Tectonic Convection Currents

❧ The magma below the crust flows from the core, upwards towards the crust and after it cools it returns to the core to be reheated. This process is called a CONVECTION CURRENT. ❧ This has a marked affect on the plates that make up the Earth’s surface.

❧ South America are two continents for which there is plenty of evidence that once they were joined together.

❧ As these two continents have drifted apart, the Atlantic Ocean has formed in the new basin between them. ❧ The water is very heavy and stretches the crust down into a deep basin many kilometres deep.

❧ The Convection current movement of magma can be likened to what happens to rice as it boils in a pan of water.

❧ The following animation sequence explains what happens as convection currents flow through the magma below the crust.

The core sends a plume of mantle upwards towards the crust.

CORE

The plume rises away from the core.

The magma current spreads out sideways under the crust.

As it spreads it cools down

Heat is transferred to the lithosphere

The cooler magma sinks back towards the CORE.

Where it gets reheated ….

The movement of the magma under the crust pulls the continetal plates apart and allows magma to well up through the gap. Continental Plate Eg: S.America

Continental Plate. Eg: Africa

The gap is quickly filled by cooling basalt lava.

The process repeats itself…

.. And new , thinner crust is formed between the two continents

The new crust quickly get flooded by water flowing of the continents to form a new ocean basin. Hence the crust below is called oceanic crust.

This is how it all works again …. S. America

Africa

These are the key features associated with sea floor spreading.

This map shows the main Plate Boundaries North America

Atlantic Ridge U.K.