Alteration conditions on the CM and CV parent bodies – Insights from hydrothermal experiments with the CO chondrite Kainsaz

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

“…Thus, we hypothesize that Fe that was not incorporated into ferrihydrite was likely mobile through the matrix and resulted in the Fe‐rich compositions at the edges of MIL 7a1‐1 o1, MIL 10a2‐6 o1, and MIL 10b2‐5 o1. Similar alteration textures to those observed in MIL 07687 are reported in previous work by Keller and Buseck (1990), Hanowski and Brearley (2000), and Suttle et al (2022). Keller and Buseck (1990) identified poorly crystalline ferrihydrite that formed through the release of Fe from olivine and metal during alteration processes in the Lancé CO3 chondrite.…”

“…The Adelaide meteorite is more thermally altered than MIL 07687, which likely experienced temperatures less than those of Adelaide (<600°C). Indeed, as noted above, laboratory experiments on the CO3 chondrite Kainsaz by Suttle et al (2022) indicate the formation of ferrihydrite, the primary alteration phase in MIL 07687, via hydrothermal processing at temperatures ranging from 50 to 150°C, which is in agreement with temperatures reported for thermal metamorphism of CO3 chondrites (~200°C; Huss et al, 2006), to which MIL 07687 has affinities. Alteration at low temperature is also in agreement with the Cr 2 O 3 measurements by Haenecour et al (2020) that suggest little to no thermal alteration in MIL 07687.…”

“…Similar alteration textures to those observed in MIL 07687 are reported in previous work by Keller and Buseck (1990), Hanowski and Brearley (2000), and Suttle Their study showed that Fe-oxyhydroxides form early in the alteration process at low temperatures (50°C), compared with phyllosilicates, Ni-rich sulfides, Fesulfate, and calcite that form later. They also observed the formation of reaction fronts, where minimally altered material is in direct contact with heavily altered material, similar to the textures observed in MIL 07687 and suggesting that fluids rapidly react with matrix materials (Suttle et al, 2022). Given that we observe ferrihydrite, a metastable precursor, as the dominant alteration phase in the FIB sections in this study and none of the later-stage alteration minerals, such as goethite or phyllosilicates, our data suggest that the alteration experienced by MIL 07687 was early stage and restricted by the availability of water-bearing fluid.…”

“…identified poorly crystalline ferrihydrite that formed through the release of Fe from olivine and metal during alteration processes in the Lancé CO3 chondrite Hanowski and Brearley (2000). identified Fe-rich aureoles in CM chondrites that formed as a result of the in situ alteration of metal grains Suttle et al (2022). performed laboratory alteration experiments on chips of the CO3 chondrite Kainsaz to simulate hydrothermal processing under alkaline and oxidizing conditions on carbonaceous chondrite parent bodies.…”

Iron-60 in the Early Solar System Revisited: Insights from In Situ Isotope Analysis of Chondritic Troilite

“…Thus, rim troilite is not part of the original chondrule mineral assemblage. Fayalite (forsterite content below 50%), with or without hedenbergite, magnetite, saponite, and troilite, has been observed in assemblages of various sizes and shapes, including veins, in carbonaceous chondrites that underwent low-temperature (T < 150°C) aqueous alteration at low water/rock ratios (<1; Krot et al 2000;Jogo et al 2009;Tomeoka & Ohnishi 2014;Suttle et al 2022). However, a hydrothermal origin seems unlikely in the case of our rim assemblages because our rim troilite never forms veins that extend into the surrounding matrix, and the mineral assemblage of our rim troilites also includes euhedral, chromium-rich hercynite (Figures 6(d) and 8(b)), which is absent among the aqueous alteration products generally observed.…”