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Zircon U-Pb ages of granitoid apophyses in the western part of the Kłodzko–Złoty Stok Granite Pluton (SW Poland)

Mikulski S.Z., Williams I. S.

Geological Quarterly

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2014

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Vol. 58, No. 2

251--262

EN

Granitoids from the Graniec–Bardo and Myszak apophyses of the Kłodzko–Złoty Stok (KZS) Granite Pluton that intrude the Upper Paleozoic flysch of the Bardo Unit have zircon U-Pb ages, measured by SHRIMP, of 341.6 ± 2.8 Ma and 341.4 ± 2.2 Ma, respectively. These results augment our previous dating that recorded a short period of Middle Mississippian (Visean) hypabyssal magmatism that produced a variety of KZS igneous rocks of different compositions between ca. 341 and 331 Ma. The Graniec–Bardo and Myszak apophyses belong to the earliest stage of the pluton emplacement. Geochemical and petrographic studies of the dated samples indicate that they are biotite- and hornblende-rich tonalite and syenogabbro of diverse composition and typical of rocks originating from hybrid magmas formed in the geotectonic transition from an early stage collisional granitoid emplacement to its fast orogenic uplift. The polymetallic auriferous ore mineralisation of contact metasomatic type found in intimate contact with the Graniec–Bardo apophysis near Bardo Śląskie may also be of Visean age.

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Zircon U-Pb dating of igneous rocks in the Radzimowice and Wielisław Złotoryjski auriferous polymetallic deposits, Sudetes, SW Poland

Mikulski S. Z., Williams I. S.

Annales Societatis Geologorum Poloniae

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2014

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Vol. 84, No. 3

213--233

EN

A rhyolite porphyry in the Radzimowice deposit at Bukowinka Hill has a SHRIMP zircon U-Pb age of 314.9 ± 3.1 Ma. This is consistent with previous zircon dating of a monzogranite and a rhyodacite (ca. 315 Ma) in the Żeleźniak sub-volcanic intrusion (ZI), considered to be the igneous rocks, representing the oldest magmatic pulses in the region. First-stage mesothermal auriferous sulphide mineralization in the deposit was connected to hydrothermal processes, associated with the rhyodacite intrusions. This was followed by tectonic activity and younger alkaline magmatism in a post-collisional geotectonic setting. The first-stage Au-bearing sulphide mineralization was cataclased and overprinted by younger epithermal base-metal sulphides with microscopic Au, associated with Bi-Te-Ag minerals. The younger magmatic pulses are represented by porphyritic andesites and lamprophyric dykes, which cut the ZI. Zircon from these dykes yielded ages of 312.8 ± 2.8 Ma for an andesite porphyry and 312.4 ± 4 Ma for a lamprophyre. All these magmatic pulses, evidenced in the Radzimowice deposit, are considered to be the oldest post-orogenic sub-volcanic magmatism cutting the basement of the intramontane basins in the Sudetes, on the NE margin of the Bohemian Massif. A rhyolite porphyry in the famous 'Organy' exposure at Wielisław Złotoryjski (WZ) on the SE margin of the North-Sudetic Basin is younger, 297.5 ± 2.8 Ma. Vein-type auriferous ore mineralization, hosted by Early Palaeozoic graphitic schists in intimate contact with rhyolite porphyry in WZ, is also correlated with this magmatism. The auriferous ore mineralization at Radzimowice and Wielisław Złotoryjski formed at different times, during different magmatic pulses and successive hydrothermal stages, despite several similarities in geologic setting and country- and host-rock compositions. There was a transition from a post-collisional to a within-plate setting over about 20 Ma in Late Carboniferous-Early Permian times, with the older Żeleźniak and Bukowinka sub-volcanic intrusions in the uplifted part of the Kaczawa Metamorphic Complex (ZI) and the younger Wielisław Złotoryjski sub-volcanic intrusion in the metamorphic basement of an intramontane basin.

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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.

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Lower Carboniferous bentonites in the Bardo Structural Unit (central Sudetes): geological context, petrology and palaeotectonic setting

Kryza R., Muszer J., August C., Haydukiewicz J., Jurasie M.

Geologia Sudetica

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2008

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Vol. 40

19-31

EN

The Lower Carboniferous Paprotnia beds of the Bardo Structural Unit in the central Sudetes, composed predominantly of mudstones with Upper Viséan fossils, include several bentonite layers. The bentonites, composed mainly of kaolinite, illite/smectite and smectite, with minor amounts of quartz, calcite and iron hydroxides, also contain abundant zircons, the features of which indicate their volcanic derivation. The main population of the zircons yielded a SHRIMP U-Pb age of ~ 334 Ma corresponding with, and numerically constraining, the biostratigraphic data. The field evidence, biostrati- graphic and geochronological results, together with mineralogical data from the bentonites, indicate continental margin-type sedimentation and contemporaneous volcanic (andesitic-rhyolitic) activity in the neighbouring region during the ongoing Variscan orogeny in central Europe in Late Viséan times.