Caption of figure from:
Anderson, Don L., Scoring Hotspots; the Plume & Plate paradigms, in: Melting Anomalies: Their Nature and Origin, G.R. Foulger, D.L. Anderson, J.H. Natland and D.C. Presnall, eds. Special Paper, Geological Society of America, in preparation, 2004.
A schematic cross-section of the Earth showing the plume model (to the left, modified from Courtillot et al., 2003 with additions from other sources) and the plate model (to the right). The left side illustrates three proposed kinds of hotspots/plumes. In the deep mantle, narrow tubes (inferred) and giant upwellings coexist. Melting anomalies are localized by narrow upwelling plumes, which bring material from great depth to the volcanoes. In the various plume models the deep mantle provides the material and the deep mantle or core provides the heat for hotspots; large isolated but accessible reservoirs, rather than dispersed components, and sampling differences account for geochemical variability. Deep slab penetration, true polar wander, core heat and mantle avalanches are important. Red regions are assumed to be hot and buoyant; blue regions are cold and dense. Only a few hotspots are claimed to be the result of deep narrow plumes extending to the core-mantle boundary – different authors have different candidates. The schematic is based on fluid dynamic experiments that ignore pressure effects and, of necessity, have low viscosity relative to conductivity.
The right side indicates the important attributes of the plate model; variable depths of recycling, migrating ridges and trenches, concentration of volcanism in tensile regions of the plates, inhomogeneous and active upper mantle, isolated and sluggish lower mantle, and pressure-broadened ancient features in the deep mantle. Low-density regions in both the shallow and deep mantle cause uplift and extension of the lithosphere. Melting anomalies are localized by stress conditions and fabric of the plate and fertility of the mantle. Large-scale features are consistent with the viscosity-conductivity-thermal expansion relations of the mantle. In the plate model the upper mantle (down to about 1000 km, the Repetti Discontinuity) contains recycled and delaminated material of various ages and dimensions. These materials equilibrate at various times and depths. Migrating ridges, including incipient ridges and other plate boundaries, sample the dispersed components in this heterogeneous mantle. The upper 1000 km (Bullen’s Regions B & C) is the active and accessible layer. The deep mantle (Regions D and D”), although interesting and important, is sluggish and inaccessible. The geochemical components of MORB, OIB etc. are in the upper mantle and are mainly recycled surface materials. Red and blue regions are respectively low and high seismic velocity regions, not necessarily hot and cold, although some of the red regions at the top and base of the mantle are due to the presence of a melt.