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| Titel |
Noble gases signature of mantle beneath Stromboli (Aeolian Islands, Italy), as inferred from fluid inclusions investigation in mafic phenocrysts from HP-LP products and from ultramafic xenoliths |
| VerfasserIn |
Andrea Rizzo, Mauro Martelli, Alberto Renzulli, Filippo Ridolfi, Alberto Rosciglione |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053310
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| Zusammenfassung |
| We present a study of noble gases abundances (He, Ne, Ar) and isotopic ratios
(He, Ar) in olivine- and clinopyroxene-hosted fluid inclusions from basaltic Low
Porphyritic (hereafter LP) pumices and High Porphyritic (hereafter HP) scorias,
respectively of paroxysms and mild explosions of the Stromboli present activity
and from ultramafic xenoliths retained in the ~2 ka ago San Bartolo lavas. New
petrologic studies on such ultramafic xenoliths show that they are mostly wherlites
(subordinately lherzolites), with slightly protogranular to porphyroclastic texture.
New thermo-barometric estimates on the mineralogical assemblage indicate that
ultramafic xenoliths equilibrated at depth close to the crust-mantle transition of
Stromboli.
While Ar isotopes are dominated by a clear atmospheric signature in all the samples,
3He/4He from LP pumices and S. Bartolo ultramafic xenoliths converge to a value of 4.2-4.7
Ra, with relatively high gas content. Conversely, the low gas content of the HP scorias
allowed us to measure chemical concentrations but not their 3He/4He ratio. Inferences found
out from gas content are therefore in full agreement with previous knowledge about
differences in volatile content between HP and LP magmas. The 3He/4He measured values
are much lower than those of most primitive mantle terms of the Sicilian volcanism (7±0.6
Ra), due to contamination at mantle level beneath Stromboli, operated by the Ionian
subducting slab.
On the basis of the measured 3He/4He in the LP pumices and ultramafic xenoliths, helium
in thermal waters from the Stromboli basal aquifer is a mixing of a mantle-derived and an
atmospheric term. The 3He/4He values measured in the rocks constitute the upper limit
that should be expected in thermal fluids in case of effusions and/or paroxysms. |
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