998;Singerling et al, 2021).…”

“…Siderophile element systematics among sulfides during R chondrite metamorphism share some similarities with observations for ordinary chondrite metals. Some variability in trace element concentrations remains among individual grains even at high petrologic type (Figures 5 and 7), indicating that equilibration of siderophile elements is localized within individual grains (Gilmour & Herd, 2020). However, the two processes deviate regarding the primary carrier phases of siderophile elements: pentlandite in R chondrite NWA 11304 ( K d pn/po ~ 2–500) versus both kamacite and taenite in ordinary chondrites ( K d T‐K ~ 1–7; Gilmour & Herd, 2020).…”

“…Some variability in trace element concentrations remains among individual grains even at high petrologic type (Figures 5 and 7), indicating that equilibration of siderophile elements is localized within individual grains (Gilmour & Herd, 2020). However, the two processes deviate regarding the primary carrier phases of siderophile elements: pentlandite in R chondrite NWA 11304 ( K d pn/po ~ 2–500) versus both kamacite and taenite in ordinary chondrites ( K d T‐K ~ 1–7; Gilmour & Herd, 2020). The high concentrations and interelement proportions of siderophile elements in R chondrite pentlandite are consistent with formation of chondritic sulfides through the sulfidation of nebular Fe,Ni metal (Kerridge, 1976; Lauretta et al, 1998; Singerling et al, 2021).…”

Metallographic Cooling Rate and Petrogenesis of the Recently Found Huoyanshan Iron Meteorite Shower

“…For NC meteorites, enstatite chondrite formed in strongly reducing conditions with Ni <10 wt% in its Fe‐Ni metal (Horstmann et al., 2014; van Acken et al., 2012). The H and L type of ordinary chondrites formed in reduced parent bodies with <15 wt% Ni in Fe‐Ni metal, while the Fe‐Ni metal in LL contains ∼30 wt% Ni and formed in oxidized parent bodies (Gilmour & Herd, 2020; Scott et al., 2014). Rumeruti chondrite has high oxidization state parent body but contains negligible Fe‐Ni metal (Krot et al., 2014).…”

“…Therefore, even Rumeruti chondrite has high oxidization state parent body but contains negligible Fe‐Ni metal (<0.1 vol%) (Krot et al., 2014), it seems unlikely to extract iron metal from its precursor materials. In contrast, LL group represents the low Fe and low metal group of ordinary chondrite, and contains 2.0 vol% Fe‐Ni metal with high Ni content (∼30 wt%) in an oxidized parent body (Gilmour & Herd, 2020; Krot et al., 2014). In general, in the known NC reservoir, an oxidized, probably LL like, parent body should the sLH subgroup have.…”