Thermochronology and Exhumation History of the Northeastern Fennoscandian Shield Since 1.9 Ga: Evidence From 40 Ar/ 39 Ar and Apatite Fission Track Data From the Kola Peninsula

Abstract

Results from thermochronological studies have multiple applications to various problems in tectonics and landform evolution. However, up to now a lack of thermochronological data from the northeastern Fennoscandian Shield has complicated the interpretation of tectonothermal evolution of the region. Here, we use both new and previously published multimineral Ar-40/Ar-39 data (amphibole, mica, and feldspar) on the various Precambrian magmatic and metamorphic complexes to reconstruct the thermal history of NE Fennoscandia within the Kola Peninsula area in the interval 1900-360 Ma. Using the apatite fission track method as well as a numerical model of the heating-cooling process of northeastern Fennoscandia's upper crust, we have reconstructed its thermal evolution for the interval 360-0 Ma. According to our model, since Lapland-Kola orogenesis (1930-1905 Ma) northeastern Fennoscandia experienced a quasi-monotonous cooling with the average rate of 0.15 degrees C/Myr, which is equal to an exhumation rate of 1-2 m/Myr. New apatite fission track data and time-temperature modeling reveal a hidden endogenous thermal event in the NE Fennoscandia that took place between 360 and 300 Ma. This we attribute to an elevated geothermal gradient due to Baltica's drift over the African large low shear-wave velocity province in the lowest mantle and/or thermal blanketing by insulating Devonian-Carboniferous sedimentary/volcanic cover. Our model is further supported by evidence of Late Devonian-Carboniferous rifting in the East and South-Western Barents Basin, as well as various 360-300 Ma magmatic events within SW Fennoscandia and the Baltic countries.