$^{26}$Al-$^{26}$Mg isotopic, mineralogy, petrography of a Hibonite-Pyroxene Spherule in Allan Hills 77307 (CO3.03): Implications for the origin and evolution of these objects

TL;DR

This study analyzes a rare hibonite-pyroxene spherule from Allan Hills 77307, revealing diverse isotopic anomalies and distinct origins of mineral components, shedding light on early solar system processes.

Contribution

It provides detailed isotopic, mineralogical, and petrographic analysis of a large hibonite-pyroxene spherule, highlighting its complex formation history and origin.

Findings

Discordant $^{26}$Al-$^{26}$Mg abundances in hibonite and pyroxene suggest different formation regions.

The petrography indicates minimal alteration, preserving original isotopic signatures.

Distinct mineral origins imply complex formation and alteration processes in early solar system materials.

Abstract

10 Hibonite-pyroxene/glass spherules discovered hitherto are a rare suite of refractory inclusions that show the largest range of exotic isotopic properties (anomalies in neutron rich isotopes (e.g., $^{48}$Ca, $^{50}$Ti), abundance of $^{26}$Al) despite their defining simple spherical morphology and mineralogy consisting predominantly of few hibonites nestled within/with glassy or crystallised calcium, aluminium-rich pyroxene. $^{26}$Al-$^{26}$Mg chronological studies along with petrography and mineralogy of a relatively large (~120 micron diameter), found in Allan Hills 77307 (CO3.03) has been performed. Uniquely, both hibonite and pyroxene show discordant abundance of short-lived now-extinct radionuclide $^{26}$Al that suggest disparate and distinct regions of origin of hibonite and pyroxene. The pristine petrography and mineralogy of this inclusion allow discernment of their genesis and trend of alteration in hibonite-pyroxene/glass spherules.