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Rocks, Sediment and Soils Products of an Active Planet

Rocks, Sediment and Soils Products of an Active Planet. Crust : Rigid, Thin. Earth’s structure leads to intense geologic activity Inner core: Solid iron Outer core: Liquid iron, convecting (magnetic field) Mantle (Asthenosphere) : Solid iron-magnesium silicate, plastic, convecting

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Rocks, Sediment and Soils Products of an Active Planet

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  1. Rocks, Sediment and SoilsProducts of an Active Planet Crust: Rigid, Thin Earth’s structure leads to intense geologic activity • Inner core: Solid iron • Outer core: Liquid iron, convecting (magnetic field) • Mantle(Asthenosphere): Solid iron-magnesium silicate, plastic, convecting • Crust(Lithosphere):Rigid, thin • O, Si, Al, Fe, Ca, Na, K, Mg… Mantle: Plastic, Convecting 47%, 28, 8, 5, 4, 3, 3, 2 TDE pg.8-11

  2. The Major Lithospheric PlatesAnd directions of movement (TDE pg.5)

  3. Geologic Phenomena at Plate Boundaries • Divergent Plate Boundaries: where plates move away from each other new oceanic crust is generated from melting mantle material that cools and forms Basaltic Rock (a.k.a. Mafic rock) • Iron-rich • Silicon-poor • Dense • Young TDE pg.15-20, 32-36 Lithosphere Lithosphere Simplified Block Diagram Asthenosphere

  4. Geologic Phenomena atDivergent Plate Boundaries • Divergent Plate Boundary Lithosphere Asthenosphere New Oceanic Crust Forming at Mid-Ocean Ridge Fissure Eruptions Shallow Earthquakes Oceanic Crust Magma Generation Lithospheric Plate Movement Welling up of hot mantle rock (solid but soft)

  5. Locations of Divergent Plate BoundariesMid-Ocean Ridges (Mid-Arctic Ridge) • East Pacific Rise • Mid Atlantic Ridge • Mid Indian Ridge • Mid Arctic Ridge Mid- Mid-Atlantic Ridge East Pacific Rise Indian Ridge

  6. Flood Basalts on Uplift Divergent Plate Boundaries and Hotspots Beneath Continents • Shallow earthquake activity • Volcanic activity • Fissures eruptions • Lava floods, and volcanoes • Hot, non-explosive • Basaltic rocks formed (i.e. iron-rich/silica poor) • The Rocks (igneous) • Basalt bedrock is usually formed in the shallow crust by recent (<~200mya) volcanic activity at divergent plate boundaries or hotspots (>1,000oC) • E.g., volcanoes, feeder dikes, volcanic stocks, basalt floods Hawaii, Ship Rock NM, Devils Tower AZ, Yellowstone WY

  7. E.g., Red Sea and East African Rift Valleys • Fig. 19.21 • Fig. 19.22 Thinning crust, flood basalts, long lakes Shallow Earthquakes Linear sea, uplifted and faulted margins Rift Valley Rift Valley Oceanic Crust Passive continental shelf and rise

  8. Formation of MaficIgneous Rocks • Mafic Magmas • Hot(>1000oC) • Non-Viscous(runny, flows easily) • “Dry”(no H2O or C02) • Mafic Rocks • UsuallyExtrusive, Fine-grained, Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Flood Basalts • If Intrusive, course-grained mafic rocks are formed Gabbro. • If intrusive, Dikes and Sills more common. (Plutons don’t form) Sill Sill Sill Dike Dike Dike

  9. Geologic Phenomena at Plate Boundaries • Convergent Plate Boundaries: where plates move toward each other, oceanic crust and the underlying lithosphere is subducted beneath the other plate (with either oceanic crust or continental crust) Oceanic Trench Simplified Block Diagram TDE 37-43 Lithosphere Lithosphere Subducted Plate Asthenosphere

  10. Formation ofMagma • How are rocks melted? • 1. Heating ■ 2. Depressurization • 3. Increase water content • 4. Increased silica content • Where do rocks melt? • Subduction zones (Silicic andIntermediate) • Mantle Plumes (“Hot Spots”) not only at Divergent Boundaries Mafic Hot and Low Pressure Hot and High Pressure

  11. Formation of SilicicIgneous Rocks • Silicic (a.k.a, felsic) Magmas • Cool(<700oC) • Viscous(sticky, doesn’t flow easily) • Gaseous(steam of H2O and C02) • Silicic Rocks • Usuallyintrusive, course-grained, Silicic (Granite) to Intermediate (Diorite) rock forms plutons • If extrusive, fine-grained rocks formed by explosive volcanoes Rhyolite or Andesite Volcanoes • Also injects surrounding rocks with silica laden steam Composite Volcano Batholith of Plutons

  12. Dikes: Intruded near a pluton • Silica rich fluids are injected into cracks in all directions • Discordant: cutting across layers • Ores, rare elements and minerals, gems

  13. Geologic Phenomena atConvergent Plate Boundaries • Volcanic Activity • Explosive, Composite Volcanoes • Granitic rocks formed (iron-poor/silica-rich) • Shallow earthquakes near trench • Shallow and Deep Earthquakes over subduction zone

  14. Physiographic Features atConvergent Plate Boundaries Island Arcs Chains of Volcanoes (chains of volcanic Islands), Oceanic Trenches

  15. Aleutian Island Arc Fujiyama Cascade Range Japanese Isls. Phillipines. Pinatubo Siarra Madre East Pacific Rise Indonesia Andes Mountains New Zealand The “Ring of Fire” A ring of convergent plate boundaries on the Pacific Rim • New Zealand • Tonga/Samoa • Philippines • Japanese Isls. • Aleutian Island arc and Trench • Cascade Range • Sierra Madre • Andes Mtns. Composite Volcanic Arcs (Granitic, Explosive) Basaltic Volcanism (Non-Explosive)

  16. Depth of Earthquakes at convergent plate boundaries Seismicity of the Pacific Rim 1975-1995 0 33 70 • Shallow quakes at the oceanic trench (<33km) • Deep quakes over the subduction zone (>70 km) 150 300 500 800 Depth (km)

  17. Sedimentary Rock: Sediments (e.g., ocean sand, silt, and clay) are compressed cemented (lithified) Metamorphic Rocks: rocks are compressed, heated and change minerals but do not melt Igneous Rocks: When rocks melt, Magma is formed, rises, cools and crystallizes. Below surfaceIntrusive. LavaExtrusive The3 rock typesform at convergent plate boundaries Sedimentary Rocks Metamorphic Rocks Igneous Rocks Magma

  18. Transform Plate Boundaries • Where plates slide parallel to each other: • Transform faults are created • Mid-ocean ridges are offset • If occurring beneath a continent the continent is sheared and faulted

  19. Examples Every mid-ocean ridge is offset along by transform faults San Andreas Fault Shallow earthquakes are generated Volcanic activity is rare See Figure 19.27 http://pubs.usgs.gov/publications /text/San_Andreas.html Transform Plate Boundaries

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