Large Igneous Provinces, Delamination, and Fertile Mantle

Abstract

When continental crust gets too thick, the dense eclogitic bottom detaches, causing uplift, asthenospheric upwelling, and pressure-release melting. Delamination introduces warm blocks of lower crust with a low melting point into the mantle; these eventually heat up, ascend, decompress, and melt. The mantle below 100 km depth is mainly below the melting point of dry peridotite, but its temperature will be above the melting point of recycled fertile (basaltic or eclogitic) components, obviating the need for excess temperature to form “hotspots” or “melting anomalies”. When plates pull apart or delaminate, the mantle upwells; entrained crustal fragments of various ages are fertile and create melting anomalies along developing mid-ocean ridges, fracture zones, and old suture zones. Eclogites associated with delamination are warmer and less dense than subducted oceanic crust and more susceptible to melting and entrainment.