Gregory Timothy, Luu Tu-Han, Coath Christopher D, Russell Sara S, Elliott Tim
School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK.
Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
Sci Adv. 2020 Mar 11;6(11):eaay9626. doi: 10.1126/sciadv.aay9626. eCollection 2020 Mar.
Understanding the spatial variability of initial Al/Al in the solar system, i.e., (Al/Al), is of prime importance to meteorite chronology, planetary heat production, and protoplanetary disc mixing dynamics. The (Al/Al) of calcium-aluminum-rich inclusions (CAIs) in primitive meteorites (~5 × 10) is frequently assumed to reflect the (Al/Al) of the entire protoplanetary disc, and predicts its initial Mg/Mg to be ~35 parts per million (ppm) less radiogenic than modern Earth (i.e., Δ'Mg = -35 ppm). Others argue for spatially heterogeneous (Al/Al), where the source reservoirs of most primitive meteorite components have lower (Al/Al) at ~2.7 × 10 and Δ'Mg 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 Δ'Mg are within uncertainty of -35 ppm. Our data thus affirm a model of a largely homogeneous protoplanetary disc with (Al/Al) of ~5 × 10, supporting the accuracy of the Al→Mg chronometer.
了解太阳系中初始铝-26与铝-27的空间变异性，即（铝-26/铝-27），对于陨石年代学、行星热产生以及原行星盘混合动力学至关重要。原始陨石中富钙铝包体（CAIs）的（铝-26/铝-27）（约为5×10）常被假定反映了整个原行星盘的（铝-26/铝-27），并预测其初始镁-26/镁-24比现代地球的放射性低约百万分之35（ppm）（即，Δ'Mg = -35 ppm）。其他人则主张空间上不均匀的（铝-26/铝-27），其中大多数原始陨石成分的源储库在约2.7×10时（铝-26/铝-27）较低，且Δ'Mg为-16 ppm。我们测量了起源于CAI形成储库之外的原始陨石橄榄石的镁同位素组成，并报告了五个颗粒，其Δ'Mg在-35 ppm的不确定度范围内。因此，我们的数据证实了一个原行星盘在很大程度上是均匀的模型，其（铝-26/铝-27）约为5×10，支持了铝-26→镁-26计时计的准确性。
