Mathematics – Logic
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.126...23m&link_type=abstract
Earth and Planetary Science Letters (ISSN 0012-821X), vol. 126, no. 1-3, p. 23-39
Mathematics
Logic
37
Earth Crust, Earth Mantle, Geochronology, Geodynamics, Geomorphology, Magma, Planetary Evolution, Volcanoes, Argon Isotopes, Helium Isotopes, Italy, Neodymium Isotopes, Olivine, Oxygen Isotopes, Pyroxenes, Strontium Isotopes, Subduction (Geology)
Scientific paper
The 0.5 Ma history of the origin and evolution of Mount Etna, Sicily has been investigated by analysing the isotopic composition of He, Ar, O, Sr and Nd in 21 selected lava samples. The near constancy of the isotopic compositions of oxygen δ18O = 5.4 +/- 0.3%) and of helium trapped in olivine phenocrysts (6.7 +/- 0.4 Ra) is interpreted as evidence of a single mantle source, despite drastic petrological changes during the volcano's history. He analyzes performed by crushing cogenetic pyroxene and olivine phenocrysts show a tendency to lower He-3/He-4 ratios in pyroxenes. This is best explained by crystallization of pyroxenes at a depth shallower than that of olivines and/or by exchange of helium trapped in pyroxenes with atmospheric or radiogenic He before eruption. Sr-87/Sr-86 ratios of recent lavas tend to increase with time and to correlate with Rb/Th ratios, and, for historical lavas, these variations are tentatively attributed to shallow selective contamination from underlying sediments. Based on the similarity of the He-3/He-4 ratios at Etna to those of European mantle xenoliths, we propose that the 'baseline' geochemical signature of isotopic tracers at Etna reflects the composition of the subcontinental mantle. Comparison to other southern Italian active volcanoes (Etna, Vulcano Ischia, Campi Flegrei, Vesuvius) shows gradual dilution of the predominantly mantle Etnean end member by more radiogenic Sr and He and material with higher δ18O and C/He-3, which is reasonably explained by the progressively important influence of subducted continental crust.
Basile Isabelle
Lussiez Patricia
Marty Bernard
Tanguy Jean-Claude
Trull Thomas
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