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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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Last stage of Variscan granitoid magmatism in the Strzelin Massif (SW Poland) : petrology and age of the biotite-muscovite granites

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

Geological Quarterly

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2015

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Vol. 59, No. 4

718--737

EN

New petrographic and geochemical data show some differences between Variscan Bt-Ms granites occurring either as small plutons or dykes in the Strzelin Massif (SW Poland). The granites of the Gromnik and Górka Sobocka plutons are rich in micas and crystallized from "wet" magmas; the granites in the dykes and in the Gębczyce pluton are mica-poorer and cordierite-bearing rocks, derived from “dryer” magmas. The lower initial eNd values in the Bt-Ms granites of the dykes, compared with those in the plutons, reflect a more "crustal" signature of the former, possibly due to local crustal assimilation, via AFC, shortly before emplacement. Much more radiogenic initial 87Sr/86Sr ratios in the dykes, up to 0.726, further suggest the involvement of extraneous, hydrous crustal fluids enriched in 87Sr during the evolution of late-stage magma derivatives. The new U-Pb SHRIMP zircon age of 296 ± 6 Ma for the Gębczyce Bt-Ms granite shows that this body belongs to the third stage of magmatism in the Strzelin Massif. The U-Pb SHRIMP zircon data for the Bt-Ms granite dykes provide ages similar to those of their host rocks: c. 295 Ma for the Gęsiniec tonalite and the enclosed Bt-Ms granite, and c. 285 Ma for the Strzelin biotite granite and its Bt-Ms granite dykes. These new data from peraluminous rock-types complement our previous studies focused on the tonalites, granodiorites and biotite granites, and shed light on the late-stage igneous evolution of the Strzelin Massif.

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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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Late stage Variscan magmatism in the Strzelin Massif (SW Poland): SHRIMP zircon ages of tonalite and Bt-Ms granite of the Gęsiniec intrusion

Oberc-Dziedzic T., Kryza R.

Geological Quarterly

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2012

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Vol. 56, No 2

225-236

EN

The Gęsiniec composite intrusion in the northern part of the Strzelin Massif (Fore-Sudetic Block, SW Poland) was formed in the course of three late Variscan magmatic episodes: tonalitic I, granodioritic, and tonalitic II/granitic. The age of the Gęsiniec tonalite, 295 š3 Ma, is the same as that of another tonalite body in the southern part of the Strzelin Massif, the Kalinka tonalite. The younger biotite-muscovite (Bt-Ms) granite, in a dyke cutting the Gęsiniec tonalite, has an indistinguishable isotopic age of 295 š5 Ma; it contains, however, inherited zircons with ages between ca. 1.5 Ga to 374 Ma, similar to zircon ages from surrounding gneisses. This suggests that the magmatic protolith of gneisses and the magma of the Bt-Ms granite could have come from similar sources, or that the magma of the Bt-Ms granite was contaminated by the gneisses. Both the tonalite and Bt-Ma granite represent a late stage of the granitoid magmatism in the eastern part of the Variscan orogen.

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Variscan multistage granitoid magmatism in Brunovistulicum: petrological and SHRIMP U-Pb zircon geochronological evidence from the southern part of the Strzelin Massif, SW Poland

Oberc-Dziedzic T., Kryza R., Białek J.

Geological Quarterly

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2010

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Vol. 54, No 3

301-324

EN

U-Pb SHRIMP ages of one granodiorite and two tonalite samples from the Strzelin Massif, northern part of Brunovistulicum, reveal three distinct stages of Carboniferrous-early Permian granitoid magmatism: tonalitic I - 324 Ma, granodioritic - 305 Ma and tonalitic II/granitic - 295 Ma. The first stage of magmatism coincided with the first migmatization event which took place shortly after the first deformation. The second stage of granitoid plutonism was coeval with the second migmatization event which produced abundant pegmatites. It took place after compressional phases of the second deformation and was related to decompression at the beginning of tectonic denudation. The third, most abundant stage of magmatism was connected with late extension in that part of the Variscan Orogen.

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Palaeo- to Mesoproterozoic inheritance and Ediacaran anatexis recorded in gneisses at the NE margin of the Bohemian Massif: SHRIMP zircon data from the Nowolesie gneiss, Fore-Sudetic Block (SW Poland)

Klimas K., Kryza R., Mark Fanning C., M.

Geologia Sudetica

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2009

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Vol. 41

25-42

EN

Recent geochronological studies, including sensitive high mass-resolution ion microprobe (SHRIMP) zircon dating, have helped to differentiate into specific age groups the various gneisses that occur within the basement units of the central-European Variscides. The Fore-Sudetic Block basement unit, for example, has been divided into two major gneiss groups of Neoproterozoic and Cambrian/Ordovician age, respectively. These two gneiss groups have been assigned to different tectonic units, themselves separated by a major tectonic boundary that is interpreted to be the northern continuation of the Moldanubian (Lugodanubian) Thrust. This thrust divides the main tectonostratigraphic units of the Bohemian Massif: the Moldanubian and Saxo-Thuringian units to the west, and the Moravo-Silesian unit to the east. This paper interprets new SHRIMP zircon data from the Nowolesie gneiss at Skalice (sample S6) and integrates the results with data from the Strzelin gneiss at Dębniki (sample S3), which is within the Strzelin Massif (E part of the Fore-Sudetic Block). Both the Nowolesie and Strzelin gneisses contain numerous inherited zircons within the age range of 1.5-2.0 Ga, indicating Meso- and Palaeoproterozoic sources for the zircons and suggesting that these zircons were recycled into younger units that subsequently underwent partial melting. The ages derived from samples S6 and S3, together with the absence of the Grenvillian ages (~1.3-0.9 Ga), suggest a West-African and/or Amazonian cratonic crust as the source for both the Nowolesie and Strzelin gneiss protoliths. The main zircon populations from both gneisses fall into two similar age groups: 602 +-7 Ma and 587 +- 4 Ma for the Nowolesie gneiss; 600 +-7 Ma and 568 +- 7 Ma for the Strzelin gneiss. These sets of Ediacaran (late Neoproterozoic) dates possibly reflect anatexis of the gneiss protoliths during the Cadomian orogeny.