Petrology and Geochemistry of Adak Island Plutonic Xenoliths: Implications for Primitive Magma Generation and Crustal Differentiation in the Aleutian Island Arc.

This article focuses on the petrogenesis and crystallization conditions of deep crustal cumulate xenoliths erupted from Mt. Moffett and Mt. Adagdak volcanic centers on Adak Island in the Central Aleutians. Detailed petrographic, major, and trace element analyses reveal that both suites crystallized from hydrous, oxidized parental melts containing a basaltic eclogite melt component, likely derived from slab melting or forearc subduction erosion. The study identifies distinct crystallization sequences and geochemical signatures between the two suites, with primitive cumulates showing strong positive Sr anomalies and fractionated rare earth element patterns indicative of slab melt contributions, which diminish in more evolved lithologies due to plagioclase and amphibole fractionation. Modeling suggests that interactions between basaltic eclogite melts and mantle peridotite, melt mixing, or partial melting of metasomatized mantle can explain the parental melt compositions, supporting a complex magmatic plumbing system beneath Adak Island with spatial or temporal heterogeneity in mantle source characteristics.