Primordial formation of major silicates in a protoplanetary disc with homogeneous 26Al/27Al.

ABSTRACT: Understanding the spatial variability of initial 26Al/27Al in the solar system, i.e., (26Al/27Al)0, is of prime importance to meteorite chronology, planetary heat production, and protoplanetary disc mixing dynamics. The (26Al/27Al)0 of calcium-aluminum-rich inclusions (CAIs) in primitive meteorites (~5 × 10-5) is frequently assumed to reflect the (26Al/27Al)0 of the entire protoplanetary disc, and predicts its initial 26Mg/24Mg to be ~35 parts per million (ppm) less radiogenic than modern Earth (i.e., ?'26Mg0 = -35 ppm). Others argue for spatially heterogeneous (26Al/27Al)0, where the source reservoirs of most primitive meteorite components have lower (26Al/27Al)0 at ~2.7 × 10-5 and ?'26Mg0 of -16 ppm. We measured the magnesium isotope compositions of primitive meteoritic olivine, which originated outside of the CAI-forming reservoir(s), and report five grains whose ?'26Mg0 are within uncertainty of -35 ppm. Our data thus affirm a model of a largely homogeneous protoplanetary disc with (26Al/27Al)0 of ~5 × 10-5, supporting the accuracy of the 26Al?26Mg chronometer.

SUBMITTER: Gregory T 

PROVIDER: S-EPMC7065882 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature