26Al‐26Mg isotope systematics of the first solids in the early solar system. (19th July 2013)

• Record Type: Journal Article
• Authors: Kita, Noriko T.; Yin, Qing‐Zhu; MacPherson, Glenn J.; Ushikubo, Takayuki; Jacobsen, Benjamin; Nagashima, Kazuhide; Kurahashi, Erika; Krot, Alexander N.; Jacobsen, Stein B.
• Is Part Of: Meteoritics & planetary science. Volume 48:Number 8(2013:Aug.)
• Page Start: 1383
• Page End: 1400
• Publication Date: 2013-07-19
• Subjects: Meteorites -- Periodicals; Planetology -- Periodicals; 523.4
• DOI: 10.1111/maps.12141
• Languages: English
• ISSNs: 1086-9379

Abstract

<abstract abstract-type="main" id="maps12141-abs-0001"> <title>Abstract</title> <p>High‐precision bulk aluminum‐magnesium isotope measurements of calcium‐aluminum‐rich inclusions (CAIs) from CV carbonaceous chondrites in several laboratories define a bulk <sup>26</sup>Al‐<sup>26</sup>Mg isochron with an inferred initial <sup>26</sup>Al/<sup>27</sup>Al ratio of approximately 5.25 × 10<sup>−5</sup>, named the canonical ratio. Nonigneous CV CAIs yield well‐defined internal <sup>26</sup>Al‐<sup>26</sup>Mg isochrons consistent with the canonical value. These observations indicate that the canonical <sup>26</sup>Al/<sup>27</sup>Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI‐forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial <sup>26</sup>Al/<sup>27</sup>Al ratios, (4.2–5.2) × 10<sup>−5</sup>, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial <sup>26</sup>Al/<sup>27</sup>Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in <sup>26</sup>Al. At least some of these refractory objects may have formed prior to injection of <sup>26</sup>Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium‐isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of <sup>26</sup>Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial <sup>26</sup>Al/<sup>27</sup>Al ratios of chondrules indicate that most chondrules formed 1–3 Ma after CAIs with the canonical <sup>26</sup>Al/<sup>27</sup>Al ratio.</p> </abstract>