Two Cenozoic igneous events on the Alaska Peninsula: A section in Geological Survey research 1980

Potassium-argon dating work and geologic mapping in the Chignik and Sutwik Island quadrangles (loc. 23) by F. H. Wilson, R. L. Detterman, J. E. Case, M. E. Yount, and others (Wilson and others, 1978; Detterman and others, 1979) have shown the existence of two major Cenozoic igneous episodes on the Alaska Peninsula. These events range in age from Eocene to late Oligocene and from early Miocene and late Miocene to Holocene. Both events include andesitic volcanism and shallow plutonism. Porphyry copper deposits are associated with each event. Dates on mineralized zones are Oligocene, Miocene, and Pleistocene, and undated zones probably span the entire range of the two igneous events. Compositions range from dacite to leuco-basalt (Streckeisen, 1979) for volcanic rocks and from tonalite to granodiorite (Streckeisen, 1973) for plutonic rocks.