Far-field tectonic influence on the Paleoproterozoic A-type Puula granite in Fennoscandia: Implications for Svecofennian orogeny, crustal growth, and continental stabilization

This study examines the evolution and structural history of the Paleoproterozoic A-type Puula granite to assess the impact of far-field tectonic events on granites within the core of the Svecofennian orogen. The Puula granite is classified into three magma types based on K-feldspar phenocryst size, presence of country-rock xenoliths, complex phenocryst overgrowths, and the abundance of felsic to intermediate sills and dykes. Geochronological data indicate an emplacement period from approximately 1880–1878 Ma to 1875 Ma. The granite’s structural evolution began with sub-horizontal NW-vergent stacking (1875–1865 Ma), followed by significant NE–SW shortening (1865–1850 Ma) and minor NW–SE shortening (1840–1800 Ma). It is proposed that the Puula granite, along with the Suontee and Joutsa granites, originally formed a larger, zoned Puula batholith that was subsequently deformed into separate units. The Puula batholith exemplifies geochemically A-type magmatism (1880–1875 Ma) characteristic of the Central Finland Granitoid Complex. Volcanic and sedimentary rocks of similar age are found from Skellefte in Sweden to central and southern Finland. Of the three tectonic scenarios considered for the Svecofennian orogen at 1.89(1.88)–1.87 Ga, the preferred model is accretionary orogeny with an intervening extensional phase and orocline formation. Primary crustal thickening in the Central Finland Granitoid Complex resulted from both magmatic accretion and tectonic processes, with orocline formation playing a key role in stabilizing the thick crust and preventing orogenic collapse and promoting cooling of the crustal core.