GEO-SCI 103 Lecture 5Outline of Last Lecture I. Earthquakes and Seismic Waves: Earth Structures RevealedII. Continents, Ocean Basins and EquilibriumIII. Features of the Ocean FloorOutline of Current Lecture: Plate Tectonics; shifting continents & seafloor spreading (9/16/14)I. Basic Concepts of Plate Tectonics A. Behavior of Earth’s LayersB. Tectonic Plates C. Plate Tectonics II. Plate Boundaries, Earthquakes and VolcanismA. Earthquakes and the 3 types of Plate Boundaries B. VolcanismIII. Divergent Plate BoundariesIV. Convergent Plate Boundaries A. DefinitionB. Types of Collisions V. Transform Plate BoundariesA. Strike-Slip BoundariesB. San Andreas FaultVI. Mantle Plumes and Hot SpotsA. Mid-Atlantic RidgeB. Volcanic Island ChainsCurrent LectureI. Basic Concepts of Plate Tectonics A. Behavior of Earth’s Layersa) Region of the upper mantle underlying the lithosphere behaves like a ductile substance and is capable of flowing like hot plastic though it is not a liquidb) The low strength region of the upper mantle is the asthenosphere, also knownas the low velocity zone, where seismic waves passing through slow down.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c) The Earth has been slowly losing heat by conduction (transfer of heat from one atom to another) and convection (differential heat loss that causes movement of mass)d) Upwellings are sites at the surface where old continents are rifted apart, oceanic crust is produced and new ocean basins are formede) Downwellingssites where old oceanic crust is recycled back into the mantle,volcanic islands, volcanic mountain ranges are formed and where continents collide. B. Tectonic Platesa) Because of these deep seated stresses that occur with upwellings and downwellings, the outer shell of the Earth is broken into numerous rigid lithospheric plates (tectonic plates) which move slowly around the globe at rates of 2 to 20 cm/yearC. Plate Tectonicsdivides the lithosphere into seven major rigid plates and several minor ones that move about on the Earth’s surfaces a) Continental Driftwhen large continents spread apart, such as Pangaea, which split up in the present continents of South America and Africa.b) Sea Floor spreading ocean crust is produced at mid ocean ridges then movesymmetrically away from the ridge as new material is added in the central rift valley. c) Plates are separated by the zones of convergence, divergence or transform motion and their movement d) Margins of lithospheric plates are characterized by zones of extensive volcanism, earthquakes and mountain buildingII. Plate Boundaries, Earthquakes and Volcanism:A. EARTHQUAKES: 3 types of plate boundariesa) Convergent plate boundaries “colliding” 2 plates collide, the denser one is subducted beneath the other (downwelling) (always oceanic crust because they are denser)1. Zone of subduction is marked by a trench, volcanism on the over riding plate and deep focus earthquakes along the slope of the subducting slab(Benioff Zone)2. They collide 3. Ocean-ocean collisions (produce island arcs—the plate that is not being subducted. Ex: Japan)4. Ocean continent collisions (volcanic mountain chains near the edge of acontinent ex: Peru and Chile)5. Continent-Continent collisions (large mountain ranges including the Himalaya Mountains in Asia)b) Divergent Boundaries “move apart”1. 2 plates move apart as new oceanic crust is produced at spreading centers 2. Spreading center of the Arctic Basin and North Atlantic3. Move apart4. Indicated by the presence of oceanic ridges, and at these ridges new ocean crust is being produced, and the two plates are moving away fromeach other5. Iceland (divergent plate boundary)c) Transform Plate Boundaries  “slide-slip”1. Transform faults and spreading center of Atlantic2. Slide past one another3. Occur as faults that separate two plates sliding past each other4. Produce shallow focus earthquakes B. Volcanism:a) Divergent plate boundaries are the sites of extensive volcanic activity. Often called spreading centers, the oceanic ridges produce new oceanic crust as magma rises from the asthenosphereb) Convergent plate boundaries produce significant volcanic activity on the landward side of the trenches. The plate that is being subducted is partially melted, which results in the generation of magma and volcanism on the overriding plate1. Island arcs (Japan, Aleutian Islands of South Alaska—ocean-ocean collisions)2. Volcanic Mountain Chains (continent-continent collisions: Andes)c) Magmatic arcs (2 types: convergent plate boundaries and subduction of oceanic lithosphere)1. Convergent plate boundaries2. Subduction of the oceanic lithosphere  the rocks begin to melt and produce molten rock called magma. The presence of water in the subducted sediments lowers the melting point a. Recycling of old oceanic crust back into the mantle with earthquakes along Benioff Zoneb. Partial melting of subducting platec. Volcanism on over riding plate 3. Volcanic Mountain Chains (due to ocean-continent collisions)4. Island Arcs (ocean-ocean collisions)d) Spreading centers (divergent plate boundaries)1. Mid-ocean ridges2. Convection in the Asthenosphere creates upwelling of mantle: decompression causes rocks to melt resulting in rising hot magma that produces volcanism at the seafloor. 3. Occurs at Plate Margin4. “hot rocks” in contact with cold sea watere) Hot spots (not related to plate boundaries)1. Linear chains of islands, seamounts or ridges2. Plates move over stationary hot spot rooted deep in the mantle 3. Plates continue to move over stationary hot spot resulting in linear chains of exist, dormant and active volcanoesf) The asthenosphere is the source for magmatic arcs and spreading centers and the deep mantle is the source for Hot spotsIII. Divergent Plate BoundariesA. Divergent plate boundaries are identified by oceanic ridges or spreading centers where new oceanic crust is created as two plates move aparta) Spreading centers are a continuous chain of undersea volcanic mountains that extend from the Arctic Ocean to the Pacific Oceanb) Mid-Atlantic Ridge and the East Pacific Rise are parts of this continuous active volcanic mountain range on the seafloorc) The extrusion of hot magma into the cold sea results in structures called pillowbasaltd) As an old continent is split (rifted) in two, a new ocean basin