Plate Tectonics

Objective 1  Define the word plate as it is used in geology.

The Earth’s crust is made of several plates that are in constant slow motion.

Objective 3,4,5,6 3. Describe in words the difference between the motions of the major types of plate boundaries: Convergent Divergent Transform 4. Describe how each of the following form as a result of plate tectonics Mid-Ocean ridge (or rise) Deep Ocean Trench Island Arc Volcanoes 5. Explain why deep focus earthquakes are only at converging plate boundaries 6. Explain how each of the following mountain ranges formed as a result of plate tectonics. Haiwaiian Island Mountains Himalayan Mountains Appalachian Mountains Cascade Mountains

Three types of plate boundaries 1. Divergent 2. Convergent 3. Transform

Divergent Boundary Two crustal plates moving away from each other.

Divergent Boundary  HOT MAGMA FROM THE ASTHENOSPHERE RISES UNDER THE OCEAN CRUST. SOME MAGMA COMES OUT ON TO OCEAN FLOOR AND SOLIDIFIES AS NEW OCEAN FLOOR. CURRENTS IN THE ASHTHENOSPHERE PUSH THE CRUSTAL PLATES AWAY FROM EACH OTHER.

Divergent Boundary  MID OCEAN RIDGES FORM WHERE MAGMA PUSHES UP BETWEEN SEPARATING PLATES. THIS IS CALLED SEA FLOOR SPREADING BECAUSE THE SEA FLOOR ENLARGES FROM THE DIVERGENT PLATE BOUNDARIES. A RIFT VALLEY FORMS WHERE THE CRACK IS BETWEEN THE SEPARATING PLATES.  Example : Iceland

Divergent Boundary  A RIFT VALLEY FORMS WHERE THE CONTINENT IS SPLIT APART.  SOME VOLCANOES OCCUR IN THE RIFT VALLEY. Example: East Africa

Convergent Boundary  One plate slides into another plate.  There are 3 types of convergent boundaries.  Oceanic-continental  Oceanic-oceanic  Continental-continental

Convergent Boundary  ONE OCEANIC PLATE SLIDES UNDER A CONTINENTAL PLATE.  OCEANIC PLATE IS PUSHED DOWN INTO ASTHENOSPHERE WHERE THE OCEANIC PLATE MELTS.  WHERE ONE PLATE GOES UNDER ANOTHER IS CALLED A SUBDUCTION ZONE.

Ocean-Continental  Jean De Fuca Plate is being pushed under N. American plate off the coast of Washington and Oregon… Forming the Juan de Fuca trench and the Cascade Volcanoes  Nazca Plate is bing pushed under the South American Plate, forming the Andes Volcanic Mountains and the Peru-Chili Deep Ocean Trench

Oceanic-Oceanic  One Oceanic plate slides into and under another Oceanic plate… Forms a subduction zone.  The Oceanic plate that subsides melts in the Asthenosphere and the magma rises to form island arc volcano chains.

Continental-Continental  ONE CONTINENTAL PLATE CONVERGES WITH ANOTHER CONTINENTALPLATE  NO SUBDUCTION ZONE FORMS

Transform Boundary  One plate slides sideways past another plate.  Form huge fault zones on land  Many shallow focus earthquakes  No volcanoes  Example: San Andreas Fault Zone