Age and structural constraints on the tectonic evolution of the Paleoproterozoic Central Lapland Granitoid Complex in the Fennoscandian Shield.

Abstract The Paleoproterozoic Central Lapland Granitoid Complex (CLGC) forms the northern core of the Fennoscandian Shield. We present here new U-Pb age data and review the existing ones from plutonic and metasedimentary rocks of the CLGC, and integrate the results with the structural field observations to decipher the tectonic history of this region. Granitoids vary in age from 2.43 Ga to 1.78 Ga, whereas metamorphic zircon overgrowths, both in granites and metasedimentary rocks, vary between 1.90 Ga and 1.76 Ga with several age peaks indicating prominent metamorphic pulses. The almost continuous growth of metamorphic zircon domains favors that the central part of the CLGC was near solidus for 100–120 Ma. A succession of five deformations and associated foliation-producing events, which were near-orthogonal to each other, have been identified. East-vergent thrusting and stacking (D1) commenced at ca. 1.92 Ga, and led to the onset of Barrovian-type metamorphism followed by a radical tectonic shift that yielded E-W trending D2 structures. Exhumation at 1.88–1.87 Ga caused decompression melting of thermally evolved thickened crust and led to the emplacement of large volumes of granites and triggering of Buchan-type metamorphic conditions. NE-SW collision (D3) at the southwestern margin of Fennoscandia heterogeneously overprinted the S3 fabric on D2 structures. Orogen parallel (NNW-SSE) buckling at 1.87–1.85 Ga formed oroclines in the hot linear arc segments. Renewed NNW-SSE shortening (D4) at 1.84–1.81 Ga produced long wavelength folds and caused the formation of domal structure in the CLGC. The final 1.78–1.76 Ga far-field collision (D5) in the west overprinted all the pre-existing structures. This complex multi- directional tectonic scenario provoked the intermittent exhumation phases between different contraction events of the CLGC. Highlights • Central part of the Lapland Granitoid Complex (CLGC) was near solidus for 100–120 Ma. • Five major deformation events (D1-D5) occurred between 1.92 Ga and 1.76 Ga. • Barrovian- to Buchan-type metamorphism at 1.88–1.87 Ga. • Migmatitic core was transformed to long wavelength folds during D4. [ABSTRACT FROM AUTHOR]