Continental lithosphere during the Meso-Proterozoic: the Gardar Rift in Greenland as a case-study

The main objective of the PROTERO-LITHO project is to characterize the mechanical properties and tectonic behavior of the continental lithosphere at an early stage of plate tectonics. The Gardar Province in southern Greenland (~1.3 to 1.1 109 years old) exposes a remarkable Middle Proterozoic intracontinental rift system. This system is poorly eroded and outcrops in its original geometry. It cuts through a compositionally homogeneous granodioritic crust of Late Proterozoic age. Compared to younger rifts of Phanerozoic age, the Gardar system has distinctive features, such as giant mafic dykes ~500-600m thick. The thickness of these dykes is 30-200 times greater than that observed in active or recent volcanic rifts. This suggests that the Gardar continental lithosphere had distinct rheological properties and perhaps a different thermal regime than the present continental lithosphere. We propose to seismically image this lithosphere in 3D at the southern Gardar rift and to geologically characterize the mode of emplacement of the giant dykes. Our final objective is to constrain the rheology of the continental crust and lithosphere of the Middle Proterozoic from these results. This multidisciplinary and international study will contribute to establish the time evolution of the thermo-mechanical properties of the continental lithosphere in the global context of inner Earth cooling.