Chapt 14-The Internal Process

Chapt 14-The Internal Process - Chapter 14: The Internal...

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Chapter 14: The Internal Processes I. The Impact of Internal Processes on the Landscape A. internal processes are the supreme builders of the terrain II. From Rigid Earth to Plate Tectonics A. intro 1. igneous rocks of the upper crust occur in 2 layers a. oceanic crust; partially underlies continents too 1) 2 dominant mineral compounds: si lica and ma gnesium (sima) 2) alkaline, dark, relatively young, basaltic , relatively dense b. continental crust 1) 2 dominant mineral compounds: si lica and al uminum (sial) 2) more acidic, lighter in color, generally granitic , less dense 2. general crustal structure: Continents of buoyant granitic material floating on a foundation of denser basaltic material a. continents free to move B. Isostacy 1. crust is floating on the denser, deformable, mantle below 2. addition of significant amount of mass onto a portion of the crust causes crust to sink; removal of a large mass allows crust to rise 3. causes: a. deposition of large amount of sediment on a continental shelf b. accumulation of glacial ice c. weight of water trapped behind a dam C. Continental Drift 1. continents are quite mobile 2. history of theory a. geographer Abraham Ortelius – 1590s b. philosopher Francis Bacon – 1620 c. meteorologist Alfred Wegener – 1920s 3. Wegener’s theory : a. Pangaea : super continent existed 250 million years ago b. broke up into large sections that continue to move today 4. Wegener’s evidence: a. continental margins of South America and Africa fit together b. petrologic and paleontologic records on both sides of Atlantic match up c. ancient glacial deposits and fossilized plant remains match up across continents 5. response to Wegener’s theory: disbelief III. Plate Tectonics A. The Evidence 1. theory of seafloor spreading a. the theory: 1) oceanic ridges are formed by currents of magma rising up from the mantle and causing the ocean floor to spread laterally Chapter 14: The Internal Processes – p. 1 of 12
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2) oceanic ridges contain newest crust formed on planet 3) subduction : descent of the edge of a lithospheric plate under the edge of an adjoining plate, involving melting of the subducting material 4) amount of new seafloor formed is compensated for by amount lost at subduction zone b. oceanic v. continental crust 1) oceanic crust has short life a) within 200 million years it’s returned to the mantle by subduction b) average age = 100 million years 2) lower density continental crust cannot be subducted a) virtually permanent b) some continental crust is 4 billion years old c. confirmation of theory of seafloor spreading 1) paleomagnetism: relatively symmetrical pattern of magnetic orientation on both sides of oceanic ridges 2) core sampling: sediment thickness and seafloor age increase with increasing distance from the oceanic ridges ; sediments farthest from the ridges are oldest d. seafloor spreading is quite rapid : about as fast as fingernails grow 2. theory of plate tectonics a. lithosphere is mosaic of rigid plates floating over the underlying
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This note was uploaded on 11/19/2008 for the course CJC 101 taught by Professor Brown during the Spring '07 term at Ball State.

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Chapt 14-The Internal Process - Chapter 14: The Internal...

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