The GGT/SVEKA Transect: Structure and Evolution of the Continental Crust in the Paleoproterozoic Svecofennian Orogen in Finland

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Abstract
The Global Geoscience Transect SVEKA (GGT/SVEKA), a 160 km wide, 840 km long strip in the central part of the Fennoscandian shield, covers the western part of the Archean Karelian Province in the northeast, crosses the boundary zone between the Karelian Province and the Paleoproterozoic Svecofennian arc complex, traverses the main tectonic units of the northern part of the Svecofennian complex, and ends in the Subjotnian region in the southwest. The transect area is well suited for investigation of the Svecofennian orogeny and its effects on the Archean Karelian crust as well as the later extensional events of the Svecofennian crust. The purpose of the GGT/SVEKA program was the construction of a tectono-evolutionary model of the crust along the transect. By combining geophysical (seismic, electrical, gravimetric, thermal, magnetic, and petrophysical) and geological (lithological, structural, metamorphic, isotopic, and geochemical) data, the study focuses on solving the temporal and causal relationship between deformation, metamorphism, and magmatism and, in particular, on investigating the crustal thickness and density variations, the high metamorphic temperatures during the Svecofennian orogeny, and the significance of crustal conductors. The major stages of the crustal evolution include: (1) the prolonged rifting of the cratonized Archean crust between 2.5 and 1.97 Ga; (2) the final break-up and ocean development in the southwest at 2.1 Ga; (3) the formation of the largely unknown 2.06 Ga protolith for Svecofennian arc magmatism, evidenced by geochemical data and detrital zircon ages; (4) the amalgamation of the Pyhasalmi primitive island arc, the central Finland continental arc, and the southern Finland sedimentary-volcanic complex in two major collisions at 1.91 to 1.885 Ga and before 1.885 Ga; (5) the high-temperature, low-pressure metamorphism between 1.885 and 1.800 Ga caused by magmatic underplating and partial crustal thinning after subduction and crustal thickening; (6) the Subjotnian extension associated with bimodal magmatism at 1.558 to 1.540 Ga and the development of Jotnian sedimentary basins; and (7) diabase dike magmatism at 1.27 to 1.26 Ga.