Breakup of strong cratonic lithosphere causes extensive magmatism by rift shoulder subsidence

Extensive magmatism and the formation of Large Igneous Provinces (LIPs) along continental margins are commonly attributed to anomalously high mantle temperatures and/or mantle fertility, such as plume activity. However, the role of lithospheric strength in controlling magmatic productivity remains poorly explored. Using 2-D thermo-mechanical numerical models, we identify a new mechanism for syn-breakup magmatic surges that does not require anomalous mantle properties. Instead, enhanced asthenospheric upwelling is triggered by the gravitational collapse of elevated rift flanks, a process that occurs only when lithospheric strength is sufficiently high. Multidisciplinary observations from the Labrador Sea–Baffin Bay rift system—including tectonic, magmatic, and geophysical constraints—are consistent with this mechanism and link excessive magmatism to a strong lithosphere. Our results highlight the overlooked influence of lithospheric strength on melt production rates during rifting and continental breakup. This study offers a complementary framework for understanding volcanism and LIP formation along continental margins, without requiring anomalously hot or fertile mantle, while not excluding such contributions where independently supported.