Plate Tectonics The grand unifying theory of Geology

Plate Tectonics The grand unifying theory of Geology n Plate tectonics controles n Distributions of geologic materials and resources (e. g. , Minerals, Energy, Water…) n n Geologic Hazards (e. g. , earthquakes, volcanoes, landslides, tsunamis…) Landscape features (e. g. , mountain ranges, oceanic trenches, continents, rift valleys…)

Formation of Earth Birth of the Solar System Nebular Theory (pg. 24, Kehew) n n Rotating nebula contracts Begins to flatten and collapse into center to form the sun. Clusters of asteroids coalesced to form planetesimals and moons (planetary accretion) around 4. 6 billion years ago (bya) (Meteorites are iron-rich or rocky fragments left over from planetary accretion) http: //www. psi. edu/projects/planets. html

Orion Nebula www. hubblesite. org www. geol. umd. edu/~kaufman/ ppt/chapter 4/sld 002. htm www. psi. edu/projects/ planets/planets. html

Formation of the Planets n n n The mass of the center of the solar system began nuclear fusion to form the sun The inner planets were hotter and gas was driven away leaving the terrestrial planets (Fe, O, Si, Mg…) The outer planets were cooler and more massive so they collected and retained the gasses forming the “Gas Giants” Terrestrial Planets Gas Giants www. amnh. org/rose/backgrounds. html

Differentiation of the Planets n n The relatively uniform iron-rich proto planets began to separate into zones of different composition: 4. 5 bya Heat from impacts, pressure and radioactive elements cause iron (and other heavier elements) to melt and sink to the center of the terrestrial planets (Kehew Fig. 2 -4) Lab. Man. , Fig. 1. 7 a: Zones of the earth’s interior

Further Differentiation of Earth n n Lighter elements such as Oxygen, Silicon, and Mid-Ocean Ridge Aluminum rose to form a (New Crust) thin, rigid crust The crust, which was originally thin and basaltic (iron rich silicate), further differentiated to form continental crust which is thicker, iron poor, silica rich and lighter Deepest Mine Deepest Well Continental Crust (Silicic) Oceanic Crust (Basalt) Kehew Fig. 2. 5

Composition of Earth and Crust Element (Atomic #) Chemical Symbol % of Crust Earth (by Weight) Change in Crust Due to Differentiation Oxygen (8) O 30 46. 6 Increase Silicon (14) Si 15 27. 7 Increase Aluminum (13) Al <1 8. 1 Increase Iron (26) Fe 35 5. 0 Decrease Calcium (20) Ca <1 3. 6 Increase Sodium (11) Na <1 2. 8 Increase Potassium (19) K <1 2. 6 Increase Magnesium (12) Mg 10 2. 1 Decrease ~8 1. 5 All Others

Crust and Mantle Lithosphere and Asthenosphere n n The uppermost mantle and crust are rigid, solid rock (Lithosphere) The rest of the mantle is soft and solid (Asthenosphere) The Continental Crust “floats” on the uppermost mantle The denser, thinner Oceanic Crust comprises the ocean basins

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

Pangea 225 million years ago 135 mya 65 mya Today

Evidence of Continental Drift n Glacial striations match across oceans Kehew, Fig. 2. 27

Evidence of Continental Drift n Matching rock types and mountain ranges Kehew, Fig. 2. 27

Evidence of Continental Drift n Fossils of land plants and animals

Evidence of Continental Drift n Magnetic Evidence n Reversals in Earth’s magnetic field are recorded in newly formed rocks Kehew, Fig. 2. 7

Evidence of Continental Drift n Age of Earth’s Oceanic Crust Kehew, Fig. 2. 32

Lithospheric Plates See Kehew, Figure 1. 19 n n n The Lithosphere is broken into “plates” (7 maj. , 6 or 7 min. ) Plates that “ride around” on the flowing Asthenosphere Carrying the continents and causing continental drift

Lithospheric Plates Kehew, Fig 2. 24

Three Types of Plate Boundaries n Divergent | n Convergent | n Transform e. g. , Pacific NW See Kehew, Fig. 2. 38

Divergent Plate Boundaries n n n Where plates move away from each other the iron-rich, silica-poor mantle partially melts and Extrudes on to the ocean floor or continental Lithosphere crust Simplified Asthenosphere Cool and solidify to form Basalt: Iron-Rich, Silica-Poor, Dense Dark, Fine-grained, Igneous Rock Block Diagram

Characteristics of Divergent Plate Boundaries n Divergent Plate Boundary n n n Stress Earthquakes Volcanism Rocks Features Lithosphere New Oceanic Crust Forming at Mid-Ocean Ridge Shallow Earthquakes lt a s a B ense, ent D Dark, vem Mo e t a l eric P h p s o Lith Asthenosphere Fissure Eruptions Ocean ic Crust Magma Generation d but soft) li o s ( k c o r e tl n a p of hot m u g in ll e W See Kehew, Fig. 2. 29

Characteristics of Divergent Plate Boundaries n Divergent Plate Boundary n n n Stress: Tensional extensional strain Volcanism: non-explosive, fissure eruptions, basalt floods Earthquakes: Shallow, weak Rocks: Basalt Features: Ridge, rift, fissures Ocean ic Magma Generation Crust

Locations of Divergent Plate Boundaries Mid-Ocean Ridges East Pacific Rise n Mid Atlantic Ridge n Mid Indian Ridge n Mid Arctic Ridge Fig. 1. 10 (Mid-Arctic Ridge) ian Ind e Mid-Atlantic Ridg Mid- East Pacific Rise n Rid ge See Kehew, Figure 2. 24

Divergent Plate Boundaries Rifting and generation of shallow earthquakes (<33 km) 0 30 70 150 0 33 70 150 300 500 800 Depth (km)

E. g. , Red Sea and East African Rift Valleys n n Thinning crust, basalt floods, long lakes Fig. 19. 21 Fig. 19. 22 Rift Valley Shallow Earthquakes Linear sea, uplifted and faulted margins Oceanic Crust Rift Valley Passive continental shelf and rise See Kehew, Figure 2. 33

Convergent Plate Boundaries n n 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) Wet crust is partially melted to form silicic (Silicarich, iron-poor, i. e. , granitic) magma Stress: Compression Oceanic Trench n Earthquakes Volcanic Arc Plate Movement n Volcanism Lithosphere n Rocks Magma Subducted Generation Simplified n Features Plate Shallow and Deep Block Asthenosphere Diagram Earthquakes n

Convergent Plate Boundary e. g. , Pacific Northwest n Volcanic Activity n n n Strong Earthquakes n n n Explosive, Composite Volcanoes (e. g. , Mt. St. Helens) Arc-shaped mountain ranges Shallow near trench Shallow and Deep over subduction zone Rocks Formed n Granite (or Silicic) Iron-poor, Silica-rich n Less dense, light colored Usually intrusive: Cooled slowly, deep down, to form large crystals and course grained rock n n

The “Ring of Fire” (e. g. , current volcanic activity) sls. nes. se I e Ris cific ne sia nd e Z ew n Also: Himalayans to the Alps N a al Moun tains n In do dre Andes n rra Ma t Pa n Sia Eas n Pinatubo llipi n Fujiyama ane n n Aleutia Arc Island Phi n New Zealand Tonga/Samoa Philippines Japanese Isls. Aleutian Island arc and Trench Cascade Range Sierra Madre Andes Mtns. Jap n e ad e c s g Ca Ran A ring of convergent plate boundaries on the Pacific Rim Composite Volcanic Arcs (Granitic, Explosive) Basaltic Volcanism (Non-Explosive)

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

Major Plates and Boundaries n n See Kehew, Figure 2. 24 Each major plate caries a continent except the Pacific Plate. Each ocean has a mid-ocean ridge including the Arctic Ocean. n n Divergent bounds beneath E. Africa, gulf of California The Pacific Ocean is surrounded by convergent boundaries. n Also Himalayans to the Apls

Divergent Plate Boundaries Rifting and Formation of new Basiltic Oceanic Crust n Visuvius d Re a Se Afri can Rift Kilimanjaro Ridg ian e Mid-Atlantic Ridge Gulf of Aden -Ind n Etna Mid Thin (<10 km) n Young (<200 my) n Iron Rich (>5%) / Silica Poor (~50%) n Dense (~ 3 g/cm 3) n Low lying (5 -11 km Iceland East Oceanic Crust* deep) Formed at Divergent Plate Boundaries *Make a “Comparison Table” on a separate page Composite Volcanic Arcs (explosive) Basaltic Volcanism (non-explosive)

Convergent Plate Boundaries Formation of Granitic Continental Crust Oceanic Crust Continental Crust Thin (<10 km) n Young (<200 my) n Iron Rich (~5%) / Silica Poor (~50%) n Dense (s. g. ~3 x H 2 O) n Low lying (5 -11 km deep) Thick (10 -50 km) n Old (>200 m. y. and up to 3. 5 b. y. ) n Iron Poor (<1%) / Silica Rich (>70%) n Less Dense (~ 2. 5 g/cm 3) n High Rising n n n (mostly above see level) n Formed at Convergent Plate Boundaries Formed at Divergent Plate Boundaries

Isostatic Adjustment Why do we see, at the earths surface, n n n n Intrusive igneous rocks and Metamorphic rocks Formed many km deep? Thick, light continental crust buoys up even while it erodes Eventually, deep rocks are exposed at the earth’s surface Minerals not in equilibrium weathered (transformed) to clay Sediments are formed

The Hydrologic Cycle Works with Plate -Tectonics to n Shape the land n Weathering clay, silt, sand… n n Erosion Transport Sedimentation Geologic Materials n n Sediments Sedimentary Rocks Se e K eh ew Fi g. 2 . 45

n Rock entar y n Igneous Rocks: When rocks melt, Magma is formed, rises, cools and crystallizes. Sedimentary Rocks: All rocks weather and erode to form sediments (e. g. , gravel, sand, silt, and clay). When these sediments accumulate they are compressed and cemented (lithified) Metamorphic Rocks: When rocks are compressed and heated but not melted their minerals re-equilibrate (metamorphose) to minerals stable at higher temperatures and pressures Sedim n s The 3 rock types form at convergent plate boundaries Metam orphi Rocks c Igneous Rocks Magma See Kehew, Figure 2. 34

The Rock Cycle See Kehew, Fig. 2. 53

Igneous and Sedimentary Rocks at Divergent Boundaries and Passive Margins n n n Igneous Rocks (basalt) are formed at divergent plate boundaries and Mantle Hot Spots. New basaltic, oceanic crust is generated at divergent plate boundaries. Sedimentary Rocks are formed along active and passive continental margins from sediments shed from continents Sedimentary Rocks are formed on continents where a basin forms and sediments accumulate to great thicknesses. E. g. , adjacent to mountain ranges and within rift valleys. See Kehew, Figure 2. 30

“Continental Accretion” How continents are built n The Ancestral Atlantic Ocean looked like today’s Pacific n n Island Arcs Oceanic Trenches Bounding Continents ~500 mya Convergent Boundaries n n Cause new terrains to collide and be accreted to the old continental Cratons ~400 mya

“Continental Accretion” How continents are built n Mountains are built during accretion n n Rocks are folded (bent) and faulted (broken and shifted) Volcanoes continue to form Rocks are metamorphosed in the Cores Mountains Weathering and Erosion of Mountains n n n Sediments are shed and Lithified to produce A venire of Sedimentary rocks ~350 mya ~300 mya ~250 mya

Rock Types of Continents

Rock Types of Continents n Metamorphic n n Formed by intense pressure and heat Deep within mountain cores Exposed by isostacy and erosion Igneous n n n Magma intruded into cores of mountains Lava extruded at volcanoes Sedimentary n n Weathered and eroded mountains shed sediments Covering the continental interior with a venire of sedimentary rocks

Rock Types of Continents B A A B Virginia / Penn. Ohio Michigan Canada

Deciphering the Geology of Ohio Using Steno’s Principles Sandstone Shale Limestone n By characterizing the sequence of sedimentary rocks found in Ohio, we can decipher the geologic history preserved in the rocks using the basic principles of geology

Deciphering the Geology of Ohio Using Steno’s Principles (~1650 s) n n Uniformitarianism Original Horizontality Original Continuity Superposition Sandstone Shale Limestone

Sedimentary Rocks of Ohio Demonstrate the Use of Steno’s principles n Generalized sequence of rocks and ages in millions of years Sandstone Shale Limestone 350 380 450 n n Principle of Uniformitarianism Principle of Original Horizontality Principle of Original Continuity Principle of Superposition

Sedimentary Rocks of Ohio n Uplift during the Tertiary period (26 mya) Erosion Sandstone Shale Limestone 350 380 450 Regional Uplift

Sedimentary Rocks of Ohio n Exposed older rocks in central and western Ohio Erosion Sandstone Shale Limestone 350 380 450 Regional Uplift

Sedimentary Rocks of Ohio n Forming the Findley Arch (with east flank in eastern Ohio) Erosion Sandstone Shale Limestone 350 380 450 Regional Uplift

Sedimentary Rocks of Ohio n And the pattern of rocks found across Ohio Erosion Sandstone Shale Limestone 350 380 450 Regional Uplift

Sedimentary Rocks of Ohio n The oldest rocks are found in southwestern Ohio (along the axis of the Findley Arch) Sandstone Shale Limestone Erosion 350 380 450 Regional Uplift

Sedimentary Rocks of Ohio Sandstone Shale Limestone 350 380 450

Sedimentary Rocks of Ohio Sandstone Shale 350 380 Limestone 450

Sedimentary Rocks of Ohio Sandstone Shale Limestone 350 380 450

Sedimentary Rocks of Ohio Sandstone 350 380 Limestone 450 Shale

Sedimentary Rocks of Ohio Sandstone Shale Limestone Sandstone 350 380 Limestone 450 Shale

Sedimentary Rocks of Ohio Sandstone Shale Limestone Sandstone 350 380 Limestone 450 Shale

Sedimentary Rocks of Ohio Sandstone Shale Limestone (325 my) Thus rocks are younger and change lithology (rock type) as you go west or east from Ottawa County (400 my)

The Geologic Record in the Rocks Sandstone Shale Limestone Gneiss Granite

Relative Age and the “Principles” n n n Uniformitarianism Superposition Original horizontality n n n Lateral continuity Cross cutting relationships Inclusions Sandstone Shale Limestone Gneiss Granite Gabbro See Figure 8. 1 – 8. 12

1. Regional Uplift, Tilting, or folding) causes Erosion 2. Erosion surface indicates gap in geologic record Formation of Unconformities Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 240 million years ago

Formation of an Angular Unconformity 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation (e. g. , clay) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 220 million years ago

Formation of an Angular Unconformity 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation (e. g. , lime mud) Shale (220) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 210 million years ago

Formation of an Angular Unconformity 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation (e. g. , quartz sand) Limestone (210) Shale (220) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 200 million years ago

Formation of an Angular Unconformity Quartz Sandstone (200) Limestone (210) Shale (220) 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation (e. g. , immature sand) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 190 million years ago

Formation of an Angular Unconformity Quartz Sandstone (200) Limestone (210) Shale (220) 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation Arkose (190) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 180 million years ago

Formation of an Angular Unconformity Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) 1. Regional Uplift, Tilting (or folding), Erosion 2. Erosion surface, gap in geologic record 3. Continuous Sedimentation 4. Sedimentation ceases Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 170 million years ago

1. Erosion of horizontal beds Formation of a Disconformity Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) Erosion Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 160 million years ago

Formation of an Disconformity Quartz Sandstone (200) Limestone (210) Shale (220) Arkose (190) 1. Erosion of horizontal beds 2. Loss of geologic record (i. e. , Arkose) 3. Formation of a horizontal erosion surface Erosion Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 150 million years ago

Formation of an Disconformity Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i. e. , Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose Sedimentation (e. g. , reef) (190) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 140 million years ago

Formation of an Disconformity Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i. e. , Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose (190) Limestone (140) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (280) Gabbro (790) 130 million years ago

Formation of an Disconformity Quartz Sandstone (200) Limestone (210) Shale (220) 1. Erosion of horizontal beds 2. Loss of geologic record (i. e. , Arkose) 3. Formation of a horizontal erosion surface 4. Renewed Sedimentation Arkose (190) Limestone (140) Sandstone 350 Shale 380 Limestone 450 Gneiss (1, 500) Granite (290) Gabbro (790) 120 million years ago

Summary: Types of Unconformities n Deciphering Relative Ages n n Limestone Quartz Sandstone Limestone Shale Sandstone Shale Limestone Principles give sequences of geologic events Unconformities indicate gaps in the geologic record Disconformity Angular Unconformity Gneiss Granite Gabbro Nonconformities

The Grand Staircase n Correlation n Physical Continuity Similar Rock Types Fossils (index and assemblage)