Early Tertiary plutons of biotite tonalite, granodiorite, and granite are found in a curvilinear 2,000-km-long belt along the margin of the Gulf of Alaska. These plutons intrude flyschoid rocks that were accreted to the continental margin during Late Cretaceous and/or early Tertiary time. Field, petrologic, age, and Rb-Sr data on plutonic and metamorphic rocks in eastern Chugach Mountains suggest that the granitic magmas were produced by partial melting of deeper parts of the accretionary prism after it was deformed against the continent. Such magmas may be a common product of heating at the termination of certain major accretionary episodes; they are not subduction-related magmas from subcrustal sources.

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