<scp>⁵³Mn‐⁵³Cr</scp> chronology and <scp>ε⁵⁴Cr‐Δ¹⁷O</scp> genealogy of Erg Chech 002: The oldest andesite in the solar system

Abstract

Abstract The meteorite Erg Chech (EC) 002 is the oldest felsic igneous rock from the solar system analyzed to date and provides a unique opportunity to study the formation of felsic crusts on differentiated protoplanets immediately after metal–silicate equilibration or core formation. The extinct 53 Mn‐ 53 Cr chronometer provides chronological constraints on the formation of EC 002 by applying the isochron approach using chromite, metal–silicate–sulfide, and whole‐rock fractions as well as “leachates” obtained by sequential digestion of a bulk sample. Assuming a chondritic evolution of its parent body, a 53 Cr/ 52 Cr model age is also obtained from the chromite fraction. The 53 Mn‐ 53 Cr isochron age of 1.73 ± 0.96 Ma (anchored to D'Orbigny angrite) and the chromite model age constrained between and Ma after the formation of calcium‐aluminium‐rich inclusions (CAIs) agree with the 26 Al‐ 26 Mg ages (anchored to CAIs) reported in previous studies. This indicates rapid cooling of EC 002 that allowed near‐contemporaneous closure of multiple isotope systems. Additionally, excess in the neutron‐rich 54 Cr (nucleosynthetic anomalies) combined with mass‐independent isotope variations of 17 O provides genealogical constraints on the accretion region of the EC 002 parent body. The 54 Cr and 17 O isotope compositions of EC 002 confirm its origin in the “noncarbonaceous” reservoir and overlap with the vestoid material Northwest Africa 12217 and anomalous eucrite Elephant Moraine 92023. This indicates a common feeding zone during accretion in the protoplanetary disk between the source of EC 002 and vestoids. The enigmatic origin of iron meteorites remains still unresolved as EC 002, which is more like a differentiated crust, has an isotope composition that does not match known iron meteorite groups that were once planetesimal cores.

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