Textural and mineralogical evidence of crystal fractionation from evolving aluminous magma; Ca and P increase in garnet as Cr and Ti decrease in most spinels. Several parental magmas. Corundum in alkremites contains 0.1-0.2 wt.% TiO 2 , 0.2-0.5 Cr 2 O 3 , and 0.5-1.2 Fe 2 O 3 . Mica (0.7-3.4 TiO 2 ) in grain boundaries is secondary. Foundering or subduction of Al-rich sediments (perhaps chloritized ocean crust) may have generated local Al enrichment in the upper mantle to provide diverse source regions for alkremite magmas.--Modified journal abstract.

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