Lithogeochemistry and Sr-Nd isotopic composition of Neoproterozoic metasedimentary rocks of the Teplá Crystalline Complex, western Bohemian Massif: a geotectonic interpretation

Clastic metasedimentary rocks from the Tepla Crystalline Complex (western Bohemian Massif) were analysed for major and trace elements, Sr and Nd isotopes. The metamorphic grade of these rocks of presumed Neoproterozoic protolith age increases from SE to NW from very low-grade to amphibolite-facies conditions. Geochemistry indicates that the sedimentary protoliths for the whole sequence consisted of immature (pelitic) greywackes chiefly derived from an ensialic island arc. No significant changes in composition from the lowest to the highest grade or across the strike of isograds were observed. Chemical variations between original slates and greywackes within a single locality often considerably exceed the variation among samples of different metamorphic grades or of different geographic positions. The prevailing REE spectra with distinct negative Eu anomalies show a close similarity with those of modern turbidites from ensialic island arcs. Several samples without any Eu anomaly resemble the REE patterns of less differentiated island arc andesites. LREE leaching under oxidizing conditions is suggested by several REE patterns with positive Ce anomalies. The Sm–Nd model ages TDM of samples with Ce positive anomalies are higher (TDM 1.8–2.0 Ga) than those of all other samples (TDM = 1.1–1.5 Ga). Initial Sr isotopic ratios for all samples are fairly constant and compatible with an assumed dominance of isotopically less evolved detrital material. Geochemical characteristics of the clastic metasediments of the Tepla Crystalline Complex are thus consistent with a model of incorporation and preservation of arc-derived sediments in a Cadomian accretionary wedge.