How does mantle convection work

Although mantle convection is so slow that we don't really see it happening a few cm per year , over geologic time spans millions of years this velocity amounts to considerable travel distances for the moving material.

We all have seen convection before. Everytime we cook a pot of water, for example, convection occurs. At the left we see a picture of a pot of water that is heated from below. Mantle Convection on Earth. How do convection cells work? Why do convection cells have a circular movement? Where does mantle convection occur? How does mantle convection drive plate tectonics?

How does this relate to continental drift? How does plate tectonics activate volcanoes and earthquakes?

When hot water rises up, it will try to go into an equilibrium. So at first, that means that it mixes into the cold water above. But how does this relate to continents? Are continents actually moving? Each continent rides on plate tectonics like a colossal conveyor belt. Overview of Forces. All the forces listed above can be summarised in the diagram below. Driving mechanism of plate tectonics. Slab pull, slab trench suction and ridge push forces drive plate motion Slab resistance, continental reistance, transform fault resistance and basal drag oppose plate motion When resisting forces become greater than the driving forces, collision between the plates will eventually cease.

The pattern of mantle convection deep in geological time is uncertain. More or different types or rates of mantle convection may have helped to allow the early Earth to lose heat more efficiently. Further research is needed on linking the preserved record of mantle convection in the deformed continents to help interpret the past history of convection.

Convergent plate margin processes structural, igneous, metamorphic, and sedimentological processes that occur in the region affected by forces associated with the convergence of two or more plates are grouped under the heading of convergent plate margin processes.

Convergent plate boundaries are of two fundamental types, subduction zones and collision zones. The second type of subduction zone forms where an oceanic plate descends beneath a continental upper plate, such as in the Andes of south America. Arcs have several different geomorphic zones defined largely on their topographic and structural expressions. The active arc is the topographic high with volcanoes, and the backarc region stretches from the active arc away from the trench, and it may end in an older rifted arc or continent.

The forearc basin is a generally flat topographic basin with shallow to deep-water sediments, typically deposited over older accreted sediments and ophiolitic or continental basement. The accretionary prism includes uplifted, strongly deformed rocks scraped off the downgoing oceanic plate on a series of faults.

The trench may be several to six miles up to 10 or more kilometers deep below the average level of the seafloor in the region and marks the boundary between the overriding and underthrusting plate.

The outer trench slope is the region from the trench to the top of the flexed oceanic crust that forms a several hundred to one-thousand-foot few hundred-meter high topographic rise known as the forebulge on the downgoing plate. Trench floors are triangular shaped in profile and typically are partly to completely filled with grey-wacke-shale turbidite sediments derived from erosion of the accretionary wedge.

They may also be transported by currents along the trench axis for large distances, up to hundreds or even thousands of miles thousands of kilometers from their ultimate source in uplifted mountains in the convergent orogen.

Flysch is a term that applies to rapidly deposited deep marine syn-orogenic clastic rocks that are generally turbidites. Trenches are also characterized by chaotic deposits known as olistostromes that typically have clasts or blocks of one rock type, such as limestone or sandstone, mixed with a muddy or shaly matrix.

These are interpreted as slump or giant submarine landslide deposits. They are common in trenches because of the oversteepening of slopes in the wedge. The sediments are deposited as flat-lying turbi-dite packages, then gradually incorporated into the accretionary wedge complex through folding and the propagation of faults through the trench sediments.

It causes the rotation and uplift of the accretionary prism, which is a broadly steady-state process that continues as long as sediment-laden trench deposits are thrust deeper into the trench. Typically new faults will form and propagate beneath older ones, rotating the old faults and structures to steeper attitudes as new material is added to the toe and base of the accretionary wedge. This process increases the size of the overriding accre-tionary wedge and causes a seaward-younging in the age of deformation.

Parts of the oceanic basement to the subducting slab are sometimes scraped off and incorporated into the accretionary prisms. These tectonic slivers typically consist of fault-bounded slices of basalt, gabbro, and ultramafic rocks, and rarely, partial or even complete ophiolite sequences can be recognized.

Major differences in processes occur at Andean-style compared to Marianas-style arc systems.