Crustal thickening and lateral flow during compression of hot lithospheres, with particular reference to Precambrian times

Many ancient deformation belts, especially of Archean and Palaeoproterozoic age, show large areas marked by primary flat-lying fabrics associated with rather monotonous metamorphic conditions of HTLP type and affected by steep transpressive zones involving vertical stretch. These features do not support strain localization along large-scale thrusts and (or) extensional detachments, as common in modern orogens. Instead, they are consistent with hot and weak lithospheres where gravity-driven horizontal flow may compete with distributed thickening from early stages of collisional processes. Relevant deformation features are reviewed and highlighted by lithosphere-scale analogue models involving low-viscosity lower crust and sub-Moho mantle. Both nature and models argue that compression of such lithospheres may induce combined distributed thickening and lateral channel flow of the ductile crust accommodated by transpressive zones.