Geology and 40Ar/39Ar geochronology of the medium- to high-K Tanaga volcanic cluster, western Aleutians

Geological Society of America Bulletin
By: , and 



We used geologic mapping and geochemical data augmented by 40Ar/39Ar dating to establish an eruptive chronology for the Tanaga volcanic cluster in the western Aleutian arc. The Tanaga volcanic cluster is unique in comparison to other central and western Aleutian volcanoes in that it consists of three closely spaced, active, volumetrically significant edifices (Sajaka, Tanaga, and Takawangha), the eruptive products of which have unusually high K2O contents. Thirty-five new 40Ar/39Ar ages obtained in two different laboratories constrain the duration of Pleistocene–Holocene subaerial volcanism to younger than 295 ka. The eruptive activity has been mostly continuous for the last 150 k.y., unlike most other well-characterized arc volcanoes, which tend to grow in discrete pulses. More than half of the analyzed Tanaga volcanic cluster lavas are basalts that have erupted throughout the lifetime of the cluster, although a considerable amount of basaltic andesite and basaltic trachyandesite has also been produced since 200 ka. Major- and trace-element variations suggest that magmas from Sajaka and Tanaga volcanoes are likely to have crystallized pyroxene and/or amphibole at greater depths than the older Takawangha magmas, which experienced a larger percentage of plagioclase-dominated fractionation at shallower depths. Magma output from Takawangha has declined over the last 86 k.y. At ca. 19 ka, the focus of magma flux shifted to the west beneath Tanaga and Sajaka volcanoes, where hotter, more mafic magma erupted.

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Publication type Article
Publication Subtype Journal Article
Title Geology and 40Ar/39Ar geochronology of the medium- to high-K Tanaga volcanic cluster, western Aleutians
Series title Geological Society of America Bulletin
DOI 10.1130/B30472.1
Volume 124
Issue 5-6
Year Published 2012
Language English
Publisher Geological Society of America
Publisher location Boulder, CO
Contributing office(s) Volcano Hazards Program, Volcano Science Center
Description 15 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Geological Society of America Bulletin
First page 842
Last page 856
Country United States
State Alaska
Other Geospatial Tanaga Island;Aleutian Islands
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