Tectonic Origin of the Belomorian Mobile Belt and Belomorian Eclogites (N–E Baltic Shield)

Belomorian mobile belt is defined as the belt of high-grade metamorphic rocks which is made up predominantly of the Meso- to Neoarchean tonalite-trondhjemite-granodiorite (TTG) gneisses in which sealed numerous blocks of strongly retrogressed eclogites. It is fringed with the Karelian granite-greenstone craton (i), and the hinterland of the late Paleoproterozoic Lapland-Kola compressed orogen (ii), being its foreland. It is long been assumed that the origin of Belomorian eclogites was related to a subduction of the hypothetical Lapland-Kola oceanic crust followed by a collision of Lapland-Kola and Karelian lithospheric plates at ca.1.9 Ga. It is shown that there is no any evidence for subduction geodynamics of this time. Therefore, the origin of the Belomorian mobile belt was triggered by a far-field stress and as a result an emergence of the fore-bulge during the development of the Lapland-Kola compressional orogeny and related to flexural bending of the Archean lithosphere, which led to its shortening by ~10%, culminated both in significant enhancement of a rate of dislocation creep in its crustal level and compaction-derived fluid activity. The maximum tectonic pressure had been expressed in the area of the North-Belomorian syntax where the overwhelming majority of eclogite blocks sealed in the Meso- to Neoarchean TTG gneisses occurred.