Download Volcanoes and Igneous Activity Earth - Chapter 4

Chapter 1
An Introduction to
Geology and Plate
Tectonics
PowerPoint Presentation
Stan Hatfield . Southwestern Illinois College
Ken Pinzke . Southwestern Illinois College
Tark Hamilton . Camosun College
Copyright © 2009 Pearson Education Canada
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The Science of Geology
Geology is the science that pursues an
understanding of planet Earth
• Physical geology - examines the materials
composing Earth and seeks to understand
the many processes that operate beneath
and upon its surface
• Historical geology - seeks an
understanding of the origin of Earth and
its development through time
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The Science of Geology
Geology, people, and the environment
• There are many important relationships
between people and the natural
environment
• Some of the problems and issues
addressed by geology involve natural
hazards, resources, world population
growth, and environmental issues
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The Science of Geology
A Canadian Profile
• Sir William Edmond Logan
has been called Canada’s #1
scientist in history
• He was the first director of
the GSC and was active in the
outdoor pursuits of geology
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The Science of Geology
Some historical notes about geology
• The nature of Earth has been a focus of
study for centuries
• Catastrophism: shaping of the Earth’s
landscape by rare catastrophes
• Uniformitarianism: a principle first
proposed by James Hutton that
represented the Birth of Modern Geology
(processes that operate today also operated
in the past; Gradualism + Vast Time)
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Geologic Time
Relative dating and the geologic time scale
• Relative dating means that dates are placed in their
proper sequence or order without knowing their age in
years (apply Principles of Superposition and Fossil
Succession)
Geologists are now able to assign fairly accurate
dates to events in Earth history
• Absolute radiometric dating means that particular
isotope clocks determine exact ages
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Geologic Time
The magnitude of geologic time
• Involves vast times – millions or billions of
years (the Earth is 4.6 billion years old!)
• An appreciation for the magnitude of
geologic time is important because many
processes are very gradual (name some?
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Geologic Time
The Geologic Time Scale. The
numbers are absolute ages in
millions of years before present.
Note that the Precambrian
accounts for 88% of geologic
time and yet the Phanerozoic with
its wealth of fossils includes many
divisions (Eras, Periods, Epochs).
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Early Evolution of Earth
Origin of planet Earth
• Most researchers believe that, following
the Big Bang, The Solar System: Earth
and the other planets formed at essentially
the same time from the same primordial
material as the Sun
• Nebular hypothesis
Layered structure developed by chemical
segregation early in the formation of
Earth (Differentiation)
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The Nebular Hypothesis
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Plate Tectonics: a geologic paradigm
• Provides modern geologists with the first
comprehensive model of Earth’s internal
workings (Convection, Heat Loss)
• Began in the early part of the twentieth
century with a proposal called continental
drift – the idea that continents moved
about the face of the planet and "drifted"
to present positions
• Sea Floor Spreading was post WWII from
seismology and ocean mapping
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Plate Tectonics
Alfred Wegener and continental drift
• First proposed his continental drift
hypothesis in 1915; an idea before its time
• Published The Origin of Continents and
Oceans
Continental drift hypothesis
• Supercontinent called Pangaea began
breaking apart about 200 million years ago
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Plate Tectonics
Pangaea approximately 200 million years ago.
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Plate Tectonics
Evidence used in support of the
continental drift hypothesis
• Fit of the continents: Africa-S. America
• Fossil evidence: Glossopteris, Mesosaurus
• Rock type and structural similarities
• Paleoclimatic evidence: S. Hemisphere
Late Paleozoic glaciation (places now hot)
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Plate
Tectonics
Wegener’s matching of mountain ranges on different continents.
Lithologies, Mountain
Belts & Orogenies
Match across Atlantic
Appalachians =
Caledonides =
Svecofennides,
Devonian Granites
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Plate Tectonics
Paleoclimatic evidence for continental drift.
Late Paleozoic
reconstruction of
Pangea puts ice
over Antarctica,
S.Pole
Modern position
of icy facies near
Equator!
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Mesosaurus teniudens: (Faunal ties Pangea)
Early Permian Period (286 to 258 Ma)
Irati Formation, Brazil
Namibia, Africa
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Glossopteris: (Floral ties Pangea)
Early Permian Period (286 to 258 Ma)
Gloss. browniana
Distribution of Gloss. & Vertebraria
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Planet of Shifting Plates
Plate boundaries (3 types)
• All major interactions among individual plates
occur along their boundaries
• Divergent boundary – two plates move apart,
resulting in upwelling of material from the
mantle to create new seafloor between them
• Convergent boundary – two plates move together
with subduction of oceanic plates or collision of
two continental plates, ocean crust is recycled
• Transform boundary – two plates slide laterally
past each other (rotation)
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Planet of Shifting Plates
Brittle cold rigid
Lithosphere plates
slide over warm
plastic Upper
Mantle
Thermal convection
in Mantle at a few
cm/year is the
driver
Mosaic of rigid lithospheric plates and divergent and convergent boundaries.
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Planet of Shifting Plates
Plate boundaries
• Transform fault boundaries - located where
plates slide past each other without either
generating new lithosphere or consuming old
lithosphere
• These are the fracture zones of Mid Ocean
Ridges
• Others cut Contintents or are Continent Ocean
Boundaries: Anatolian, Queen Charlotte, San
Andreas, Alpine Fault NZ
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Planet of
Shifting Plates
Mosaic of rigid plates and a transform
fault boundary.
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Earth’s Internal Structure
Earth’s internal layers can be defined by
• Chemical composition (Different Rock Types)
• Physical properties (Brittle, Plastic, Liquid,
Solid)
Layers defined by composition
• Crust: SIAL - Granodiorite
• Mantle: SIMA - Peridotite
• Core: Fe-Ni – like Meteorites:
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Earth’s Internal Structure
Four main layers of Earth are based on
physical properties and hence mechanical
strength (heat content, pressure &
composition)
• Lithosphere: rigid
• Asthenosphere: weak, plastic, few% partial
melts
• Mesosphere (or Lower Mantle) weak plastic
entirely solid
• Outer Core: 100% molten
• Inner Core: 100% solid
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Earth’s
Internal
Structure
Views of the Earth’s
layered structure.
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Earth as a System
The Earth system is powered by the Sun that
drives external processes in/on/above the
• Atmosphere
• Hydrosphere
• Cryosphere
• Lithosphere (Earth’s Surface)
How long do cycles take to modify each?
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System Science View of Earth & Cycles
Earth is a planet that is small and self-contained,
all matter is conserved & recycled
Earth’s four conceptual spheres & cycles
• Hydrosphere: daily-annual evaporation &
precipitation
• Atmosphere: daily-annual-long term changes
• Cryosphere: Ice caps, glaciers, sea ice, permafrost
• Biosphere: How far does this extend?
• Geosphere: The Solid Earth as in the last slides.
Tectonic “Wilson Cycles” last ~500 Ma
• Climate
isEducation
the long
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Canada term interplay of all these!1-27
Cryosphere: Ice Crystals with
Hydrogen Bonding
Red negative
ends of the
water
molecule
attract Green
positive ends
forming
hexagonal
ice
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Greenhouse Gases Warm the Earth’s
Exterior: H2O , CO2 , O3 , CH4 , SOx , NOx
Any molecular gas that
absorbs thermal (infra-red)
radiation is a greenhouse
gas.
Mainly asymmetric
molecules and ones with
resonant bonds
Predominant N2 and O2 are
transparent to heat (short
strong multiple bonds)
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Bill Comes Ashore at Peggy’s Cove, NS
What “Spheres”
does this involve?
What Global Cycles
does this involve?
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A View of Earth: Observations ~ Scale
The breathtaking beauty of Earth as seen by the Apollo astronauts in the
1960s and 1970s. (What can we see here and deduce?)
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The Face of Earth
Earth’s surface has two principal divisions
• Continents
• Ocean basins
• Significant difference between the continents
and ocean basins is their relative elevations
• Why are there 2 different elevations and not
just a continuous range of elevations & water
depths?
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The Face of Earth
Continents
• Most prominent features are linear mountain
belts: folds & faults or intrusions
• Shields, Precambrian crystalline rocks
Ocean basins
• Oceanic ridge system – the most prominent
topographic feature on Earth, ~50 km wide X
2.5 km tall
• Deep-ocean trenches up to 13 km deep
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EARTH’s Topography & Bathymetry
NGDC/NOAA W. Smith
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Earth as a System
Earth’s four conceptual spheres are linked as
a system through their interactions
Characterized by processes that
• Vary on spatial scales from fractions of a
millimetre to thousands of kilometres
• Have time scales that range from milliseconds
to billions of years
• How big is ___ & How long did it take to form?
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Earth as a System
The Earth system is also powered by the
Earth’s interior
• Heat remaining from Earth’s formation, and
heat that is continuously generated by
radioactive decay, power the internal processes
that produce volcanoes, earthquakes, and
mountains
• Volcanoes alone account for 5% of Earth’s
heat loss to space
• There is less radioactivity than in Precambrian
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Earth as a System: The Rock Cycle
The Rock Cycle is the loop involving the
processes by which one rock type can change
into another taking hours to Ga!
Illustrates the various processes and paths as
earth materials change both on the surface and
inside the Earth
Weathering to Sediments; Recrystallization to
Metamorphics; Melting & Cooling to Igneous
Most of the steps in the Rock Cycle happen at
Plate
Margins
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Rock Cycle
Somewhere rocks
constantly form, change,
and re-form over longs
spans of time.
Mountain Belts take 10’s
of Ma to form
Ocean Basins take
~500Ma to form & be
destroyed
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End of
Chapter 1:
Physical Processes
Plate Tectonic Engine
Geohazards
Resources
Scales of Observation &
Global Spheres & Cycles
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