The Theory of Tectonic Plates Chapter 7 Section 3

The Theory of Plate Tectonics The Earth’s lithosphere (crust and upper mantle) is divided into tectonic plates. These plates move on top of the asthenosphere (lower mantle). We know that these plates move in different ways.

Tectonic Plates

Tectonic Plate Boundaries A boundary is a place where tectonic plates touch. There are 3 types of tectonic plate boundaries: Convergent Divergent Transform

The numbers on the map represent the rate at which plates are moving in centimeters.

Plate Movement

Convergent Boundary When two plates collide, or move toward each other, the boundary is called convergent There are 3 types of convergent boundaries, depending on what type of crust comes together. Continental-continental Continental-oceanic Oceanic-oceanic

Convergent Boundary Continental-Continental The two continental plates come together Buckle Thicken Push continental crust upward

Convergent Boundary Continental-Oceanic Dense oceanic crust sinks below the continental crust and sinks into the asthenosphere. This is a subduction zone. Sub means below (submarine, subway) Old ocean crust is pushed below the asthenosphere and gets re-melted and recycled.

Convergent Boundary Oceanic-Oceanic One oceanic plate sinks below the other. Another subduction zone

Divergent Boundary Two tectonic plates move away from each other. On the sea floor at the mid ocean ridge this is called sea floor spreading. As the plates move apart, magma rises to fill the gaps. The magma is cooled and forms new ocean floor. The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.

Divergent Boundary Sea Floor Spreading On-land exposure of the Mid-Atlantic Ridge in Iceland. Sea Floor Spreading

Transform Boundary Two tectonic plates move past one another. Their edges are jagged and irregular. As they grind together and jerk, they slide past each other creating earthquakes.

Possible Causes of Plate Movement Convection Currents: hot rock deep in the Earth rises, cooler rock sinks. This movement of magma causes plates to move Ridge push Slab pull

Tracking Tectonic Plate Movement Plates move very slowly, centimeters to inches a year. GPS, Global Positioning System, measures the rate of movement. Radio signals beam continuously from satellites to the Earth. By recording the time it takes for the Ground station to move a given distance, scientists can measure the speed at which plates move. Plate Boundary Animation http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapter_no=visualization http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm