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Inclusions in Mount St. Helens dacite erupted from 1980 through 1983

Journal of Volcanology and Geothermal Research

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DOI: 10.1016/0377-0273(94)00074-Q

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Abstract

Inclusions of plutonic, metavolcanic and volcanic rocks are abundant in dacite pumice and lava from the 1980-1986 eruption sequence at Mount St. Helens. Point counts of inclusions exposed in talus blocks from the dome from 1980 through 1983 show that inclusions form approximately 3.5 vol.% of the lava. Eighty-five percent of the inclusions are medium-grained gabbros. The gabbroic inclusions are of four distinct type. The most abundant type is laminated gabbronorite. Various types of gabbroic inclusions, including the laminated gabbronorite, are common in Mount St. Helens lavas of approximately the last 3000 years. This coincides with the interval in which Mount St. Helens first erupted basalt and basaltic andesite lavas. These observations, together with the fact that the gabbroic inclusions are compositionally unlike any of the Tertiary intrusive rocks in the Mount St. Helens area, strongly suggest that the inclusions are related to the introduction of basalt to the Mount St. Helens magmatic system. -from Author

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Inclusions in Mount St. Helens dacite erupted from 1980 through 1983
Series title:
Journal of Volcanology and Geothermal Research
DOI:
10.1016/0377-0273(94)00074-Q
Volume
66
Issue:
1-4
Year Published:
1995
Language:
English
Publisher:
Elsevier
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
115
Last page:
135
Number of Pages:
21