Tectono-magmatic history of meta-igneous rocks from Nordaustlandet, Svalbard, inferred from 40Ar/39Ar and U-Pb geochronology and microstructural analyses

Situated in the High Arctic, the island of Nordaustlandet is one of the least understood geological terranes on Earth regarding Precambrian and Paleozoic geodynamic processes. Such knowledge is, however, essential to reconstruct the geological evolution of the continental crust surrounding the Arctic Ocean. To elucidate the age of intrusion and tectono-metamorphic activity, the foliation-forming mineral phases, alkali feldspar and zircon grains from a total of 10 samples of meta-igneous rocks from northern Nordaustlandet were dated by ⁴⁰Ar/³⁹Ar and U-Pb geochronology. The geochronological study was complemented by a regional compilation of planar metamorphic fabrics and a microstructural analysis. The geochronological results reveal that the emplacement of metagranitoid rocks occurred during the Late Meso- to Early Neoproterozoic era (Stenian - Tonian), followed by Late Caledonian (Scandian) deformation and metamorphism during a Late Silurian to Early Devonian event. Neoproterozoic magmatic bodies intruded at mid-crustal level and were exhumed during the Caledonian orogeny between 420.1 ± 2.3 Ma and 399.9 ± 1.7 Ma. Structural observations allowed us to constrain the mechanisms, intensities and shortening directions of this deformation, which occurred under medium-grade metamorphism. This study indicates that Meso- to Neoproterozoic granitoid rocks, pervasively exposed at the northern coast of Nordaustlandet, were exhumed during Late Silurian to Early Devonian times and served as host to Late Caledonian felsic intrusions.