An insight into a gneiss core of the Orlica-Śnieżnik Dome, NE Bohemian Massif: New structural and U-Pb zircon data

Aleksandra Redlińska-Marczyńska*, Andrzej Żlażniewicz, C. Mark Fanning

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    9 Citations (Scopus)

    Abstract

    The Orlica-Śnieżnik Dome in the Sudetes, the NE Bohemian Mas sif, embraces two formations offelsic gneisses of controversial origin and evolution. Our study shows that despite similar geo chemical signatures, they carry systematic minor differences in mineral, isotope, zircon and geothermobarometric characteristics. Four variants of the Gierałtów gneisses include migmatites and have a longer structural history than the Śnieżnik augen orthogneisses. U-Pb SHRIMP anal y ses yielded U-Pb ages of ~500 Ma for cores and ~498 Ma for wide outer parts of zir con grains in the twice-folded Gierałtów gneisses, and an age of ~500 Ma for a discordant neosome vein. Neoproterozoic meta sediments were among precursors of the lithologically diversified Gierałtów Gneiss Formation. First deformation, meta morphism, and migmatisation of these rocks occurred at 515-475 Ma and over lapped with the development and emplacement of a porphyritic S-type granite precursor to the Śnieżnik Gneiss Formation. Themetagranite (= Śnieżnik augen orthogneiss) embraced migmatitic xe no liths. Zircon grains from such xe no liths revealed distorted and replaced cores which yielded U-Pb ages that dispersed around 507-487 Ma, whilst wide darker poorly zoned out growths yielded ages from ~343 Ma to ~325 Ma (mean ~340 Ma). These out growths were in ter preted as a record of Carboniferous meta morphism assisted by rich Zr- and U-carrying fluids. The Variscan meta morphic over print was heterogeneous, and variously affected rocks of the two gneiss formations.

    Original languageEnglish
    Pages (from-to)714-736
    Number of pages23
    JournalGeological Quarterly
    Volume60
    Issue number3
    DOIs
    Publication statusPublished - 2016

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