Wall rock-magma interactions in Etna, Italy, studied by U---Th disequilibrium and rare earth element systematics

Details Wall rock-magma interactions in Etna, Italy, studied by U---Th disequilibrium and rare earth element systematics Wall rock-magma interactions in Etna, Italy, studied by U---Th disequilibrium and rare earth element systematics

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.1169v&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 57, Issue 6, pp.1169-1180

Computer Science

2

Scientific paper

230 Th / 238 U disequilibria have been studied in xenoliths and associated lavas of the 1892 and 1989 eruptions of Etna. Most xenoliths are out of secular equilibrium within 1 errors and have lower 230 Th / 232 Th ratios than their host magmas. Siliceous and peraluminous xenoliths display large ranges of Th / U ratios for similar 230 Th / 232 Th values, which are interpreted in terms of Th isotopic rehomogenization. The siliceous xenoliths have also suffered thorium and uranium enrichments, which are best explained by chemical diffusion between xenolith melts and differentiated magmas. Estimates of thorium self-diffusivities and 230 Th- 238 U disequilibria give age constraints on these events corresponding to the last major volcanic event of Etna at 14 ka (formation of the elliptic crater caldera). These results suggest that magma storage in superficial and long-lived magma chambers favours the thorium isotopic homogenization of wall rocks by a thermal effect. Chemical diffusion of uranium and thorium and isotopic homogenization between siliceous melts of wall rocks and differentiated magmas may significantly modify the initial thorium isotopic compositions. Such contamination processes could explain the large variations of the 230 Th / 232 Th initial ratios of Etna magmas.

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