Abstract
Juvenile glass fragments in phreatic explosion debris from Turrialba Volcano, Costa Rica
Mineralogical magazine, Vol.75(3), p.1700
Goldschmidt2011
06/2011
Abstract
After several years of increasing fumarolic activity, Turrialba volcano experienced small phreatic explosions on January 5-6, 2010, leaving a 55x20 m crater with an incandescent floor. Ash and lapilli from the explosions consists mostly of crystal-rich and altered material originally erupted in 1864-1866 and earlier. Nevertheless, careful examination of the tephra revealed that approximately 1% of the medium to coarse ash-sized particles consists of fresh glass. The freshness of the glass and its unusual chemical traits suggest that this glass is juvenile. EMP analysis of the glass fragments showed them to be calcalkaline andesites, whose major element compositions were largely consistent with derivation by low-P crystal fractionation of basaltic parental magmas. Na (sub 2) O, however, is depleted in most glass fragments (1.1-2.8 wt. %) compared to Turrialba's basaltic lavas (2.8-3.8). Incompatible trace element compositions determined by LA-ICPMS are broadly similar to those of the 1864-1866 basalts. REE element patterns are strongly light enriched and most fragments have the elevated Ba/Ce and La/Nb ratios (8-16 and 1.8-2.2 respectively, which is commonplace for calcalkaline lavas. However, one fragment had Ba/Ce and La/Nb ratios (5 and 1.1) more typical of an ocean island basalt, but was otherwise similar in composition to the other fragments. The concentrations of S in all fragments were near the EMP detection limit, and Cl in most samples were also unusually low for a Turrialba basalt. The concentrations of F, however, were highly variable, ranging from 0.03 to 0.6 wt. %. High F was associated lower concentrations of Na, REE and HFS elements. We speculate the F was enriched by interaction with high-T fumarolic gasses which also leached highly-charged cations and Na. Important findings are: (1) phreatic explosion debris can contain juvenile glass fragments that provide compositional information about the magma triggering the unrest; (2) magmas intruding into Turrialba's upper edifice at present are basalts or basaltic andesites with varying La/Nb; and (3) gas streaming can affect compositions of apparently fresh glass, particularly Na concentrations.
Details
- Title: Subtitle
- Juvenile glass fragments in phreatic explosion debris from Turrialba Volcano, Costa Rica
- Creators
- Mark K Reagan - University of Iowa Iowa City, IA USA United StatesMichael C RoweEliecer DuarteErick Fernandez
- Resource Type
- Abstract
- Publication Details
- Mineralogical magazine, Vol.75(3), p.1700
- Conference
- Goldschmidt2011
- Publisher
- Mineralogical Society
- ISSN
- 0026-461X
- eISSN
- 1471-8022
- Alternative title
- Goldschmidt 2011 abstract volume
- Language
- English
- Date published
- 06/2011
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240800702771
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