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

Abstract

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.

Provenance of the early Palaeozoic volcano-sedimentary successions from eastern part of the Central Sudetes: implications for the tectonic evolution of the NE Bohemian Massif

“…Kamieniec Metamorphic Belt (this work), 4b. Doboszowice Crystalline Massif (this work and Jastrzębski et al 2023), 4c – Lipowe Hills (Oberc-Dziedzic et al 2018); 4d. Kamieniec Metamorphic Belt (Jastrzębski et al 2020); 5.…”

“…However, more recently published U-Th-Pb monazite data indicate that DMC experienced metamorphic episode at ca. 346–340 Ma (Jastrzębski et al 2023). This is confirmed by Lu-Hf and Sm-Nd garnet dating of the Chałupki paragneiss, which shows that these rocks were metamorphosed between 347 ± 3.6 Ma and 337.3 ± 6.6 Ma (Szczepański et al 2022).…”

“…The protolith age of the volcano-sedimentary successions exposed in the KMB and DMC is poorly known. Available data suggest that the maximum depositional age (MDA) of the KMB and the adjacent Lipowe Hills mica schists is in the range of c. 560–570 Ma (Oberc-Dziedzic et al 2018; Jastrzębski et al 2020), while the Chałupki paragneiss from the DMC has a late Cambrian MDA (Jastrzębski et al 2023).…”

“…The DMC may be divided into a western and an eastern parts. The western part exposes the Doboszowice orthogneiss with protolith age dated on zircons using U-Pb SHRIMP at 488 ± 6 Ma (Mazur et al 2010) or at 494 ± 5 Ma using U-Pb ICP-MS (Jastrzębski et al 2023). The eastern part is mainly composed of the migmatic Chałupki paragneiss interleaved with scarce mica schists and metabasalts of unknown age (Fig.…”

“…670 o C and 8 kbar (Puziewicz et al 1999;Szczepański & Marciniak, 2018). The age of the tectonothermal event recorded in the KMB has recently been estimated at c. 330 Ma (Jastrzębski et al 2020) and in the DMC at c. 346-341 Ma based on ICP-MS U-Th-Pb dating of monazite (Jastrzębski et al 2023). This is in agreement with Lu--Hf and Sm-Nd garnet dating of the Chałupki paragneiss, which shows that these rocks were metamorphosed between 347 ± 3.6 Ma and 337.3 ± 6.6 Ma (Szczepanski et al 2022).…”