Plate Movements Part 2 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. Divergent 2. Convergent 3. Transform • Each type of boundary produces unique features on Earth’s crust. . .
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 Feature: Mid-Ocean Ridges • Mid-Ocean ridges occur when the divergent boundary is underwater at an oceanic-oceanic divergent boundary. • This is also the site of sea floor spreading since new material is added as the plates separate.
Divergent Boundary Feature: Rift Valley • Rift valleys occur when the divergent boundary is on land at a 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. • These boundaries consume crust as it subducts.
Convergent Boundary Feature: Subduction Zone • When the two plates collide and one is denser than the other, then the denser plate SUBDUCTS (slides under) the less dense plate. • The area where the denser plate slides underneath is called the subduction zone.
Convergent Boundary Feature: Trenches • Trenches form at oceanic-continental convergent boundaries • As the oceanic plate bends down, it leaves a gap in the sea floor.
Convergent Boundary Feature: Continental Volcanoes • Continental volcanoes form at oceaniccontinental 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 • Volcanic Island Arcs occur at oceanic-oceanic convergent boundaries. • The denser oceanic crust slides under less dense crust, melts, and then magma pushes up through the upper oceanic crust.
Convergent Boundary Feature: Mountain Ranges • Mountain Ranges form at continental-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.
Transform Boundary • At a Transform Boundary, 2 plates scrape past each other. • Crust is not formed or consumed at these boundaries. • Transform boundaries have numerous volcanoes and shallow earthquakes.