Isotopically Heavy Micrometeorites—Fragments of CY Chondrite or a New Hydrous Parent Body?

Abstract

Cosmic dust grains sample a diverse range of solar system small bodies. This includes asteroids that are not otherwise represented in our meteorite collections. In this work we obtained 3D images of micrometeorite interiors using tomography before collecting destructive high‐precision oxygen isotope measurements. These data allow us to link textures in unmelted micrometeorites to known chondrite groups. In addition to identifying particles from ordinary chondrites, CR and CM chondrites we report two micrometeorites derived from an anomalous 16O‐poor source (δ17O: +16.4‰, δ18O: +28.4‰, and Δ17O: +1.4‰). Their compositions overlap with a previously reported micrometeorite (TAM50‐25) from Suttle et al. (2020), https://doi.org/10.1016/j.epsl.2020.116444 (EPSL: 546:116444). These particles represent hydrated carbonaceous chondrite material derived either from a new group or from the CY chondrites (thereby extending the isotopic range of this group). In either scenario they demonstrate close petrographic and isotopic connections to the CO‐CM chondrite clan. Furthermore, their position in O‐isotope space makes them the most likely candidate for the parent body of the anomalous “group 4” cosmic spherules previously reported by Suavet et al. (2010), https://doi.org/10.1016/j.epsl.2010.02.046 (EPSL: 293:313‐320) and several subsequent isotopic studies. We conclude that the “group 4” cosmic spherules originate from hydrated C‐type asteroid parents.

Oxygen isotopic compositions of fresh rooftop micrometeorites from the Budel collection—Insights into the contemporary cosmic dust flux

“…At least some of the 16 O-poor spherules associated with group 4 may thus originate from isotopically heavy parts of aqueously altered CM/CO/CV/CK-like chondrites, rather than representing a previously unidentified chondrite group. This further supports the potential genetic link between 16 O-poor particles and the CM mixing line as proposed by Suttle et al (2022). Yet, this does not fully explain why the most 16 O-depleted values are not encountered in larger meteorites.…”

“…(2010), but are unlikely based on the mineralogical and textural variability observed among group 4 particles (Goderis et al., 2020). Additionally, these sources would require extreme mass‐dependent fractionation of oxygen, which is not indicated by the CS textures, the general absence of micrometeorites with compositions of Δ 17 O > 1‰ and δ 18 O < 20‰, and low chemical and iron isotope fractionation (Lampe et al., 2022; Suavet et al., 2011; Suttle et al., 2022). It is therefore commonly assumed that the precursor of group 4 particles is already 16 O depleted.…”

“…The existence of 16 O-poor particles in micrometeorite collections has long been acknowledged by multiple independent studies (Goderis et al, 2020;Lampe et al, 2022;Rudraswami, Prasad, Dey, et al, 2016;Rudraswami et al, 2020;Suavet et al, 2010Suavet et al, , 2011Suttle et al, , 2022van Maldeghem et al, 2023;Yada et al, 2005). The micrometeorites analyzed in these studies originate from various collections that record a large variation in terms of size fractions, geographic locations, and terrestrial ages.…”

High precision triple oxygen isotope composition of small size urban micrometeorites indicating constant influx composition in the early geologic past

“…Atmospheric O 2 exchange furthermore pulls the oxygen isotope composition toward the TFL. Another explanation could be a to date unidentified hydrated carbonaceous chondrite type parent body with high δ 18 O VSMOW , as is postulated for the group 4 cosmic spherules (Suttle et al., 2022). The second ungrouped specimen in this study is the BO type THMM231.…”

“…Samples down to 150 μg can be analyzed by means of dual inlet IRMS (Crespin et al., 2008; Fischer et al., 2021; Greenwood et al., 2007; Suttle et al., 2022). Smaller sample down to 30 μg can be measured with a microvolume device attached to the dual inlet system with good precision.…”