The 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 cutting through a compositionally homogeneous granodioritic crust of Late Proterozoic age. Compared to younger rifts, the Gardar system is distinct and comprises for example giant mafic dykes ~500-600m thick. This suggests that the Gardar continental lithosphere had distinct rheological properties and perhaps a different thermal regime than the present continental lithosphere. To learn more about the strucutre and rheology of the Proterozoic lithosphere, we propose to image this lithosphere in 3D at the southern Gardar rift using 15 boradband seismometers crossing the Gardar RIft in two profiles, and to geologically characterize the mode of emplacement of the giant dykes.