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The magma source at Mount Etna volcano : perspectives from the Hf isotope composition of historic and recent lavas

Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.; Cristofolini, Renato. 2011 The magma source at Mount Etna volcano : perspectives from the Hf isotope composition of historic and recent lavas. Chemical Geology, 281 (3-4). 343-351. 10.1016/j.chemgeo.2010.12.020

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Abstract/Summary

High-precision Hf isotopic data for selected historic (pre-1971 eruption) and recent (post-1971) Etnean lavas are discussed in light of their covariation with previously reported Sr-Nd-Pb isotope ratios. (176)Hf/(177)Hf ranges between 0.282961 and 0.282989 in the historic lavas, and between 0.282943 and 0.282990 in the recent ones, displaying, especially among the most recently erupted products, an overall decrease. In Hf-Nd and, to a minor extent, Hf-Sr-Pb isotope spaces, Etnean lavas plot slightly below the linear array defined by MORB and OIB, between the enriched end of the FOZO and HIMU fields. This may suggest that, prior to the formation of Etnean melts, the garnet-bearing source experienced an episode of low-degree melting; this source then evolved for enough time to produce the (176)Hf/(177)Hf and (143)Nd/(144)Nd decoupling observed in the historic and recent lavas. In addition, the distinct epsilon Hf values of the historic and recent lavas may be accounted for by portions of the mantle with distinct Lu/Hf ratios, likely related to decreasing modal proportions of garnet in favour of metasomatic phases involved in partial melting. Integration of all the available data suggests that FOZO is the dominant component in the source of Etnean magmas, although this is not enough to solve the observed (176)Hf/(177)Hf change coupled with the Sr-Nd-Pb variation through time. Binary mixing between FOZO and EM-type components demonstrates that addition of about 10% of an EM1-type component to FOZO can account for the isotopic variability of Etnean magmas, a feature more emphasized in the most recent lavas. Divergences from a dominant FOZO signature of erupted magmas at Mt. Etna may therefore be attributed to small-scale heterogeneity produced by access into the source of enriched material with an EM1-type signature. The coupled analysis of (176)Hf/(177)Hf and trace element ratios, such as Sm/Hf and Th/Hf, provides evidence that this enriched infiltrating component could be metasomatizing silicate melts rather than aqueous, low-T fluids.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.chemgeo.2010.12.020
Programmes: BGS Programmes 2010 > NERC Isotope Geoscience Laboratory
ISSN: 0009-2541
Date made live: 05 Aug 2011 11:41
URI: http://nora.nerc.ac.uk/id/eprint/14838

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