Tackley P.J. (2000). Mantle convection and plate tectonics: toward an integrated physical and chemical theory. Science, 288, 2002-2007

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Fig. 1 Numerical simulations of mantle convection with self-consistently generated plate tectonics [from (38)]. The rheotogical model incorporates temperature-dependent viscosity varying by up to five orders of magnitude, a constant (with depth) yield stress, and a factor of 10 viscosity reduction when the temperature reaches the solidus. The left column shows the logarithm of viscosity relative to a reference mantle value; red corresponds to the strongest material and purple corresponds to the weakest material. The right column shows cold downwellings (where the temperature is 250 K colder than the horizontal average). System behavior depends critically on the yield strength: With low yield strength (A and B), plate-like surface motion is observed but plates are weak. With intermediate yield strength (C and D), plate-like behavior is observed with strong plates and weak boundaries. With high yield strength (E and F), rigid lid behavior is observed.

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Fig. 2 Some possible locations of mantle reservoirs and relationship to mantle dynamics. Convective features: blue, oceanic plates/slabs; red, hot plumes. Geochemical reservoirs: dark green. DMM. purple, high 3He/4He ("primitive"); light green, enriched recycled crust (ERC).

(A) Typical geochemical model layered at 660 km depth (7).
(B) Typical geodynamical model: homogeneous except for some mixture of ERC and primitive material at the base.
(C) Primitive blob model (71) with added ERC layer.
(D) Complete recycling model (83, 84).
(E) Primitive piles model [developed from (85)].
(F) Deep primitive layer (86).

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Fig. 3  Structure in the mantle, as imaged by seismic tomographic model SB4L18 (58). Blue isocontours show where the shear wave velocity is 0.6% higher than normal ("cold" material), and red isocontours show where the shear wave velocity is 1% lower than normal ("hot material).
(A) looking from the south, with the CMB at the bottom of the image and Earth's surface at the top of the image. Downwelling former oceanic plates (blue) appear to sink to the CMB in most areas. Two large megaplumes (red) are observed underneath Africa (left of image) and the Pacific (center of image). (B) Looking down from above, the pattern of continents and oceans is clearly visible.