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Plate TectonicsThe grand unifying theory of Geology
Plate tectonics controles Distributions of geologic materials and
resources (e.g., Minerals, Energy, Water…)
Geologic Hazards (e.g., earthquakes, volcanoes, landslides, tsunamis…)
Landscape features (e.g., mountain ranges, oceanic trenches, continents, rift valleys…)
Formation of Earth
http://www.psi.edu/projects/planets/planets.html
Birth of the Solar System Nebular Theory
(pg. 24, Kehew) 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)
www.psi.edu/projects/planets/planets.html
www.geol.umd.edu/~kaufman/ppt/chapter4/sld002.htm
Orion Nebulawww.hubblesite.org
Formation of the Planets
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”
Gas Giants
Terrestrial Planets
www.amnh.org/rose/backgrounds.html
Differentiation of the Planets
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. 1.7a: Zones of the earth’s interior
ContinentalCrust
(Silicic)
Further Differentiation of Earth
Lighter elements such as Oxygen, Silicon, and Aluminum rose to form a 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
Kehew Fig. 2.5
Mid-OceanRidge
(New Crust)
OceanicCrust
(Basalt)
Deepest Mine
Deepest Well
Composition of Earth and Crust
Element(Atomic #)
Chemical Symbol
% of Earth
% of Crust(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
All Others ~8 1.5
Crust and MantleLithosphere and Asthenosphere 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 SedimentProducts of an Active PlanetRocks and SedimentProducts of an Active PlanetEarth’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
Pangea 225 million years ago
135 mya
65 mya
Today
Evidence of Continental Drift
Glacial striations match across oceans
Kehew, Fig. 2.27
Evidence of Continental Drift
Matching rock types and mountain ranges
Kehew, Fig. 2.27
Evidence of Continental Drift Fossils of land plants and animals
Evidence of Continental Drift
Magnetic Evidence Reversals in Earth’s magnetic field
are recorded in newly formed rocks
Kehew, Fig. 2.7
Evidence of Continental Drift Age of Earth’s Oceanic Crust
Kehew, Fig. 2.32
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
See Kehew, Figure 1.19
Lithospheric Plates
Lithospheric Plates
Kehew, Fig 2.24
Three Types of Plate Boundaries
Divergent |
Convergent |
Transform
e.g., Pacific NWSee Kehew, Fig. 2.38
Where plates move away from each other the iron-rich, silica-poor mantle partially melts and
Divergent Plate Boundaries
Asthenosphere
Lithosphere LithosphereSimplified Block Diagram
Extrudes on to the ocean floor or continental crust
Cool and solidify to form Basalt: Iron-Rich, Silica-Poor, Dense Dark,
Fine-grained, Igneous Rock
New Oceanic CrustForming at Mid-Ocean Ridge
Oceanic Crust
Lithospheric Plate MovementMagma
Generation
Characteristics of Divergent Plate Boundaries
Divergent Plate Boundary Stress Earthquakes Volcanism Rocks Features
Lithosphere
Asthenosphere
See Kehew, Fig. 2.29
Welling up of hot mantle rock (solid but soft)
Fissure Eruptions
Shallow Earthquakes
Dark, Dense, Basalt
Characteristics of Divergent Plate Boundaries
Oceanic Crust
Magma Generation
Divergent Plate Boundary Stress: Tensional extensional strain Volcanism: non-explosive, fissure eruptions,
basalt floods Earthquakes: Shallow, weak Rocks: Basalt Features: Ridge, rift, fissures
Locations of Divergent Plate Boundaries
Mid-Ocean Ridges
East Pacific Rise Mid Atlantic Ridge Mid Indian Ridge Mid Arctic Ridge
Fig. 1.10
(Mid-Arctic Ridge)
Eas
t P
acifi
c R
ise
Mid
-Atla
ntic
Rid
ge
Indian
Ridge
Mid-
See Kehew, Figure 2.24
030
70
150
300
500
Divergent Plate BoundariesRifting and generation of shallow earthquakes (<33km)
Depth(km)
03370
300
150
500
800
Fig. 19.21 Fig. 19.22
Rift Valley
Passive continental shelf and rise
Rift Valley
E.g., Red Sea and East African Rift Valleys
Thinning crust, basalt floods, long lakes
ShallowEarthquakes
Linear sea, uplifted and faulted margins
Oceanic Crust See Kehew, Figure 2.33
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)
Wet crust is partially melted to form silicic (Silica-rich, iron-poor, i.e., granitic) magma Stress: Compression Earthquakes Volcanism Rocks Features
Lithosphere
Simplified Block DiagramAsthenosphere
Subducted Plate
Oceanic Trench
Plate Movement
Magma Generation
Volcanic Arc
Shallow and Deep Earthquakes
Lithosphere
Convergent Plate Boundary e.g., Pacific Northwest
Volcanic Activity Explosive, Composite
Volcanoes (e.g., Mt. St. Helens)
Arc-shaped mountain ranges
Strong Earthquakes Shallow near trench Shallow and Deep over
subduction zone Rocks Formed
Granite (or Silicic) Iron-poor, Silica-rich Less dense, light colored
Usually intrusive: Cooled slowly, deep down, to form large crystals and course grained rock
Composite Volcanic Arcs (Granitic, Explosive)Basaltic Volcanism (Non-Explosive)
The “Ring of Fire” (e.g., current volcanic activity)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.
Also: Himalayans to the Alps
Indonesia
Fujiyama
Eas
t P
acif
ic R
ise
Pinatubo
An
des
Mo
un
tain
s
Cas
cade
Ran
ge
Aleutian
Island Arc
Siarra Madre
Jap
anes
e Is
ls.
New Z
ealand
Ph
illip
ines
.
Depth of Earthquakes at convergent plate boundaries
Seismicity of the Pacific Rim 1975-1995 03370
300
150
500
800
Shallow quakes at the oceanic trench (<33km)
Deep quakes over the subduction zone (>70 km)
Depth(km)
Each major plate caries a continent except the Pacific Plate. Each ocean has a mid-ocean ridge including the Arctic Ocean.
Divergent bounds beneath E. Africa, gulf of California The Pacific Ocean is surrounded by convergent boundaries.
Also Himalayans to the Apls
See Kehew, Figure 2.24
Major Plates and Boundaries
Iceland
Kilimanjaro
RedS
ea
Gulf of
Aden
Etna
Visuvius
Eas
t A
fric
an
Rif
t
Mid
-Atl
anti
c R
idg
e
Mid
-Ind
ian R
idg
e
Divergent Plate BoundariesRifting and Formation of new Basiltic Oceanic Crust
Oceanic Crust* Thin (<10 km) Young (<200my) Iron Rich (>5%) / Silica Poor (~50%) Dense (~ 3 g/cm3) Low lying (5-11 km
deep) Formed at Divergent Plate
Boundaries
Composite Volcanic Arcs (explosive)
Basaltic Volcanism (non-explosive)
*Make a “Comparison Table” on a separate page
Convergent Plate BoundariesFormation of Granitic Continental Crust
Continental Crust Thick (10-50 km) Old (>200 m.y. and up to 3.5 b.y.) Iron Poor (<1%) / Silica Rich (>70%) Less Dense (~ 2.5 g/cm3) High Rising (mostly above see level) Formed at Convergent Plate
Boundaries
Oceanic Crust Thin (<10 km) Young (<200 my)
Iron Rich (~5%) /
Silica Poor (~50%)
Dense (s.g. ~3 x H2O)
Low lying (5-11 km deep) Formed at Divergent Plate
Boundaries
Isostatic Adjustment Why do we see, at the earths surface,
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 Shape the land
Weatheringclay, silt, sand…
Erosion Transport Sedimentation
Geologic Materials Sediments Sedimentary
Rocks
See Kehew Fig. 2.45
The 3 rock types form at convergent plate boundaries
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
MetamorphicRocks
Sedi
men
tary
Roc
ks
Magma
IgneousRocks
See Kehew, Figure 2.34
The RockCycle
See Kehew, Fig. 2.53
Igneous and Sedimentary Rocks at Divergent Boundaries and
Passive Margins 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
The Ancestral Atlantic Ocean looked like today’s Pacific Island Arcs Oceanic Trenches Bounding Continents
Convergent Boundaries Cause new terrains to
collide and be accreted to the old
continental Cratons
~500 mya
~400 mya
“Continental Accretion” How continents are built
Mountains are built during accretion 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 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
Metamorphic Formed by intense
pressure and heat Deep within
mountain cores Exposed by isostacy
and erosion
Igneous Magma intruded
into cores of mountains
Lava extruded at volcanoes
Sedimentary Weathered and
eroded mountains shed sediments
Covering the continental interior with a venire of sedimentary rocks
Rock Types of Continents
A B
A
B
Virginia / Penn. CanadaOhio Michigan
Deciphering the Geology of OhioUsing Steno’s Principles
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
Sandstone
Shale
Limestone
Deciphering the Geology of OhioUsing Steno’s Principles (~1650s)
Uniformitarianism Original Horizontality Original Continuity Superposition
Uniformitarianism Original Horizontality Original Continuity Superposition
Sandstone Shale Limestone
Sedimentary Rocks of Ohio Demonstrate the Use of Steno’s principles
Generalized sequence of rocks and ages in millions of years
Principle of Uniformitarianism Principle of Original Horizontality Principle of Original Continuity Principle of Superposition
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
Uplift during the Tertiary period (26 mya)
Regional Uplift
450
380
350Sandstone
Shale
Limestone
Erosion
Sedimentary Rocks of Ohio
Exposed older rocks in central and western Ohio
450
380
350Sandstone
Shale
Limestone
Regional Uplift
Erosion
Sedimentary Rocks of Ohio
Forming the Findley Arch (with east flank in eastern Ohio)
450
380
350Sandstone
Shale
Limestone
Regional Uplift
Erosion
Sedimentary Rocks of Ohio
And the pattern of rocks found across Ohio
450
380
350Sandstone
Shale
Limestone
Regional Uplift
Erosion
Sedimentary Rocks of Ohio
The oldest rocks are found in southwestern Ohio (along the axis of the Findley Arch)
450
380
350Sandstone
Shale
Limestone
Regional Uplift
Erosion
Sedimentary Rocks of Ohio
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
Sandstone Shale Limestone
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
Sandstone Shale Limestone
450
380
350Sandstone
Shale
Limestone
Sedimentary Rocks of Ohio
Thus rocks are younger and change lithology (rock type) as you go west or east from Ottawa County
Sandstone (325 my)
Shale Limestone (400 my)
The Geologic Record in the Rocks
Sandstone
Shale
Limestone
Gneiss Granite
Relative Age and the “Principles”
Uniformitarianism Superposition Original horizontality
Lateral continuity Cross cutting
relationships Inclusions
Sandstone
Shale
Limestone
Gneiss Granite Gabbro
See Figure 8.1 – 8.12
Formation of
Unconformities
240million years ago
1. Regional Uplift, Tilting, or folding) causes Erosion
2. Erosion surface indicates gap in geologic record
450
380
350Sandstone
ShaleLimestone Gneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Sedimentation (e.g., clay)
220million years ago
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Sedimentation (e.g., lime mud)
Shale (220)
210million years ago
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Sedimentation (e.g., quartz sand)
Limestone(210)
200million years ago
Shale (220)
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Sedimentation (e.g., immature sand)
Shale (220)
Limestone(210)
Quartz Sandstone(200)
190million years ago
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Shale (220)
Limestone(210)
Quartz Sandstone(200)
180million years ago
Arkose (190)
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Angular Unconformity
Arkose (190)
Shale (220)
Limestone(210)
Quartz Sandstone(200)
170million years ago
1. Regional Uplift, Tilting (or folding), Erosion
2. Erosion surface, gap in geologic record
3. Continuous Sedimentation
4. Sedimentation ceases
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of a
Disconformity
ErosionArkose (190)
Shale (220)
Limestone(210)
Quartz Sandstone(200)
160million years ago
1. Erosion of horizontal beds
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Disconformity
Shale (220)
Limestone(210)
Arkose (190)
Quartz Sandstone(200)
150million years ago
1. Erosion of horizontal beds2. Loss of geologic record
(i.e., Arkose)3. Formation of a horizontal
erosion surface
Erosion
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Disconformity
Shale (220)
Limestone(210)
Arkose (190)
Quartz Sandstone(200) Sedimentation (e.g., reef)
140million years ago
1. Erosion of horizontal beds2. Loss of geologic record
(i.e., Arkose)3. Formation of a horizontal
erosion surface4. Renewed Sedimentation
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Disconformity
Shale (220)
Limestone(210)
Arkose (190)
Quartz Sandstone(200)
130million years ago
1. Erosion of horizontal beds2. Loss of geologic record
(i.e., Arkose)3. Formation of a horizontal
erosion surface4. Renewed Sedimentation
Limestone (140)
450
380
350Sandstone
Shale
LimestoneGneiss (1,500) Granite (280)
Gabbro (790)
Formation of an
Disconformity
450
380
350Sandstone
Shale
Limestone
Shale (220)
Limestone(210)
Arkose (190)
Quartz Sandstone(200)
120million years ago
1. Erosion of horizontal beds2. Loss of geologic record
(i.e., Arkose)3. Formation of a horizontal
erosion surface4. Renewed Sedimentation
Limestone (140)
Gneiss (1,500) Granite (290)
Gabbro (790)
Summary: Types of
Unconformities
Deciphering Relative Ages Principles give
sequences of geologic events
Unconformities indicate gaps in the geologic record
Shale
Limestone
Quartz Sandstone
Limestone
Sandstone
Shale
LimestoneGneiss Granite
Disconformity
Angular Unconformity
NonconformitiesGabbro
The Grand Staircase
Correlation Physical Continuity Similar Rock Types Fossils (index and assemblage)
Recommended