Constraints on the Devonian-Carboniferous closure of the Rheic Ocean from a multi-method geochronology study of the Stare Mesto Belt in the Sudetes (Poland and the Czech Republic)

This paper attempts to clarify the complex nature of how and when the Rheic Ocean closed in what is now Central Europe and, with respect to the various terranes that were involved, offer a regional chronology for the associated structural, metamorphic and igneous processes that accompanied and followed this closure. The Variscan orogen in Europe originated from the multiple collisions of Gondwana-derived terranes (the Armorican Terrane Assemblage) with Laurussia: however, many important structural details on the timing of these collision-related events remain obscure. In the Sudetes, the Stare Mesto Belt represents a WNW-dipping part of the Rheic suture that developed from the continental collision of the eastern terranes of the Armorican Terrane Assemblage (now in the Bohemian Massif) with the Brunovistulian Terrane (a part of Laurussia/Old Red Continent). In this study, the results of monazite Th-U-total Pb, garnet Lu-Hf and zircon U-Pb geochronology were integrated into a newly established D1-D3 tectonometamorphic sequence. A Th-U-total Pb age of similar to 368 Ma from a monazite that grew concurrently with D2 metasedimentary garnet, as well as Lu-Hf ages of similar to 361 Ma and similar to 355 Ma obtained from D2 metasedimentaly garnets, implies that the regional contractional deformation and progressive metamorphism of D2 took place mainly during the Famennian (Late Devonian) and extended into the Visean (Middle Mississippian of the Early Carboniferous). The ion probe U-Pb zircon ages of similar to 355 Ma and similar to 359 Ma obtained from leucocratic neosomes in migmatized amphibolites confirmed a lag in the peak temperature that followed crustal thickening during D1-D2. Metamorphic monazites dated at similar to 340 Ma provide a time for the subsequent D3 dextral transpressional regime. The closure of the Stare Mesto Belt segment of the Rheic Ocean probably resulted from a head-on hard collision between the westerly subducting Brunovistulian promontory of Laurussia and the eastern members of the Armorican Terrane Assemblage. Thus, the Rheic Ocean closed during the Late Devonian at similar to 370-360 Ma and preceded the collision of the Armorican Terrane Assemblage with East Avalonia at the western margin of what is now the Bohemian Massif. Following ocean closure, the Rheic slab may have broken off, resulting in the suture zone becoming dominated by lateral tectonic escape movements of the colliding terranes at similar to 340-330 Ma (Visean). Syntectonic D3 intrusions of granodiorite/tonalite magma acted as a hot lubricant and stitched the suture zone together. (C) 2013 Elsevier B.V. All rights reserved.