0301temp_WorkOfPlates-stu

0301temp_WorkOfPlates-stu - The work of the plates EARTH...

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Unformatted text preview: The work of the plates EARTH SCIENCE in ARIZONA and the SOUTHWEST The mountains are no more fixed than the stars. Annie Dillard What causes volcanism and tectonism? What accounts for different thicknesses of the crust? What builds continents and mountain belts? The work of the plates 2 Deformation of the crust is evidence that the solid Earth is mobile Southern Rocky Mountains Basin and Range Colorado Plateau Transition Zone Río Grande Rift Earthquakes ! Is it still moving? The work of the plates 3 Is terra firma still moving? 20,200 km orbit (geosynchronous) GPS receiver in Canyon de Chelly We can measure displacements of the crust (even a few mm per year) with the Global Positioning System The work of the plates 4 GPS measurements in real time show a continuing global pattern of movement. Slower Faster Sella, Dixon, and Mao, 2002 / UNAVCO archive The work of the plates 5 Theory of plate tectonics J. Vigil, USGS The work of the plates 6 The theory of plate tectonics: Lithosphere and asthenosphere Crust Lithosphere Asthenosphere Tasa Upper mantle Earth is layered by strength as well as by composition. The rigid lithosphere rides on the ductile asthenosphere. The work of the plates 7 Compare the distribution of earthquakes (yellow), volcanoes (orange), and high elevations (brown) Volcanism, deformation, EQs, mountain building = tectonic activity Belts of tectonic activity divide lithosphere into tectonic plates The work of the plates Reynolds, Johnson, Kelly, Morin & Carter, 2008 8 Mosaic of rigid tectonic plates The work of the plates 9 Three types of relative plate motions Move apart: divergent boundary Move toward each other: convergent boundary Reynolds, Johnson, Kelly, Morin & Carter, 2008 Move horizontally past one another: transform boundary 10 The work of the plates Observe the locations of different types of plate boundaries Reynolds, Johnson, Kelly, Morin & Carter, 2008 Compare these locations with mid‐ocean ridges, oceanic trenches, mountain belts, island chains, etc. The work of the plates 11 What happens when plates move apart at divergent boundaries? Oceanic plates move apart at mid‐ocean ridges (seafloor spreading) Forms new oceanic crust (and new plate) Mid‐Atlantic Ridge Reynolds, Johnson, Kelly, Morin & Carter, 2008 The work of the plates 12 Observe what happens when continents rift apart Initial uplift from rising mantle Stretching and faulting form rift Melting forms magma Can lead to seafloor spreading and new ocean basin Ocean widens with spreading Reynolds, Johnson, Kelly, Morin & Carter, 2008 The work of the plates 13 Two divergent boundaries in the Southwest: Grotzinger et al. (2007) Río Grande Rift Press et al. (2004) An ocean opening up The work of the plates A continental rift that may open farther? 14 What happens when plates converge? Oceanic‐Oceanic convergent boundary Trench and volcanic island arc Subducting slab releases water Water causes melting of mantle Reynolds, Johnson, Kelly, Morin & Carter, 2008 One plate moves down= subduction The work of the plates 15 What happens when plates converge? Oceanic‐Continental convergent boundary Volcanic eruptions and crustal compression form mountain belt Trench Oceanic plate subducted beneath continent Overlying mantle melted Reynolds, Johnson, Kelly, Morin & Carter, 2008 The work of the plates 16 Ring of Fire Oceanic plates subducted on both sides Subduction beneath oceanic plates = island arcs Subduction beneath continental plates = mountain belts with volcanoes The work of the plates Reynolds, Johnson, Kelly, Morin & Carter, 2008 17 The USA has its share of the Ring of Fire Mt. Rainier, WA …..?? Press et al. (2004) Erupted ~ 940 years ago Mt. St. Helens, WA 1980, 2005 USGS The work of the plates Sunset Crater N of Flagstaff, AZ Colorado Plateau 18 Volcanism across the Southwest Extinct? Hazardous? Rift zone The work of the plates 19 Continental collision = wide zone of deformation Pieces sliced off Thick crust = high elevation Few volcanoes Continental plate buoyant, so subduction ends Reynolds, Johnson, Kelly, Morin & Carter, 2008 The work of the plates 20 What happens when plates slip past each other? Transform boundary Plates move horizontally past one another Transform boundaries link other types of plate boundaries, Reynolds, Johnson, Kelly, Morin & Carter, 2008 like two divergent boundaries shown here 21 The work of the plates The San Andreas is a continental transform‐fault boundary As plates move past each other... …the surface is offset arroyos displaced Sa Los Angeles San Francisco n An dr ea s fau lt Grotzinger et al. (2007) Carrizo Plain, CA The work of the plates 22 What moves the plates? Convection: movement of matter due to differences in density produced by differential heating or cooling. The work of the plates Grotzinger et al. (2007) 23 The theory of plate tectonics: Convection moves the plates Slab pull Reynolds, Johnson, Kelly, Morin & Carter, 2008 Ridge push Slab pull The plates play an active role in convection. Grotzinger et al. (2007) The work of the plates 24 Plate tectonic theory well explains the global distribution of earthquakes, volcanoes, and mountains Earthquakes www.iris.edu/seismon Mountain belts in brown The work of the plates 25 Plate‐tectonic boundaries in the Southwest today cr ex ust te b n d e in ed g NW Fixed relative to Southwest The work of the plates 26 The legacy of plate tectonics in the Southwest Ro cky M ou nta ins Great Plains Stretched and rifted Basin and Range Sheared in San Andreas transform fault zone High, uplifted in earlier episode of plate convergence Tran sitio n Zo ne Stretched and rifted away from Colorado Plateau, dropped down Colorado Plateau Río Grande Rift Stretched and rifted open Zone where Plateau is crumbling away The work of the plates 27 ...
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This note was uploaded on 03/01/2011 for the course GLG 394 taught by Professor Semken during the Fall '10 term at ASU.

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