plate tectonics the grand unifying theory of geology plate tectonics controles distributions of...

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


Matching rock types and mountain ranges

Kehew, Fig. 2.27

Evidence of Continental Drift Fossils of land plants and animals


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-


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


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


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.


“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


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


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


Exposed older rocks in central and western Ohio

450

380

350Sandstone

Shale

Limestone

Regional Uplift

Erosion


Forming the Findley Arch (with east flank in eastern Ohio)

450

380

350Sandstone

Shale

Limestone

Regional Uplift

Erosion


And the pattern of rocks found across Ohio

450

380

350Sandstone

Shale

Limestone

Regional Uplift

Erosion


The oldest rocks are found in southwestern Ohio (along the axis of the Findley Arch)

450

380

350Sandstone

Shale

Limestone

Regional Uplift

Erosion


450

380

350Sandstone

Shale

Limestone


Sandstone Shale Limestone

450

380

350Sandstone

Shale

Limestone


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)


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


Sedimentation (e.g., lime mud)

Shale (220)





450

380

350Sandstone

Shale


Gabbro (790)

Formation of an


Sedimentation (e.g., quartz sand)

Limestone(210)


Shale (220)




450

380

350Sandstone

Shale


Gabbro (790)

Formation of an


Sedimentation (e.g., immature sand)

Shale (220)

Limestone(210)

Quartz Sandstone(200)





450

380

350Sandstone

Shale


Gabbro (790)

Formation of an


Shale (220)

Limestone(210)



Arkose (190)




450

380

350Sandstone

Shale


Gabbro (790)

Formation of an


Arkose (190)

Shale (220)

Limestone(210)






4. Sedimentation ceases

450

380

350Sandstone

Shale


Gabbro (790)

Formation of a

Disconformity

ErosionArkose (190)

Shale (220)

Limestone(210)



1. Erosion of horizontal beds

450

380

350Sandstone

Shale


Gabbro (790)

Formation of an

Disconformity

Shale (220)

Limestone(210)

Arkose (190)



1. Erosion of horizontal beds2. Loss of geologic record

(i.e., Arkose)3. Formation of a horizontal

erosion surface

Erosion

450

380

350Sandstone

Shale


Gabbro (790)

Formation of an

Disconformity

Shale (220)

Limestone(210)

Arkose (190)

Quartz Sandstone(200) Sedimentation (e.g., reef)




erosion surface4. Renewed Sedimentation

450

380

350Sandstone

Shale


Gabbro (790)

Formation of an

Disconformity

Shale (220)

Limestone(210)

Arkose (190)






Limestone (140)

450

380

350Sandstone

Shale


Gabbro (790)

Formation of an

Disconformity

450

380

350Sandstone

Shale

Limestone

Shale (220)

Limestone(210)

Arkose (190)






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


NonconformitiesGabbro

The Grand Staircase

Correlation Physical Continuity Similar Rock Types Fossils (index and assemblage)

plate tectonics the grand unifying theory of geology plate tectonics controles distributions of...

Documents

rigid crust

continental crust silicic

crust element atomic

terrestrial planets

outer planets

inner planets

iron poor

terrestrial planets