Distribution of lithium, beryllium, and boron in meteoritic chondrules

Abstract

Abstract— The distribution of Li, Be, and B was studied by ion microprobe mass spectrometry in 36 chondrules from the Semarkona, Bishunpur, Allende, Clovis #1, and Hedjaz meteorites. Within a single chondrule, Li‐Be‐B concentrations can vary up to one order of magnitude. For example, in a chondrule from Hedjaz, concentrations range from 0.3 to 2.4 ppm for Li, from <0.001 to 0.17 ppm for Be, and from 0.4 to 5.5 ppm for B. Among chondrules from Semarkona and Bishunpur, clear crystal‐mesostasis partitioning was observed in nine chondrules for Li, in nine chondrules for Be, and in three chondrules for B. The heterogeneities in the distribution of Li, Be, and B in chondrules from Semarkona and Bishunpur appear to be primary features that were inherited from the chondrules' precursors and not totally obscured during the chondrules' formation. A redistribution of B was nevertheless observed at the whole‐rock scale for Allende (B‐Al2O3 correlation) and Hedjaz (B–SiO2 correlation).At the scale of bulk chondrules, a robust correlation is observed for all studied meteorites between the B/Be and the B/Li ratios, which indicates that Li and Be are much less heterogeneously distributed in chondrites than B. Mean Li, Be, and B concentrations of chondrules ([Li] ≅ 0.83+0.86 ppm; [Be] ≅ 0.0430.027 ppm; [B] ≅ 0.89+3.71‐0.72 ppm) are consistent with those of Orgueil ([Li] ≅ 1.49 ppm; [Be] ≅ 0.0249 ppm; [B] ≅ 0.87 ppm), but the mean Li/Be ratio of chondrules (24.5+6.5‐9.1) is a factor of ∼4 depleted relative to Orgueil (Li/Be ratio of ∼78). Such a depletion is puzzling because no correlation between Li and Na or B has been found as would be expected to result from volatilization processes during chondrule melting and cooling. As a consequence, the exact abundance of solar system Li remains an open question.