The post-Caledonian thermo-tectonic evolution of Fennoscandia

• Published in: Gondwana research 2022-07, Vol.107, p.201-234
• Main Authors: Green, Paul F., Japsen, Peter, Bonow, Johan M., Chalmers, James A., Duddy, Ian R., Kukkonen, Ilmo T.
• Format: Article
• Language: English
• Subjects: AFTA; Craton; Exhumation; Missing section; Peneplain
• ISSN: 1342-937X; 1878-0571; 1878-0571
• DOI: 10.1016/j.gr.2022.03.007

[Display omitted] •Fennoscandia underwent five phases of post-Caledonian regional km-scale exhumation.•Each exhumation episode was followed by formation of a regional peneplain.•Results define a history involving repeated kilometre-scale burial and exhumation.•Tectonic offsets are seen in Norway but in the continental interior effects are more uniform.•Synchronous episodes on adjacent continents imply plate-scale control. The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides only partial documentation of the geological evolution. A more complete understanding is obtained by also considering evidence of rocks that were formerly present but have since been removed. We report apatite fission track data and associated thermal history constraints in 331 samples of Precambrian basement, younger sedimentary cover, Paleozoic and Mesozoic igneous rocks from outcrops and boreholes (up to 6 km depth) across Fennoscandia, which define thirteen phases of cooling (each representing kilometre-scale exhumation) over the last 1100 Myr. Key post-Caledonian episodes began in the intervals 311–307 Ma (late Carboniferous), 245–244 Ma (Middle Triassic), 170–167 Ma (Middle Jurassic), 102–92 Ma (mid-Cretaceous) and 23–21 Ma (early Miocene). These episodes, varying in magnitude, are recognised across Fennoscandia, and their effects are documented in the stratigraphic record and as prominent regional peneplains. The results define a history involving repeated episodes of regional burial and exhumation. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasising the tectonic nature of the history. Results from Finland record the same events recognised in Norway and Sweden (though less pronounced), and are not consistent with long-term cratonic stability. The lack of preserved Phanerozoic sedimentary cover in Finland is interpreted to be due to complete removal during multiple episodes of denudation. In southern Norway and Sweden, early Miocene exhumation led to creation of a peneplain, which in Pliocene times was uplifted and dissected, producing the modern landscape. Post-Caledonian exhumation episodes defined here are broadly synchronous with similar events in Greenland, the British Isles and North America. Far-field transmission of