The Cambrian volcanic arc terrane: a peri-East European Craton assemblage in the heart of the European Variscan Belt

Cambrian age volcanic arc-related rocks crop-out in high-grade metamorphic complexes marking the principal Devonian age suture zone in the Bohemian Massif. The age and tectonic setting of these rocks are established from whole-rock geochemical and isotopic data from basic-intermediate rocks transformed to eclogite and granulite, and U-Pb and Lu-Hf isotopic data of detrital zircon in associated meta-sediments. Recent works have established that these rocks can be correlated on the basis of their age and tectonic setting as well as their Variscan metamorphic evolution with allochthonous complexes in NW Iberia, and potentially, the whole European Variscan Belt (Martínez Catalán et al., 2020). Detrital zircon spectra from the high-grade metasediments associated with the Cambrian volcanic arc are superficially similar to the classically interpreted ‘West African signature’ with Neoarchean, Paleoproterozoic and late Neoproterozoic maxima. Nonetheless, limited Cryogenian input and shifting of the late Neoproterozoic maxima into the early Cambrian is in contrast to Variscan autochthonous complexes. Moreover, Lu-Hf isotopic data show important contrasts in the source of the Paleoproterozoic detritus. The Variscan autochthon is charecterised by Paleoproterozoic detritus with negative ɛHf_i values indicating reworking of an Archean crust. However, the Paleoproterozoic detritus in the Cambrian arc terrane exhibits mostly positive ɛHf_i values indicating a juvenile Paleoproterozoic source.

In fact, the data from the Cambrian arc terrane show remarkable similarity to detrital zircon data from early Cambrian sediments on the southern margin of the East European Craton (Paszkowski et al., 2021). These sediments incorporate significant juvenile late Neoproterozoic-early Cambrian detritus from an as yet unidentified volcanic arc and their whole-rock geochemical composition is consistent with immature sediments sourced from intermediate igneous rocks. If true, this correlation suggests that the Cambrian arc terrane is a peri-East European Craton assemblage and necessitates a re-evaluation of the role of the East European Craton within the Variscan Orogeny.

Catalán, J. R. M., Collett, S., Schulmann, K., Aleksandrowski, P., and Mazur, S., 2020. Correlation of allochthonous terranes and major tectonostratigraphic domains between NW Iberia and the Bohemian Massif, European Variscan belt. International Journal of Earth Sciences, 109, 1105-1131.

Paszkowski, M., Budzyń, B., Mazur, S., Sláma, J., Środoń, J., Millar, I.L., Shumlyanskyy, L., Kędzior, A. and Liivamägi, S., 2021. Detrital zircon U-Pb and Hf constraints on provenance and timing of deposition of the Mesoproterozoic to Cambrian sedimentary cover of the East European Craton, part II: Ukraine. Precambrian Research, 362, 106282.