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The Origin of Mountains g110

The Origin of Mountains Points to Be Covered. Simple Mountains

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The Origin of Mountains g110

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    1. The Origin of Mountains g110 Lecture prepared by Bob Hall. Revised 8/6/2000

    2. The Origin of Mountains Points to Be Covered Simple Mountains – examples Volcanoes Dome or Fold Mts. Erosional Fault-Block Complex Mountain Systems Characteristics of Complex Mtn. Systems Geosynclinal theory: Strange, unworkable fiction, begging to be replaced with a nonfiction theory.

    3. Origin of Mountains Points to Be Covered (cont.) Geosynclinal Theory (cont.) Basic Concept The Big Trough Sedimentation The Cycle Continental Accretion – A Corollary The Past is the Key to the Present Plate Tectonics to the Rescue

    4. Origin of Mountains Simple Mountains - Volcanoes

    5. Origin of Mountains Simple Mountains Dome and Fold Mountains

    6. Origin of Mountains Simple Mountains Erosional Mountains

    7. Origin of Mountains Simple Mountains Fault-Block Mountains

    8. Complex Mountains Appalachians – An Example Eastern Part: The Piedmont and BlueRidge Igneous and metamorphic rocks Complexly faulted. Thrust westward over many thousands of feet of sedimentary rocks.

    9. Complex Mountains Appalachian Example Middle Part: Ridge and Valley Northern part: intensely folded sedimentary rocks Southern part: thrust faulting (more intense deformation) Ridges and valleys alternating because of differential erosion.

    10. Complex Mountains Appalachian Example Western Part: Allegheny and Cumberland Plateaus Sedimentary Rocks in horizontal position. Carved into mountains by erosion.

    11. Complex Mountains Characteristics Sedimentary rock thousands of feet thick, elsewhere represented by a few hundred ft. Volcanic rocks interbedded with sedimentary rocks. Metamorphic rocks. Granitic roots (batholiths) Many faults, especially thrust faults. Erosion of rocks of different hardness.

    12. Geosynclinal Theory Geological Fiction Geosyncline: Slow subsiding trough thousands of miles long and 100’s of miles wide Along continental margin. Receives marine sediments

    13. Geosyncline Theory - Sedimentation Outer Trough Sediments from the continent. Volcanics from island arcs. Subsides more rapidly than inner trough. Much greater thickness of sediments. Inner Trough Sediments from continent Not many volcanics Subsides less rapidly Less thickness of sediments

    14. Geosynclinal Theory The Cycle Subsidence and sedimentation. - All deposition in shallow water as trough slowly subsides. - Sedimentation just keeping up with subsidence. Downwarp, compression, thrust faulting, metamorphism Intrusion of batholiths Isostatic uplift to form mountains. Erosion to carve out details.

    15. Geosynclinal Theory The Cycle

    16. Origin of Mountains Geosynclinal Theory – Continental Accretion – A Corollary Continents increasing in size through time by welding of geosynclinal sediments. Oldest rocks should be in center of continents. Successively younger rocks should be found outward. North America supported this view.

    17. Origin of Mountains Geosynclinal Theory – Continental Accr.

    18. Origin of Mountains Geosynclinal Theory – The Past is the Key to the Present Where are all the modern geosynclines? No area seemed to fit the classic model. Change the model. - No longer visualized as a trough. - Thick wedge along continental margin. But, do these areas subside? - Not for the most part – too low density.

    19. Origin of Mountains Plate Tectonics to the Rescue Plate collisions Plate subduction Continental accretion

    20. Origin of Mountains Terms Complex mountains Continental accretion Dome mountain Erosional mountain Fault-block mountain Fold mountain Geosynclinal theory

    21. Origin of Mountains Student Responsibilities Know about the different forms of simple mountains. Know the characteristics of complex mountains. What were the fallacies of the geosynclinal theory of complex mountain systems? How have these ideas been replaced by plate tectonic?

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