 |
| Titel |
A geochemical study of lithospheric mantle beneath Northern Victoria Land (Antarctica): main evidences from volatile content in ultramafic xenoliths |
| VerfasserIn |
Alessandra Correale, Beatrice Pelorosso, Andrea Luca Rizzo, Massimo Coltorti, Francesco Italiano, Costanza Bonadiman |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152625
|
| Publikation (Nr.) |
 EGU/EGU2017-17484.pdf |
|
|
|
|
|
| Zusammenfassung |
| A geochemical study of ultramafic xenoliths from Northern Victoria Land (Green Point, GP
and Handler Ridge, HR), is carried out in order to investigate the features of the lithosphere
mantle beneath the Western Antarctic Ridge System (WARS).
The majority of samples is spinel anhydrous lherzolite with rare presence of secondary
phases (secondary cpx and glass). Geothermobarometric calculations, based on the Fe/Mg
distribution among the peridotite minerals reveal that Sub Continental Lithospheric Mantle
(SCLM) beneath Handler Ridge records temperatures and redox conditions higher then
Greene Point (P fixed at 15 Kbar). Moreover, geochemical models evidence that, GP
mantle domain represents a residuum after ∼7 to 21 % of partial melting in the
spinel stability field, which was variably affected by interaction with infiltrating
melts, acting in different times, from at least Jurassic to Cenozoic (Pelorosso et al.,
2016).
Fluid inclusions (FI) entrapped in olivine and pyroxene crystals were investigated for
elemental and isotopic contents of both, noble gases (He, Ne, Ar) and CO2. He, Ar and Ne
concentrations range from 1.52×10−14 to 1.07×10−12, from 4.09×10−13 to 3.47×10−11and
from 2.84×10−16 to 7.57×10−14 mol/g, respectively, while the CO2amounts are between
7.08×10−10 and 8.12×10−7 mol/g.
The 3He/4He varies between 5.95 and 20.18 Ra (where Ra is the 3He/4He ratio of air),
being the lowest and the highest values measured in the He-poorer samples. Post-eruptive
input of cosmogenic 3He and radiogenic 4He seems to influence mainly the samples
associated to a lower He concentrations, increasing and decreasing respectively their
primordial 3He/4He values, that for all the other samples range between 6.76 and 7.45 Ra.
This range reasonably reflects the isotope signature of mantle beneath the investigated
areas.
The 4He/40Ar* ratio corrected for atmospheric-derived contamination ranges between
0.004 and 0.39. The lowest 4He/40Ar* values (4He/40Ar*<0.1) are systematically in
correspondence of the He-poorer samples and probably derive by a selective loss of He with
respect to Ar. The 4He/40Ar* values, ranging between 0.12 and 0.39 are lower than the
typical mantle production ratio (4He/40Ar=1-5; Marty, 2012) and suggest that the pristine
signature could have been modified by partial melting processes in agreement with major and
trace element geochemistry of opx, cpx and sp. The carbon isotope composition of CO2 is
reported as δ13C (where δ13C=[13C/12Csample – 13C/12Cstd]/13C/12Cstd×103) and varies
between -2.5‰ and -4.5‰ with a more homogeneous value (at about -3.5) measured in
the CO2-richest samples. This range of δ13C is compatible with typical mantle
values (δ13C in average -5‰ Deines, 2002) and reasonably reflects the local mantle
signature.
References:
Deines P., 2002. The carbon isotope geochemistry of mantle xenoliths. Earth-Science
Reviews, 58, 247–278.
Marty B. 2012. The origins and concentrations of water, carbon, nitrogen and noble gases
on earth. Earth and Planetary Science Letters 313–314, 56–66.
Pelorosso B., Bonadiman C., Coltorti M., Faccini B., Melchiorre M., Ntaflos T. &
Gregoire M. 2016. Pervasive, tholeiitic refertilisation and heterogeneous metasomatism in
Northern Victoria Land lithospheric mantle (Antarctica). Lithos, 248–251, 493–505. |
|
|
|
|
|
|