New data on the Neoproterozoic ? Cambrian geotectonic setting of the Tepl�-Barrandian volcano-sedimentary successions: geochemistry, U-Pb zircon ages, and provenance (Bohemian Massif, Czech Republic)

Abstract

The Teplµ-Barrandian unit (TBU) of the Bohemian Massif was a part of the Avalonian-Cadomian belt at the northern margin of Gondwana during Neoproterozoic and Early Cambrian times. New detrital zircon ages and geochemical compositions of Late Neoproterozoic siliciclastic sediments confirm a deposition of the volcano-sedimentary successions of the TBU in a back-arc basin. A change in the geotectonic regime from convergence to transtension was completed by the time of the Precambrian-Cambrian boundary. The accumulation of around 2,500 m Lower Cambrian continental siliciclastics in a Basin-and-Range-type setting was accompanied by magmatism, which shows within-plate features in a few cases, but is predominantly derived from anatectic melts displaying the inherited island arc signature of their Cadomian source rocks. The geochemistry of clastic sediments suggests a deposition in a rift or strike-sliprelated basin, respectively. A marine transgression during Middle Cambrian times indicates markedly thinned crust after the Cadomian orogeny. Upper Cambrian magmatism is represented by 1,500 m of subaerial andesites and rhyolites demonstrating several geochemical characteristics of an intra-plate setting. Zircons from a rhyolite give a U-Pb-SHRIMP age of 499€4 Ma. The Cambrian sedimentary and magmatic succession of the TBU records the beginning of an important rifting event at the northern margin of Gondwana.

Nomenclature of Cambrian lithostratigraphy of the Skryje-Týřovice Basin

“…The nature of quartzitic grains and the other lithoclasts fit well with their provenance from the adjacent Neoproterozoic sequences (see also Drost et al 2004Drost et al , 2007.…”

“…1B). The Cambrian sedimentary sequence is overlain by extrusive rocks (dacites, andesites and rhyolites) of the Křivoklát-Rokycany Complex, Furongian to earliest Ordovician in age (Drost et al 2004).…”

Sm–Nd isotope geochemistry and tectonic setting of the metasedimentary rocks from the basal allochthonous units of NW Iberia (Variscan suture, Galicia)

“…These are generally highly deformed and variably metamorphosed azoic metasedimentary series; consequently little information can be obtained from traditional studies based in paleontology or stratigraphy. In these cases, provenance anal ysis based in U-Pb dating of detrital zircons can be a complement to major and trace element geochemistry and Sm-Nd systematics (Dlez Femandez et al, 2010;Drost et al, 2004;Iinnemann and Romer, 2002;Linnemann et al, 2004). In favourable situations, these data allow to determine the tectonic setting and location of the sedimentary pal eo-basins.…”

“…Only few works have applied so far this methodology in the metasedimentary rocks of the Variscan Belt (Fuenlabada et al, 201 0;linnemann et al, 2004, 2007Ugidos et al, 2003 the margin of Gondwana (Fig. 1 a).…”

Cambrian biostratigraphy in the Příbram-Jince Basin (Barrandian area, Czech Republic)

“…Unfossiliferous sandstones of the Ohrazenice and Pavlovsko formations cap the Jince Formation and mark the end of sedimentation before the onset of the late Cambrian volcanites of the Strašice Volcanic Complex (e.g. Drost et al 2004). Consequently, only the Paseky Shale and the Jince Formation can be subdivided biostratigraphically.…”