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. Th...