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[Display omitted] • Western juvenile and eastern mature Ordovician arcs intruded the Altai wedge. • Late Ordovician–Silurian volcanic gaps were related to Altai wedge thickening. • An early Devonian back-arc formed in the western part of the Altai wedge. • Back-arc extension migrated to the east in the late Devonian. • This diachronous evolution resulted from lateral variations in subduction modes. The early Palaeozoic volcano–sedimentary evolution of the Khovd and Gobi-Altai zones of the Mongol–Altai Domain was investigated by quantitative petrographic analysis of sediments, whole-rock geochemistry of volcanic rocks, and U–Pb zircon dating. Three evolutionary stages were identified in the Khovd Zone: (1) Cambrian–mid Ordovician basaltic (Nb/Yb = 0.09–1.25) and rhyodacitic (Nb/Yb = 4.36) volcanism and sedimentation of immature greywackes in the fore-arc basin in front of the juvenile continental arc, (2) late Ordovician flysch-type sedimentation accompanied by a volcanic gap coincided with Barrovian metamorphism in footwall sequences reflecting a compressional stage, and (3) Silurian–Devonian within-plate bimodal volcanism (with a strong asthenospheric imprint; Nb/Yb = 4.45–20.34) followed by mature siliciclastic deposition interpreted as transformation of the former fore-arc region into a back-arc domain associated with HT metamorphism. In the Gobi-Altai Zone the three stages were: (1) Cambro–Ordovician marginal greywacke–sandstone succession adjacent to a mature continental arc (mafic rocks Nb/Yb = 0.71–4.36), (2) Silurian siliciclastic sedimentation associated with migration of the volcanic gap and Barrovian metamorphism, and (3) Lower Devonian deep-marine sedimentation followed by shallow-marine carbonate sedimentation, initially accompanied by calc-alkaline basalts (Nb/Yb = 0.74–4.57) and andesites to rhyolites (Nb/Yb = 0.69–4.87), evolving in the mid–late Devonian to within-plate alkali basalts (Nb/Yb = 11.05) thus reflecting back-arc basin development. These temporal and spatial variations in the Mongol-Altai Domain are interpreted as a diachronous sequence of retreating and advancing subduction modes instead of juxtaposition of suspect terranes as proposed in previous studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Contrasting detrital zircon age and Hf isotopic patterns of Brunovistulian basement. • Rodinia internal or peripheral position and Baltica/Amazonia sources in Tonian. • Ediacaran deposition in a back-arc basin with active magmatic arc dominant source. • Transition from Rodinia formation/break-up to Gondwana or Baltica active margin. • Model of the Bohemian Massif as a single Neoproterozoic crustal domain. In this study, U–Pb ages and Hf isotopic composition of detrital zircons from the Precambrian metasedimentary autochthon of the Brunovistulian Domain in the eastern Bohemian Massif were investigated to understand the pre-collisional evolution of the eastern periphery of the European Variscan belt. Detrital zircons of the Tonian sequences have mostly Paleoproterozoic to Neoproterozoic ages (c. 2.1–0.9 Ga) and are interpreted as detritus derived from the basement of either Baltica or Amazonia. The mostly positive ε Hf(t) values (–4 to + 16) indicate a juvenile nature of their magma sources with minor older crustal components. In contrast, the Ediacaran sequences contain dominantly Neoproterozoic zircons (c. 600 Ma) and only rare Paleo- and Mesoproterozoic ages indicate that they were sourced from the adjacent Neoproterozoic magmatic arc with very limited input of recycled cratonic detritus. The large spread of ε Hf(t) values (–15 to + 13) of the Neoproterozoic zircons suggests significant mixing of mantle-derived magmas with mature crustal material, typical of large continental magmatic arc systems. The zircon age patterns of the Ediacaran sequences, characterized by a dominance of the late Neoproterozoic zircons and limited Mesoproterozoic zircons, are nearly identical to those from the Teplá–Barrandian Unit and Moldanubian Zone, pointing to their similar sources. We consider such age populations as a record of sources actually exposed at the time of deposition, rather than the real provenance signature of the continental basement. The change in detrital zircon U–Pb age and Hf record of the Brunovistulian Domain took place between the early and late Neoproteorozoic, and probably reflects the plate-tectonic reconfiguration from the Rodinia formation/break-up to the evolution of the Gondwana or Baltica active margins. Our data challenge the main arguments for an existence of the Rheic oceanic suture between the Brunovistulian Domain and Moldanubian Zone and allow for an alternative pre-collisional model of the Bohemian Massif as a single Neoproterozoic crustal domain. [ABSTRACT FROM AUTHOR]