Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Plate Tectonics Types of Plate Boundaries Divergent Convergent Transform Plates move apart, resulting in upwelling of material from the Mantle to create new sea floor. Divergent Plates move together, causing one of the slabs of lithosphere to be consumed into the Mantle as it decends beneath the overriding plate. Convergent Plates slide past each other, without creating or destroying lithosphere. Transform Fault W. W. Norton. Modified from Cox and Hardt, 1986. Each plate is bounded by some combination of types of boundaries. Directions and Rates of Plate Motion Upon entering the hot asthenosphere, the plunging plate (which is relatively cold) begins to warm and loses its rigidity. New lithosphere is continually being created at spreading centers: Since the total surface area of the Earth remains constant, lithosphere must also be destroyed somewhere else. Zones of Plate Convergence When two plates collide, the leading edge of one is bent downward, allowing it to descend beneath the other plate. Three types of convergent plate boundaries: Oceanic - Continental Oceanic - Oceanic Continental - Continental Oceanic-Continental Convergence The less dense continental material (granitic) remains “floating”, while the more dense oceanic slab (basaltic) sinks into the asthenosphere. A region where an oceanic plate descends into the asthenosphere is called a subduction zone. As the oceanic plate slides beneath the overriding plate, the oceanic plate bends, producing a deep-ocean trench. Oceanic-Continental Convergence As the oceanic plate subducts, partial melting occurs at depth. Magma rises to the surface to form continental volcanic arcs. Oceanic-Continental Convergence Most of this magma will be emplaced in the continental crust and form intrusive igneous rocks. The remaining magma will eventually migrate to the surface as volcanic eruptions and will form extrusive igneous rocks. Major Volcanoes of the World Fig. 6.18 W. W. Norton The Cascade Mountain Range, in western US, is a volcanic mountain range that was formed as a result of oceanic-continental convergence. Eruption of Mount St. Helens in 1980 The Cascade Mountain Range is a result of the “Juan de Fuca Plate” subducting under the western US. Earthquakes & Volcanoes Deep earthquakes occur at subduction zones. The deepest earthquakes occur at depths as great as 700 km below the surface. W. W. Norton Largest Earthquakes Ever Recorded 4. Japan, 2011 Magnitude 9.0 3. Sumatra, 2004 Magnitude 9.1 5. Kamchatka, 1952 Magnitude 9.0 2. Alaska, 1964 Magnitude 9.2 1. Chile, 1960 Magnitude 9.5 The largest earthquake ever recorded occurred along the Nazca-South American plate boundary. Chile May 22, 1960 Magnitude 9.5 Berkeley, CA Seismogram Japan quake of 2011 is the 4th largest earthquake since 1900. From: www.pbs.org/wgbh/nova/insidenova/2011/03/earthquake-geology.html Three types of convergent plate boundaries: Oceanic - Continental Oceanic - Oceanic Continental - Continental Oceanic - Oceanic Convergence When two oceanic plates converge, one descends beneath the other initiating volcanic activity (similar to the oceanic - continental case), but the volcanoes form on the ocean floor rather than on continents. Dry land emerges from the ocean depths, forming a chain of volcanic islands called a volcanic island arc. Examples of island arcs are the island chains of the western Pacific Ocean, such as Japan. In the case of Japan, volcanic islands are being created by the collision of the Pacific plate with the Eurasian plate. The Pacific plate being subducted beneath the Eurasian plate. From: www.pbs.org/wgbh/nova/insidenova/2011/03/earthquake-geology.html The Deadliest Tsunami in History Sumatra, 2004 Banda Aceh, Sumatra, Indonesia: 2004 Tsunami aerial photos December 26, 2004 March 11, 2011 Sumatra, 9.1 Japan, 9.0 228,000 fatalities 21,000 fatalities www.sms-tsunami-warning.com/pages/tsunami-sumatra-2004#.Up0-Z41RbP9 Three types of convergent plate boundaries: Oceanic - Continental Oceanic - Oceanic Continental - Continental Continental - Continental Convergence When two plates carrying continental crust collide, a continental collision occurs. Continental - Continental Convergence Continental collisions occur because of the relatively low density, and thus the buoyant nature, of continental crust (granitic). W. W. Norton. Modified from Cox and Hardt, 1986. India Colliding with Asia A continental collision occurred when the onceseparated continent of India collided with Asia, forming the Himalayan mountains. The Himalayas This process results in a new mountain range composed of deformed and metamorphosed sedimentary rocks and fragments of volcanic rocks. Plates move apart, resulting in upwelling of material from the Mantle to create new sea floor. Divergent Convergent Plates move together, causing one of the slabs of lithosphere to be consumed into the Mantle as it decends beneath the overriding plate. Plates slide past each other, without creating or destroying lithosphere. Transform Fault Divergent Plate Boundaries