Ternary feldspar crystallization in high-temperature felsic magmas

Ternary feldspars crystallizing at equilibrium under conditions of high temperature and low H₂O content in trachytic and dry granitic magmas show distinctly different evolutionary paths once two feldspars are stabilized if crystallization occurs under conditions of fixed H₂O activity (H₂O buffered) or under conditions in which the H₂O of Qz content is to decrease the extent of Or enrichment in alkali feldspar, the amount of Or depletion in plagioclase, and the amount of resorption of plagioclase. Decompression can lead to crystallization or resorption of either feldspar, as well as significant changes in the compositions of the feldspars. -from Author