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| Titel |
Neoproterozoic-Ordovician Sebes-Lotru compozite terrane from South Carpathians, Romania |
| VerfasserIn |
I. Balintoni, C. Balica, M. Ducea, H. P. Hann, V. Sabliovschi |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023432
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| Zusammenfassung |
| The Romanian Carpathians pre-Alpine basement is formed of peri-Gondwanan terranes.
They originated close to the north-eastern margin of Gondwana, together with other eastern
Mediterranean terranes (Balintoni et al., 2008, submitted). The Carpathian terranes offered
dominantly Ordovician U/Pb protolith ages (e.g. Balintoni et al., 2008 submitted and
references therein), except the Sebes-Lotru terrane, the main constituent of the South
Carpathians basement, which also shown Neoproterozoinc protolith ages (Balintoni et al.,
2004). Meanwhile, we performed new high quality LA-ICP-MS U/Pb zircon dating on
magmatic and detrital zircons extracted from the Sebes-Lotru terrane rocks, which are the
subject of this contribution.
1. Neoproterozoic protoliths. We dated two Neoproterozoic protoliths, one of them
representing a migmatitic vein crosscutting a paragneiss at the bottom of the Lotru
metamorphic unit in Godeanu Mountains, and another one from the Frumoasa metagranites,
intruded within amphibolites, in the Sebes Mountains, upstream of Oasa dam. First sample
yielded a weighted mean age of 549.3±3.8 Ma and the other one of 587.5±3.8
Ma.
2. Ordovician protoliths. We dated also two Ordovician protoliths, the Capalna augen
gneiss in the northern part of the Sebes Mountains and Latorita orthogneiss in the
Lotru Mountains. The first sample yielded 458.9±3.5 Ma and the second 466.0±4.2
Ma.
3. Detrital zircon ages. A paragneiss sample, downstream of Oasa dam on the Sebes
River furnished detrital zircon. Out of 75 detrital, 17 ages have been rejuvenated
during the Variscan Orogeny and the rest of 58 ages arranged between 500 Ma and
2781 Ma. The main peak is Neoproterozoic, an important gap between 1.15 and 1.6
Ga, and significant age groups are visible between 1.85 and 2.8 Ga. The youngest
ages indicate a maximum upper Cambrian age for the sediment deposition and the
provenance model is similar with those of the other Carpathian terranes, suggesting a
north-eastern Gondwanan origin (Balintoni et al., 2008, submitted). Thus it is quite clear,
that the Sebes-Lotru terrane is a composite terrane formed by a Neoproterozoic
lower part and an upper Paleozoic part, superposed probably during the Variscan
Orogeny.
4. Variscan overprint. The high U grains recorded the Variscan thermo-tectonic
event. Medaris et al. (2003) demonstrated that during the Variscan Orogeny, the
Sebes-Lotru terrane suffered continental crust subduction, supporting an eclogite
facies metamorphism during the 350Ma to 320 Ma interval. Three of our samples
showed partial or complete resetting of their U/Pb zircon ages between 400 Ma and
320 Ma. In this way, we can constrain the Variscan Orogeny to the above time
span with two periods: (i) between 400 Ma and 350 Ma, when the temperatures
increased towards 650oC, the lower limit of the zircon resetting by diffusion, and
(ii) between 350 Ma and 320 Ma, when the temperature exceeded 650oC causing
some zircons to recrystallize, rare anatectic melts production and pegmatitic veins
generation.
References
Balintoni, I., Balica, C., Ducea, M. N., Chen, F., Hann, H. P., Sabliovschi, V., 2008, Late
Cambrian-Early Ordovician Gondwanan terranes in the Romanian Carpathians: A zircon
U/Pb provenance study. Submitted to Gondwana Research.
Medaris, G., Ducea, M., Ghent, E., Iancu, V., 2003. Conditions and timing of
high-pressure Variscan metamorphism in the South Carpathians, Romania. Lithos, 70,
141-161 |
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