Plate Movements Part 2 Earths Layers Mantle Convection

Plate Movements Part 2 Earth’s Layers & Mantle Convection

How the Plates Move • See website for video link.

Mechanism of Plate Movement Part 1: Mantle Convection • Rigid lithospheric plates lie on top of the semi-fluid asthenosphere • Heat from the Earth’s core powers mantle convection currents

Mechanism Part 1: Mantle Convection Currents a. The core heats the magma in the asthenosphere b. Hot magma is less dense and rises up toward the surface c. Near the surface, magma cools, making it more dense, causing it to sink back down d. The cycle repeats as the magma nears the core.

Mantle Convection • The lithospheric plates “surf” on top of the asthenosphere as the magma cycles

Mechanism of Plate Movement Part 2: Ridge Push • 2 convection currents meet and… 1. Both cells push magma up at the same spot 2. Some magma breaks through the crust and forms a ridge of new crust 3. The ridge of new crust pushes the older crust/ lithospheric plates away from the area —this is called RIDGE PUSH! • Separating plates = DIVERGENT BOUNDARY

How the Plates Move: Ridge Push Oldest Youngest Oldest

How Plates Move

Mechanism of Plate Movement Part 3: Slab Pull/Gravity Pull • 2 convection currents meet and… 1. Both cells are pulling magma down 2. The plates floating on top are pulled together a. Mountains: Plates with continental crust (have same low density) push crust up to make mountains.

Slab Pull/Gravity Pull b. Subduction: with plates with different densities (one or both are oceanic crust), cause the denser plate to slide under the less dense plate

Slab Pull/Gravity Pull § Bottom/denser plate is pulled down into the mantle—this is called SLAB/GRAVITY PULL § This plate melts, becomes new magma, and cycles through the convection current • Colliding plates = CONVERGENT BOUNDARY

Partner Discussion: Is the Earth getting smaller or larger? • NEITHER!!! It stays the same size! • The new rock that forms at the ridge/rift is really recycled rock from a plate that was pulled into the mantle