ABSTRACT The very first scientific paper by Eduard Suess (1831–1914) treats the graptolites of Bohemia in the present-day Czech Republic (in the Upper Proterozoic to Middle Devonian “Barrandian” extending between Prague and Plzeň). This paper is accompanied by superb drawings of his observations in which Suess took great care not to insert himself between Nature as he perceived it in the framework of the knowledge of his day and his readers. His only limitation was the one imposed by the size of his study objects. His technological means did not allow him to see what we today consider the “right” picture. Nevertheless, we can see what he saw and interpret it through a modern lens of understanding. In his drawings, Suess exercised what the great German geologist Hans Cloos later called “the art of leaving out.” This meant that in the drawings, the parts not relevant to the discussion are left only in outline, whereas parts he wished to highlight are brought to the fore by careful shading. Even the parts left only in outline are not schematic, however; instead they are careful reconstructions true to Nature as much as the material and his technological aids allowed. This characteristic of Suess’ illustrations is seen also in his later field sketches concerning stratigraphy and structural geology and in his depiction of the large tectonic features of our globe representing a window into his manner of thinking.

Nd-Sr-Pb isotope data are used to characterize the sources of Late Neoproterozoic and Early Paleozoic siliciclastic rocks of the Teplá-Barrandian unit of the Bohemian Massif. Geochemical and isotopic signatures of samples from different stratigraphic levels reflect changing sources and weathering conditions through time and allow a correlation with shifting geotectonic regimes. Late Neoproterozoic rocks were deposited in a magmatic arc–related setting within the Avalonian-Cadomian belt at the periphery of West Gondwana. Fine-grained graywackes yield crustal residence ages (T DM ) of 2.17–1.49 Ga, documenting contributions of old crust. Their ϵNd 570 values, as well as Pb and Sr isotopic compositions, reflect mixing of detritus derived from old crust with a Neoproterozoic magmatic arc component. The change in the geo-tectonic regime to transtension/rifting occurred during the terminal Neoproterozoic and is documented by more radiogenic ϵNd T values (−6.0 to +1.0) and younger T DM (1.65–1.12 Ga) of the Cambrian sediments. Besides the involvement of a post-Neoproterozoic juvenile source, the Lower Cambrian basin was also fed from an old upper crustal domain, as indicated by their high 207 Pb/ 206 Pb values. In contrast, Middle Cambrian siliciclastic rocks are mainly derived from the Cadomian basement. In the Ordovician pelites, ϵNd T values of −9.6 to −8.3 and radiogenic Sr and Pb isotopic compositions reflect an increasing input of material derived from the cratonic hinterland. Their T DM values range from 2.02 to 1.88 Ga. The uniform geochemical and isotopic compositions of the Ordovician samples indicate efficient mixing of the detritus prior to deposition in a mature rift or shelf environment at the Gondwanan margin.

On the basis of immobile trace elements and Nd isotope signatures, the Barrandian meta-basalts may be ascribed to two major groups, extracted from contrasting mantle sources: A depleted group, with strong light rare earth element depletion, elevated Zr/Nb ratios (>30), and highly radiogenic Nd isotopes (ϵNd 600 from +7.8 to + 9.3). Multi-element patterns normalized to normal mid-ocean ridge basalt all show negative anomalies of Nb, and to a lesser degree, Zr and Ti. Eight samples may define a 605 ± 39-Ma whole-rock isochron with ϵNd i of +8.8 ± 0.2. An enriched group, comprising both mildly enriched (Zr/Nb 12–18) and strongly enriched (Zr/Nb 4–7) samples, with ϵNd 600 ranging from +8.2 to +3.8. The depleted group is interpreted to reflect generation from depleted mantle sources fluxed by subduction-related components, probably in an intraoceanic back-arc basin. In contrast, the younger enriched group is typical of the within-plate style of mantle enrichment and documents the extinction of the subduction-related component. The switch from suprasubduction zone to within-plate magmatism suggests that new mantle material flowed into the former arc and back-arc system sources. This flow might have occurred simply as a result of ocean-ward migration of the subduction zone. Alternatively, the subduction fluxing might have stopped as a result of impingement of a spreading ridge with the intraoceanic trench, leading to mutual annihilation, a switch to a transform plate boundary, and opening of a slab window that allowed the inflow of new mantle and the generation of late-stage, within-plate enriched basalts. In terms of modern analogues, the Neoproterozoic of the Barrandian and other Cadomian regions of western Europe resemble arc and back-arc systems from the western Pacific region, where large intraoceanic subduction systems fringe major continental masses with a complex mosaic of microplates and magmatic arcs, including intervening basins floored either by oceanic crust or attenuated continental crust.