Cadomian protolith ages of exotic mega blocks from Bugaj and Andrychów (Western outer Carpathians, Poland) and their palaeogeographic significance

Abstract

This study presents the first zircon U-Pb LA-MC-ICP-MS ages and whole-rock Rb/Sr and Sm/Nd data from exotic blocks (Bugaj and Andrychów) from the Western Outer Carpathians (WOC) flysch. The CL images of the zircon crystals from both samples reveal typical magmatic textures characterized by a well-defined concentric and oscillatory growth zoning. A concordia age 580.1 ± 6.0 Ma of the zircons from the Bugaj sample is considered to represent the crystallization age of this granite. The zircon crystals from the Andrychów orthogneiss yield an age of 542 ± 21 Ma, interpreted as the uppermost Proterozoic, magmatic crystallization age of the granitoid protholith. The initial (at ca. 580 Ma) 87Sr/86Sr ratios of the Bugaj granitoids (0.72997 and 0.72874) are highly radiogenic, pointing to the assimilation of an older, possibly strongly Rb enriched source to the Bugaj melt. The Nd isotope systematics (εNd580 –1.4 and 0.4) also point to a significant contribution of such a distinct mantle source. On the basis of the sequence of magmatic events obtained from U-Pb zircon ages, we suggest that exotic mega blocks deposited to the WOC basins were related to the Brunovistulicum Terrane. They belong to the group of Vendian/Cambrian granitoids representing the latest, posttectonic expression of the Cadomian cycle.

Neoproterozoic crystalline exotic clasts in the Polish Outer Carpathian flysch: remnants of the Proto-Carpathian continent?

“…25-2.7 Ga;Michalik et al 2006;c. 1.7-1.8 Ga and c. 2.1 Ga;Burda et al 2019), which are consistent with a Svecofennian provenance, suggest Baltican affinity of the inherited zircon fraction (e.g. Wiszniewska et al 2007 and references therein), without any typical Gondwanan signature.…”

“…Earlier studies of exotic clasts from the Silesian Nappe also yielded similar ages (610 ± 6 Ma; 604 ± 6 Ma and 599 ± 6 Ma; Budzyń et al 2011; 580 ± 6 Ma and 542 ± 21 Ma; Burda et al 2019) potentially also implying a linkage between the Silesian Ridge and Brunovistulia. The granite from Nowe Rybie yields the youngest age in this study (565.5 ± 2.9 Ma) and overlaps in age with the youngest age population obtained from the basement of the Upper Silesia Coal basin and exotic clasts of inferred Brunovistulian provenance in the Outer Carpathians (Burda et al 2019), Cadomian pebbles within glaciomarine deposits on the Bohemian massif (Linneman et al 2018), as well as the Svratka Dome metagranite from Brunovistulia, which also shares a similar age and geochemistry (Soejono et al 2017). These data support inferences that the Proto-Carpathian basement represents the eastern continuation of Brunovistulia.…”

“…1 A simplified geological sketch of the Carpathian Chain within the Europe with the location of the study area in the Outer Western Carpathians (a) and the geological map of the Polish Outer Carpathi-ans with the locations of the sampling points (b). Modified from Starzec et al (2017) the only remnants of the Proto-Carpathian basement and are poorly characterized and understood; the majority is being derived from the Silesian Ridge (Budzyń et al 2011;Burda et al 2019).…”

Tracing Pre-Mesozoic Tectonic Sutures in the Crystalline Basement of the Protocarpathians: Evidence from the Exotic Blocks from Subsilesian Nappe, Outer Western Carpathians, Poland

“…The Protocarpathian region is characterized by the Neoproterozoic basement overlain by Upper Paleozoic sedimentary sequences, similar to the Brunovistulia and Małopolska massifs [5,48,49]. As was previously mentioned, the other analyses of the Subsilesian exotics indicate the prevailing Neoproterozoic (Cadomian) age of the substratum in this area [5,13,14]. The Neoproterozoic rocks of the Protocarpathian basement were the source for the Variscan magmas formation, which subsequently was emplaced within this Late Variscan transpressional zone.…”

“…It included the Central Carpathian collisional zone The Subsilesian Ridge, the source of the exotic clasts, was surrounded by a slope region characterized by mixed pelagic and turbiditic sedimentation that corresponds to the Subsilesian Sedimentary Zone. The large size of these blocks (more than 1 m in diameter, locally up to some tens of meters or even more than 100 m in diameter-see [14])indicates short transport distances and intense tectonic activity during the deposition of the host Campanian-Maastrichtian grey marls [57] on the slope of the Subsilesian Ridge. This tectonic activity may have triggered earthquakes (see e.g., [58]) and produced mélange complexes.…”