Spinel lherzolites of the Northern Kraka massif (Southern Urals): first REE ID-ICP-MS,87Sr/86Sr AND147Sm-143Nd AL ID-TIMS isotope constrains

Abstract

The results of a REE ID-ICP-MS,86Sr/87Sr and147Sm-143Nd AL ID-TIMS study of the isotope systematics of spinel lherzolites from the northern Kraka massif, which is part of the largest (more than 900 km2) lherzolite allochthon thrust over the bathyal and shelf deposits of the passive continental margin, East European platform are presented. As a result, an isochron dependence (MSWD = 0.85) was revealed for the first time, which determines the age of 545±26 Ma and the high value of the initial ratio (143Nd/144Nd)0 = 0.512390±0.000054, corresponding, within the framework of model representations, to εNd = +8.9. The resulting REE,87Sr/86Sr, and147Sm-143Nd isotopic signatures indicate the melting of an already depleted protolith, which can be identified as a mantle source, with MORB-like parameters. The isochron age calculated in the framework of the147Sm-143Nd AL ID-TMS study, in combination with the available complex of geological and geochemical data, allows us to state the manifestation of the Late Vendian phase (epoch) of folding and orogeny in the Urals in the interval of 545 ± 26 Ma. Comparison of these data with materials on the geology of Central and Western Europe makes it possible to correlate the Timanid structures formed as a result of this phase of folding with Cadomides, which ultimately, based on global reconstructions of continents for the end of the Proterozoic, will authorize the hypothesis of the existence of the Cadomian orogen on the periphery of Gondwana.