Fig. 3. Boron isotope systematics of the Marcy and Morin anorthosites.

Symbols are averages of multiple measurements for each grain (tables S1 and S2). Error bars show ±2σ SE. Dehydration trends of eclogite are from (28); other references are given in Materials and Methods. Marginal histograms were calculated from grain averages using the default kernel smoothing in MATLAB (v.2020b); interlaboratory comparisons on the same grain were averaged for histograms. (A) Plagioclase and nonmegacrystic pyroxene show significantly higher and lower δ¹¹B values than bulk depleted mantle and continental crust and overlap with subduction zone lithologies. Pyroxene megacrysts can reach values similar to abyssal serpentinites. Plagioclase values closely resemble dehydrated slab eclogite and its melt(s) (28, 33). Tie lines connect results for the same grain from SIMS and LA-MC-ICP-MS. (B) Detail of (A)’s left edge.