Résumé
Deformation of the continental lithosphere is usually modeled assuming that heat production in the subcontinental lithospheric mantle is negligible. Although this may be appropriate for highly depleted Archean lithosphere, studies of mantle xenoliths and lithospheric-derived mafic rocks suggest that heat productions of up to 0.4 MW/m (super 3) may be attained in the mantle of Phanerozoic and Neoproterozoic regions due to modal metasomatism. To investigate the effect of a local enrichment in heat-producing elements within the lithospheric mantle on the continental deformation, we performed a series of 2D thermo-mechanical models simulating the deformation of a lithospheric plate 1000 km long, which contains in its central part a 200 km wide and 10 to 40 km-thick mantle layer with a heat production of 0.05-0.25 MW/m (super 3) between 40 and 80 km depth. Compression models show that a 20 km-thick layer with a heat production > or =0.10 MW/m (super 3) within the lithospheric mantle produces a local enhancement in the thermal gradient leading to significant strain localization in both the enriched mantle and the overlying crust. This effect is proportional to the increase in heat flux in the enriched mantle and hence depends on both the volume of metasomatized mantle and the heat production. Strain localization is observed for radiogenic enrichments increasing the mantle heat flow by > or = 2 mW/m (super 2) . In the crust, strain localization is more effective for stiff rheologies corresponding to basic compositions. Weaker crustal layers, displaying quartz-dominated rheologies, show a more distributed deformation. The effect of a heat producing layer within the lithospheric mantle is much weaker in extensional settings. These results provide an explanation for strain localization in intraplate environments, leading to the formation of orogenic belts situated hundreds to thousands of kilometers away from known plate boundaries, as observed in the Neoproterozoic belts of Gondwana and in the present-day deformation of the Asian plate.