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

Jastrzębski Mirosław, Żelaźniewicz Andrzej, Stawikowski Wojciech, Budzyń Bartosz, Krzemińska Ewa, Machowiak Katarzyna, Madej Stanisław, Białek Dawid, Sláma Jiří, Czupyt Zbigniew, Jaźwa Aleksandra

Annales Societatis Geologorum Poloniae

2023

Vol. 93, No. 3

229--249

In the Variscan Bohemian Massif, orthogneiss complexes of different sizes, derived from early Palaeozoic granitoids, are accompanied by metavolcano-sedimentary successions. They are common in the Sudetes, SW Poland, and belong mainly to the Saxothuringian Terrane. In order to better characterize the evolution of the latter, new U-Pb and O isotopic zircon analyses, combined with zircon typology and new U-Th-Pb isotopic monazite analyses, were performed. The present data show that the S-type granitic precursors of the Doboszowice orthogneisses (Fore-Sudetic Block) and the Śnieżnik gneisses (Sudetes) were formed at ca. 495 Ma from differently evolved magmas. Protoliths of the Doboszowice orthogneisses developed entirely in the crust, whereas the precursors to the Śnieżnik gneisses received some mantle input. Metasediments that accompany the Doboszowice orthogneisses reveal zircon spectra, which point to a late Cambrian-Early Ordovician sedimentary age. These spectra, in addition to predominant grains with Ediacaran ages, contain up to 10% of zircons dated at ca. 1.0 Ga. Therefore, it is suggested that the parent basin was supplied with detritus coming from areas, located in the Libyan-Nubian part of North Africa. Using also earlier published data, such a provenance is assigned to the units that now occur in the eastern part of the Fore-Sudetic Block. Late Cambrian-Early Ordovician granite intrusions and the concurrent accumulation of sediments originated in an extensional setting of the peri-Gondwana rifted continental margin or a back-arc setting. The Pb/U and Pb/Th monazite data constrain the ca. 346–341-Ma peak of the Variscan regional metamorphism in the eastern Saxothuringian Terrane and the prolonged juxtaposition of now adjacent tectonic units at least until 330 Ma.

Historia Oddziału Wrocławskiego Polskiego Towarzystwa Geologicznego w latach 1970–2021

Żelaźniewicz Andrzej, Kowalski Aleksander

Przegląd Geologiczny

2022

Vol. 70, nr 4

307--313

In 2022, the Wrocław Branch of the Polish Geological Society celebrates its 70 jubilee. It was founded in 1951 and has been active since 1952. During the last 50 years, there were organized nearly 700 scientific lectures on widely different geological topics, five full plenary meetings of the Society in the Lower Silesia venues with dedicated field excursions, several thematic conferences (with on-spot field examination) during trips to various outcrops all over the region. Other occasional activities included celebration of the 250^th anniversary of Abraham Gottlob Werner's birthday honoured by placing a sandstone triptych commemorative plaque on his family home in Osiecznica near Bolesławiec.

Age constraints on the Pre-Variscan and Variscan thermal events in the Kamieniec Ząbkowicki Metamorphic belt (the Fore-Sudetic Block, SW Poland)

Jastrzębski Mirosław, Żelaźniewicz Andrzej, Budzyń Bartosz, Sláma Jiří, Konečny Patrik

Annales Societatis Geologorum Poloniae

2020

Vol. 90, No. 1

27--49

The Kamieniec Ząbkowicki Metamorphic Belt (KZMB) is a narrow zone of mainly mica schists, subordinate acid metavolcanics and scarce eclogites, sandwiched between Brunovistulia and the northern tip of the Teplá-Barrandia microplates. Locally occurring high-pressure relics indicate subduction of the metasedimentary succession of the KZMB, the origin and provenance of which remain unclear. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) investigations of detrital zircons show that the metapelites represent an Ediacaran-Cambrian sedimentary basin, with a maximum depositional age of 561±9 Ma. This basin was filled with detritus from a source or sources, composed of rocks containing zircons that are mainly Cryogenian-Ediacaran and Palaeoproterozoic in age. No younger component was found in the zircon population studied. The isotopic U-Pb LA-ICP-MS and chemical U-Th-total Pb electron probe microanalysis (EPMA) monazite geochronology data indicate an important regional tectono-metamorphic event at ca. 330 Ma. Though these data do not permit determination of the peak pressure from the peak temperature stages, the event was part of a complex collision of the Saxothuringian plate with Brunovistulia.