Edge-driven asthenospheric convection beneath the North China Craton: A numerical study

The North China Craton (NCC) is one of the most tectonically active cratons in the world today. Its scattered late Cenozoic volcanism, as well as small-scale low-velocity anomalies in the upper mantle, suggests a major role of asthenospheric upwellings in the NCC tectonism. Such asthenospheric upwellings, however, cannot be readily explained by the Indo-Asian continental collision or subduction of the Pacific plate, two of the plate boundary processes previously suggested for causing the Cenozoic tectomagmatism in the NCC. Here we propose that edge-driven convection, resulting from the large changes of lithospheric thickness under the NCC, is likely a major cause of the observed upper mantle structure and late Cenozoic volcanism in the NCC. Using a two-dimensional thermo-mechanical finite element model, we found that the contrast of lithospheric thickness between the Eastern and Western blocks of the NCC can cause significant edge-driven small-scale convection, especially if the viscosity of the asthenosphere is reduced by melts and volatiles from dehydration and decarbonization of the stagnant slabs of the subducted Pacific plate under the NCC.