Apparent episodicity of magmatic activity based on radiometric age determination: A section in The United States Geological Survey in Alaska: Accomplishments during 1980

Results of recent potassium-argon age studies in the Chignik region, Alaska, (Wilson, 1980; Wilson and others, 1982) have suggested a distinct episodicity in igneous activity during Tertiary time. To date work on the Aleutian magmatic arc indicates that plutonic activity took place along the present outer Pacific margin and in the northern Alaska-Aleutian Range batholith (Reed and Lanphere, 1973; Kienle and Turner, 1976; DeLong and others, 1978) in latest Cretaceous and earliest Tertiary time (70-58 m.y.) and was followed by a hiatus lasting until late Eocene ( 45 m.y~) time. Late Eocene to earliest Miocene ( 45-20 m.y.) magmatic activity was followed by a middle Miocene hiatus (10 m.y.). Since that time, magmatic activity in the Aleutian arc has been continuous.