Article

Nd, Sr, Pb isotope study of the Western Carpathians: implications for Palaeozoic evolution

Schweizerische Mineralogisch-Petrologische Mitteilungen, v.81, 159-174 (2001) 01/2001;
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    ABSTRACT: A combined geochemical, isotopic and detrital zircon dating study has been carried out on metasedimentary rocks of the Lower Unit from the Western Tatra Mountains (Slovakia) forming an eastern border of European Variscides. Geochemical data suggest derivation of the protolith – magmatogenic greywackes and claystones from the recycled continental island arc source. 87Sr/86Sr(350) isotopic ratios between 0.713 and 0.723 together with low εNd(350) values of –9.5 to –11.1 and/or Pb isotope composition indicate a crustal origin of the investigated rocks. Detrital zircons from the metasediments often display homogeneous magmatic zoning with 207Pb/206Pb ages from 660 to 515Ma and/or inherited components, with old cores displaying ages from ca. 1980 to 1800Ma. These late Paleoproterozoic detrital source ages are similar to the Nd model ages of the studied metasedimentary rocks with t(DM2st) ca 1960 ~ 1830 Ma. The Late Cambrian (ca 500 Ma) age represents the last magmatic activity of the precursor rocks and/or it defines the maximum age for sedimentation of the present day metasediments. A possible source for the clastic material of the Lower Unit from theWestern TatraMountains was the peri-Gondwanan continental margin alike the eastern border of the Bohemian Massif – Moravo-Silesian zone or Sudetic block.
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    ABSTRACT: A combination of four thermochronometers [zircon fission track (ZFT), zircon (U–Th)/He (ZHe), apatite fission track (AFT) and apatite (U–Th–[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic, exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132.1 ± 8.3, 155.1 ± 12.9, 146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures >210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55–40 and ~45–40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions, Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55–90°C during Oligocene–Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline bodies during the post-Eocene period.
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    ABSTRACT: Detailed cathodoluminescence (CL) imaging of zircon crystals, coupled with Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) U-Pb zircon dating was used to develop new insights into the evolution of granitoids from the High Tatra Mountains. The zircon U-Pb results show two distinct age groups (350±5 Ma and 337±6 Ma) recorded from cores and rims domains, respectively. Obtained results point that the last magmatic activity in the Tatra granitoid intrusion occurred at ca. 330 Ma. The previously suggested age of 314 Ma reflects rather the hydrothermal activity and Pb-loss, coupled with post-magmatic shearing.
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