Why do lithospheric plates float on the mantle

Magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents. Thus, at convergent boundaries, continental crust is created and oceanic crust is destroyed. It is the only place in the world where you can swim between two tectonic plates. Skip to content Common questions.

The mantle can then rise and create volcanoes. The point is that magma is created in small pockets small relative to the size of the earth as part of the tectonic plate movement, and does not exist as a global sea of magma just under the crust.

The confusion about the state of the upper mantle perhaps arises from the way diagrams are presented. For instance, the image above shows the mantle in a glowing orange color. This coloring can be confused to mean that this layer is hot liquid rock, like lava. In reality, the mantle is solid, and the coloring is just meant to indicate that the rock is hot and flowing slowly under heat convention. But natural seismic waves are kilometres in length — too long to resolve the fine-grained structure below the plates.

So the New Zealanders took matters into their own hands. The resulting waves are about metres long and able to resolve finer structures. The team set up Coke can-sized seismometers strung like beads along 85 kilometres. Then from multiple boreholes they detonated half a tonne of TNT in each. The New Zealand team suggests the jelly rock gains its consistency from a higher concentration of water or magma than is present in the lithosphere above it. But it would not have to be too high. While the lithosphere contains 0.

The finding of the jelly channel might also help resolve a year debate about whether the plates move as a result of being pushed or pulled. An early idea was that magma being extruded from the mid-oceanic ridges was pushing the plates apart. According to the theory of plate tectonics, the outer part of the Earth is a layer of rock about kilometers thick.

This shell is divided into at least 25 pieces, which are called plates. These plates move very slowing on the partially molten Earth layer asthenosphere below them.