The long-wavelength thermal anomalies in the lower mantle have been mapped out, using seismic tomographic models in conjuction with thermodynamic parameters derived from high-pressure mineral physics experiments. These parameters are the depth variations of thermal expansivity and of the proportionality factor between density and seismic velocity. The giant plume-like structures in the lower mantle under the Pacific Ocean and Africa have outer fringes with thermal anomalies around 300 to 400 K, but very high temperatures are found in the center of the plumes near the base of the core-mantle boundary. These extreme values can exceed +1500 degrees and may reflect large hot thermal anomalies in the lower mantle, which are supported by recent measurements of high melting temperatures of perovskite and iron. Extremely cold anomalies, around -1500 degrees, are found for anomalies in the deep mantle around the Pacific rim and under South America. Numerical simulations show that large negative thermal anomalies of this magnitude can be produced in the lower mantle, following a catastrophic flushing event. Cold anomalies in the mid lower mantle have modest magnitudes, around -500 K. A correlation pattern exists between the present-day locations of cold masses and the sites of past subductiun since the Cretaceous. Results from correlation analysis show that the slab mass-flux in the lower mantle did not conform to steady-state nature but exhibited time-dependent behaviour.