HR: 0800h
AN: T31B-0476    [Abstracts]
TI: The Age of the intra-Danubian Suture (Southern Carpathians, Romania)
AU: * Balica, C
EM: balica@bioge.ubbcluj.ro
AF: Department of Geology, Babes-Bolyai University, Kogalniceanu str, Cluj Napoca, 400084, Romania
AU: Hann, H P
EM: hann@uni-tuebingen.de
AF: Institut für Geowissenschaften, Lehrstuhl für Allgemeine Geologie, Universitaet Tübingen, Sigwartstr. 10, Tübingen, 72076, Germany
AU: Chen, F
EM: fukun-chen@mail.iggcas.ac.cn
AF: Laboratory for Radiogenic Isotope Geochemistry, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
AU: Balintoni, I C
EM: ibalinto@bioge.ubbcluj.ro
AF: Department of Geology, Babes-Bolyai University, Kogalniceanu str, Cluj Napoca, 400084, Romania
AU: Zaharia, L
EM: lumiok@yahoo.com
AF: Department of Geology, Babes-Bolyai University, Kogalniceanu str, Cluj Napoca, 400084, Romania
AB: The Southern Carpathians, as an Alpine chain are formed of two domains, namely the Getic Domain (GD) and the Danubian Domain (DD). The basement of DD is represented by two terranes, named Dragsan and Lainici- Paius sutured through Tisovita-Iuti ophiolitic complex. The two terranes were invaded by large granitic plutons, some of them being dated as Late Proterozoic by U/Pb method. Yet, along the inferred suture there are four granitic bodies whose ages have been only assumed by their geological relations. From North to South the four bodies sampled for LA-ICP-MS zircon U/Pb dating are: Muntele Mic, Sfardinu, Cherbelezu and Ogradena. The previously CL imaged zircon crystals were ablated at the China's University of Geosciences facilities in Wuhan. The zircons from all samples showed quite complex structures, with many inherited cores or affected by lead loss processes. In order to get a mean age for every pluton, we used the weighted average plots by projecting the ²⁰⁶Pb/²³⁸U apparent ages. The crystallization age of the Poiana Marului pluton is around 326.7±7 Ma (MSWD 1.6). A set of sixteen apparent ages ranging between 400 to 648 Ma together with other tree points indicating 897, 1353 and 1693 Ma, represent inheritances. There was no observable lead loss process in this data set. The Sfardinu granite crystallized at 310±7.9 Ma (MSWD 4.8). The inheritances found in this sample are at 427 and 723 Ma, but an important lead loss process occurred later, as indicated by ten apparent ages between 240-292 Ma. Cherbelezu granite gave a crystallization mean age of 326.9±4.9 Ma (MSWD 1.9). A single inherited core appears at 502 Ma, yet eight apparent ages ranging between 239-295 Ma signalize again an important lead loss process. Other two ages at 176 and 193 Ma confirm the presence of this process. The Ogradena pluton zircons display two possible crystallization ages for the outer zones of zircon grains, at 356.6±7.8 Ma (twelve apparent ages, MSWD 12) and 314.1±7.8 Ma (nine apparent ages, MSWD 13) respectively. It is difficult to explain this situation, and we suppose the second figure as the probable crystallization age. Inheritances are represented by a number of 37 ²⁰⁶Pb/²³⁸U apparent ages scattered between 400 and 612 Ma, only one apparent age of 265 Ma possibly proving the presence of lead loss. The geochemical parameters ASI, Fe-number and MALI calculated from the major oxides analyses showed that all four plutons are metaluminous and magnezian. Both Cherbelezu and Ogradena have a calcalkaline character near to alkalicalcic while Muntele Mic and Sfardinu are alkalicalcic. Geochemically, all four plutons are closed to Cordilleran type, main portion or a little inboard of it. Out of these data several conclusions can be drawn. The age of the intra-Danubian suture is late Visean to Bashkirian or late Variscan. Muntele Mic and Ogradena granites exhibit abundant Cadomian inheritances, while Cherbelezu and Sfardinu plutons seem affected by lead loss processes due to an important thermotectonic event happened during 250 to 290 Ma interval. The emplacement of the four plutons probably reflects a subductional process. Finally, the inheritances suggest a Gondwanan source for the anatectic material.
DE: 1115 Radioisotope geochronology
DE: 8035 Pluton emplacement
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting