Long-lived Northern Hemisphere convergence systems driven by upper-mantle thermal inhomogeneity

Plate reconstructions reveal that two secular centers of convergence formed beneath eastern Eurasia and North America no later than 200 Ma. The cause of these convergence centers, which featured flat subduction, slab stagnation, and/or continental margin subduction, remains uncertain. Here, we propose that upper-mantle thermal inhomogeneity, particularly an anomalously cool Northern Hemispheric upper mantle, was a fundamental driver of this long-lived convergence. By considering the pattern of observed thermal inhomogeneity, our numerical models show that flow-induced asymmetrical subduction will tend to develop toward cold mantle domains, even when the subducting plate is buoyant. The models can reproduce the diverse subduction styles observed in the Northern Hemisphere by including proposed pre-subduction plate distributions and/or properties.