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

Oberc-Dziedzic T., Kryza R., Madej S., Pin C.

Geological Quarterly

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2018

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Vol. 62, No. 2

237--256

EN

The Saxothuringian Terrane defined in the western part of the Bohemian Massif is regarded to have easterly continuations in the Karkonosze–Izera Massif, the Kamieniec Ząbkowicki Belt and the Orlica–Śnieżnik Dome. All these units comprise Early Ordovician (~500 Ma) metagranites associated with mica schists. Even more to the east, ~500 Ma metagranites and metasedimentary rocks occur also in the Strzelin Massif of the East Sudetes, where they are known as the pale and dark Stachów gneisses, respectively. Altogether, these rocks form the Stachów Complex which was thrust on the Strzelin Complex of the Brunovistulicum Terrane during the Variscan Orogeny. The contribution presents lines of evidence for a Saxothuringian affinity of the Stachów Complex rocks: (1) the new SHRIMP U-Pb age data of zircons from both the pale and dark Stachów gneisses; (2) the indication that the zircon age spectra from the ~500 Ma granitoids and their accompanying metasedimentary rocks are similar to those found in other parts of the Sudetes; (3) the “Armorican” age pattern of inherited zircons of the pale Stachów gneisses, as also observed in the Saxothuringian Terrane; (4) the similarity of trace elements and Sm-Nd isotope data of the Stachów gneisses and correlative rocks from the Karkonosze–Izera Massif and the Orlica–Śnieżnik Dome.

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Variscan granitoid plutonism in the Strzelin Massif (SW Poland) : petrology and age of the composite Strzelin granite intrusion

Oberc-Dziedzic T., Kryza R., Pin C., Madej S.

Geological Quarterly

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2013

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Vol. 57, No. 2

269–-288

EN

Petrological data and recently published U/Pb zircon SHRIMP ages reveal a protracted Variscan magmatic evolution in the Strzelin Massif (SW Poland), with three main stages of granitoid plutonism: 1 – tonalitic I, 2 – granodioritic and 3 – tonalitic II/granitic. The granitoids of the second and third stages form the Strzelin intrusion that is composed of three varieties: medium-grained biotite granite, fine-grained biotite granite and fine-grained biotite-muscovite granite. New SHRIMP data show that the medium-grained and fine-grained biotite granites comprise different zircon populations that reflect complex and prolonged plutonic processes. Two distinct magmatic events seem to be represented by well-defined zircon populations with apparent 206Pb/238U ages of 303 ± 2 Ma in the medium-grained biotite granite, and 283 ± 8 Ma in the fine-grained biotite granite. These dates, however, do not necessarily reflect the true magmatic ages, possibly being “rejuvenated” by radiogenic lead loss in zircons (impossible to resolve based on routine SHRIMP data). Based on field evidence, the third variety, the biotite-muscovite granite, postdates both types of biotite granites. The petrographic and geochemical features, including Nd isotope signature, along with various zircon inheritance patterns and ages, suggest that the parental magmas of the three granites originated from different crustal sources and were emplaced during three successive magmatic pulses.

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Gneiss protolith ages and tectonic boundaries in the NE part of the Bohemian Massif (Fore-Sudetic Block, SWPoland

Oberc-Dziedzic T., Kryza R., Klimas K., Fanning M.C., Madej S.

Geological Quarterly

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2005

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Vol. 49, No. 4

363--378

EN

Published geochronological data, petrology, geochemistry and geological context of orthogneisses in the Strzelin and the Stachów complexes (NE-part of the Fore-Sudetic Block), together with structural observations help to locate the northern extension of the boundary between the East and West Sudetes within the poorly exposed NE margin of the Bohemian Massif. The Strzelin complex, in the east, comprises the Strzelin gneiss, with zircon ages of 600š7 and 568š7Ma, and the Nowolesie gneiss with a mean zircon age of 1020_ 1Ma. The Stachów complex to the west, which forms several tectonic klippen in the Strzelin Massif and in the Lipowe Hills Massif, contains the Gościęcice gneiss and pale Stachów gneiss, both yielding Late Cambrian zircon ages (~500š5 Ma). The orthogneisses in both complexes correspond to peraluminous S-type granites, but have different inherited zircon ages and display contrasting trace element characteristics, indicating different sources and petrogenetic histories. Based on the ages, petrology and overall geological context, the Strzelin orthogneiss is similar to the Keprník orthogneiss of the East Sudetes, whereas the orthogneisses of the Stachów complex correspond to rocks known from theWest Sudetes (e.g. the Izera and Śnieżnik orthogneisses). The Stachów and the Strzelin complexes are separated by the Strzelin Thrust, which may be interpreted as the northern extension of the boundary between the East and West Sudetes, i.e. part of the boundary between the Brunovistulian and Moldanubian terranes of the NE part of the Bohemian Massif.

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The Variscan overthrust of the Lower Palaeozoic gneiss unit on the Cadomian basement in the Strzelin and Lipowe Hills massifs, Fore-Sudetic Block, SW Poland: is this part of the East-West Sudetes boundary?

Oberc-Dziedzic T., Madej S.

Geologia Sudetica

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2002

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Vol. 34

39-58

EN

The problem of the position of the boundary between the geological structures of the West and the East Sudetes has been a topic of discussion since 1912, when F.E. Suess developed the concept of the Moldanubian overthrust as a boundary between the Moldanubian and Moravo-Silesian zones. The West Sudetes comprise gneisses of Cambro-Ordovician protolith age with inclusions of high pressure metamorphic rocks. The Cadomian basement, referred to as the Brunovistulian and overlain by Devonian rocks, is characteristic of the East Sudetes. The location of the East-West Sudetes boundary is well-defined in the mountainous part of the Sudetes but still a matter of debate in the Fore-Sudetic Block. This paper puts forward a new approach to this problem. The Proterozoic Strzelin gneiss with its Proterozoic (the older schist series) and Devonian envelope (the Jegłowa beds) are tectonically overlain by the Early Palaeozoic Gościęcice gneiss and the light Stachów gneiss with its envelope. The former occurs in the footwall and the latter in the hanging wall rocks of the Strzelin Thrust. This juxtaposition resembles the situation along the East-West Sudetes boundary separating two domains with contrasting protolith ages. Consequently, the Strzelin Thrust is considered part of the border zone between the East and West Sudetes, i.e. the northern continuation of the Ramzova/Nyznerov thrust to the Fore-Sudetic Block. At the present erosion level, the hanging wall rocks of the Strzelin Thrust are separated from their roots and form klippen. The minimum transport distance along the thrust is estimated at 10 km. The Strzelin Thrust forms a generally shallowly dipping domed surface. It becomes steeper east of the Strzelin massif, where it is hidden beneath Cenozoic sediments, and west of the Lipowe Hills, where it follows the eastern border of the Kamieniec Ząbkowicki Metamorphic Complex. The hanging wall is probably rooted in the strongly mylonitised mica schists exposed along the Mała Ślęza river. The thrust zone is a wide mylonitic belt carrying relatively HT and HP garnet-bearing amphibolites in the northern part of the Strzelin massif and the strongly mylonitised Henryków gneiss and quartzites in the southern part at the Lipowe Hills. This paper discusses the problem of the East-West Sudetes boundary, mainly in the framework of the Strzelin massif. The attitude of this boundary in other parts of the Fore-Sudetic Block is still unclear because of poor exposure and numerous faults of E-W and NW-SE orientation that displace it from its original position.