New Jersey; Rutgers University; may 1977. 71 p. mapas, tab, graf. Trabajo Académico: Apresentada la Rutgers University para obtención del grado de Master of Science.
Descriptores:
GEOLOGIA. VULCANOLOGIA. ERUPCIONES VOLCANICAS. ANALISIS QUIMICO. GESTION DEL RIESGO --------------------------------------------------------------------------------
Resumen:
The magmatic evolution of the volcano consists of a long-term trend toward increasingly acidic lavas. Superimposed on this trend are four trends from andesitic to basaltic compositions, each terminated by an abrupt return to basaltic lava in each cycle is slightly more acidic than the most basaltic sample of the previous cycle. Short-term changes in lava composition are recognized during the 1917eruption. Petrography, major element chemistry, mineral chemistry, and least-squares mixing analysis suggest that near-surface crystal fractionation, involving Ca-rich plagioclase, augite, olivine, and Titianium-rich magnetite, produced the observed trends to increasing acidity. Returns to basaltic composition are explained by injections of basalt from a deep source, followed by mixing of the basalt with residual andesite remaining in the chamber. The model requires the observed cyclicity and the gradual, long-term trend to increasing acidity (Au) - en
