Subduction of Plates. Because ocean plates are denser than continental plates, when these two types of plates converge, the ocean plates are subducted beneath the continental plates. Subduction zones and trenches are convergent margins. The collision of plates is often accompanied by earthquakes and volcanoes.
http://www.ucmp.berkeley.edu/education/dynamic/session1/sess1_earthcurrents.html
This video features a demonstration I performed for my 6th grade science class. It shows how convection occurs in the mantle of the earth and its relationship to the theory of Plate Tectonics. 1  Education.
http://www.youtube.com/watch?v=jkKlGXG4lG8
Heat is transferred by convection in numerous examples of naturally occurring fluid flow, such as: wind, oceanic currents, and movements within the Earth's mantle. Convection is also used in engineering practices of homes, industrial processes, cooling of equipment, etc.
https://en.wikipedia.org/wiki/Convection
Click the image to see the animation. This animation shows a cross section of Earth; it illustrates a mathematical model of how convection might occur in the mantle. Diagrams of convection cells in the mantle are often highly simplified, but researchers are finding that the real world is much more complex. In the model, red represents heated materials that are less dense than their surroundings. Dark blue represents cooler materials that are denser than their surroundings. Examine the motion of mantle material near the outer edge of the model. Consider how the motions you observe might affect Earth's tectonic plates.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0805/es0805page01.cfm
Convection currents in the magma drive plate tectonics. Heat generated from the radioactive decay of elements deep in the interior of the Earth creates magma (molten rock) in the aesthenosphere. The aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the Earth that extends to 2900 km.
http://www.ucmp.berkeley.edu/education/dynamic/session1/sess1_earthcurrents.html
It contrasts with the more rigid lithosphere, the outer shell of the Earth (0 ~ 70 km) that contains the continental crust (made up of less dense granitic rocks) and the oceanic crust (more dense basaltic rocks) that are broken up into more than a dozen rigid plates. For more info, see:
http://www.ucmp.berkeley.edu/education/dynamic/session1/sess1_earthcurrents.html
Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be seen as clouds, with stronger convection resulting in thunderstorms. Natural convection also plays a role in stellar physics.
https://en.wikipedia.org/wiki/Convection
Diffusion of heat can take place in solids, but that is called heat conduction. Convection can be demonstrated by placing a heat source (e.g. a Bunsen burner) at the side of a glass full of a liquid, and observing the changes in temperature in the glass caused by the warmer ghost fluid moving into cooler areas.
https://en.wikipedia.org/wiki/Convection
Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the earth to the surface. It is one of 3 driving forces that causes tectonic plates to move around the Earth's surface.
https://en.wikipedia.org/wiki/Convection
In the context of heat and mass transfer, the term convection is used to refer to the sum of advective and diffusive transfer. In common use the term convection may refer loosely to heat transfer by convection, as opposed to mass transfer by convection, or the convection process in general.
https://en.wikipedia.org/wiki/Convection
where is the convection currents in the mantle
In the mantle convection currents from the interior of the earth to the surface. The convection currents are in the magma drive plate tectonics. The convection currents in the mantle is in the magma drive plate tectonics.