Improved resolution of Paleoproterozoic orogenesis: Multi-directional collision tectonics in the Sodankylä belt of northern Finland

Abstract

Abstract The geodynamic system of Earth is controlled by the horizontal motion of fragmented tectonic plates due to complex interaction between the mantle and the crust. Land and marine paleomagnetic signatures, along with extensive petrochronological and structural data, suggest non-continuous, multi-directional convergence histories for modern orogenic belts, as seen in the Himalayas and Betic Cordillera, among others. The consequences of radical changes in the direction of plate motions are obscured by complex structural settings and repeated cycles of metamorphism in orogenic belts. Although, subduction was operational on Earth in the Paleoproterozic, one of the major questions is: how far back in geological time can we trace the scale of modern-style subduction, collisional tectonics and poly-metamorphism? The metasedimentary and volcanic rocks (2.5 to 2.05\xa0Ga) of the Sodankyla belt of northern Finland were deformed and metamorphosed during a prolonged period, now represented by the Svecofennian orogen (ca. 1.92–1.77\xa0Ga). The orogenic belt represents a window into the deep levels of a Paleoproterozoic crust, where the interplay between deformation and metamorphism can be compared with the modern orogenic settings. In this study, five discrete heterogeneously developed superimposed, near-orthogonal, deformation events (D1 to D5) have been identified and mapped based on the high-resolution aeromagnetic data and field studies. Regional correlation of tectonic fabrics, along with metamorphic textures across the Sodankyla belt and northern Finland, suggest that each deformation event was a regional-scale phenomenon rather than a local one. Previous geochronological data obtained from the Sodankyla belt and adjacent Central Lapland Granitoid Complex on different Paleoproterozoic deformed rocks allow us to propose a time-constrained tectono-metamorphic model for the Sodankyla belt. The sequence of near-orthogonal deformation history and the polymetamorphic evolution offer comparisons with modern-style orogenic settings. The most notable aspect is the occurrence of Mesoarchean and Paleoproterozoic eclogitic high-pressure granulites reported from the Belomorian belt of Fennoscandian Shield, which lies to the east of the Sodankyla belt. From a tectono-metallogenic viewpoint, the Sodankyla belt is located in the centre of Ni-Cu-PGE, orogenic gold-cobalt deposits of the northern part of Fennoscandian Shield, therefore, the tectonic processes and overprinting role of multiple deformation phases need to be well understood as they directly link mineral exploration to the timing and controls on mineralization.