HR: 1340h
AN: V13A-1139 INVITED    [Abstracts]
TI: The Age of the Variscan Suture in the Apuseni Mountains, Romania, as revealed by LA-ICP- MS Zircon Dating
AU: * Balintoni, I C
EM: ibalinto@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AU: Balica, C
EM: balica@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AU: Zaharia, L
EM: ibalinto@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AU: Cliveti, M
EM: ibalinto@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AU: Chen, F
EM: fukun-chen@mail.igcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
AU: Hann, H P
EM: hann@uni-tuebingen.de
AF: Institut für Geowissenschaften, Universität Tübingen, Sigwartstr. 10, Tübingen, 72076, Germany
AU: Li, L Q
EM: fukun-chen@mail.igcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
AB: The structure of the Apuseni Mountains, Romania, consists of several Alpine nappe systems thrust over an autochthonous unit. The Bihor autochthonous unit and some components of the Biharia and Codru nappe systems are dominantly metamorphic basement unit. Three metamorphic complexes, called Someş, Biharia and Baia de Arieş, were separated in the metamorphic basement and ascribed to three different terranes amalgamated during Variscan Orogeny. During the collision, the Someş assumed the position of upper plate and the Baia de Arieş was included in the lower plate, squeezing the Biharia between them. The southern margin of the Someş terrane was invaded by the Arieş migmatites in its eastern part and several granite plutons in its western side. Migmatites and the Codru Moma granite have been sampled in order to date the collisional event. LA-ICP-MS dating of previously CL-imaged zircon crystals was conducted at the China's University of Geosciences, Wuhan. From the Codru Moma granite, eleven ²⁰⁶Pb/²³⁸U apparent ages ranging between 341.1±3.7 Ma and 360.9±3.88 Ma out of nineteen apparent ages ranging between 321.5±3.47 Ma and 371±3.98 Ma were considered for a weighted average projection, resulting a mean early Variscan age of 350.5±4.9 Ma (MSWD = 3.8). At this scale, the MSWD reflects the presence of non analytical scattering, being probably connected to a crystallization interval reasonably extending over 20 Ma or more. A single late Neoproterozoic age of 567±5.97 Ma was found in an inherited core. From the Arieş migmatites, we selected thirty U-Pb apparent ages between 342.5±3.67 Ma and 363.8±3.78 Ma (the same range as the Codru Moma granites), out of forty apparent ages between 323.5±5.74 Ma and 383±4.32 Ma. The mean age resolved by weighted average plot is of 351.8±2.6 Ma, (MSWD = 3.5). It clearly resulted that the Codru Moma granite and Aries migmatites were emplaced in the same time span, extending over a crystallization period around 20 Ma. We remark three inherited cores confined to the 460.8±4.86 Ma - 467.5±4.81 Ma interval (i. e. middle Ordovician). Major element geochemistry indicates for both Codru Moma granite and Arieş migmatites a metaluminous, magnesian, and calc-alkaline to calcic composition, similar for instance to Cordilleran batholiths, either on the outboard side (Arieş migmatites) or in the main range (Codru Moma granite). On this basis we conclude that they were generated in a subductional tectonic setting. The suture from the Apuseni Mountains between the Someş and Baia de Arieş terranes is the result of early Variscan subduction and amalgamation between the two terranes. Such geological processes are known in the Western Carpathians and Bohemia, indicating the Apuseni Mountains as the eastern prolongation of Variscan Western Europe.
DE: 1115 Radioisotope geochronology
DE: 8035 Pluton emplacement
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting