Large igneous provinces generated from the margins of the large low-velocity provinces in the deep mantle

There is a clear correlation between downward projected large igneous province (LIP) eruption sites of the past 200 Myr and the margins of the large low-velocity provinces (LLVPs) at the base of the mantle. We established this correlation by using palaeomagnetic as well as fixed and moving hotspot reference frames. Our finding indicates that the majority of the LIPs have been generated by plumes that rose from the D'' zone at the edges of the LLVPs. Most LIP eruption sites project radially downwards to the core-mantle boundary (CMB) within +/-10° of the 1 per cent slow shear wave velocity contour in the SMEAN tomographic model. Steep shear wave velocity gradients have been mapped near the CMB along much of the lengths of the LLVP margins close to that contour which marks a faster/slower boundary (FSB) within the D'' zone. The observation that eruption sites of LIPs as old as 200 Myr can be linked to this prominent present day seismic structure shows that the FSBs of the two LLVPs have occupied their current positions for at least as long and that the process that leads to the generation of deep-seated plumes has been localized on the FSBs at the margins of the African and Pacific LLVPs for the same interval. The persistence of the LLVPs over 200 Myr is consistent with independent evidence that they are compositionally distinct and are not just simply hotter than the material making up the rest of the D'' zone.