The Orthogneiss and Schist Complex of the Karkonosze-Izera Massif (Sudetes, SW Poland): U-Pb SHRIMP zircon ages, Nd-isotope systematics and protoliths

Teresa Oberc-Dziedzic¹, Ryszard Kryza¹, Christian Pin², Ksenia Mochnacka³ & Alexander Larionov⁴

¹ Institute of Geological Sciences, University of Wrocław, Plac M. Borna 9, 50-204 Wrocław, Poland, e‑mail: teresa.oberc‑dziedzic@ing.uni.wroc.pl ; ryszard.kryza@ing.uni.wroc.pl
² Département de Géologie, UMR 6524 CNRS, Université Blaise Pascal, 5 rue Kessler, 63 038 Clermont-Ferrand, France, e‑mail: c.pin@opgc.univ‑bpclermont.fr
³ Faculty of Geology, Geophysics and Environmental Protection, Department of Economic Geology, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland, e-mail: kmoch@geol.agh.edu.pl
⁴ Centre of Isotopic Research, A.P. Karpinsky All-Russian Geological Research Institute (VSEGEI), 74 Sredny Pr, St Petersburg 199 106, Russia, e-mail: Alexander_Larionov@vsegei.ru

Key words:  orthogneisses, mica schists, SHRIMP zircon geochronology, Nd isotopes, Sudetes, Variscides.

Abstract
Many basement units of the Variscan orogen that are exposed in the Sudetes, SW Poland, comprise widespread ~500 Ma orthogneisses and associated mica schists, the latter often of unknown age and derivation. Our new U-Pb sensitive high resolution ion microprobe (SHRIMP) zircon ages from two samples of the Izera metagranites, both around 503 Ma, are in a good agreement with the well established late Cambrian-early Ordovician magmatism in the West Sudetes. An Archean inherited zircon age of ~ 3.4 Ga is one of the oldest zircon ages reported so far from the Bohemian Massif. The orthogneisses of the Karkonosze-Izera Massif (KIM) have calculated TDM ages of between 1.50 and 1.93 Ga, but these ages are not necessarily evidence for a Mid-Proterozoic crustal derivation: more probably, they reflect the average of several detrital components mixed into the granitoid magma sources. In spite of likely age differences, the Lusatian greywackes, which outcrop to the west, and the mica schists of the KIM display similar geochemical characteristics, suggesting that both could have been derived from similar sources. However, the presence of lower Ordovician products of within-plate volcanism - intercalations of quartzofeldspathic rocks and amphibolites within the mica schists - supports an idea that the mica schist protoliths, derived mainly from crustal rocks, could have also contained an admixture of contemporaneous volcanic materials. The age spectra of inherited zircons from the KIM orthogneisses and their Nd-isotopic signatures are comparable to the Lusatian greywackes: this suggests that the Lusatian greywackes, or very similar rocks, could have been the source material for the granitic protoliths of the KIM orthogneisses.

Geologia Sudetica, 41: 25-42.

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)

Krystyna Klimas¹, Ryszard Kryza¹ & Christopher Mark Fanning²

¹ Institute of Geological Sciences, Wrocław University, ul. Cybulskiego 30, 50–205 Wrocław, Poland; e‑mail: klim@ing.uni.wroc.pl
² Research School of Earth Sciences, The Australian National University, 0200 Canberra, Australia

Key words:  zircon, SHRIMP geochronology, anatexis, Strzelin Massif, Bohemian Massif, Fore-Sudetic Block, Variscides.

Abstract

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.

Geologia Sudetica, 41: 43-56.

New insights into the mineralization of the Czarnów ore deposit (West Sudetes, Poland)

Ksenia Mochnacka¹, Teresa Oberc-Dziedzic², Wojciech Mayer¹, Adam Pieczka¹ & Michał Góralski³

¹ Faculty of Geology, Geophysics and Environmental Protection, Department of Economic Geology, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland, e-mail: kmoch@geol.agh.edu.pl ; wmayer@geol.agh.edu.pl ; pieczka@geol.agh.edu.pl
² Institute of Geological Sciences, University of Wrocław, Plac M. Borna 9, 50-204 Wrocław, Poland, e‑mail: teresa.oberc‑dziedzic@ing.uni.wroc.pl
³ Faculty of Management, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland, e‑mail: mgoralsk@zarz.agh.edu.pl

Key words:  Karkonosze-Izera Massif, Izera-Kowary Unit, Czarnów Schist Formation, Czarnów deposit, arsenopyrite, pyrrhotite, geothermometry, fluid inclusions, hydrothermal mineralization.

Abstract

This paper provides new data on the mineralogy and mineral chemistry of the Czarnów ore deposit, a polymetallic vein that occurs within the eastern envelope of the Karkonosze Pluton (West Sudetes). New data are also provided on the deposits’ geothermometry, mineral succession, and origins.
The Czarnów ore vein is about 500 m long, strikes SW–NE, dips 80° SE and continues to a depth of 200 m. It is hosted within the albite-mica schists, quartzofeldspathic rocks and striped amphibolites that comprise the Czarnów Schist Formation (CSF); its western part is composed of almost monomineral arsenopyrite, whereas the southwestern part locally contains a pyrrhotite lens that extends downwards. Although many types of sulphides, sulphoarsenides, sulphosalts and native phases accompanied by oxides and arsenates have been previously reported, this paper describes four minerals that have not been previously identified from the Czarnów deposit: ferrokësterite, ikunolite, bismite and pentlandite. Geothermometry data suggest formation temperatures of arsenopyrite between 551 °C and 420 °C and that of sphalerite between about 400 °C to about 200 °C. Fluid inclusion data from vein quartz gave homogenization temperatures between 430 °C and 150 °C. Integrat on of textural and other data suggests the following primary mineral succession: early arsenopyrite and cassiterite as the high-temperature phases; then combinations of pyrrhotite, pyrite, chalcopyrite and sphalerite, all of which formed over a wide temperature range; finally, low temperature galena and Bi phases. Secondary weathering products overprint the primary sequences. Cataclasis of the first-formed arsenopyrite imply that mineralization was related to at least one tectonic event in the region. The Czarnów ore deposit probably resulted from hydrothermal activity associated with the near Karkonosze granite.

Geologia Sudetica, 41: 57-66.

Occurrence of the trace fossil Zoophycos from the Upper Viséan Paprotnia Beds of the Bardo Structural Unit (Sudetes, SW Poland)

Jolanta Muszer & Joanna Haydukiewicz

Institute of Geological Sciences, Wrocław University, ul. Cybulskiego 30, 50-205 Wrocław, Poland; e‑mails: jolanta.muszer@ing.uni.wroc.pl ; joanna.haydukiewicz@ing.uni.wroc.pl

Key words:  Zoophycos, trace fossils, Upper Viséan, Sudetes, Poland.

Abstract
This paper presents evidence for the first confirmed occurrence of the trace fossil Zoophycos from any geological unit of the Polish Sudetes. The Zoophycos specimens were found in the Lower Carboniferous fossil-rich Paprotnia Beds, which are located in the Bardo Structural Unit of the Sudetes. The beds belong to Goniatites crenistria Zone of the Upper Viséan and are thought to represent shallow-water platform deposits. Several dozen Zoophycos specimens were studied in detail, and two morphotypes (termed A1 and A2) of different sizes were distinguished. There was a marked concentration of Zoophycos trace fossils in the lower part of the Paprotnia section, the sediments of which we interpret as probably having been formed between storm wave base and fair-weather wave base within oxygenated water.

Geologia Sudetica, 41: 67-84.

Refining the granite, gneiss and schist interrelationships within the Lusatian–Izera Massif, West Sudetes, using SHRIMP U-Pb zircon analyses and new geologic data

Andrzej Żelaźniewicz^1,2, Christopher M. Fanning³ & Stanisław Achramowicz¹

¹ Instytut Nauk Geologicznych PAN, Podwale 75, 50-449 Wrocław, Poland; e‑mail: pansudet@pwr.wroc.pl
² Instytut Geologii, Uniwersytet Adama Mickiewicza, ul. Maków Polnych 16, 61-616 Poznań, Poland
³ RSES, the Australian National University, Canberra

Key words:  Bohemian Massif, granite, leucogranite, magma, orthogneiss, SHRIMP, zircon age.

Abstract
The eastern part of the Lusatian–Izera Massif, West Sudetes, comprises different types of gneissose rocks, collectively known as the Izera gneisses, with a subordinate component of petrographically varied mica schists. Coarse-grained gneisses and their protoliths have been dated at 515–480 Ma, but the lack of age data for other rocks has impeded accounts of their mutual relationships and, thus, the region’s geological evolution. This paper reports new sensitive high-mass resolution ion microprobe (SHRIMP) U-Pb zircon data, and some new field and petrographic observations, for three representative rock types: 1) the Złotniki schist (a fine-grained quartz–albite–chlorite–sericite–biotite schist); 2) a fine-grained gneiss that grades to ‘porphyroblastic’ granite and which occurs on the slopes of Mt. Stóg Izerski; 3) a leucogranite found just the south of the village of Kotlina. A volcanogenic intercalation in the Złotniki Lubańskie schists developed at 560 Ma and contained xenocrystic zircons that grew in the source at 620 Ma and 600–580 Ma. The schists are interpreted as the metamorphosed equivalent of the Lusatian greywackes, which were derived from a dissected arc and deposited in a convergent-margin basin along northern peri-Gondwana. The zircons from the fine-grained gneisses yielded four age groups: 515 ± 7 Ma, 500 ± 12 Ma, 487 ± 13 Ma and 471 ± 8 Ma. Similar age groups of zircons can also be found in the coarse-grained metagranites. Rifting of Gondwana during the mid-Cambrian–early Ordovician was a protracted thermal event lasting ~30–45 m.y., with episodic attenuation of the mainland crust every ~5–10 m.y. before continental fragments finally became separated. Each episode successively promoted an increased heat flux from the mantle that facilitated melting of the crust, causing metamorphism and fusion of the Precambrian Lusatian–Izera basement and a final phase of S-type felsic magmatism. The leucogranite sample yielded zircons in two age groups, 508 ± 5 Ma and 483.1 ± 3.6 Ma, with low Th/U ratios, which is interpreted as a product of an anatectic melting at deeper crustal levels. These leucogranites are in close spatial relation with belts of mica schist, which could mean that these granites used some rheologically weak zones that were introduced into the Izera pluton where large fragments of country rocks were trapped within the ~500 Ma granites.