Driving pressures of Plate movements

Does mantle convection drive plate tectonics?

After the discovery of radiation by Marie Curie and also Henri Becquerel in 1896 it became clear the the Earth"s inner would it is in heated by radioactive decay in the mantle and crust. Rock is a negative conductor that heat. If there were not some other device to cool the interior the Earth"s internal would be mainly molten. However the growing seismic data from about the turn of the and an initial two decades of the 20th century showed that the crust and mantle were solid. Holmes proposed that the interior was cooled by convection the the solid, ductile mantle. By 1928 Holmes used mantle convection as a mechanism to develop continental drift as discussed by Wegener and also DuToit. However the concept of a convecting heavy mantle wasn"t an extremely palatable to the clinical mainstream of the time.

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In the 1960s through the plate tectonics revolution, very early hypothesis for a driving force for seafloor dispersing was earlier to mantle convection. In fact, convection practically certainly does happen in the mantle. Seismic tomography that the mantle shows locations of reduced seismic velocities - lower density (hotter) mantle rock which presumably room rising and other locations of greater seismic velocity - greater density (not as hot) rock which have to be sinking. But some key are very wide, thousands of kilometers from the ridge to the trench, and it doesn"t seem plausible to have a convection cell that is really wide (thousands of kilometers) in comparison come its depth (less than 670 km). Seismic tomography shows that increasing mantle product beneath ridges only extends down 200 come 400 km. Moreover, interpretation of geoid anomalies, based upon variation in gravity produced by upwelling and also downwelling regions, suggests that there are multiple convection cell beneath the Pacific plate. The linked effect would certainly not it is in one that would certainly drive the motion of the key - part cells would help, some would certainly hinder. Additionally, the asthenosphere is weak enough that relatively little pressure would be applied to the base of the oceanic lithosphere by convecting mantle.

So, if no convection, then what?

The most crucial forces: gravity = "ridge push" and "slab pull" (Forsyth and also Uyeda, 1975)

"ridge push" The lithosphere thickens v distance (and time) away from the midocean ridge. This is since it cools as it moves away from the ridge and also the boundary between the heavy lithosphere and also slightly molten asthenosphere becomes deeper - the boundary in between the lithosphere and asthenosphere is essentially a temperature boundary. The an outcome of this thickenning with distance indigenous the ridge is the the lithosphere/asthenosphere border slopes away from the ridge. The weight of the lithosphere ~ above this sloping surface ar produces a downslope force. And also since the asthenosphere is weak, the load of the lithosphere close to the ridge sliding down the "slippery slope" of the asthenosphere "pushes" the older component of the key in front of it. Note that together the lithosphere slides under away from the ridge, tensional forces and also normal error earthquakes take place at the ridge axis where 2 plates room sliding (pulling) apart.

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"slab pull" together lithospheric plates relocate away from midocean ridges lock cool and also become denser. They at some point become an ext dense 보다 the underlying hot mantle. After subducted, cool, thick lithosphere sinks into the mantle under its very own weight. This helps to pull the remainder of the bowl down with it.

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resisting forces The main effect of the underlying mantle is to produce a shearing or frictional pressure resisting the motion of lithospheric plates. And also for recently subducting slabs, the resisting force of the mantle together the slab tries to force its way through is stronger than the shearing ~ above the top and bottom the the descending slab. Friction between the converging bowl and likewise the pressure required to bending a plate stand up to the motion of the plate at subduction zones.

It seems likely that heaviness drives the plates and also the activities of the plates help to row the mantle, rather than the convection that the mantle steering the plates.

However, mantle circulation may be vital locally v respect come the activity of continents v deep keels (thickened lithosphere, particularly in old orogenic belts), yet not for oceanic lithosphere.