Plate Movements Part 3 Plate Boundaries Divergent Convergent

Plate Movements Part 3 Plate Boundaries: Divergent, Convergent, and Transform

Tectonic Plates Review • The Earth’s rigid lithosphere (crust and upper mantle) is broken into numerous plates. • The plates move around on top of the molten asthenosphere (lower mantle). • As the plates move individually, this motion means some plates move apart while others collide. • This motion is driven by the mantle’s convection currents, ridge push, and gravity pull.

Types of Plate Boundaries • There are three types of plate boundaries: 1. Transform 2. Divergent 3. Convergent • Each type of boundary produces unique features on Earth’s crust. . .

Transform Boundary • Here, 2 plates scrape past each other. • Crust is NOT formed or consumed at these boundaries. • Land features include numerous volcanoes , shallow earthquakes, and maybe misaligned rivers.

Divergent Boundary • At a divergent boundary, 2 plates separate. • These plates create new crust from magma. § Magma pushes aside the old crust as new rocks form. § The type and magnetism of the rock makes a mirror image on both sides of the ridge.

Divergent Boundary Land Feature: Mid-Ocean Ridges • Only occur when 2 separating plates are underwater; called an oceanic-oceanic divergent boundary. • This is the area where sea floor spreading happens (the new crust pushes apart the old sea floor).

Divergent Boundary Land Feature: Rift Valleys • Only occur when the 2 separating plates are on land; called a continental-continental divergent boundary.

Convergent Boundary • At a Convergent Boundary, 2 plates collide. • The result of the collision depends on the types of crusts where the plates hit. § Oceanic crust is always denser than continental crust. • Convergent boundaries consume or destroy crust.

Convergent Boundary Feature: Mountain Ranges • Only occur at continental convergent boundaries. • Continental crust is too buoyant (not dense enough) to be pulled into the mantle, detaches from the bottom of the plate, and piles up into mountains.

Convergent Boundary Land Feature: Subduction Zone • When the 2 plates collide and one is denser (oceanic) than the other, then the denser plate SUBDUCTS under the less dense plate. • The area where the denser plate slides underneath is called the subduction zone.

Convergent Boundary Land Feature: Trenches • Occur at oceanic-continental and oceanic convergent boundaries • As the oceanic plate bends down, it leaves a gap in the sea floor.

Convergent Boundary Land Feature: Continental Volcanoes • Only occur at oceanic-continental convergent boundaries. • The oceanic crust melts underneath the continental crust, and then magma pushes up through the continent. Continental Volcanoes

Convergent Boundary Feature: Volcanic Island Arcs • Only occur at oceanic-oceanic convergent boundaries • The denser oceanic crust slides under less dense crust, melts, and then magma pushes up through the ocean above.