Derivation of Large Igneous Provinces of the past 200 million years from long-term heterogeneities in the deep mantle

Large Igneous Provinces (LIPs) result from local catastrophically rapid dissipation of great quantities of internal heat. LIPs are overwhelmingly of basaltic affinity representing partial melting of the mantle at shallow depths but whether any of the heat or material involved in the generation of LIP rocks comes from great depth has remained controversial. To address this fundamental issue we restored 25 LIPs of the past 200 My to their eruption sites using a new global palaeomagnetic reference model. Ninety percent of the LIPs, when erupted, lay above low-velocity seismic-shear-wave regions of the D zone just above the core-mantle boundary (CMB) and similar to50% overlay CMB low-velocity regions with deltaV(s)less than or equal to-1%. Considering the modifying effects of plume advection, palacolongitudinal uncertainty and plate circuit errors, the majority of the restored LIPs may in fact overlie regions with deltaV(s)less than or equal to - 1%. Because those low velocity regions occupy only 27% of the D zone, the concentration of LIPs above them indicates that the low velocity (hotter?) regions are the sources of the mantle plumes that generated the LIPs. We demonstrate that most LIPs of the past 200 My owe their origin to plumes that rose from low-velocity regions of the lower mantle, and that this long-term association indicates that the low-velocity regions have been relatively stationary with respect to the Earth's spin-axis and the core since the Early Jurassic, and perhaps since the Permo-Triassic boundary. (C) 2004 Elsevier B.V. All rights reserved.