Conference proceeding
From mantle to ash cloud; quantifying magma generation, ascent, and degassing rates at Kilauea during short-lived explosive episodes using short-lived U-series radionuclide disequilibria
American Geophysical Union Fall Meeting, Vol.2012
American Geophysical Union 2012 fall meeting
12/2012
Abstract
We analyzed for (super 238) U-series isotopes lava, scoria and ash samples erupted from Kilauea volcano, Hawai'i between 1982 and 2008, in order to investigate processes and timescales of magma generation in the mantle, magma ascent through the crust, and eruption. Timescales of degassing during steady-state lava flow activity occurring in Kilauea East Rift Zone and short-lived explosive episodes that occurred in both the East Rift Zone (Pu'u 'O'o vent opening in 1983 and episode 54 at Napau crater in January 1997) and on the summit (Halema'uma'u crater eruptions in March 2008) are compared and contrasted. All samples were found to have small but variable (super 230) Th and (super 226) Ra activity excesses over (super 238) U and (super 230) Th, respectively, with ( (super 230) Th/ (super 238) U) ratios ranging from 1.00 to 1.13 and ( (super 226) Ra/ (super 230) Th) ratios ranging from 1.03 to 1.17. These two variable isotopic disequilibria may reflect local heterogeneities in the mantle underneath Kilauea, with sources in relatively primitive mantle with ( (super 238) U)-( (super 230) Th)-( (super 226) Ra) in secular equilibrium and in recently (<8000 years) depleted mantle with ( (super 230) Th) and ( (super 226) Ra) deficits over parent nuclides. In this model, both types of mantle melt to generate Kilauea magmas and subsequently mix in variable proportions. Samples from the brief explosive episodes span the entire composition range, suggesting that they were fed by heterogeneous magma batches which did not homogenize during ascent from the mantle. ( (super 210) Pb/ (super 226) Ra) ratios range from 0.75 to 1.00. The lack of correlation between ( (super 210) Pb/ (super 226) Ra) and ( (super 226) Ra/ (super 230) Th) or ( (super 230) Th/ (super 238) U), and the rapid return to secular equilibrium of (super 210) Pb (<100 years) suggest a fractionation process distinct from and subsequent to the Ra-Th-U fractionation inherited from mantle melting. We hypothesize that (super 210) Pb deficits originate from (super 222) Rn degassing during magma ascent, and estimate magma ascent from lower crust to surface to take place in a maximum of nearly equal 7 years for the lava flow samples. Products from the explosive episodes have ratios from nearly equal 0.75 to near equilibrium, suggesting that they comprise of a mix of young melts and degassed magmas which were stored in the shallow volcanic edifice for a few decades, in agreement with existing petrologic models.
Details
- Title: Subtitle
- From mantle to ash cloud; quantifying magma generation, ascent, and degassing rates at Kilauea during short-lived explosive episodes using short-lived U-series radionuclide disequilibria
- Creators
- Guillaume Girard - University of IowaMark K ReaganK. W SimsM. O GarciaA. J PietruszkaC. R Thornber
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2012
- Conference
- American Geophysical Union 2012 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2012 fall meeting
- Language
- English
- Date published
- 12/2012
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240899702771
Metrics
2 Record Views