How lithospheric thickness and strength variations facilitate the rifting of ancient cratonic lithosphere

Geodynamic models can aid understanding the evolution of rifting in North China and other rift systems. The North China Craton (NCC) formed by the collision of two Archean blocks in the Paleoproterozoic resulting in a broad collision zone known as Trans-North China Orogen. The NCC shows two different modes of extension that are separated by space and time. Wide, distributed rifts formed during the Paleogene above the Eastern NCC, in the Neogene migrated to the Western NCC forming narrow, localised rifts near the Paleoproterozoic orogens. However, the mechanism that led to development of these fundamentally different rifts and the migration of rifting remains debated. Here we use the geodynamical tool ASPECT to perform 2D thermo-mechanical modelling to explain the role of variable lithospheric strength and inherited lithospheric weaknesses in the development of rift systems. We found that a wide, distributed rift develops over non-cratonic lithosphere, while the adjacent cratonic lithosphere will accommodate little strain. To explain rift migration in North China we require 1.) a period of tectonic quiescence that strengthens the lithosphere following distributed initial rifting 2.) a specific range of relative lithospheric thickness variations and 3) presence of a lithosphere scale weak zone, i.e., an inherited feature. Our results show how lithospheric thickness and strength variations as well as discrete zones of lithospheric weaknesses can influence the style of rifting and facilitate the breakup of an ancient craton. These results are applicable to other multiphase rift systems around the world such as the North Atlantic.