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40Ar/39Ar geochronology and geochemical reconnaissance of the Eocene Lowland Creek volcanic field, west-central Montana

Journal of Geology

By:
, , ,
DOI: 10.1086/651523

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Abstract

We report geochronological and geochemical data for the calc-alkalic Lowland Creek volcanic field (LCVF) in westcentral Montana. 40Ar/ 39Ar age determinations show that the LCVF was active from 52.9 to 48.6 Ma, with tuff-forming eruptions at 52.9 ?? 0.14 and 51.8 ?? 0.14 Ma. These dates span the age range of vigorous Eocene igneous activity in the Kamloops-Absaroka-Challis belt. The LCVF evolved upward from basal rhyolites (SiO 2>71 wt%) to dacites and andesites (SiO 2 > 62 wt%). Compositional change parallels a transition from early explosive volcanism to late effusive activity. Four geochemical components can be detected in the rocks. A component with 206Pb/204Pb < 16.5 and epsilon;Nd near-15 is predominant in anhydrous, two-pyroxene dacites; hydrous rhyolites, rhyodacites, and dacites with epsilon;Nd below-10 are dominated by a second component; hydrous rocks with 206Pb/ 204Pb > 18.3 and epsilon;Nd>-9 contain a third component; and an andesite with low Nd content and epsilon;Nd near-9 probably contains a fourth component. The first three components probably derive from the lower and middle crust, whereas the fourth is probably from the lithospheric mantle. ?? 2010 by The University of Chicago.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
40Ar/39Ar geochronology and geochemical reconnaissance of the Eocene Lowland Creek volcanic field, west-central Montana
Series title:
Journal of Geology
DOI:
10.1086/651523
Volume
118
Issue:
3
Year Published:
2010
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geology
First page:
295
Last page:
304
Number of Pages:
10