Abstract
Pb-210/Ra-226 disequilibria in dacite from Mount St. Helens, 1980-1986
Abstracts with programs - Geological Society of America, Vol.39(3), p.22
Geological Society of America, South-Central Section, 41st annual meeting; Geological Society of America, North-Central Section, 41st annual meeting
04/2007
Abstract
The US Geological Survey reference suite of four Mount St. Helens samples erupted between 1980 and 1986, were analyzed for activities of (super 210) Po (half-life = 138 d), which are assumed to be equal to activities of (super 210) Pb (half-life - 22.6 y) because of the ages and freshness of the samples. These data will be compared with (super 226) Ra activities obtained by analyzing the same sample powders for its descendent (super 214) Pb. The goal will be to investigate whether large scale fluxing of (super 222) Rn-bearing volcanic gasses affected these samples, as has been postulated for other samples erupted from Mount St. Helens in the 1980s (Berlo et al., 2006, Earth and Planetary Science Letters), but not for samples erupted in 2004-2005 (Reagan et al., in press). Disequilibria in ( (super 210) Pb/ (super 226) Ra) can be produced through the fractioning of (super 210) Pb from (super 226) Ra through extensive crystal fractionation or partial melting of the crust. Another mechanism for producing (super 210) Pb/ (super 226) Ra disequilibria are (super 222) Rn excesses or deficits caused by persistent degassing over a number of years. The reference suite rocks show a slight a variation in (super 210) Pb activities between the samples (1.02-1.09 dpm/g), which is above the 1-sigma analytical error of 0.02, but not 2-sigma error, suggesting a relatively steady-state system during the six year period.
Details
- Title: Subtitle
- Pb-210/Ra-226 disequilibria in dacite from Mount St. Helens, 1980-1986
- Creators
- Greg J Stark - University of Iowa, Department of Geosciences Iowa City, IA USA United StatesMark K Reagan
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.39(3), p.22
- Conference
- Geological Society of America, South-Central Section, 41st annual meeting; Geological Society of America, North-Central Section, 41st annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, South-Central Section, 41st annual meeting; Geological Society of America, North-Central Section, 41st annual meeting
- Language
- English
- Date published
- 04/2007
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240790502771
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