Late Mesozoic creation and destruction of an Andean-type retro-arc foreland system of South China revealed by SINOPROBE profiling.

Abstract:

In the Late Mesozoic, South China’s eastern margin evolved into a convergent margin with the subduction of the Paleo-Pacific plate, providing a natural laboratory to unravel the interactions among deformation, sedimentation and magmatism in a retroarc tectonic setting. The crustal architecture of South China—displayed by SINOPROBE deep seismic reflection profiles—reveals from west to east: (1) nearly flat-lying reflectors in the Sichuan Basin of west Yangtze that allow interpreting the basin as a weakly deformed depocentre; (2) folded and truncated reflectors in the upper crust of central Yangtze, which correspond to thin- and thick-skinned thrust systems indicative of northwestward structural imbrication and shortening; (3) the crustal-scale flat-ramp-flat Yangtze decollement, which forms a weak, viscous layer accommodating strain decoupling in the thin- and thick-skinned systems; (4) East Cathaysia is underlain by two seismically distinct terranes, separated by a low-angle, northwest-dipping set of mantle-penetrating reflectors interpreted as the Zhenghe-Dapu fault zone, which documents Neoproterozoic terrane amalgamation and Cretaceous extensional reactivation; (5) the Coastal terrane shows low reflectivity truncated by high-reflective, subhorizontal bands of layered reflectors, in which the latter are interpreted to represent mantle-derived mafic sills, documenting magmatic underplating beneath the terrane in an extensional tectonic setting. Such seismic observations, coupled with surface geology, allow the definition of a retro-arc foreland system that could be traced >800 km away from the continental margin. Seismic profiles of western South China document retroarc thrust propagation associated with the Jurassic creation of the retro-arc system, whereas those of eastern South China record extensional overprinting reflecting the Cretaceous destruction of the retro-arc system. The magmatic underplating added large volumes of mantle-derived material to the crust, capable of compensating for the crustal thinning and creating the broadly flat Moho of eastern South China during the Cretaceous.