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

Abstract

The Staré Mìsto Belt (SMB) in the Cen tral Sudetes forms a Variscan tec tonic bound ary zone that is lo cated be tween the Saxothuringian and Brunovistulian ter ranes of the Bo he mian Mas sif. The three thrust-bounded up per, mid dle and lower lithotectonic units of the SMB are com posed of metasedimentary and Late Cam brian meta vol can ic rocks. A new LA-ICP-MS zir con geo chron ol ogy sup ported by zir con typology stud ies of the mica schists of the up per unit and the migmatitic paragneisses of the mid dle unit pro vides new in sights into the prov e nance and evo lu tion of the SMB. Our new data were ob - tained from metasedimentary rocks and com pared to the pre vi ously pub lished zir con ages of the SMB meta vol can ic rocks. The re sults in di cate that the metasedimentary and bi modal meta vol can ic rocks in the sep a rate lithotectonic units of the SMB orig i nally formed Late Cam brian vol cano-sed i men tary suc ces sions. The source ar eas of the sed i men tary bas ins stud ied were dom i nated by Neoproterozoic and Paleoproterozoic crys tal line rocks that were pre sum ably lo cated near the West Af ri - can Craton of Gond wana. A com par i son of the de tri tal age spec tra ob tained with those pre vi ously pub lished from the re gion in di cates a strong as so ci a tion of the en tire SMB with the Saxothuringian terrane of the Bo he mian Mas sif. Dur ing par tial melt - ing of the metasedimentary rocks of the mid dle unit of the SMB, Cam brian and older zir con grains were af fected by solid-state trans for ma tions that caused par tial re set ting of the U-Pb dates, changes in in ter nal zir con tex tures and re duc tions in Th/U ra tios.