HR: 1340h
AN: V13A-1138 INVITED    [Abstracts]
TI: The Apuseni Mountains, Romania, a Variscan Collage of Ordovician Gondwanan Terranes
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: Chen, F
EM: fukun-chen@mail.igcas.ac.cn
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
AU: Cliveti, M
EM: ibalinto@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AU: Hann, H P
EM: hann@uni-tuebingen.de
AF: Institut für Geowissenschaften, Universität Tübingen, Sigwartstr. 10, T 72076, Germany
AU: Ghergari, L
EM: lghergari@bioge.ubbcluj.ro
AF: Dept. of Geology, Babeş-Bolyai University, 1 Kogàlniceanu str., Cluj Napoca, 400084, Romania
AB: The basement of the Apuseni Mountains, Romania, consists of three pre-Variscan terranes, sutured during an Early Variscan amalgamation around 351 Ma (Balintoni et al., this volume). The northern Someş Terrane (ST) is predominantly gneissic, while the southern Baia de Arieş Terrane (BAT) is dominated by the presence of large carbonate lenses, although metagranites and other types of orthogneisses can be found. These two terranes are sutured through the Biharia terrane, probably an accreted island arc. LA-ICP-MS datings on zircons extracted from orthogneisses and metagranites were performed in order to constrain the age of ST and BAT. A number of previously CL-imaged crystals were ablated at the China's University of Geosciences, Wuhan. From ST we dated an orthogneiss occurring in structurally lowermost position, a metatuff situated in the upper strongly retrogressed part and a twenty detrital crystal population sampled from a metasandstone. The ²⁰⁶Pb/²³⁸U apparent ages were projected using the weighted average plots.A magmatic crystallization age of 472.8±5.0 Ma (Upper Early Ordovician) resulted for one of the orthogneiss samples, besides several older ages at 505.7, 566.3 and 708.2 Ma corresponding to inherited cores. Another sample from the same rock appeared strongly affected by lead loss during a later thermotectonic event, most of the apparent ages grouping around 352±14 Ma. This age is similar with the age of the suture between ST and BT (Balintoni et al., this volume). The main zircon population of one metatuff sample furnished an averaged age of 423±7.2 Ma, also found in two additional samples, but their significance is obscure for the moment. Two primary magmatic ages arise at 464.2 and 473.8 Ma, an older value of 758.7 Ma corresponding to an inherited core. Detrital zircon ages range between 534.8 and 2596.8 Ma. The younger value represents an upper age constraint for the protolith age of ST-rocks. From BAT we dated the Lupşa metaporphyroid and the Mihoeşti (MiG) and Muncel (MuG) metagranites. The 466±11 Ma age value recorded in the metaporphyroid was inferred to represent the primary crystallization age. Many inherited cores yielded ages scattered between 523±32 Ma and 1914 Ma, while no ages younger then 466±11 Ma were recorded. The MiG crystallized at 469.2±7.5 Ma, inherited ages of 501±22, 554.9 and 685.6 Ma being also recorded. A 468.4±4.8 Ma primary magmatic age was found for the MuG, this sample also containing abundant inherited ages dispersed between 507.3±5.5 Ma and 1018.2 Ma. A group of ages at 429±13 Ma, corresponds to the dominant population in the ST metatuff. The results indicate that the main episode of crustal construction for the ST and BAT was the Ordovician; both terranes possess an abundant Cadomian inheritance. Pre-Cadomian inheritances are rare, except for the detrital zircons. Only the zircons from the ST appear strongly affected by lead loss processes, possibly related with the profuse Variscan magmatism affecting the upper plate. The history of the ST and BAT is compatible with a primitive North-Gondwanan origin.
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