State of mantle (re-)mixing and large igneous provinces

Large igneous provinces are the largest expression of magmatism on the Earth, and they are usually associated with hypothetical mantle plumes, thereby playing a fundamental role in forming a currently prevailing view of mantle dynamics; mantle convection is characterized by large-scale plate-tectonic circulation and small-scale plume upwelling. The actual origins of large igneous provinces are, however, still poorly understood. In this contribution, I review geophysical and geochemical constraints on the origin of the North Atlantic igneous province, which is one of the best-studied provinces. By combining various constraints ranging from mantle and crustal tomography to igneous petrology and geochemistry, I suggest that this igneous province has most likely resulted from strong chemical heterogeneity in source mantle without notable thermal anomaly. A long-standing dynamical problem regarding the upwelling of fertile (thus dense) mantle is also shown to be resolved by considering the physics of a self-contained whole-mantle convection system. The significance of chemical heterogeneity in the genesis of large igneous provinces may not be limited to the North Atlantic province. The efficiency of convective remixing is not expected to be globally uniform, which implies that spatially variable mantle composition is a natural outcome. The distribution of large igneous provinces may simply reflect the pattern and intensity of such inherent chemical heterogeneity in convecting mantle.