PALEOZOIC AMPHIBOLITE-GRANULITE FACIES MAGMATIC COMPLEXES IN THE HINTERLAND OF THE URALIDE OROGEN

Abstract

Within the hinterland of Urals, there occur a variety of high-grade complexes that have been interpreted to be fragments of continents that were accreted to Baltica during Paleozoic orogeny. Some workers have inferred the high-grade complexes to have rifted off Baltica during the Early Paleozoic; others claim that they were derived from elsewhere (perhaps Siberia) and are truly exotic terranes. In the Middle Urals, the amphibolite- to granulite-facies complexes of ``micro-continental'' affinities are generally composed of mafic to intermediate gneisses, overlain by Paleozoic mélange and island-arc volcanics. New Pb-Pb single zircon dating provides evidence only of a Paleozoic history for one of these high-grade units, the Salda Metamorphic Complex. Eight intrusion ages have been obtained from these granulite-facies gneisses and younger intrusions. The protoliths of the gneisses, the Teliana and the Brodovo intrusive suites, were formed at around 350Ma (359 +/-5, 357+/-7 and 343+/-9Ma) and at 393+/-5Ma, respectively. They are cut by the East Emekh granite (334+/-4Ma) and the Basianovo gabbro (336+/-2Ma). The new single zircon data fit well with previously conventional K-Ar, Pb-Pb and U-Pb ages by A.P. Grevtsova et al. (unpublished data). It is proposed here that the hinterland of the Middle Urals is dominated by Devonian to Middle Carboniferous subduction-related magmatic complexes that were emplaced prior to and during collisional orogeny in the Urals. The evidence presented here and age-data from other hinterland high-grade complexes casts doubt on the ``micro-continent'' interpretation.