Temporal magmatic variation at Boqueron volcano, El Salvador

  • Gregg E. Fairbrothers
  • Michael J. Carr
  • Darrell G. Mayfield


The relative ages of 21 lavas from Boqueron volcano in El Salvador were determined by superposition. The lavas are grey to black, porphyritic basalts, basaltic andesites and andesites with phenocrysts of plagioclase, augite, olivine, and magnetite. The andesitic lavas appear to have evolved from basaltic magma by fractionation of the observed phenocryst phases.

The temporal variation in the chemical composition of the lavas at Boqueron is composed of three components. First, there is a crudely cyclical alternation of basalts and andesites. Second, these cycles are progressively shifted toward higher SiO2 contents. Third, approximately in the middle of the stratigraphic section sampled, there is an abrupt change in chemical variation trends from an Al-rich and Fe-poor trend to an Fe-rich and Al-poor trend. This change is interpreted to have been caused by an increased proportion of plagioclase fractionation and a decreased porportion of augite fractionation. The crudely cyclical change in SiO2 content with time is interpreted as a combination of crystal fractionation that increases SiO2 content, followed by influxes of basaltic magma that mix with residual magma to decrease SiO2 content. Successive cycles are shifted toward higher SiO2 content because there is a significant volume of fractionated magma remaining in the chamber before each influx of basalt.


Fractionation Magnetite Olivine Basaltic Andesite Basaltic Magma 
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Copyright information

© Springer-Verlag 1978

Authors and Affiliations

  • Gregg E. Fairbrothers
    • 1
  • Michael J. Carr
    • 1
  • Darrell G. Mayfield
    • 1
  1. 1.Department of Geological SciencesRutgers UniversityNew BrunswickUSA

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