(super 238) U- and (super 232) Th-series chronology of phonolite fractionation at Mount Erebus, Antarctica
Geochimica et Cosmochimica Acta
DOI of Published Version
U, Th, Ra and Ba elemental and U and Th isotopic analyses are presented of anorthoclase crystals dislodged manually from vesicular phonolite erupted in 1984 and 1988. The data are used to constrain the time scales of anorthoclase megacryst growth and the residence times and history of anorthoclase phonolite differentiation. The results indicate that differentiation from basanite to phonolite was < 150 000 yr. On a plot of (super 226) Ra/Ba vs (super 230) Th/Ba, the glass-anorthoclase pairs produce isochrons averaging 2380 yr, which represents the average age of anorthoclase growth in the shallow magma system of this volcano. The implied residence time of phonolite magmas is approx 3000 yr. Final crystal growth occurred after intrusion into the convecting lake less than decades before eruption.
Published Article/Book Citation
Geochimica et Cosmochimica Acta, 56:3 (1992) pp.1401-1407.