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Titel |
A two-component mantle extending from Hyblean Plateau to Mt Etna (Eastern Sicily) as inferred by an integrated approach with noble gases, trace elements and isotope geochemistry. |
VerfasserIn |
A. Correale, M. Martelli, A. Paonita, A. Rizzo, S. Rotolo |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250066539
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Zusammenfassung |
We carried out a geochemical investigation of the mantle beneath Hyblean and Etnean area
through ultramafic xenoliths (peridotites and pyroxenites) retained in Miocenic age
Hyblean volcanics and primitive Etnean lavas and tephra, respectively. Major and trace
elements and Sr-Nd isotopes (whole rock and /or minerals) were analysed together
with noble gases entrapped in fluid inclusions hosted in olivines and pyroxenes
phenocrysts.
The geochemical results from Hyblean xenoliths study highlighted the presence of two
distinct compositional groups: the peridotites, featured by a more enriched geochemical
fingerprint (3He/4He ~7 Ra, 143Nd/144Nd ~0.5129 and Zr/Nb ~ 4) and the pyroxenites,
characterized by a more primitive character (3He/4He up to 7.6 Ra, 143Nd/144Nd ~0.5130
and Zr/Nb ~30). Our interpretation is that metasomatic processes interested the Hyblean
lithosphere and the pyroxenites (former primitive mantle melts) represent the metasomatizing
agent. During their ascent these primitive melts permeated the peridotitic mantle at different
levels, producing a variable degree of refertilization. The metasomatic processes affected
distributions of both trace elements and noble gases, even though these geochemical tracers
displayed very different sensitivity to the effects of metasomatic mixing between two
end-members.
The investigated primitive Etnean magmas showed a variable REE enrichment respect to
MORB (Lan/Ybn =11-26) and isotopic values of Sr, Nd and He in the following ranges:
143Nd/144Nd = 0.512869-0.512896; 86Sr/87Sr = 0.70330-0.70370; 3He/4He = 7-7.6 Ra. A
variable melting degree of a common mantle source together with a variable level of
crystallization and crustal contamination is hypothesised to explain the variations exhibited
by the above Etnean dataset. Numerical simulation performed on MELT code allowed to
estimate the trace elements content of the Etnean mantle source. These results, joined to the
most primitive isotopic values of He- Sr- Nd among the investigated products helped to
geochemically characterize the mantle beneath the Etnean area, suggesting a strict
relation with that Hyblean. Indeed, the modeled Etnean source locates on the mixing
zone between the Hyblean peridotite and pyroxenite, so testifying a simultaneous
contribution of two components in the genesis of the investigated lavas and supporting the
hypothesis of an heterogeneous and metasomatized lithosphere common to both areas. |
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