Fig. 21

Three-isotope oxygen diagrams on primary melilite and anorthite, and secondary andradite, calcite, grossular, sodalite, and wollastonite in the Allende CAIs TS-31 (B2), All-2 (FoB), TS-34 (B1), and 160 (C). Grossular and wollastonite (yellow circles) replace melilite and appear to have formed contemporaneously. Andradite, calcite, and wollastonite in veins (black-and-yellow circles) crosscutting the grossular±wollastonite-bearing assemblages precipitated directly from aqueous solutions. Primary melilite and anorthite are ¹⁶O-depleted relative to spinel, Al,Ti-diopside (except TS-34), and forsterite; melilite is more ¹⁶O-depleted than anorthite. Secondary minerals have similar compositions to those of anorthite and melilite. In TS-31 and All-2, secondary minerals plot along mass-dependent fractionation line slightly below the TF line (∆¹⁷O ~ −3‰). Insets in “a” and “b” show O-isotope compositions of grossular and wollastonite that appear to have formed contemporaneously by replacing primary melilite; there is a small range of δ¹⁸O between these secondary minerals, 4 and 6‰ in TS-31 and All-2, respectively. In TS-34 and 160, secondary grossular together with primary melilite and anorthite plot along CCAM line