Journal article
Trace element and U-series systematics for 1963-1965 tephras from Irazú Volcano, Costa Rica: implications for magma generation processes and transit times
Geochimica et cosmochimica acta, Vol.62(15), pp.2689-2699
1998
DOI: 10.1016/S0016-7037(98)00179-3
Abstract
In order to investigate fluid fluxing and the time-scales of magma genesis in the mantle below Costa Rica, basaltic andesites erupted in 1963–1965 from Irazú volcano were analyzed for major and trace element compositions as well as thorium isotope and
226Ra abundances. The 1963–65 eruption of Irazú produced two groups of tephras termed high-Ra, with (
226Ra)/(
230Th) = 1.13–1.21 and low-Ra with near equilibrium (
226Ra)/(
230Th) values. Low-Ra and high-Ra samples have similar overall compositions. For example, barium and HSF element concentrations are about the same in the two magma groups, and all tephras have (
230Th)/(
232Th) ratios of about 1.20 and (
238U)/(
230Th) ≅ 0.9. However, low-Ra samples have 6–16 % higher concentrations of many highly incompatible elements compared to high-Ra samples, whereas REE, Sr, and P
2O
5, concentrations are higher by about 3–8% in the high-Ra samples. These compositional differences can be explained by variations in the degree of melting and in the compositions of fluids involved in magma genesis. Low-Ra magmas were generated by dehydration partial melting of garnet-bearing mantle that had been enriched previously by a slab fluid. High-Ra magmas were generated by a similar mechanism, but involved an additional mantle-derived fluid. Trace element compositions of the high-Ra magmas suggest that this fluid was similar to a carbonatite. The temperature and pressures during melting were appropriate for carbonatite-silicate melt miscibility, and the carbonatitic fluid was consumed or partly consumed during melting. The lower concentrations of many highly incompatible trace elements in the high-Ra samples resulted from a higher degree of partial melting of its mantle source caused by fluid-silicate melt miscibility. The approximately equal HFS element and Ba concentrations in the low- and high-Ra samples, and the relatively high REE, Sr, and P
2O
5 concentrations in the high-Ra samples reflects the addition of these elements to the high-Ra magma from the fluid. Ra-Ba-Th geochronometry suggests that the enrichment event occurred between a few centuries and eight millennia before the eruption.
Details
- Title: Subtitle
- Trace element and U-series systematics for 1963-1965 tephras from Irazú Volcano, Costa Rica: implications for magma generation processes and transit times
- Creators
- S.K Clark - University of IowaM.K Reagan - University of IowaT Plank - University of Kansas
- Resource Type
- Journal article
- Publication Details
- Geochimica et cosmochimica acta, Vol.62(15), pp.2689-2699
- Publisher
- Elsevier Ltd
- DOI
- 10.1016/S0016-7037(98)00179-3
- ISSN
- 0016-7037
- eISSN
- 1872-9533
- Language
- English
- Date published
- 1998
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229293202771
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