Structural–kinematic evolution of the central Belomorian–Lapland belt in the paleoproterozoic

A model of the evolution of the central Belomorian–Lapland Granulite–Gneiss Belt is proposed on the basis of analysis of the Paleoproterozoic structural–kinematic assemblages. It is shown that this tectonic zone is a long-lived mobile structural unit that evolved through several stages of tectonic transformation and metamorphism of rocks, including (1) the Reboly stage, which comprises subduction (2.88–2.82 Ga) and collision (2.74–2.53 Ga) substages; (2) the Selet stage of rifting and extension of the continental crust according to the model of simple shear (2.45–2.35 Ga); and (3) the Svecofennian stage, characterized by collision and general transpression (1.94–1.75 Ga). The results of structural–kinematic study indicate that tectonic flow in the Svecofennian time was nonuniform and related to the formation of the Kolvitsa–Umba near-horizontal protrusion. The propagation of this protrusion was caused by transpressional extrusion of plastic lower-crustal masses to the surface as a gently ascending tectonic flow directed to the northwest (in present-day coordinates). Thereby, a thrust–normal-fault kinematic effect was expressed in pushing-out of deep-seated complexes contemporaneously with tectonic erosion of the upper portions of the sequence owing to the development of low-angle normal faults.