Rift Propagation Interacting With Pre-Existing Microcontinental Blocks

Rift propagation is a 3D thermo-mechanical process that often precedes continental breakup. Pre-existing microcontinental blocks and the associated lithospheric strength heterogeneities influence the style of rift propagation. Interestingly, some rifts propagate into pre-existing blocks and eventually cut through them (e.g., the Zhongsha Block and the Reed Bank), while others bypass these microcontinental blocks forming distinct overlapping rift branches (e.g., the East African Rift System). In this study, we use 3D numerical models to investigate the interaction between microcontinental blocks and rift propagation under different far-field extension rates. In doing so, we assess the impact of mantle lithospheric thicknesses and lower crustal rheology on the style of rift propagation. Our models reproduce the two types of rift propagation, characterized by propagating rifts that either split or bypass the pre-existing microcontinental blocks. We find that lithospheric thickness exerts dominant control, while lower crustal rheology of microcontinental blocks and the extension rate have less effect on rift propagation. Our model results can explain rift propagation patterns, block rotation and strong lithospheric thinning in the South China Sea, the East African Rift System, and the Woodlark Basin. Rift propagation is an essential process during continental rifting, which rarely follows a straight line due to the heterogeneous nature of continental lithosphere. Here, we use 3D geodynamic numerical modeling to simulate the dynamic evolution of rift propagation interacting with pre-existing microcontinental blocks. We find that rift propagation is inhibited by strong microcontinental blocks with thick mantle lithosphere, while it splits through weaker microcontinental blocks. We suggest that the strength of microcontinental blocks explains the observed pattern of rift propagation in the South China Sea, the East African Rift System, and the Woodlark Basin. Pre-existing microcontinental blocks affect rift propagation Lithospheric heterogeneities play a dominant role in rift propagation patterns Model results elucidate rift propagation patterns in the South China Sea, the East African Rift System, and the Woodlark Basin