Detrital zircon analysis of metasedimentary rocks of the Stare Most Belt, Sudetes: implications for the provenance and evolution of the eastern margin of the Saxothuringian terrane, NE Bohemian Massif

The Stare Mesto Belt (SMB) in the Central Sudetes forms a Variscan tectonic boundary zone that is located between the Saxothuringian and Brunovistulian terranes of the Bohemian Massif. The three thrust-bounded upper, middle and lower lithotectonic units of the SMB are composed of metasedimentary and Late Cambrian metavolcanic rocks. A new LA-ICPMS zircon geochronology supported by zircon typology studies of the mica schists of the upper unit and the migmatitic paragneisses of the middle unit provides new insights into the provenance and evolution of the SMB. Our new data were obtained from metasedimentary rocks and compared to the previously published zircon ages of the SMB metavolcanic rocks. The results indicate that the metasedimentary and bimodal metavolcanic rocks in the separate lithotectonic units of the SMB originally formed Late Cambrian volcano-sedimentary successions. The source areas of the sedimentary basins studied were dominated by Neoproterozoic and Paleoproterozoic crystalline rocks that were presumably located near the West African Craton of Gondwana. A comparison of the detrital age spectra obtained with those previously published from the region indicates a strong association of the entire SMB with the Saxothuringian terrane of the Bohemian Massif. During partial melting of the metasedimentary rocks of the middle unit of the SMB, Cambrian and older zircon grains were affected by solid-state transformations that caused partial resetting of the U-Pb dates, changes in internal zircon textures and reductions in Th/U ratios.

Automated summary

The Stare Mesto Belt in the Central Sudetes is a tectonic boundary zone composed of metasedimentary and metavolcanic rocks. New research suggests that these rocks originally formed in the Late Cambrian volcanic sedimentary successions, with the sedimentary basins dominated by Neoproterozoic and Paleoproterozoic crystalline rocks. Comparisons with previous studies indicate a strong association between the Stare Mesto Belt and the Saxothuringian terrane. Partial melting of the middle unit's metasedimentary rocks caused the resetting of U-Pb dates.