Black, Stuart and Macdonald, Ray and Devivo, Benedetto and Kilburn, Christopher R. J. and Rolandi, Guiseppe (1998) U-series disequilibria in young (A.D.1944) Vesuvius rocks : preliminary implications for magma residence times and volatile addition. Journal of Volcanology and Geothermal Research, 82 (1-4). pp. 97-111. ISSN 0377-0273Full text not available from this repository.
The results of a preliminary U-series study of the timescale of magmatic processes at Vesuvius are presented. Phonotephrites of the 1944 eruption of Vesuvius show 0–15% 230Th–238U and 350–1150% 226Ra–230Th disequilibria. Apparent U–Th internal isochrons for a lava and a cumulate nodule suggest crystal residence times of 12 and 39 ka, respectively. A tephra sample shows isotopic heterogeneity, possibly related to mixing of younger crystal-laden melt and older crystals giving apparent U–Th ages of 0.4 and 18 ka, respectively. Mineral 226Ra–230Th disequilibria on Ba-normalised internal isochron diagrams suggest Ra–Th ages of 1730–3300 years for the same rocks and phenocrysts. Minor 226Ra/230Th heterogeneity between minerals and groundmass (or whole rock) is evidence of open-system Ra–Th behaviour. This heterogeneity suggests that there have been recent, post-crystallisation changes in melt composition that affected 226Ra more than 230Th. Continued crystallisation in a Ra-enriched magma has subsequently resulted in Ra–Th disequilibria probably as a result of addition via a fluid-rich phase. Magma differentiation, residence time, transport, and pervasive gas addition at Vesuvius apparently occur over geologically short periods.
|Journal or Publication Title:||Journal of Volcanology and Geothermal Research|
|Uncontrolled Keywords:||U-series ; magma residence times ; volatile ; crystallisation ages|
|Subjects:||G Geography. Anthropology. Recreation > GE Environmental Sciences|
|Deposited On:||09 Feb 2009 09:20|
|Last Modified:||26 Jul 2012 15:52|
Actions (login required)