Plate Tectonics Earth Science

Continental Drift The theory of Continental Drift was created by Alfred Wegener in ~ 1915 His theory stated that the continents were one large land mass called Pangea and drifted to their present locations

Evidence For Pangea Jig-Saw Puzzle Fit Of Continents PANGAEA Jig-Saw Puzzle Fit Of Continents B) Similar Rocks and Fossils C) Glacial evidence D) Coal Deposits E) Mountain Ranges 225 million years ago 135 million years ago 65 million years ago Present

Theory of Plate Tectonics The Theory of Plate Tectonics states that Earth’s crust is made up of a number of solid pieces called plates, and these plates move in relation to each other. The term tectonics refers to the forces that deform Earth’s Crust.

INDIAN-AUSTRLIAN PLATE Reykjanes Ridge EURASIAN PLATE EURASIAN PLATE Mid- Atlantic Ocean Ridge ANATOLIAN PLATE JUAN DE FUCA PLATE NORTH AMERICAN PLATE CHINA SUBPLATE CARIBBEAN PLATE Transform fault PHILIPPINE PLATE ARABIAN PLATE PACIFIC PLATE COCOS PLATE AFRICAN PLATE Mid- Indian Ocean Ridge Transform fault SOUTH AMERICAN PLATE Carlsberg Ridge East Pacific Rise SOMALIAN SUBPLATE INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( ) boundaries Plate motion at divergent plate boundaries Convergent plate boundaries

Oceanic vs. Continental Crust Oceanic Crust (predominately igneous basalt) Mafic – rich in iron High density, thin Continental crust (predominately granite) Felsic – rich in feldspars and Al Low density, thick

What is the Driving Force? The driving force to move the plates comes from convection cells in the mantle

Spreading center Oceanic tectonic plate Oceanic tectonic plate Ocean trench Collision between two continents Plate movement Plate movement Tectonic plate Oceanic crust Oceanic crust Subduction zone Continental crust Continental crust Material cools as it reaches the outer mantle Cold dense material falls back through mantle Mantle convection cell Hot material rising through the mantle Two plates move towards each other. One is subducted back into the mantle on falling convection current. Mantle Hot outer core Inner core

Divergent Boundary 2 plates separate Example: Mid-Atlantic Ridge Features Formed: Mountains Volcanoes Ridges Rift Valleys

Convergent Boundary 2 plates come together Example: land/land (Collisional Boundary) India/Asia Features Formed: Mountains - Himalayas

Convergent Boundary 2 plates come together Features Formed: Example: ocean/land Nazca plate/S. American plate Features Formed: Subduction Zones Ocean Trenches Mountains Volcanoes

Transform (lateral) Boundary 2 plates slide past each other Example: San Andreas Fault Features Formed Fault Line

San Andreas Fault

Plate Tectonics

Evidence for Sea Floor Spreading Igneous Ocean Rock – evidence shows that igneous material along the center of the mid-ocean ridge is younger (it formed most recently) than the igneous material farther from the ridges. As new crust is generated at the mid-ocean ridges, the ocean floor widens.

Sea Floor Spreading

Reversal of Magnetic Polarity The strips of basaltic igneous rock which lie parallel to the mid-ocean ridges show matched patterns of magnetic reversals Over thousands of years, the magnetic poles of Earth reverse their polarities, the north magnetic pole becomes the south magnetic pole and vice versa

Magnetic Polarity Cont. When basaltic magma flows up into the ridge and cools, crystals of magnetic minerals align themselves with Earth’s magnetic field like tiny compass needles, thus recording the magnetic polarity at the time of formation.

Magnetic Reversals

Hot Spots

Hot Spots

Hot Spots Hot Spots: Places on Earth’s surface found within the plates, with unusually high heat flow. The cause of these hot spots are plumes of magma rising up from the mantle producing active volcanoes.

Hot Spots Continued As the plate passes over a hot spot, a chain of volcanic mountains form. The only mountain that remains active is the mountain located directly over the hot spot.

Hot Spots

Crustal Activity Normal Deposition of Rock Layers (Strata): Horizontal layers show no movement (crustal activity) Sedimentary Rock Lava Flows

Folding Caused by strata (layers) bending due to mountain building. Example: Appalachian Mountains

Tilting Layers of rock that have moved from a horizontal position to an angular position Example: Any fault or an area uplifted by an intrusion

Faulting A zone of weakness or a crack in the crust along which rocks have moved. If there is no movement it is called a fracture. Examples: Teton Mountains San Andreas Fault

Fault-block Mountains

Evidence of Crustal Activity Displaced Fossils: Marine fossils found in layers of sedimentary rock thousands of feet above sea level Suggests that layers rock (strata), have been uplifted.

Evidence of Crustal Activity Subsidence: The sinking of rock strata. Shallow water organisms have been found as fossils deep within the ocean, indicating the land is sinking