Isotope anomalies in meteorites reveal a fundamental dichotomy between non-carbonaceous (NC) and carbonaceous (CC) materials [1]. This dichotomy is recognized in both early- and late-formed planetesimals, but whether these formed from the same or distinct materials remains uncertain. To address this, we analyzed Fe and Ni isotopes in a large suite of ungrouped iron meteorites representing ~22 parent bodies. These samples, previously characterized for Mo and W isotopes, derive from early-formed differentiated bodies of NC (9) or CC (16) affinity [2].

Our new Fe and Ni isotope data show that early- and late-formed NC and CC planetesimals span similar isotopic ranges as their respective chondrites. This indicates that bodies in each reservoir accreted from similar dust mixtures, either in long-lived disk structures or in different sub-reservoirs containing the same materials. Among CC bodies, two findings stand out. First, many ungrouped irons match the isotopic composition of late-formed CR chondrites, suggesting the CR reservoir formed early and remained isolated throughout disk evolution. Second, CI chondrites are the only CC meteorites whose isotopic composition is absent among differentiated meteorites, implying planetesimals with this signature formed late by a distinct mechanism [3] and/or in a separate reservoir [4].

References: [1] Kleine et al. (2020) Space Sci. Rev. 216, 55. [2] Spitzer et al. (2025) Geochim. Cosmochim. Acta, in press. [3] Spitzer et al. (2024) Sci. Adv. eadp2426. [4] Hopp et al. (2022) Sci. Adv. eadd8141.

Carbonaceous chondrites (CC) are some of the most primitive meteorites in our Solar System, and their parent bodies likely formed a few Myr after the formation of the Solar System began. CC contain three major components: refractory inclusions, chondrules, and CI chondrite-like matrix. Isotopic studies reveal that the relative abundances of these components correlate with the formation time of their parent bodies. It has been proposed that variations in these abundances reflect the trapping of refractory inclusions and chondrule precursors within pressure maxima in the protoplanetary disk, likely associated with the gap created during Jupiter’s formation.

In this talk, we present Monte Carlo simulations of dust evolution to test whether CC parent bodies could have formed in the outer regions of a Jupiter-induced gap. Our model tracks the transport and collisional evolution of refractory inclusions, chondrules, and matrix-like grains during the late stages of disk evolution. We demonstrate that the observed correlation between the component abundances and the accretion time of the parent body is consistently reproduced if CC formed in a common region over an extended period.

Magmatic iron meteorites sample the metal cores of differentiated planetesimals formed through segregation and crystallization of metallic melts. Group IVB irons are the most depleted in volatile elements and have the youngest Hf–W ages among magmatic irons [1]. Variations in their metallographic cooling rates suggest that the IVB core cooled without an insulating mantle, likely removed during a collisional disruption of the parent body [2]. To better understand the chronology of the IVB parent body, and to search for isotopic signatures that may record post-core formation re-mixing of metal and silicates, we applied the ⁵³Mn-⁵³Cr system to chromites from four IVB irons. Chromites were chosen because they are unaffected by cosmic ray-induced Cr isotope shifts [3]. All four samples exhibit indistinguishable nucleosynthetic ⁵⁴Cr, similar to CV chondrites, supporting a genetic link to the carbonaceous chondrite (CC) reservoir. However, the samples show distinct radiogenic ⁵³Cr, corresponding to an apparent ⁵³Mn–⁵³Cr model age spread of ~3 Ma. This spread likely does not reflect differences in metal segregation timing, as all samples yield identical Hf–W ages [1]. Instead, the ⁵³Cr variations likely result from the addition of mantle-derived radiogenic ⁵³Cr during partial metal–silicate re-equilibration caused by impact disruption. This interpretation is supported by metallographic cooling rates for outward crystallization of the IVB core [2] and our observation that later-crystallized IVBs display more radiogenic ⁵³Cr.

Ref. [1] Kruijer et al. (2014) Science, 344, 1150-1154. [2] Yang et al. (2010) GCA, 74, 4493-4506. [3] Anand et al. (2021) GPL, 20, 6-10.

Magmatic iron meteorites sample the metal cores of differentiated planetesimals, and are classified into distinct chemical groups by their markedly different contents of the moderately volatile elements (MVE) Ge and Ga. The variable MVE depletions may be inherited from an iron parent body’s precursor materials or are the result of secondary losses associated with parent body accretion, differentiation, and disruption. To better understand the origin of these MVE depletions, we obtained mass-dependent Te isotopic data, using a ¹²³Te-¹²⁵Te double-spike and MC-ICP-MS, for metal and troilite samples from several magmatic irons (IC, IIF, IIIAB, and IVA). The Te concentrations vary by two orders of magnitude among the investigated samples and follow the volatile depletion trends defined by the less volatile Ge and Ga. In all samples, Te is predominantly hosted in troilite, with troilite-metal partitioning coefficients of ≈100. As such, the Te isotope composition of troilite can be taken as a proxy for that of the bulk iron meteorite and, by inference, the bulk core. Despite large differences in Te concentration, the troilites investigated in this study show only limited mass-dependent Te isotope variations and fall within the range of compositions observed among carbonaceous chondrites. Of note, all troilites investigated thus far are isotopically lighter than CI chondrites. Together these observations suggest that any MVE loss from the iron parent bodies did not induce large Te isotope fractionations and that the precursor material of these bodies was already somewhat MVE-depleted compared to CI chondrites.

The surface of Mercury is enriched in sulfur, reaching concentrations of up to 4 wt.%, according to findings from NASA’s MESSENGER mission. One proposed explanation for this enrichment involves volcanic degassing, whereby reduced sulfur is released from the planet’s interior and subsequently initiates sulfidation reactions with the surface rocks. However, the underlying mechanisms involved in the sulfidation of silicate minerals remain poorly understood. In this study, we explore the kinetics and mechanisms of the reaction between reduced gaseous sulfur and two common silicate minerals on Mercury’s surface – olivine and diopside. Our approach included high-temperature experiments, in which the silicate mineral – with a polished surface – and sulfur powder were placed separately into graphite crucibles and subsequently loaded into an evacuated silica glass tube. The samples were subjected to temperatures between 800 and 1250 °C. Under these conditions, the sulfur powder forms a gas which fills the tube, enabling a reaction with the silicate mineral. The duration of the experiments was varied between 1 hour and 1 month. The highly reducing conditions on Mercury were simulated by buffering the oxygen fugacity through the graphite-CO reaction. Our results reveal a fundamental contrast in the mechanism of the sulfidation reaction between olivine and diopside. In olivine, the reaction is primarily limited by diffusion, whereas diopside develops intermediate reaction layers at its surface, including Ca-depleted pyroxene. These findings offer new insights into sulfidation processes on Mercury, which has implications for observations by the BepiColombo mission currently en route to the planet.

Airbursts of extraterrestrial objects were likely common in the geological past but left few traces in the rock record. Three occurrences of texturally similar, vesicular natural glasses – Pica glass (Chile), Edeowie glass (Australia), and Dakhleh glass (Egypt), here termed PED glasses – may have formed during airburst events [e.g., 1] or, alternatively, through combustion metamorphism [e.g., 2]. Silicate melts can exchange oxygen isotopes with air if exposed to high temperatures for sufficient time, e.g., 50% exchange at T > 1500 °C within 15 s [1], as observed in irghizites – a type of impact glass formed in an impact-generated vapour plume. To investigate the formation conditions of PED glasses, we therefore analysed their triple oxygen isotope compositions, and compared these with a broad suite of natural glasses. The data show that PED glasses contain several tens of atom percent atmosphere-derived oxygen. Similarly, paralavas from the Canadian Arctic – melts formed via the combustion of bituminous shales and coal seams – also incorporate significant amounts of atmospheric oxygen. In contrast, tektites, basaltic glasses from subaerial eruptions, impact melts, and desert fulgurites show no detectable atmosphere-derived oxygen. Additionally, trinitite, the glass formed by the low-altitude (30 m) nuclear airburst in 1945, does not contain measurable atmospheric oxygen either. These results confirm that PED glasses formed under exceptionally high-temperature conditions, exhibiting a common formation mechanism – either similar to irghizites but not to trinitite or, alternatively, to paralavas.

[1] Schultz et al. (2022) Geology [2] Roperch et al. (2022) EPSL [3] Pack (2021) RiMG 86, 217–240