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

Conference · Mon Mar 01 00:00:00 EST 1993 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:6390736

Villemant, B ^[1]; Michaud, V; Metrich, N ^[2]

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1. Universite Paris 6 (France) CNRS URA 196, Paris (France)
2. LPS/CEA-CNRS, Gif-sur-Yvette (France)

[sup 230]Th/[sup 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 [sigma] errors and have lower [sup 230]Th/[sup 232]Th ratios than their host magmas. Siliceous and peraluminous xenoliths display large ranges of Th/U ratios for similar [sup 230]Th/[sup 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 [sup 230]Th-[sup 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 favors 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 [sup 230]Th/[sup 232]Th initial ratios of Etna magmas. 33 refs., 7 figs., 1 tab.

• OSTI ID: 6390736
• Report Number(s): CONF-911017-; CODEN: GCACAK
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 57:6; Conference: Annual meeting and exhibition of the Geological Society of America, San Diego, CA (United States), 21-23 Oct 1991; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
58 GEOSCIENCES
MAGMA
CHEMICAL COMPOSITION
ROCK-FLUID INTERACTIONS
THORIUM 230
DIFFUSION
EQUILIBRIUM
URANIUM 238
CERIUM
ENVIRONMENTAL TRANSPORT
EUROPIUM
LANTHANUM
QUANTITATIVE CHEMICAL ANALYSIS
SAMARIUM
SEDIMENTARY ROCKS
TERBIUM
THORIUM 232
YTTERBIUM
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ALPHA DECAY RADIOISOTOPES
CHEMICAL ANALYSIS
ELEMENTS
EVEN-EVEN NUCLEI
HEAVY ION DECAY RADIOISOTOPES
HEAVY NUCLEI
ISOTOPES
MASS TRANSFER
METALS
NEON 24 DECAY RADIOISOTOPES
NUCLEI
RADIOISOTOPES
RARE EARTHS
ROCKS
SPONTANEOUS FISSION RADIOISOTOPES
THORIUM ISOTOPES
URANIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
400102* - Chemical & Spectral Procedures
580000 - Geosciences