Eocene basalts from the Yakutat terrane: Evidence for the origin of an accreting terrane in southern Alaska

Basalts from the Yakutat terrane, a composite oceanic and continental tectonostratigraphic terrane, are chemically diverse large ion lithophile element (LILE)–depleted and LILE-enriched tholeiites, interpreted as normal mid-ocean ridge and oceanic island basalt, that originated on seamounts near the Kula-Farallon spreading center during the early to middle Eocene. Coeval and geochemically similar basalts, occurring sporadically in a linear belt from southern Vancouver Island to the southern Oregon Coast Range, are correlative with the Yakutat terrane basalts. Both basaltic sequences were accreted to the continental margin during subduction of the Kula-Farallon Ridge and Kula plate about 48 Ma. The Yakutat basalts were emplaced along the coast of Washington or British Columbia. The Yakutat terrane probably originated during the Neogene as a composite terrane when it was sliced off the continental margin and started to move northward along the Queen Charlotte-Fairweather transform fault toward its present location in southern Alaska.