Klimovskii Metasomatic Complex of the Belomorian Mobile Belt:Composition, Age, Geological Position

摘要

Metasomatites of the White Sea mobile belt of the Fennoscandian (Baltic) shield are considered. Metasomatites are traced from southeast to northwest for a distance of = 550 km. In mineral composition, metasomatites correspond to the paragenesis of amphibolite facies of regional high-pressure metamorphism. To determine the tectonic position of metasomatites and their place in the sequence of geological events, we carried out isotope-geochemical studies of zircons, isolated both from metasomatites and their enclosing gneisses. It was established that the host metamorphic formations formed in the Neoarchean and metasomatites formed in the Late Paleoproterozoic (approximate to 1.9 Ga). The rare-earth spectra of the studied zircons indicate that they formed from a fluid in a retrograde branch of regional metamorphism. Fluids were discharged along the deep thrust planes, thereby marking the zones of their exits to the modern surface. The results obtained indicate tectonothermal reworking of Archean complexes in the Late Paleoproterozoic.