Results of an aeromagnetic survey in the Gulf of Alaska

A regional aeromagnetic survey of the northern Gulf of Alaska shows north-south sea floor spreading anomalies continuing up to 100 km northwest of the Aleutian trench. The continental shelves east of Kodiak Island and south of the Kenai Peninsula are magnetic ‘quiet zones.’ In the eastern third of the gulf these north-south anomalies terminate abruptly at a transform or transcurrent fault that traverses the entire region. A large positive magnetic anomaly is located along the entire western edge of the continental margin in southeast Alaska. When the aeromagnetic data are combined with other available magnetic data, there is an indication that this continental margin anomaly can be traced southward to Vancouver Island. Several possible sources of this anomaly are discussed. However, a volcanic mass whose geometry is controlled by a seaward extension of the Fairweather fault is the preferred explanation.