Single zircon U–Pb ages and geochemistry of granitoid gneisses from SW Poland: evidence for an Avalonian affinity of the Brunian microcontinent

Abstract

Seven granitoid gneisses from the contact zone between the eastern margin of the Variscan belt and the Brunian microcontinent in SW Poland have been dated by ion-microprobe and207Pb/206Pb single zircon evaporation methods. The zircons define two age groups for the gneiss protoliths: (1) late Neoproterozoicc.576–560 Ma and (2) early Palaeozoicc.488–503 Ma granites. The granitoid gneisses belonging to the basement of the Brunian microcontinent contain abundant Mesoproterozoic to latest Palaeoproterozoic inherited material in the range of 1200–1750 Ma. The gneisses of the Variscan crustal domain lack Mesoproterozoic inherited zircon cores. Trace element geochemistry of Proterozoic gneisses reveals features resembling either volcanic arc or post-collisional granites. The studied rocks are geochemically similar to other Proterozoic orthogneisses derived from the basement of the Brunian microcontinent. Gneisses with early Palaeozoic protolith ages are geochemically comparable to granitoid gneisses widespread in the adjacent Sudetic part of the Bohemian Massif and are considered characteristic of peri-Gondwanan crust. Our data prove the dissimilarity between the Brunia plate and the westerly terranes of the Variscan belt. The occurrence of granitic gneisses with late Neoproterozoic protolith ages and widespread Mesoproterozoic inheritance in our dated samples support an East Avalonian affinity for the Brunian microcontinent. In contrast, the abundance of gneisses derived from an early Palaeozoic granitic protolith and devoid of Mesoproterozoic zircon cores supports the Armorican affinity of the Variscan domain bordering on the Brunia plate from the west. Structural evidence shows that the eastern segment of the Variscan belt is juxtaposed against the Brunian microcontinent along a N–S-trending tectonic contact, possibly equivalent to the Rheic suture.

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

“…The lower unit com prises rocks of the Strzelin Com plex, spe cif i cally, the Strzelin and Nowolesie gneiss es (600-570 Ma, Oberc-Dziedzic et al, 2003;Klimas, 2008;Klimas et al, 2009;Mazur et al, 2010), the older schist se ries of mica schists, amphi bo lites, calc-sil i cate rocks and mar bles of un known age, and the youn ger schist se ries (prob a bly Early De vo nian in age, Oberc, 1966), rep re sented by quartzites, quartz-seri cite schists and metaconglomerates of the Jeg³owa Beds. The rocks of the lower unit be long to Brunovistulicum (Oberc-Dziedzic and Madej, 2002;Oberc-Dziedzic et al, 2003.…”

Lithosphere thermal structure at the eastern margin of the Bohemian Massif: a case petrological and geophysical study of the Niedźwiedź amphibolite massif (SW Poland)

“…The thrust is readily recognisable in the Sudetes, whereas its location in the Fore-Sudetic Block is debatable ( Fig. 1; Oberc-Dziedzic and Madej 2002;Mazur et al 2010 and references therein).…”

“…Mazur and Józefiak 1999; Mazur et al 2010), and thus, the rocks cropping out to the east of the Niedźwiedź Massif are good candidates to occur beneath the Niedźwiedź Massif. The Niedźwiedź Massif is situated in the part of the Fore-Sudetic Block which is extremely poor in exposures of basement rocks, which are covered by Cenozoic sediments of thickness reaching a few hundred metres.…”

“…The Maciejowice gneisses are usually considered to be a part of the MoravoSilesian Zone (e.g. Mazur et al 2010), although ObercDziedzic and Madej (2002) propose that they may be thrust sheet of Western Sudetic origin.…”

Sequential granite emplacement: a structural study of the late Variscan Strzelin intrusion, SW Poland

“…The lower structural unit-the footwall of the Strzelin Thrustbelongs to Brunovistulicum. This unit is composed of the Strzelin Complex containing orthogneisses of c. 600-570 Ma (Oberc-Dziedzic et al 2003Klimas 2008;Mazur et al 2010). The upper structural unit-the hanging wall of the Strzelin Thrust-belongs to Moldanubicum (sensu Aleksandrowski and Mazur 2002).…”