Journal article
The role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at Arenal Volcano, Costa Rica; evidence from clinopyroxene and spinel
Bulletin of volcanology, Vol.64(5), pp.316-327
2002
DOI: 10.1007/s00445-002-0209-2
Abstract
Despite the near constant composition of Arenal basaltic andesite lava (SiO (sub 2) 53.6-54.9, MgO 5.0-4.5%) during constant activity from 1968-1996, clinopyroxene phenocrysts and their spinel inclusions record complex open-system evolution involving episodic injection of basaltic magma into the volcano's conduit/reservoir system. High resolution EMPA (> 14 000 analyses) of major element zoning tied to back-scattered electron images show that no two cpx phenocrysts have identical zoning profiles and the vast majority of analyses record crystallization of cpx (Cr (sub 2) O (sub 3) < 0.12%, mg 65-79, Al/Ti 2-7) from liquid similar to or more evolved than erupted magma compositions. However, over half of the cpx grains have high-Cr cores (Cr (sub 2) O (sub 3) 0.2-0.72%) or contain similar basaltic compositions as abrupt growth bands in phenocrysts with or without high-Cr cores; high-Cr cpx phenocrysts occur throughout 1968-1996, but in a few cases (especially 1968/69 and 1992/93) high-Cr occurs very near grain boundaries without an apparent growth hiatus. It is concluded: 1) all the lavas are products of magma mixing, 2) cpx records multiple basaltic replenishment events in contrast with the composition of the erupted basaltic andesites, 3) evidence of multiple interaction of cpx with basaltic magma requires magmatic processes to operate on time-scales shorter than residence time of some phenocrysts, 4) evidence from high-Cr cpx rims indicates sub-decadal frequency of basaltic replenishment, predating eruptions by months or less. It is inferred than Arenal has a continuously active small magma reservoir maintained in quasi-steady state by basaltic recharge for several decades, implying that fractionation, recharge and ascent of magmas are well balanced, although at the time of eruption the lavas contain phenocrysts with very different growth histories.
Details
- Title: Subtitle
- The role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at Arenal Volcano, Costa Rica; evidence from clinopyroxene and spinel
- Creators
- Martin J. StreckMichael A. DunganE. Malavassi - University of California, Santa CruzMark K. Reagan - University of Iowa, Earth and Environmental SciencesFrancois Bussy - University of Lausanne
- Resource Type
- Journal article
- Publication Details
- Bulletin of volcanology, Vol.64(5), pp.316-327
- Publisher
- Springer International [for the] International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)
- DOI
- 10.1007/s00445-002-0209-2
- ISSN
- 0258-8900
- eISSN
- 1432-0819
- Language
- English
- Date published
- 2002
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983557291802771
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