Geology, paleomagnetism, and potassium-argon ages of basalts from Nunivak Island, Alaska

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Abstract

Geologic mapping, paleomagnetic stratigraphy, and potassium-argon dating were used to determine the time and volume relations of tholeiitic and alkalic basalt on Nunivak Island in the Bering Sea near the coast of Alaska. Volcanism on Nunivak Island occurred in distinct episodes separated by quiet intervals that lasted from 1.6 to 0.6 m.y. During the past 6 m.y., tholeiitic basalt was erupted during at least five such episodes, and highly undersaturated alkalic basalt was erupted during at least three episodes. The oldest volcanic rock found on Nunivak Island is an alkalic basalt, succeeded by repeated alternations of tholeiitic and alkalic basalt. During the last episode of tholeiitic volcanism, 130 cu km of basalt erupted during a well-defined interval that lasted from 0.9 to 0.3 m.y. ago. A nearly contemporaneous eruption of alkalic basalt has continued vigorously to historic times and has covered the central part of the island with small cones, flows, and tephra from explosion craters. The volume of alkalic basalt of the latest episode of volcanic activity is from 0.7 to 2.0 percent of the volume of the associated tholeiite. At least one earlier eruption of alkalic basalt occurred in close association with the eruption of tholeiite. As on Hawaii, the highly undersaturated alkalic basalts on Nunivak contain abundant ultramafic inclusions.

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Publication type Book chapter
Publication Subtype Book Chapter
Title Geology, paleomagnetism, and potassium-argon ages of basalts from Nunivak Island, Alaska
DOI 10.1130/MEM116-p377
Volume 116
Year Published 1968
Language English
Publisher Geological Society of America
Description 38 p.
Larger Work Type Book
Larger Work Subtype Monograph
Larger Work Title Studies in Volcanology
First page 377
Last page 413
Country United States
State Alaska
Other Geospatial Nunivak Island
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