Geodynamics of the Early Precambrian: Evidence for the Baltic Shield

Abstract

Geological data on the Baltic Shield indicates that in the late Archean and in the early Paleoproterozoic the character of tectonic-magmatic activity was essential different from the plate tectonics. The main structural provinces were: (1) huge extensional areas with the mantle-derived magmatism in volcanosedimentary belts among more ancient sialic crust (granite-greenstone terranes in the Archean and cratons in the early Paleoproterozoic), (2) complementary compressional zones between them — granulite belts of moderate pressure with crustal-derived enderbite-charnockite magmatism, and (3) specific transitional nappe-folded zones between low- and high-grade terranes. Coeval regional structural-metamorphic zonation took place, which was characterized by strengthening of metamorphism and deformations in the direction of the granulite belts.A plume-tectonics model for the Early Precambrian of the Baltic Shield is suggested. Ascent of superplumes was the leading mechanism of geodynamics. Archean granite-greenstone terranes and the early Paleoproterozoic cratons with mantle-derived magmatism occurred above extended superplumes heads. Between them zones of intense sagging movements took place, where sedimentary basins occurred and granulite belts formed. Within the latter crustal material in process of tectonic flowage was subjected to intense deformations and warming up (probably, via the shear stress); it could lead to its melting and formation of enderbite-charnockite series magmas.The feature of the tectonic activity in the early Precambrian of the Baltic Shield was inheritance of location of its main structural provinces at least from the late Archean till the end of the Paleoproterozoic. Probably, it evidences about extremely stability of the system of the mantle convection during about 1 Ga.True geological evidence of changing of geodynamic activity for plate-tectonics in the region were noted only from 2.2-2.0 Ga ago, practically simultaneously with the first-ever appearance of Fe-Ti picrites and basalts, typical for the Phanerozoic withinplate magmatism.KeywordsGreenstone BeltBaltic ShieldLayered IntrusionDyke SwarmGranulite BeltThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.