Plate Tectonic Boundaries

Plate Tectonic Boundaries

The Crust (The surface) The thin rigid outermost layer of the Earth is the crust. The thinnest crust (oceanic) is 3 miles and the thickest (continental) is 50 miles. The Mantle (The middle) The mantle extends from 50 miles to a depth of 1,750 miles beneath the Earth's surface. The upper part is solid and the lower part is fluid. The Core (The center) The center part of the earth made of nickel and iron. Its temperature is 4,000 to 9,000 degrees F. The outer core is fluid and the inner core is solid.

Tectonic Plates The Earth's crust and rigid upper mantle are broken into eight enormous slabs called tectonic plates. There are also seven small tectonic plates.

The Nature of the Tectonic Plates The tectonic plates consist of the crust and a rigid portion of the upper mantle, together called the lithosphere. A plate is about 60 miles thick.

Tectonic Plates Float Similar to the way wood blocks float on water because they are less dense, the plates float on the much denser mantle.

Plate Mobility Tectonic plates are in constant motion. On average, plates move 2 or 3 inches each year. Global positioning satellites (GPS) allow the precise motion of the continents to be measured.

What Causes plates to move? 1.Mantle Convection 2.Ridge Push 3.Slab Pull http://www.absorblearning.com/media/attac hment.action?quick=12p&att=2775

Mantle Convection Convection currents in the mantle force tectonic plates apart along divergent ridges. http://education.sdsc.edu/optipute r/flash/convection.htm

Ridge Push The plates are pushed apart at divergent margins along ocean ridges.

Slab Pull When the ocean floor descends back into mantle, the slab of oceanic crust pulls the entire slab down.

Rift Push Slab Pull

The edges of tectonic plates are where earthquakes and volcanoes occur.

Three types of plate boundaries Divergent (spread apart) Convergent (come together) Transform (slide past each other) Transform Convergent Divergent

Let s talk about divergent plate boundaries

Major Divergent Boundaries

Sea Floor Spreading New Technology after World War II At the end of World War II, technologies were developed to study the ocean floor. Echo Sounding Creates profiles of the sea bottom using sound waves.

The Mid-Atlantic Ridge Echo-sounding shows that there is a mountain range (7000 feet high) running down the middle of the Atlantic Ocean floor.

Sea Floor Spreading

Sea Floor Spreading The Great Rift Valley The Mid- Atlantic Ridge has a v- shaped valley running down its crest. This valley is called a rift valley because here the crust of the Earth is being torn apart.

Sea Floor Spreading These v-shaped valleys are the location of recent volcanic activity.

Sea Floor Spreading The World's Mid-Ocean Ridges The mid ocean ridge system wraps around the entire planet.

Sea Floor Spreading Glomar Challenger In the Late 1960's a floating drill rig named Glomar Challenger took samples (called cores) of the ocean bottom. A core library.

Sea Floor Spreading The JOIDES Resolution This is a drilling ship of the ocean drilling program. It has recovered more than 104 miles of core samples in the Atlantic, Pacific, Indian, and Arctic oceans.

Sea Floor Spreading Alvin Alvin is a manned deep-ocean research sumersible operated by the Woods Hole Oceanographic Institute. The three-person vessel allows for two scientists and one pilot to dive for up to nine hours at 15,000feet. Click to see a 4 minute video/audio clip about Alvin.

Sea Floor Spreading In 1962, a Princeton University scientist, Harry Hess, proposed the hypothesis of sea floor spreading.

Sea Floor Spreading An Ocean Floor of Volcanic Lava Samples show that beneath a blanket of overlying mud, the ocean floors are made up of hardened lava. Pillow Lavas On the ocean floor lava squeezes out to form pillow shapes.

Sea Floor Spreading Pillow Lava Lava that forms under water has a pillow shape. The mid- ocean ridges are composed of this type of lava. Pillow lava at Avila Point, California

Black Smokers Black smokers are chimneys built by mineral-rich superheated water. They are found on the deep ocean ridges. Sea Floor Spreading

Using fossils to Date Ocean Floor Rock Scientists can determine the age of the lava floor by dating fossil skeletons of microscopic sea organisms that are found in the mud above. Sea Floor Spreading

Sea Floor Spreading Potassium-Argon Dating Lava contains a small amount of radioactive potassium. Over time potassium -40 changes into argon gas. By measuring the proportion of K-40 to argon the age of the lava can be determined.

Sea Floor Spreading Age of the Atlantic Ocean Floor Samples show that newly hardened lava forms along the Mid Atlantic Rift which gets progressively older as you approach the coasts. The oldest sea floor is 200 million years old and located near the continent s edge.

Sea Floor Spreading The Age of the World s Basaltic Lava Ocean Floor Worldwide Sea Floor All the world s ocean floors show the same pattern: The ocean floors are made of a type of hardened lava called basalt. New ocean crust forms along a central crack, called a rift. The ocean floors are younger than 200 million years.

Sea Floor Spreading Destruction of Sea Floor According to Hess, old sea floor is recycled back into the Earth along deep ocean trenches. This process, where ocean crust is destroyed is called subduction.

Let s talk about convergent plate boundaries

Tectonic Plates can converge in three ways: 1. Oceanic Plate to Oceanic Plate 2. Oceanic Plate to Continental Plate 3. Continental Plate to Continental Plate

Convergent Plate Boundaries Tectonic plates are destroyed at most convergent boundaries where one plate slides beneath the other in a process called plate subduction. Marianas

Subduction Zone A subduction zone occurs when an ocean plate is forced down into the mantle beneath a second plate. Deep Trench As the ocean plate descends beneath the overriding plate, it bends, producing a deep ocean trench.

The Destruction of Sea Floor When an oceanic plate collides with a continent or another ocean plate, it undergoes subduction which creates an ocean trench.

The Deepest Ocean Depth The deepest place in the ocean is in the Mariana Trench, south of Japan. The bottom of the trench is nearly 7 miles below the surface. Challenger Deep The deepest part of the trench (35,800 feet) is called the Challenger Deep.

Ocean Plate Ocean Plate Convergence: Volcanic Island Arc When two ocean plates collide, one descends beneath the other. Less dense magma rises creating volcanoes on the ocean floor. These volcanoes create an arc-shaped chain of volcanic islands.

The Aleutian Trench The Aleutian islands of Alaska are a Volcanic Island Arc created by the subduction of the Pacific plate beneath the North American Plate.

Ocean Plate - Continental Plate Convergence When an ocean plate collides with a continental plate, the denser ocean plate descends. Volcanoes form on the edge of the continent. These volcanoes are called Continental Volcanic Arcs.

The Andes A Continental Volcanic Arc The Andes of South America are a continental volcanic arc produced by the subduction of the Nazca oceanic plate beneath South America.

Cascade Range Volcanoes

Continental Plate-Continental Plate Convergence When two continents collide, neither one will subduct into the mantle. One plate overrides the other and mountains form. The collision of India with Eurasia is an example of continent to continent collision. The Himalaya mountains are the result.

The Himalayas The Himalayas extend along the India China border and contain most of the world's tallest mountains. Continent to Continent Mount Everest At 29,028 feet, Mount Everest is the world's tallest mountain.

The Himalayas The Himalayas are 1600 miles long and contain 9 of the 14 tallest mountains in the world. Everest and Makalu are the prominent peaks in the photo below.