Whole-mantle convection

Whole-mantle convection is a model in which mantle material circulates across the boundary between the upper and lower mantle. It contrasts with models that keep the two regions largely separate.

Mantle convection: The slow circulation of solid mantle rock driven by internal heat and buoyancy. Whole-mantle convection is the version in which this circulation spans the mantle’s full depth.
Layered mantle convection: A model in which upper- and lower-mantle circulation are partly or largely separated. It is the principal alternative to circulation through the mantle’s full depth.
Subduction: The descent of one tectonic plate beneath another into Earth’s mantle. Subduction sends surface material downward and supplies the clearest candidate flow across the transition zone.
Seismic tomography: A method that images Earth’s interior by reconstructing seismic-wave speeds from earthquake and other recordings. Tomographic images trace slabs and plumes, but interpretation of their continuity is not unique.
Mantle transition zone: The mantle region between roughly 410 and 660 kilometers depth, marked by mineral phase changes. Its phase changes can resist or assist flow between upper and lower mantle.
660-kilometer discontinuity: A seismic boundary near 660 kilometers depth associated with mineral transformations and changes in mantle properties. Its resistance to sinking slabs is central to proposals for convection divided at this depth.
Slab graveyard: A region of accumulated subducted lithosphere imaged in the deep mantle by seismic methods. Deep slab accumulations indicate that at least some subducted material reaches the lower mantle.
Mantle mixing: The redistribution of mantle material that reduces chemical and isotopic differences between regions. Whole-mantle circulation does not establish how rapidly distinct materials become chemically homogenized.
Ringwoodite: A high-pressure magnesium iron silicate mineral stable in much of the mantle transition zone. Its water storage and breakdown influence the density structure near the boundary crossed by mantle flow.
Stagnant slab: A subducted lithospheric plate that flattens or stalls near the mantle transition zone. Stagnant slabs show how the transition zone can temporarily impede downward transport.

Linked from 5 pages