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pdf file. Same as Figure 11 of main text, using TAS diagram (Middlemost 1994)

pdf file. Same as Figure 11 of main text, using the SiO2–Fe number diagram of Frost et al. (2001)

pdf file. Same as Figure 11 of main text, using the normative Ab–An–Or diagram of O'Connor (1965)

pdf file. Same as Figure 11 of main text, using the R1–R2 diagram of De la Roche et al. (1980)

pdf file. Same as Figure 11 of main text, using SiO2–α diagram. α is defined as α = (Al – Na – K)/Ca, in atomic proportions, i.e. the parameter such that Al = αCa + Na + K. Thus, A/CNK = 1 corresponds to α = 2, and A/NK = 1 to α = 0 (see main text)

pdf file. Same as Figure 11 of main text, using the projection from biotite defined by Moyen et al. (2017). See also Figure 4

pdf file. Same as Figure 11 of main text, using Shand's (1927) diagram

The Letovice Complex, composed of metamorphosed enriched mid-ocean ridge basalts with trondhjemitic sheets, as well as gabbroic and ultrabasic bodies, is exposed within an important Variscan suture separating the Moldanubian Domain (to the west) from the Brunovistulicum (to the east) in the eastern part of the Bohemian Massif, Czech Republic. A polyphase tectonic evolution of the study area was connected with underthrusting and subsequent exhumation of the former oceanic realm, which resulted in three deformation phases (D 1 –D 3 ). New U–Pb laser ablation inductively coupled plasma mass spectrometry dating of magmatic zircons from amphibolite and trondhjemite yielded statistically identical concordia ages of 530 ± 6 Ma and 529 ± 7 Ma (2σ), respectively. These are interpreted as dating intrusions of the Early Cambrian protoliths of the studied rocks. Based on this age as well as whole-rock geochemical and Nd isotopic data, the Letovice Complex is interpreted as a vestige of an incipient oceanic basin developing on attenuated crust. The most likely geotectonic setting was a post-Cadomian extensional regime at the northern margin of Gondwana that marked the onset of its break-up. Supplementary material: Photomicrographs of microstructures, sample locations, descriptions of analytical techniques, and selected electron microprobe analyses of the main rock-forming minerals are available at http://www.geolsoc.org.uk/SUP18424.

The Variscan Central Bohemian Plutonic Complex crops out between the upper-crustal Tepla–Barrandian and the high-grade Moldanubian units (Bohemian Massif). Much of the complex is made up of calc-alkaline plutonic rocks: (1) the geochemically more primitive, Na-rich 354 ± 4 Ma Sazava suite, which was emplaced syntectonically during regional shortening; (2) the younger, more evolved, potassic Blatna suite, which records both the shortening along its NW contact and the onset of normal shearing related to exhumation of the Moldanubian Unit to the SE. New ion microprobe U–Pb zircon ages for the high-K calc-alkaline Blatna suite pinpoint this major switch in the tectonic regime. Both Blatna and Kozarovice granodiorites (346 ± 2 Ma and 347 ± 2 Ma (2σ)) were generated by melting of heterogeneous crust and were emplaced contemporaneously to form the Blatna composite pluton. From age spectra preserved in inherited zircons and whole-rock Sr–Nd isotope signatures, the likely crustal sources for the magmas were immature greywackes rich in Neoproterozoic (615 ± 10 Ma, Kozarovice) or Late Cambrian–Early Ordovician (492 ± 4 Ma, Blatna) volcanogenic detritus. An additional important petrogenetic process was variable mixing with enriched mantle-derived monzonitic magmas, which may also have supplied the extra heat for crustal anatexis. Supplementary material: Analytical techniques, selected whole-rock major- and trace-element geochemical analyses and U–Th–Pb data are available at http://www.geolsoc.org.uk/SUP18391.

The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Tepla-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Tepla-Barrandian middle crust along the so-called Tepla suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Tepla-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root's massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Tepla suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes.