Rocks, Sediment and Soils Products of an Active Planet 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… Crust: Rigid, Thin Mantle: Plastic, Convecting 47%, 28, 8, 5, 4, 3, 3, 2 TDE pg.8-11

The Major Lithospheric Plates And directions of movement (TDE pg.5)

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, Geologic Phenomena at Plate Boundaries Asthenosphere Lithosphere Simplified Block Diagram

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

Locations of Divergent Plate Boundaries Mid-Ocean Ridges East Pacific Rise Mid Atlantic Ridge Mid Indian Ridge Mid Arctic Ridge (Mid-Arctic Ridge) East Pacific Rise Mid-Atlantic Ridge Indian Ridge Mid-

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

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

Mafic Magmas Hot (>1000 o C) Non-Viscous (runny, flows easily) “Dry” (no H 2 O or C0 2 ) Mafic Rocks Usually Extrusive, 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) Formation of Mafic Igneous Rocks Dike Sill

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) Lithosphere Simplified Block Diagram TDE Asthenosphere Subducted Plate Oceanic Trench

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

Formation of Silicic Igneous Rocks Batholith of Plutons Composite Volcano Silicic (a.k.a, felsic) Magmas Cool (<700 o C) Viscous (sticky, doesn’t flow easily) Gaseous (steam of H 2 O and C0 2 ) Silicic Rocks Usually intrusive, 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

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

Geologic Phenomena at Convergent 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

Island Arcs Chains of Volcanoes (chains of volcanic Islands), Oceanic Trenches Physiographic Features at Convergent Plate Boundaries

Composite Volcanic Arcs (Granitic, Explosive) Basaltic Volcanism (Non-Explosive) 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. Indonesia Fujiyama East Pacific Rise Pinatubo Andes Mountains Cascade Range Aleutian Island Arc Siarra Madre Japanese Isls. New Zealand Phillipines.

Depth of Earthquakes at convergent plate boundaries Seismicity of the Pacific Rim Shallow quakes at the oceanic trench (<33km) Deep quakes over the subduction zone (>70 km) Depth (km)

The 3 rock types form at convergent plate boundaries 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 Metamorphic Rocks Sedimentary Rocks Magma Igneous Rocks

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

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