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

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 53Mn‐53Cr 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 53Cr/52Cr model age is also obtained from the chromite fraction. The 53Mn‐53Cr isochron age of 1.73 ± 0.96 Ma (anchored to D'Orbigny angrite) and the chromite model age constrained between 1.46−0.68+0.78 and 2.18−1.06+1.32 Ma after the formation of calcium‐aluminium‐rich inclusions (CAIs) agree with the 26Al‐26Mg 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 54Cr (nucleosynthetic anomalies) combined with mass‐independent isotope variations of 17O provides genealogical constraints on the accretion region of the EC 002 parent body. The 54Cr and 17O 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.

Evidence for Very Early Planetesimal Formation and 26Al/27Al Heterogeneity in the Protoplanetary Disk

“…Our U-corrected Pb-Pb age of 4566.19 ± 0.20 Ma confirms the antiquity of EC002 defined previously by the modeldependent 26 Al-26 Mg (Barrat et al 2021;Fang et al 2022;Reger et al 2023) and 53 Mn-53 Cr (Anand et al 2022;Zhu et al 2022) 2023) is based on a three-point isochron with an unacceptable fit (MSWD = 3.3). Their age incorporates a 238 U/ 235 U ratio of 137.766 that they attained from 160 mg of leached pyroxenes, a value that is considerably lower than their bulk value ratio of 137.819 ± 0.010 and our value of 137.813 ± 0.010.…”

“…These estimates correspond to reported ages of 2.26 ± 0.01 Myr, 1.80 ± 0.01, and 1.83 ± 0.12 Myr, respectively, after CAI formation at 4567.30 ± 0.16 Ma (Connelly et al 2012), assuming the socalled canonical initial 26 Al/ 27 Al ratio for the EC002 parent body precursor material of (5.23 ± 0.13) × 10 −5 (Jacobsen et al 2008). Two 53 Mn-53 Cr ages of 1.73 ± 0.96 Myr and 0.7 ± 0.6 Myr after t 0 (anchored to D'Orbigny) were reported by Anand et al (2022) and Zhu et al (2022), respectively.…”

“…Recent reports on the andesitic Erg Chech 002 (herein EC002) suggests that it represents the most ancient silicate achondrite (Barrat et al 2021;Anand et al 2022;Fang et al 2022;Zhu et al 2022;Reger et al 2023). Such an old age would suggest that it represents a fragment of a primary, early formed planetesimal that escaped further growth during the collision and pebble accretion phases of planet formation.…”

“…Such an old age would suggest that it represents a fragment of a primary, early formed planetesimal that escaped further growth during the collision and pebble accretion phases of planet formation. However, these ages are either highly model dependent (the 26 Al-26 Mg system by Barrat et al 2021 andFang et al 2022 and the 53 Mn-53 Cr system of Anand et al 2022 andZhu et al 2022) or based on a three-point Pb-Pb isochron with an unacceptable fit (Reger et al 2023).…”

K-Ca dating and Ca isotope composition of the oldest Solar System lava, Erg Chech 002

“…The short-lived radioactive system 26 Al-26 Mg (t 1/2 = 0.705 Ma) yields a precise relative age (1.80 ± 0.01 Ma after CAI formation), which suggests that EC 002 is the oldest magmatic rock and represents the primordial crusts from a protoplanet in the early Solar System (Fang et al, 2022). 53 Mn-53 Cr dating returned consistently old ages comprising 0.7 ± 0.6 Ma (Zhu et al, 2022) and 1.73 ± 0.96 Ma (Anand et al, 2022) after CAI formation. Compared to the age of EC 002 from the 26 Al-26 Mg and 53 Cr systems relative to the initial Solary System, long lived isotopic systems, including 40 K-40 Ar (4534 þ117 −125 Ma, 1σ) and 147 2σ), returned large errors on absolute ages (Barrat et al, 2021;Fang et al, 2022).…”