HR: 1340h
AN: V13A-1140    [Abstracts]
TI: Setting and Paleozoic age of the HP-complexes in the South Carpathians
AU: * Sàbàu, G
EM: g_sabau@yahoo.co.uk
AF: Geological Institute of Romania, 1 Caransebeş St., Bucharest 32, 02271, Romania
AU: Massonne, H
EM: h-j.massonne@mineralogie.uni-stuttgart.de
AF: Institut für Mineralogie und Kristallchemie, Azenbergstr. 18, Stuttgart, 70174, Germany
AB: The metamorphic basement units of the South Carpathians (SC), being hardly overprinted by Alpine events, record a polymetamorphic evolution discernible by tectonic discontinuities, rock compositions indicative of different geotectonic settings and contrasting metamorphic assemblages. Very recent age determinations contribute to a better understanding of this evolution. Pre-Alpine high-pressure (HP) complexes appear in the structurally upper Alpine basement units of the SC: the Lotru Metamorphic Suite (LMS) of the Getic Nappe and the Fàgàraş (FM) and Leaota (LM) Massifs. In these units, HP-complexes are sandwiched in contrasting lithologies (gneisses, metapelites) forming structurally coherent metamorphic piles. This feature confirms large-scale imbrication along plate margins. However, the timing of the various HP-events is different compared to the dominant metamorphic overprint, the tectonic stacking of contrasting lithologic units, and igneous events. The deep-seated stacking (ca. 20 km) of the various units of the LMS postdates the HP-event and is coeval with the dominant metamorphic overprint and emplacement of concordant granitoids, grossly at the Ordovician- Silurian boundary (441.7±3.7 Ma, U-Pb zircon age). In the FM the gneiss unit on top of the eclogite-bearing unit records dominant ages similar to those of the LMS (442±2.4 Ma). However, this U-Pb age constrains only a maximum age for the tectonic stacking because the rocks are strongly overprinted by a medium-grade metamorphic event not recorded in zircon populations so far. Eclogites of the Leaota Massif appear as knockers in a semipelitic subduction-accretion complex overlaid by low grade thrust sheets which were paleontologically dated as Lower Paleozoic. U-Pb zircon dating yielded a metamorphic age of 537±13 Ma for the eclogites. The stacking process responsible for the enclosure of the eclogite-bearing unit postdated an intrusion age of a concordant metagranite below the subduction-accretion complex (479.1±6.5 Ma). In all three HP complexes magmatic ages reflect juvenile igneous suites (arc, back-arc basins) Late Precambrian to Early Paleozoic in age, as well as reworked crustal inheritance (by anatexis/crustal contamination) covering a wide spectrum of ages. Dominant West-African inherited age spectra and subordinate Avalonian ones attest complex (micro)plate-margin interactions of Gondwana-derived terrains during the Early Paleozoic.
DE: 1115 Radioisotope geochronology
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8178 Tectonics and magmatism
DE: 9335 Europe
DE: 9620 Ordovician
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting