2Horizontal Movement of Plate TectonicsHorizontal Movement ofEarth’s Lithosphere
3Plate Tectonics The Theory of Plate Tectonics Plate Boundaries Spreading CentersSubduction ZonesTransform FaultsPlate Movement
4The Theory of Plate Tectonics “Continental Drift” - theory* proposed byAlfred Wagner, a German meteorologist (1915)Explained by:geologic fitfossils* Not accepted by scientific community- no mechanism to explain plate movement
5found lithospheres plate boundaries, 3 types: The Theory of Plate Tectonics (cont’d.)Plate Tectonics - evidence for theory of continental drift Hess, Heezen and Tharp (1960’s)found lithospheres plate boundaries, 3 types:ridges (spreading centers)trenches (subduction zones)transform faults (plates sliding past one another)
7Convection cells cause frictional drag on lithosphere Plate Boundariesa) Spreading centers - ‘rift zones’ (cont’d.)Convection cells formDensity differences – cool vs. hotConvection cells cause frictional drag on lithosphereLithosphere stretches due to convective movementLithospheric crust weakens
8Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.)Faulting – break in overlying lithosphereMagma flows upwardNew lithospheric crust formed
9Plate Boundaries (cont’d.) a) Spreading centers - ‘rift zones’ (cont’d.)Plates split apart -‘divergent plate’ boundaryNew crust formed - ‘constructive’ plate boundaryEvolution of a mid-ocean ridge systemUpwarpingRift valleyLinear seaMid-ocean ridge systemEx. 1 - oceans: mid Atlantic Ridgeeast Pacific RiseEx. 2 - continents: E. Africa Rift Valley Baikal Rift Valley
10Plate Boundaries (cont’d.) b) Subduction zonesLithospheric Plates collide - ‘convergent’ plate boundaryCrust destroyed - ‘destructive’ plate boundaryForms trenches and mountains
11Plate Boundaries (cont’d.) b) Subduction zones (cont’d.)3 types of subduction zones:Ocean crust into continental crust – form trenches andmountain rangesEx. a): Juan de Fuca plate into the N. American plate - forms Cascade Mtn. RangeEx. b): Nazca plate into the S. American plate - forms Peru-Chile Trench andthe Andes Mtn. Range
12Plate Boundaries (cont’d.) b) Subduction zones (cont’d.)Ocean crust into ocean crust – forms trenches and island arcsEx. A): Philippine plate into the Pacific plate – formed the Marianna Trenchand the Marianna Island Arc systemEx. B): N. American plate into the Caribbean plate and then the N. Americanplate into the S. American plate – formed the Isthmus of Panama
13Plate Boundaries (cont’d.) b) Subduction zones (cont’d.)Continental crust into continental crust – form mountain rangesEx. A): Indian plate into the Eurasian plate – formed the HimalayasEx. B): Eurasian plate into the African plate - closing up of theMediterranean sea
14Plate Boundaries (cont’d.) c) Transform faultsPlates slide past one anotherLithospheric crust neither created nor destroyed - ‘conservative’ plate boundaryEx. A) Pacific plate sliding past N. American plate – forms the San Andreas Fault
15Plate Movement How do we know these rates? (Rate=distance/time) New crust is created at spreading centers at a rate of approximately1-10cm per yearOld crust is destroyed at the same rate at subduction zonesHow do we know these rates? (Rate=distance/time)
16Plate Movement (cont’d.) Magnetic anomalies in ocean crust...look at spreading centerspaleomagnetismevery so often Earth’s magnetic field flips (every 300K-500K years)magnetic signal recorded in crust at spreading center as it’s formed, forms bands of crust with either a weak or strong magnetic signaldetermine rate of plate movement by distance of band from spreading center divided by age of rock in band (r=d/t)
17Plate Movement (cont’d.) Hot spotsEmperor Sea Mount chainislands or sea mountains formed over hotspots(fixed area where magma comes up)lithosphere moves over hotspot and end up have volcanic mountain over hotspot as well as a series of mountains in ‘front’ of hotspotdetermine rate of plate movement by distance of mountain from hotspot divided by age of rock in mountain (r=d/t)
18Learning ObjectivesUnderstand the processes that are continuously changing Earth’s surface as lithospheric plates move relative to one another.Identify the role of oceanic ridges, transform faults and deep-sea trenches in defining the edges of lithospheric plates.Understand the importance of asthenospheric thermal convection in plate tectonics and the resulting compression or tensional forces at the plate boundaries.Explain the distribution of magnetic anomaly stripes, seismicity, and volcanism in terms of the concept of global plate tectonics.Calculate spreading rates of ocean basins.
36Geological Periods Precambrian 4.6 B - 570 Ma solidification Cambrian Ma Gondwana, hard shell anim.Ordovician Ma separation, coldestSilurian Ma Laurentia collides with BalticaDevonian Ma pre-Pangea, equatorial forestsEarly Carboniferous 356 MaLate Carboniferous 306 Ma western Pangea is completePermian Ma deserts, reptiles, major ext.Triassic Ma Life begins to rediversify,PangeaJurassic Ma Dinosaurs, Pangea starts to breakLate Jurassic 152 Ma Pangea rifts apart, AtlanticCretaceous 94 Ma New oceans, IndiaK/T extinction 66 Ma end of dinosaursEocene Ma India collides with AsiaMiocene 14 Ma Modern lookModernFuture World Ma N. Atlantic widens, Med. vanishFuture Ma new subductionFuture Ma new Pangea
37Precambrianbreak-up of the supercontinent, Rodinia, which formed 1100 million years ago. The Late Precambrian was an "Ice House" World, much like the present-day.Source:Cambrian Animals with hard-shells appeared in great numbers for the first time during the Cambrian. The continents were flooded by shallow seas. The supercontinent of Gondwana had just formed and was located near the South Pole.
38OrdovicianDuring the Ordovician ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana. The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana.Silurian Laurentia collides with Baltica closing the northen branch of the Iapetus Ocean and forming the "Old Red Sandstone" continent. Coral reefs expand and land plants begin to colonize the barren continents.
39DevonianBy the Devonian the early Paleozoic oceans were closing, forming a "pre-Pangea". Freshwater fish were able to migrate from the southern hemisphere continents to North America and Europe. Forests grew for the first time in the equatorial regions of Artic Canada.Early Carboniferous During the Early Carboniferous the Paleozoic oceans between Euramerica and Gondwana began to close, forming the Appalachian and Variscan mountains. An ice cap grew at the South Pole as four-legged vertebrates evolved in the coal swamps near the Equator.
40Late CarboniferousBy the Late Carboniferous the continents that make up modern North America and Europe had collided with the southern continents of Gondwana to form the western half of Pangea. Ice covered much of the southern hemisphere and vast coal swamps formed along the equator.Permian Vast deserts covered western Pangea during the Permian as reptiles spread across the face of the supercontinent.
41TriassicThe supercontinent of Pangea, mostly assembled by the Triassic, allowed land animals to migrate from the South Pole to the North Pole; and warm-water faunas spread across Tethys. The first mammals and dinosaurs appeared;Jurassic By the Early Jurassic, south-central Asia had assembled. A wide Tethys ocean separated the northern continents from Gondwana. Subduction zone Rocky Mountains
43Late Jurassic In the Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from eastern North America. CretaceousDuring the Cretaceous the South Atlantic Ocean opened. India separated from Madagascar and raced northward on a collision course with Eurasia. Notice that North America was connected to Europe, and that Australia was still joined to Antarctica.
44K/T extinction The bull's eye marks the location of impact site of a 10 mile wide comet caused global climate changes that killed the dinosaurs and many other forms of life. By the Late Cretaceous the oceans had widened, and India approached the southern margin of Asia.Eocenemillion years ago India began to collide with Asia forming the Tibetan plateau and Himalayas (destroying the last of Tethys ocean). Australia, which was attached to Antarctica, began to move rapidly northward.
463-2Whereas oceanic ridges indicate tension, continental mountains indicate compressional forces are squeezing the land together.Sedimentary Rocks Squeezed by Compression
47Miocene 20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly. The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. Arabia moved away from Africa forming Gulf of Aden and Red Sea;Last Ice AgeWhen the Earth is in its "Ice House" climate mode, there is ice at the poles. The polar ice sheet expands and contacts because of variations in the Earth's orbit (Milankovitch cycles). The last expansion of the polar ice sheets took place about 18,000 years ago.
48Modern WorldIf we continue present-day plate motions the Atlantic will widen, Africa will collide with Europe closing the Mediterranean, Australia will collide with S.E. Asia, and California will slide northward up the coast to Alaska.
49Future +100Earth is ~ 4.6 bill years old – suggested cyclic of 500 mill year pattern of assembling and disassembling the land masses;Future +250
50The Wilson Cycle uses plate tectonic processes to show development and creation of ocean floor and ocean basins;