Coordinated chemical and microstructural analyses of presolar silicate grains from AGB/RGB stars and supernovae in the CO3.0 chondrite Dominion Range 08006

Abstract

We report the structural and chemical analyses of six presolar silicate grains identified in situ in the CO3.0 carbonaceous chondrite Dominion Range (DOM) 08006. Two of the grains have O‐isotopic compositions consistent with origins in the circumstellar envelopes of low‐mass (<2M☉) asymptotic giant branch (AGB)/red giant branch (RGB) stars, although without Mg‐isotopic data, origins in supernovae (SNe) cannot be ruled out. The other four grains have O‐isotopic compositions consistent with origins in the ejecta of type‐II SNe. Transmission electron microscopy analyses reveal that all grains are crystalline (single crystal or polycrystalline) and have varied compositions. The analyzed AGB/RGB grains include an Fe‐rich crystalline olivine with an Fe‐sulfide inclusion and a chemically zoned olivine grain that also contains an Fe‐oxide rim. The grains derived from SNe include two polycrystalline assemblages with structures that overlap with both olivine and pyroxene, an assemblage composed of both a single crystal of forsterite and polycrystalline forsterite, and an orthopyroxene grain with an embedded Fe‐sulfide crystal. The thermodynamic origins of both AGB/RGB and SN grains are also diverse. The structure and compositions of two grains are consistent with equilibrium thermodynamic predictions of condensation, whereas four are not, suggesting formation through nonequilibrium or multistep processes. Our observations of presolar silicate grains suggest that the circumstellar envelopes of AGB/RGB stars and the ejecta of SNe can produce grains with comparable structures and compositions.

An in situ investigation of the preservation and alteration of presolar silicates in the Miller Range 07687 chondrite

“…Electron transparent (<100 nm in projected thickness) cross-sections of four grains were prepared using the Thermo Fisher Scientific (formerly FEI) Helios G 3 focused-ion beam scanning-electron microscope (FIB-SEM) located in the Kuiper Materials Imaging and Characterization Facility (KMICF) at the Lunar and Planetary Laboratory (LPL), University of Arizona. The general procedure for producing electron transparent cross-sections of presolar grains is described in several previous papers (e.g., Haenecour et al, 2019Haenecour et al, , 2020Holzapfel et al, 2009;Seifert et al, 2022c;Zega et al, 2007Zega et al, , 2011Zega et al, , 2014bZega et al, , 2015Zega et al, , 2020. Briefly, we first go through an alignment procedure, described in detail in Seifert et al (2022c) to ensure that we capture the presolar grain identified in the NanoSIMS with our FIB transect.…”

“…The general procedure for producing electron transparent cross-sections of presolar grains is described in several previous papers (e.g., Haenecour et al, 2019Haenecour et al, , 2020Holzapfel et al, 2009;Seifert et al, 2022c;Zega et al, 2007Zega et al, , 2011Zega et al, , 2014bZega et al, , 2015Zega et al, , 2020. Briefly, we first go through an alignment procedure, described in detail in Seifert et al (2022c) to ensure that we capture the presolar grain identified in the NanoSIMS with our FIB transect. Next, using the electron beam, we deposited protective Pt fiducial markers on top of the grain and rectangular 200 nm × 100 nm thick markers on either side of the grain fiducial to assist in the thinning process.…”

“…Zega et al (2020) reported similar findings, suggesting that Fe-rich rims could result from thermal processing of fragments of dust. In the DOM 08006 chondrite, Seifert et al (2022c) reported a forsterite grain with an Fe-rich rim and the authors argued that it formed through thermal processing of a clump of dust, similar to that of Floss and Stadermann (2012) and Zega et al (2020). Finally, a nonstoichiometric olivine-like grain and an enstatite grain with Fe-rich rims were identified in the NWA 801 and Isheyevo chondrites, and were attributed to aqueous alteration (Sanghani et al, 2022).…”

“…The detailed analysis of presolar grains can also provide information on the conditions under which they condensed in their host CSEs or SNe ejecta. The chemical compositions and crystal structures of presolar grains can be compared with thermodynamic model predictions to infer the pressure and temperature conditions under which they formed (e.g., Nguyen et al, 2007Nguyen et al, , 2010Nguyen et al, , 2016Seifert et al, 2022c;Stroud et al, 2004;Vollmer et al, 2007Vollmer et al, , 2009Vollmer et al, , 2013Zega et al, 2011Zega et al, , 2014aZega et al, , 2015Zega et al, , 2020. Such models predict when certain minerals will condense from a gas, generally defined as solar composition, under an assumed set of total pressures.…”

A petrologic and microstructural study of a compact type A calcium‐aluminum‐rich inclusion from the Northwest Africa 5028 CR2 chondrite: Implications for nebular and parent‐body processes

“…The procedure followed is a variation of that reported by Zega et al (2007), but we briefly describe it here. For the first two sections extracted, we deposited a thin layer of Pt (200-300 nm) using the electron beam (e-beam) for ease of locating the ROI in the secondary-electron image produced by the Ga + ion beam (i-beam; Seifert et al, 2022;Zega et al, 2020). The thin Pt layer also serves to protect the surface from irradiation by the i-beam during the initial alignment process.…”