Subduction zones lower mantle

Kaneshima S. and Helffrich G. (1998) Detection of lower mantle scatterers northeast of the Mariana subduction zone using short-period array data. J. Geophys. Res. 103, 4825-4838. 

Subduction Zone Processes and Implications for Changing Composition of the Upper and Lower Mantle... 

Figure 9 Examples of models proposed for the chemical structure of the terrestrial mantle, (a) Whole mantle convection with depletion of the entire mantle. Some subducted slabs pass through the transition zone to the coremantle boundary. Plumes arise from both the core-mantle boundary and the transition zone. This model is not in agreement with isotopic and chemical mass balances, (b) Two-layer mantle convection, with the depleted mantle above the 660 km transition zone and the lower mantle retaining a primitive composition, (c) Blob model mantle where regions of more primitive mantle are preserved within a variously depleted and enriched lower mantle, (d) Chemically layered mantle with lower third above the core comprising a heterogeneous mixture of enriched (mafic slabs) and more primitive mantle components, and the upper two-thirds of the mantle is depleted in incompatible elements (see text) (after Albarede and van der Hilst, 1999).

Figure 16 Schematic illustration of mechanisms for transfer of sediments, volcanics, and/or lower erustal gabbros into the mantle wedge from the subducting plate and the base of arc crust. Dark black line indicates position of the subduction zone below this line, material subducts at the convergence velocity. Above this line, material is carried downward more slowly. Any process leading to slow transport of low-melting point metasediment, metabasalt, or metagabbro into the mantle wedge would lead to partial melting of this material beneath an arc.

Fig. 2. Reservoirs and fluxes used in previous and present modelling work (not to scale). Rectangles used for reservoirs ellipses for loci of fractionation by melt processes, m-f, depleted mantle melting, oceanic crust (MORB) formation s-f, subduction zone melting leading to continental crust formation c-f, intracrustal fractionation leading to upper and lower crust formation. Bold arrows, fluxes involving trace element fractionation line arrows flirxes without trace element fractionation stippled arrows, fluxes operating only during accretion and core formation.

FIGURE 3.2 Tomographic image of the Earth s mantle beneath the Japanese Arc, down to the core-mantle boundary showing the distribution of slow and fast seismic waves. The wave velocity distribution also reflects temperature distribution and shows the penetration of a cold subducting slab through the transition zone into the lower mantle (after Fukao et al., 2001). 

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