Age and Petrogenesis of the Shumagin Batholith in Western Chugach-prince William Terrane, Alaska

The Shumagin batholith is part of the Sanak-Baranof plutonic belt in Southwest Alaska that extends approximately 2200km from Sanak Island in the west to Baranof Island in the east. (Hudson, 1979; Hudson et al., 1979; Hill et al., 1980; Bradley et al., 2000; Haeussler et al., 2003). Previous work has indicated that the crystallization ages of the Sanak-Baranof plutons young from west to east. The oldest pluton in the belt intruded the Upper Cretaceous flysch of the Chugach-Prince William accretionary complex at 61Ma (Bradley et al., 2003). The diachronous relationship of the Sanak-Baranof plutons has been interpreted both as having formed in place due to the subduction of an oceanic ridge (Bradley et al., 1993; Haeussler et al., 2003), and as having formed with the movement of the Chugach-Prince William terrain over a relatively immobile trench-ridge-trench triple junction (Cowan, 2003). These plutons are anomalous because they intrude the forearc and the diachronous age progression from the western end of the plutonic belt to the eastern end.