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Module 2 Week 1 Geologic Cycles
 

Module 2 Week 1 Geologic Cycles

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    Module 2 Week 1 Geologic Cycles Module 2 Week 1 Geologic Cycles Presentation Transcript

    • Geologic Cycles
    • Overview
      • Endogenic and Exogenic Systems
      • Geologic Cycle
        • The Earth’s Interior
        • Rock Cycle
        • Tectonic Cycle (Plate Tectonics)
    • Endogenic and Exogenic Systems
      • Exogenic systems are systems that are external to the earth
        • Driven by insolation (solar radiation)
        • Gives energy to air, water and ice, setting them in motion under the influence of gravity
        • Example: Hydrologic Cycle
      • Endogenic systems are systems internal to the earth
        • Driven by heat from pressure and radioactive decay
        • Fractures the earth’s surface, sets it in motion, builds mountains and triggers volcanoes and earthquakes
        • Example: Tectonic Cycle
    • The Geologic Cycle
      • The process by which landforms are shaped by balancing endogenic (building-up) and exogenic (wearing down) systems
      • Interaction between hydrologic, tectonic, and rock cycles
    • Earth’s Internal Structure
      • Opposition of gravity (inward pulling) and internal heating (outward pushing)
      • Differentiation into alternating rigid and plastic layers
      • Inner core is solid iron
        • possibly a single iron crystal
      • Outer core is molten iron
        • generates magnetic field
        • geomagnetic reversals
          • 9 in last 4 million years
          • strength reduces to about 25%
          • greater exposure to solar wind and high energy charged particles
      • Mantle
        • Comprises 80% of Earth’s volume
        • Composed of FeO, MgO, SiO 2
        • Rigid and Dense
          • Increases with depth, pressure and temperature
        • Gutenberg discontinuity
          • separates Mantle from Outer Core
          • Zone of transition
            • density and velocity
            • type of material
      • Upper Mantle
        • Lithosphere
          • Continental Crust
            • “ sial” and granite
          • Oceanic Crust
            • “ sima” and basalt
          • Mohorovi ĉ i ć (Moho) Discontinuity
            • Boundary between crust and uppermost mantle
          • Uppermost mantle
            • Oxides and Silicates of Fe, Mg
        • Asthenosphere: a region within the upper mantle
          • 10% molten, unevenly distributed
            • Additional heating from radioactive decay
          • Convection currents create tectonic movement
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      • Lithosphere is buoyant on the asthenosphere
        • Free to move horizontally and vertically
          • Horizontal motion expressed as plate tectonics
          • Vertical motion expressed as isostasy
      • Isostasy
        • Vertical motion of lithosphere
        • Crust exerts downward pressure on uppermost mantle and asthenosphere
        • Exogenic processes redistribute the crust’s weight, changing downward pressure
        • Results in isostatic rebound
          • vertical motion of the crust
          • does NOT contribute to horizontal tectonic motion
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    • Rock Cycle
      • Occurs where the earth’s crust comes into contact with exogenic processes
        • Hydrologic cycle
        • wind
      • Original volcanic material of the crust becomes transformed into different rock types
        • Tectonic cycle > molten mantle material > igneous rocks (e.g. basalt, granite)
        • Hydrologic cycle > physical and chemical weathering of igneous rocks > sedimentation > deposition and compression > sedimentary rocks
        • Tectonic cycle > sedimentary rocks become subducted, transform under heat and pressure to become metamorphic rocks
        • Tectonic cycle > further subduction melts metamorphic rocks, available to become igneous again
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    • Igneous Rocks
      • Formed from magma
        • Extruded as lava over the surface of the earth (Basalt)
        • Intruded beneath the surface of the earth, erosion eventually reveals them (Granite)
          • Plutons, Batholiths, Dikes, Laccoliths, Sills
      • Most of the earth’s crust is made of igneous rocks
        • Other rock types are produced through processes at the surface
    • Sedimentary Rocks
      • Produced by:
        • Sedimentation
          • Weathering and erosion of any rock type to produce sediment
          • Transportation and deposition of sediment
        • Lithification
          • Compaction, cementation, chemical actions
      • Sediments deposited on bottoms of lakes or oceans
        • Settle into horizontal layers or strata
        • Stratigraphy
        • Principle of Superposition
      • Igneous intrusions typically appear within sedimentary strata. Erosion of these sedimentary layers reveals them
      • Sandstone, shale (clay-sized particles), limestone (biotic – coral)
    •  
    • Metamorphic Rocks
      • Any rock type, when exposed to extreme temperatures and pressure over millions of years can change form
      • Metamorphic rocks can be formed by a variety of processes associated with subduction
        • Compression from plate collisions
        • Sheared and stressed along earthquake fault zones
        • From weight of overlying materials during subduction
        • Often found at the roots of mountains
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    • Tectonic Cycle
      • A function of the planet’s structure
      • Occurs in the outermost layer of the planet
        • Lithosphere and Upper mantle
      • Driven by internal heating
        • Gravitational compression
        • Impact heating
        • Radioactive decay
          • Half-life
    • Geologic Time
      • Uniformitarianism
        • The same geological processes that operated in the past are operating in the present
      • A time scale that measures the entire life of the planet
        • 4.6 billion years old
        • Eons, era, period, epoch
        • Divisions typically based on fossil evidence
          • Time system defined by interaction between biosphere and other spheres
          • Often marked by mass extinctions
        • Precambrian Eon
          • Vast majority of earth’s history (roughly 4 billion years)
          • Early period sees the first bacteria, photosynthesis and evolution of atmosphere
          • End of period marked by formation of modern atmosphere
      • Tectonic motion occurs on the timescale of hundreds of millions of years
        • Pangaea to present continental distribution: 248 million years
      • Landform building processes associated with tectonic activities occur on a timescale of tens of million of years
        • Orogeny: mountain building
      • Current time period
        • Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene epoch
        • Geomorphologists take the late Quaternary Period, inclusive of the Holocene, as their period of study
          • Separates physical geographers from geologists
          • Humans are present during this period
            • Holocene: 10,000 years ago, marks the rise of agriculture
        • End of an Era? Possibly even an Eon?
          • Mass extinction, atmospheric change
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    • Plate Tectonics
      • Two main factors:
        • Buoyancy of Lithosphere on Asthenosphere
        • Uneven heating and convection within Asthenosphere
      • Results in:
        • Fragmentation of Lithoshpere into mobile plates
        • Places where the plates move away from each other
          • Divergent plate boundaries or sea-floor spreading
        • Places where plates move toward each other and collide
          • Convergent plate boundaries or subduction zones
      • Evidence
        • Abraham Ortelius (1596), Francis Bacon (1620) noted “fit” of coastlines
        • Alfred Wegener (1915) proposed the idea of drift
          • Similarity in rocks and geographic features across continents
          • Similarity of certain fossil species across continents
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    • End of Precambrian Eon, beginning of Phanerozoic.
    • End of Paleozoic Era, beginning of Mesozoic
    • Early Cretaceous period, Mesozoic Era Opening of North Atlantic Ocean
    • End of Cretaceous Period and Mesozoic Era, beginning of Cenozoic Era Mass extinction of dinosaurs, rise of large mammals Asteroid or comet impact (in what is now the Yucatan Peninsula)? Opening of the South Atlantic Ocean
    • The continents today
    • Divergent Plate Boundaries
      • Occur where molten material from the Asthenosphere penetrate through the crust
        • A form of volcanism
      • Occur in the oceans because oceanic crust is thinner than continental crust
        • Creates new crust
        • Pushes plates apart (sea-floor spreading)
        • Basalt (extrusive)
      • Features
        • Mid-oceanic ridges
        • Fracture zone , Transform faults
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    • Convergent Plate Boundaries
      • Occurs where two plates collide
        • One plate slips beneath the other
          • Subduction (hence subduction zone )
          • Subducted plate passes back into asthenosphere
      • Friction between plates melts rocks of the lithosphere
        • Creates continental crust
        • Granite (Intrusive)
      • Features
        • Orogenesis (mountain building)
        • Oceanic trenches
        • Volcanoes
        • Earthquakes
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    • Note: Subduction zones, especially ringing the Pacific Ocean
    • Note: association of volcanoes with subduction zones Note also: Hotspots
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    • Hot spots
      • Places in the crust away from plate boundaries where molten material from the asthenosphere punches through the crust
      • Typically in oceanic crust
        • Produces basalt
      • The motion of the plate over the hot spot often creates chains of volcanic mountains
        • Island chains (such as Hawaii)
          • Mauna Loa in Hawaii is the world’s tallest mountain if measured from the ocean floor
        • Seamounts
    •