Figure F33. Plot showing the variation of K2O vs. An in plagioclase. Both secondary core and grain rim are shown when variable in a single thin section. Note change in slope around An50. This correlates with point that oxides appear in the mode (correlates with Mg# = 73–75 in clinopyroxene). This more rapid enrichment is not predicted by perfect fractional crystallization models.

Figure F33. Plot showing the variation of K₂O vs. An in plagioclase. Both secondary core and grain rim are shown when variable in a single thin section. Note change in slope around An₅₀.This correlates with point that oxides appear in the mode (correlates with Mg# = 73–75 in clinopyroxene). This more rapid enrichment is not predicted by perfect fractional crystallization models.