GEOCHRONOLOGY OF ULTRAMAFIC LAMPROPHYRE DIKES IN THE TOMTOR COMPLEX

This work studies thin ultramafic lamprophyre (UML) dikes associated with the Tomtor alkaline-ultramafic massif (Arctic Siberia). 40 Ar/ 39 Ar dating yielded an emplacement age of 710 Ma for the dikes. U-Pb dating of calcite indicates a 400 Ma year old low-temperature recrystallization event. Both age constraints correlate with some notable phases of Tomtor magmatism. The dike locations 15 km away from the main massif suggest a more extensive magmatic province than previously thought. The spatial association of the dikes with the Mesoproterozoic Udzha paleorift highlights the crucial role of inherited tectonic structures in controlling over magmatism. It is probable that the formation of both the dikes and the Tomtor massif was governed by two key factors: (1) favorable lithospheric setting due to the location at the junction of the Archean Daldyn terrane and Paleoproterozoic Khapchan orogenic belt, which is responsible for the localization of the Udzha paleorift; and (2) the reorganization of tectonic stresses within the northern Siberian Craton during the Neoproterozoic and Devonian. The magmatic and consequent recrystallization stages (710 and 400 Ma, respectively) identified within the Udzha paleorift, correspond to major regional geodynamic events, such as Neoproterozoic tectonic convergence in Central Taimyr and Devonian rifting (Vilyui rift system).