Fig. 1.

(a) Representative isochrons for canonical CAIs (e.g. Jacobsen et al. 2008; MacPherson et al. 2010) and the ranges from Semarkona (LL3.01), Yamato 81020 (CO3.05), and Acfer 094 (ungr. C3.00) chondrite chondrules (Hutcheon and Hutchison 1989; Kita et al. 2000; Kunihiro et al. 2004; Kurahashi et al. 2008a; Rudraswami et al. 2008; Villeneuve et al. 2009; Hutcheon et al. 2009; Ushikubo et al. 2013). *δ²⁶Mg is defined in Section 2.5.1 of the main text. Slopes of isochrons correspond to inferred (²⁶Al/²⁷Al)₀. (b) CR chondrite chondrule (²⁶Al/²⁷Al)₀ values (symbols) versus the range of chondrule (²⁶Al/²⁷Al)₀ from LL3, CO3, and Acfer 094 chondrites (gray shading and dashed lines). Relative ages are calculated using the canonical (²⁶Al/²⁷Al)₀ shown in (a), and a ²⁶Al half-life of 0.705 Myr (Norris et al. 1983). For CR chondrite chondrule data, references 1–4 correspond to Schrader et al. (2017), Nagashima et al. (2014), Hutcheon et al. (2009), and Kurahashi et al. (2008b), respectively. Closed and open symbols correspond to chondrules with and without resolvable excess ²⁶Mg, respectively. Three chondrules from Hutcheon et al. (2009) were re-measured by Nagashima et al. (2014); only the data from the latter study are shown. (²⁶Al/²⁷Al)₀ values and uncertainties from Hutcheon et al. (2009) were determined using Isoplot. Data from Kurahashi et al. (2008b) with unresolvable excess ²⁶Mg are only reported as (²⁶Al/²⁷Al)₀ upper limits (hence, no symbols are shown).