Theory of Plate Tectonics

Plate Tectonics Is theory that states that pieces of the Earth’s crust are in constant, slow motion. This motion is caused by convection currents in the mantle.

As the plates move, they collide, pull apart, and grind past each other. No plate can move without affecting the other plates.

How do the plates move ? 1. Convection currents – Drags the plates along. Convection current cools and sinks. Downward movement may cause subduction of plates.

2. “Slab push – slab pull” – Magma rising along the mid- oceanic ridge exerts force that pushes plates away. Pull hypothesis – force of gravity causes plate movement by pulling cooler, denser plate down. Both may work with convection currents.

Plate boundaries Edges of the Earth’s lithosphere meet at plate boundaries. Faults – breaks in the Earth’s crust where rocks slip past each other form these boundaries.

Transform Boundary A place where two plates slip past each other, moving in opposite directions. No crust is created along this boundary. Earthquakes occur frequently along these boundaries.

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Divergent Boundary Plates move apart or diverge from each other. Most occur along the mid- ocean ridge. A rift valley, a deep valley, occurs when divergent plates move past each other on land.

Divergent Boundary

Convergent Boundary A place where two plates come together. This movement results in a collision of the two plates. Density of the plates determines which one comes out on top.

Convergent Boundary

Convergent Boundaries Results of collision Oceanic/oceanic - Subduction occurs Oceanic/continental - Oceanic plate sinks Continental/continental - Mountain range