In situ single‐spot Rb/Sr cosmochronology of roedderite in the Ribbeck aubrite (asteroid 2024 <scp>BX1</scp> )

Abstract The mineralogy and textures of several fragments from the Ribbeck aubrite were analyzed using a combination of scanning electron microscopy, electron microprobe analysis, μRaman spectroscopy, and laser ablation inductively coupled reaction cell mass spectrometry (LA‐ICP‐MS/MS). The meteorite fragments are strongly brecciated and show evidence of shock melting. The silicate phases of the fragments predominantly consist of enstatite, albite, and roedderite, with subordinate forsterite, diopside, K‐feldspar. Non‐silicate phases include kamacite, troilite, oldhamite, and Fe‐Ti, Fe‐Mn, and Fe‐Cr rich sulfides. Tridymite and cristobalite, the latter contained in Si‐rich glass, are also present within one enstatite grain. Vesicular fusion crust is apparent in several fragments. The discovery of roedderite is the first reported for the Ribbeck aubrite. In situ Rb/Sr dating combined with chemical analysis of the roedderite was performed via laser ablation ICP‐MS/MS using the single‐spot dating approach. The average chemistry of 20 roedderite analyses is 68.7 wt% of SiO 2 , 23.1 wt% of MgO, 4.9 wt% of K 2 O, and 3.3 wt% of Na 2 O and is &lt;0.1 wt% of FeO. The total concentrations of Rb and Sr are 282 and &lt;1 μg g −1 , respectively. Single‐spot Rb/Sr dates from the same 20 analyses yielded a weighted average of 4570 ± 27 Ma, interpreted as the formation age of the Ribbeck aubrite parent body. The result highlights advantages of single‐spot Rb/Sr dating compared to short‐lived isotopic systems (e.g., 26 Al‐ 26 Mg, 53 Mn‐ 53 Cr, and 129 I‐ 129 Xe), long‐lived systems with radiogenic noble gasses (e.g., 40 K‐ 40 Ar and 238/235 U‐ 232 Th‐ 4 He), and the conventional Rb/Sr isochron approach for meteorite cosmochronology.