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

Abstract

The Orlica-OEnie¿nik Dome in the Sudetes, the NE Bo he mian Mas sif, em braces two for ma tions of fel sic gneiss es of con trover sial or i gin and evo lu tion. Our study shows that de spite sim i lar geo chem i cal sig na tures, they carry sys tem atic mi nor dif ferences in min eral, iso tope, zir con and geothermobarometric char ac ter is tics. Four vari ants of the Giera³tów gneiss es in clude migmatites and have a lon ger struc tural his tory than the OEnie¿nik 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 Giera³tów gneiss es, and an age of ~500 Ma for a dis cor dant neosome vein. Neoproterozoic meta sedi ments were among pre cur sors of the lithologically di ver si fied Giera³tów Gneiss For ma tion. First de for ma tion, meta mor phism, and migmatisation of these rocks oc curred at 515-475 Ma and over lapped with the de vel op ment and em place ment of a por phy ritic S-type gran ite pre cur sor to the OEnie¿nik Gneiss For ma tion. The metagranite (= OEnie¿nik augen orthogneiss) em braced migmatitic xe no liths. Zir con grains from such xe no liths re vealed dis torted and re placed cores which yielded U-Pb ages that dis persed 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 re cord of Car bon if er ous meta mor phism as sisted by rich Zr-and U-car ry ing flu ids. The Variscan meta mor phic over print was het er o ge neous, and var i ously af fected rocks of the two gneiss for ma tions.

The eastern part of the Saxothuringian Terrane characterized by zircon and monazite data from the Doboszowice Metamorphic Complex in the Sudetes (SW Poland)

“…1C). The Śnieżnik gneisses are derived from late Cambrian, S-type granites (e.g., Turniak et al, 2000;Lange et al, 2005;Buriánek et al, 2009;Redlińska-Marczyńska et al, 2016) with an anorogenic signature, consistent with the envisaged intracontinental rifting of Gondwana (Pin et al, 2007), yet also with some calc-alkaline characteristics, believed to be inherited from the Cadomian granite precursor (Oliver et al, 1993;Turniak et al, 2000). On the basis of detrital zircons, the clastic protoliths of the Młynowiec-Stronie Group have an Ediacaran to Early Ordovician maximum sedimentary age (e.g., Jastrzębski et al, 2010Jastrzębski et al, , 2015Mazur et al, 2012;Szczepański et al, 2020).…”

“…The Śnieżnik orthogneisses in the OSD and the Doboszowice orthogneisses in the DMC comprise protoliths ca. 500 Ma old (e.g., Turniak et al, 2000;Oberc-Dziedzic et al, 2003Klimas et al, 2009;Mazur et al, 2010;Redlińska-Marczyńska et al, 2016). However, besides the timing of intrusion, other characteristics of the DMC metaigneous rocks are poorly known and thus need more attention.…”

The Saxothuringian Terrane affinity of the metamorphic Stachów Complex (Strzelin Massif, Fore-Sudetic Block, Poland) inferred from zircon ages

“…3): Sniez -OEnie¿nik gneiss from the OEnie¿nik Mas sif (Turniak et al, 2000) and three gneiss sam ples from the Karkonosze-Izera Mas sif: Izera CH (Oberc-Dziedzic et al, 2009), Izera IS (¯elaŸniewicz et al, 2009) and Kowary (Oberc-Dziedzic et al, 2010). It is worth noting that re sults ob tained by Turniak et al (2000) for the OEnie¿nik gneiss es have been re cently con firmed by Redliñska-Marczyñska et al (2016).…”

Cambro-Ordovician vs Devono-Carboniferous geodynamic evolution of the Bohemian Massif: evidence fromP–T–tstudies in the Orlica–Śnieżnik Dome, SW Poland

“…)HP metamorphism occurred during either the Late Devonian (375–385 Ma) (Gordon et al 2005; Anczkiewicz et al 2007) or the Early Carboniferous (~340–350 Ma) (Štípská, Schulmann & Kröner 2004; Bröcker et al 2009; Walczak, 2011). Alternatively, isotopic U–Pb zircon dating that was interpreted in terms of the ~500 Ma migmatization of the Gierałtów gneisses could signify the occurrence of preceding, Early Palaeozoic regional metamorphism in the OSD (Żelaźniewicz et al 2006; Redlińska-Marczyńska, Żelaźniewicz & Fanning, 2016).…”

“…Despite the strong Variscan overprint, the possibility that a (tectono)metamorphic event directly preceded the emplacement of widespread ~490–500 Ma felsic intrusions has been proposed for both the NE (e.g. Don et al 1990; Lexa et al 2005; Redlińska-Marczyńska, Żelaźniewicz & Fanning, 2016) and W part of the Bohemian Massif (Peřestý et al 2017 a , b ).

Figure 1.(a) Distribution of the Variscan terranes in Europe (after Linnemann et al .

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