Scientists once believed sediment accumulated on the ocean floors over a very long time in a static environment. Magma of this composition is very low temperature (500-600 C) relative to other magmas. 2.2: Layers of the Earth - Geosciences LibreTexts 1999. Scientists have determined this cycle has been operating for at least three billion years and possibly earlier. Todo, Y., Kitazato, H., Hashimoto, J., and Gooday, A.J., 2005, Simple foraminifera flourish at the oceans deepest point: Science, v. 307, no. https://commons.wikimedia.org/wiki/File:Inge_Lehman.jpg, Figure 2.22: The outer cores spin causes our protective magnetic field. Kate Barton, David Howell, and Joe Vigil via USGS. If you are using an offline version of this text, access the quiz for section 2.2 via the QR code. 2014. Unlike the flux-melted magma found in subduction zones, rift-zone magma is created by decompression melting. USGS. NASA. Figure 2.22: The outer cores spin causes our protective magnetic field. The supercontinent that existed before Pangea, about 1 billion years ago. These deep earthquake zones congregated in planes that started near the surface around ocean trenches and angled beneath the continents and island arcs. Inter., v. 2, no. https://commons.wikimedia.org/wiki/File:CourtHotspots.png, Figure 2.56: The HawaiiEmperor seamount and island chain. Origin of the Universe and Our Solar System. verb) A theory that explains the global distribution of geological phenomena such as seismicity, volcanism, continental drift, and mountain building in terms of the formation, destruction, movement, and interaction of the earth's lithospheric plates. Res., v. 69, no. Here are the 7 major tectonic plates of the world in a bit more detail. Below this transitional zone, the mesosphere is relatively uniform until it reaches the core. Figure 2.7: GPS measurements of plate motions. 2, p. Res., v. 74, no. 12591265., doi: McCollom, T.M., 1999, Methanogenesis as a potential source of chemical energy for primary biomass production by autotrophic organisms in hydrothermal systems on Europa: J. Geophys. Int., v. 43, no. Bull., v. 60, no. Public domain. Public domain. Like the Hawaiian version, the Yellowstone hotspot is formed by magma rising through the lithosphere. Osvaldocangaspadilla. Hutson, P., Middleton, J., and Miller, D., 2003, Collision Zones: Online. Boundaries between the plates are of three types: divergent (i.e., moving apart), convergent (i.e., moving together), and transform (moving side by side). Mid-ocean ridge and spreading center are synonyms. General name of a mafic rock that is extrusive. 2006. Wegener found similar evidence when he discovered tropical plant fossils in the frozen region of the Arctic Circle. The innermost physical layer of the Earth, which is solid. What makes it different is this hotspot is located under a thick, continental plate. Zhou, Z., 2004, The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence: Naturwissenschaften, v. 91, no. The most recent major eruption of this hotspot created the Yellowstone Caldera and Lava Creek tuff formation approximately 631,000 years ago. Figure 2.23: Passive margin. Eventually plate sections located between large faults drop into deep depressions known as rift valleys, which often contain keystone-shaped blocks of down-dropped crust known as grabens. Uplifted mountain block caused by normal faulting. Scott Nash via USGS. [Solid Earth], v. 94, no. 1992. A group of all atoms with a specific number of protons, having specific, universal, and unique properties. Public domain. 2005. The ridge-push hypothesis suggests after the initial rifting event, plates continue to be pushed apart by mid-ocean spreading centers and their underlying convection currents. Stich, D., Mancilla, F. de L., Pondrelli, S., and Morales, J., 2007, Source analysis of the February 12th 2007, Mw 6.0 Horseshoe earthquake: Implications for the 1755 Lisbon earthquake: Geophys. 2017. In 1936, the Danish geophysicist Inge Lehmann analyzed seismic data and was the first to prove a solid inner core existed within a liquid outer core. 5591, p. If the built up energy between the plates is suddenly released, the result is an earthquake. As a rock cools, the iron minerals within the rock align with the current magnetic field. Rocks of the ocean floor, such as mid-ocean ridge rocks, which are brought to the surface. Toggle navigation . The United States is home to two of the largest and best-studied hotspots: Hawaii and Yellowstone. Scott Nash via USGS. Most of the Earth's geologic activity takes place at plate boundaries. What are the different types of plate tectonic boundaries? When it does emerge, the eruptions are generally much more violent. Scientific evidence indicates the Hawaiian hotspot is at least 80 million years old. AllenMcC. A plate boundary is where two plates meet and move relative to each other. Deepest part of the ocean where a subducting plate dives below the overriding plate. Located at a depth of approximately 410 and 660 km below the earths surface, the mesosphere is subjected to very high pressures and temperatures. When exposed on the surface, a craton is called a shield. The surface levels of crust are relatively brittle. a. convergent oceanic-continental plate boundary b. convergent oceanic-oceanic plate boundary c. 12, p. L12308. Mineral group in which the carbonate ion, CO3-2, is the building block. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Topographic30deg_N0E30.png, Figure 2.42: NASA image of the Basin and Range horsts and grabens across central Nevada. The next section provides the pieces of evidence that helped transform one mans wild notion into a scientific theory. This movement is caused by frictional drag created between the plates and differences in plate densities. Eric Gaba. Volcanoes are common along convergent and divergent plate boundaries. Earth Planet. Powell, R.E., and Weldon, R.J., 1992, Evolution of the San Andreas fault: Annu. 1 / 93 Flashcards Learn Test Match Created by vmberman Exploring Geology - Reynolds/Johnson/Morin/Carter, 5th edition Terms in this set (93) surface Earth's _____ is notable for many geologic features such as beautiful valley's, intricate coastlines, and deep ocean trenches. Pacific Plate The Pacific major plate is the largest which underlies the Pacific Ocean. USGS. James, D.E., Fouch, M.J., Carlson, R.W., and Roth, J.B., 2011, Slab fragmentation, edge flow and the origin of the Yellowstone hotspot track: Earth Planet. NOAA. 11, p. 9971000. These climate anomalies could not be explained by land bridges. Figure 2.55: Map of world hotspots. These seams with little or no tectonic activity are called failed rift arms. 2010. As Wegener collected more data, he realized the explanation that best fit all the climate, rock, and fossil observations involved moving continents. Figure 2.21: Lehmann in 1932. Thankfully they are also less frequent. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Releasing_bend.png, Figure 2.52: Wallace (dry) Creek on the Cariso Plain, California. 2013. Mantle convection is the slow, churning motion of Earth's mantle. Figure 2.59: Several prominent ash beds found in North America, including three Yellowstone eruptions shaded pink (Mesa Falls, Huckleberry Ridge, and Lava Creek), the Bisho Tuff ash bed (brown dashed line), and the modern May 18th, 1980 ash fall (yellow). The most recent supercontinent, which formed over 300 million years ago and started breaking apart less than 200 million years ago. Sci. Figure 2.25: Geologic provinces with the Shield (orange) and Platform (pink) comprising the craton, the stable interior of continents. Drlauraguertin. These convection currents move the surface plates aroundbringing them together, pulling them apart, and shearing them side-by-side. This is reflected as islands on oceanic plates, and volcanic mountains or craters on land. Public domain. Kelvin Case. Known as a wide rift, each graben (basin) is bounded by horsts (ranges). The resulting emitted hydrothermal water looks like black underwater smoke. As the continental plates are pulled apart, they create a region of low pressure that melts the lithosphere and draws it upwards. 4, p. 320. The Wilson Cycle is named for J. Tuzo Wilson who first described it in 1966, and it outlines the ongoing origin and breakup of supercontinents, such as Pangea and Rodinia. Compressional back-arc faults, also known as thrust faults, push them together. Eric Gaba. There are two styles of thrust fault deformation: thin-skinned faults that occur in superficial rocks lying on top of the continental plate and thick-skinned faults that reach deeper into the crust. The super-heated seawater rises back up to the surface of the plate, carrying dissolved gasses and minerals, and small particulates. The deep, flat part of the ocean. Deposition and erosion tied to glacier movement. 2006. Also known as the ocean floor. Fragments of continental material, including microcontinents, riding atop the subducting plate may become sutured to the accretionary wedge and accumulate into a large area of land called a terrane. Modified from illustration provided by Oceanus Magazine; original figure by Jack Cook, Woods Hole Oceanographic Institution; adapted by. https://oceanexplorer.noaa.gov/facts/plate-boundaries.html, Figure 2.25: Geologic provinces with the Shield (orange) and Platform (pink) comprising the craton, the stable interior of continents. The prevailing mechanism has hotspots starting in divergent boundaries during supercontinent rifting. Ingo Wlbern. Robert E. Wallace via USGS. Today these earthquake zones called Wadati-Benioff zones. Also, there are the Alps stretching from Italy to central Europe; the Zagros mountains from Arabia to Iran; and Himalaya mountains from the Indian subcontinent to central Asia. Res. As viewed across the fault, objects will move to the left. Called the Mohorovii Discontinuity, or Moho for short, this zone was discovered by Andrija Mohorovii (pronounced mo-ho-ro-vee-cheech; audio pronunciation) in 1909 after studying earthquake wave paths in his native Croatia. https://commons.wikimedia.org/wiki/File:Antonio_Snider-Pellegrini_Opening_of_the_Atlantic.jpg, Figure 2.4: Map of world elevations. Figure 2.19: The lithosphereasthenosphere boundary changes with certain tectonic situations. Zureks. CC BY-SA 4.0. https://en.wikipedia.org/wiki/File:India-Eurasia_collision.gif, Figure 2.40: Faulting that occurs in divergent boundaries. Faulting that occurs with shear forces, typically on vertical fault plaines as two fault blocks slide past each other. The land bridges eventually eroded away, leaving the continents permanently separated. (Figure 1.8). are most evident. Has more felsic minerals than mafic minerals. https://commons.wikimedia.org/wiki/File:Volcanic_Arc_System.png, Figure 2.32: Shallow subduction during the Laramide orogeny. The process in which volatiles enter the mantle wedge, and the volatiles lower the melting temperature, causing volcanism. At divergent boundaries, the plates move apart. While he did not have the precise mechanism worked out, his hypothesis was backed up by a long list of evidence. The Formation of Volcanoes | Geology | | Course Hero The resulting volcanoes frequently appear as curved mountain chains, volcanic arcs, due to the curvature of the earth. Seafloor spreading and other tectonic activity processes are the result of mantle convection. Phys. With more time, researchers discovered these thinner sediment layers were located close to mid-ocean ridges, indicating the ridges were younger than the surrounding ocean floor. Ophiolites are pieces of mantle that have risen through the crust until they are exposed as part of the ocean floor. Soc. An arrangement of many continental masses collided together into one larger mass. MagentaGreen. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Pangaea_continents.svg, Figure 2.37: The tectonics of the Zagros Mountains. Rocks made from pyroclastic tephra: either ash, lapilli, and/or bombs. 5710, p. 689., doi: Tolstoy, I., and Ewing, M., 1949, North Atlantic hydrography and the Mid-Atlantic Ridge: Geol. When earthquake epicenters were discovered along the ridges, the idea that earthquakes were linked to plate movement took hold. GeoAsh. 2010. When some studies showed less sediment than expected, these results were initially used to argue against continental movement. Am. If you are using an offline version of this text, access the quiz for chapter 2 via the QR code. Koba-chan. Convergent boundaries -- where crust is destroyed as one plate dives under another. Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism. Lithos is Greek for stone, and the lithosphere is the outermost physical layer of the Earth. A plate boundary is where two plates meet and move relative to each other. The Northeast Caribbean - Plate Tectonics in Action: Background Place where three plate boundaries (typically divergent) extendfrom a single point at 120 angles. 2006. 2013. Fossils of another reptile, Lystrosaurus, were found on Africa, India, and Antarctica. What Wegener did differently was synthesize a large amount of data in one place. Earth Planet. Sediment accumulation patterns also confirm the idea of sea-floor spreading. Melanie Moreno. Before long, scientists proposed other models showing plates moving with respect to each other, with clear boundaries between them. There are a number of hypotheses about how the Wilson Cycle works. The Geological Society 1932. CC BY 3.0. https://commons.wikimedia.org/wiki/File:HotspotsSRP_update2013.JPG, Figure 2.59: Several prominent ash beds found in North America, including three Yellowstone eruptions shaded pink (Mesa Falls, Huckleberry Ridge, and Lava Creek), the Bisho Tuff ash bed (brown dashed line), and the modern May 18th, 1980 ash fall (yellow). Mikenorton. The last period of the Mesozoic, 145-66 million years ago. 2014. This convergent boundary has a trench and mantle wedge and frequently, a volcanic arc. Lett., v. 236, no. Volcanoes are a vibrant manifestation of plate tectonics processes. There are several hotspots, current and former, that are believed to have begun at the time of rifting. Certainly the earth is composed of a countless combination of elements. This typically creates convection cells: round loops of rising and sinking material. Place with a chain of mountain volcanism on a continent, from oceanic-continental subduction. If deposited hot, where material can fuse together while hot, the rock is then called a welded tuff. 2008. The shallowly-subducting slab pushes against the overriding plate and creates an area of deformation on the overriding plate many kilometers away from the subduction zone. Public domain. Rocks found near ridges are younger than those found far away from any ridges. 2011. Its thickness ranges from 40 to 280 km. Geo Flashcards | Quizlet 2007. Public domain. Which location is on a transform boundary? 2006-10, updated 2015-09. Cadmium. 8, p. Figure 2.47: Black smoker hydrothermal vent with a colony of giant (6+) tube worms. An igneous composition or rock containing more than 50% carbonate minerals (e.g. The Eurasian continent has many examples of collision-zone deformations covering vast areas. Sci. The plate boundary on the this figure is located between: B and C Which area (s) on this world map is (are) likely to have volcanoes above sea level? When this molten magma reaches the weakened and fault-riddled rift zone, it migrates to surface by breaking through the plate or escaping via an open fault. Within the trench, ocean floor sediments are scraped together and compressed between the subducting and overriding plates. Public domain. Scientists looking at seismic data first discovered this innermost chemical layer in 1906. This model of ridge formation suggests the sections of lithosphere furthest away from the mid-ocean ridges will be the oldest. Scientists have identified a number of current and past hotspots believed to have begun this way. Figure 2.50: A transpressional strike-slip fault, causing uplift called a restraining bend. Underneath the oceans, the Moho is found roughly 5 km below the ocean floor. MagentaGreen. Lehmann, I., 1936, P, Publ: Bur. 3714, p. verb) The dynamics of plate . 3, p. 260263. The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water). Scientists have determined this by analyzing seismic waves that pass through the layer. 1924-1930. Other types of faultsnormal and reverse tend to be more destructive, obscuring or destroying these features. One example of a failed rift arm is the Mississippi Valley Embayment, a depression through which the upper end of the Mississippi River flows. At a divergent boundary, volcanic activity produces a mid ocean ridge and small earthquakes. Brittle materials are like solid glass or pottery, they break under force, especially when it is applied quickly.
