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| Titel |
Provenance and evolution of the western Mediterranean lithospheric mantle beneath the eastern Betics (S. Spain): insights from in-situ analyses of Os isotopes and platinum-group elements in sulphides from the Tallante mantle xenoliths |
| VerfasserIn |
Z. Konc, C. Marchesi, C. J. Garrido, J. M. González-Jiménez, W. L. Griffin, O. Alard, K. Hidas, S. Y. O'Reilly, N. Pearson |
| 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 |
250070406
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| Zusammenfassung |
| Pliocene alkaline lavas from Tallante (Betic cordillera, southern Spain) have entrained mantle
xenoliths representing pieces of the subcontinental mantle beneath the westernmost
SE Iberian volcanic province. Sulphides in mantle xenoliths (~30 to 100 μm in
diameter) are Fe–Ni–Cu–S minerals being Ni-rich pentlandite the most common phase.
Chondrite-normalized patterns of platinum-group elements (PGE) and Re analyzed by
LA-HR-ICP-MS are similar in sulphides located in different microstructural positions (i.e.,
interstitial between silicates or included in them). Sulphides are enriched in IPGE (Os, Ir, Ru)
compared to PPGE (Pt, Pd) and Re (Pt/IrN =0.01-0.57, Pd/IrN =0.02-0.88, Re/IrN =
0.09-0.63) supporting their origin as grains residual after partial melting. 187Os/188Os
in sulphides, measured by LA-MC-ICP-MS, varies between 0.1096 and 0.1292
(γOs= -14.43 to 0.84 relative to the Enstatite Chondrite) but almost all the analysed
grains (70/73) have subchondritic values (γOs up to -0.47). 187Re/188Os spans
from 0.01 to 0.39 and no systematic correlations exist between 187Os/188Os or
187Re/188Os and the microstructural setting of the sulphides (i.e., interstitial versus
inclusion-type). Re-depletion model ages (TRD) range from -0.1 to 2.6 Ga and Os model
ages (TMA) are much more variable (-0.2-13.6 Ga) because of the large range in
Re/Os. The meaningless future ages and ages older than 4.5 Ga reflect derivation
of Os from a source more radiogenic than the Enstatite Chondrite and the local
disturbance of the Re–Os isotopic system. The distribution of TRD in sulphides
clusters around two main peaks at ca. 0.6-0.7 and 1.1-1.4 Ga, coinciding with the
values of both metasomatic and residual pentlandite in the Ronda massif, the largest
exposure of subcontinental lithospheric mantle in the western Mediterranean. The
dominant subchondritic 187Os/188Os composition of sulphides in the Tallante mantle
xenoliths indicates that these grains have evolved for a long time in a low Re/Os
environment, most likely the subcontinental lithospheric mantle. Considering the
uncertainties inherent in model age calculations, the range of TRD in sulphides
is consistent with the extraction of melts and possible metasomatic events in the
Mesoproterozoic and the Neoproterozoic, similarly to sulphides in peridotites from
the Ronda massif. Despite Ronda was emplaced into the crust ~20 Ma before the
generation of the alkaline volcanism that entrained the Tallante mantle xenoliths,
the Os isotopic record points to a similar Proterozoic evolution for the Ronda and
Tallante mantle peridotites, suggesting their provenance from different portions
of the same subcontinental lithospheric mantle. The similarity of the Os isotopic
signature in two diachronic (~20 Ma) temporal samples of the lithospheric mantle in
the Betic cordillera (i.e., the synorogenic Ronda mantle peridotite massif and the
post-orogenic Tallante mantle xenoliths) supports the limited modification of the Os isotopic
signature of the subcontinental lithospheric mantle in the Alboran domain, despite this
region experienced important thinning, melting and extension during the Miocene. |
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