UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 3: The Rock Cycle
Instructor: Dr. Douglas W. Haywick
Last Time
1. Alfred Wegener and “Drifting Continents”
2. The Plate Tectonic Revolution
3. Plate Tectonics Mechanisms
Wegener’s hypothesis:
300 million years ago, the
continents were all grouped
together into a “supercontinent”
he called Pangaea
His supporting evidence?
Matching rock types and
fossils*
* types and ages
And although Continental Drift was rejected....
…Wegener got it right about Pangaea
The Plate Tectonics Revolution
Technological developments during the war increased our
understanding of the world’s oceans.
The Plate Tectonics Revolution
Radar, sonar, and depth sounding revealed that the ocean
bottoms were not flat planes
The Plate Tectonics Revolution
The single most important piece of
evidence for plate tectonics was also
discovered around the end of WWII
was…
…. Paleomagnetism
The Plate Tectonics Revolution
Earth has a
magnetic field
(and it isn’t
constant)
The Plate
Tectonics
Revolution
Paleomagnetism shows
that the ocean floor
youngest near the ridges
and oldest near the
continents
Paleomagnetism
The Plate Tectonics Revolution
The outer part of the Earth is broken up into several large tectonic plates
The Plate Tectonics Revolution
And where they “rub” against one another, you get…
Earthquakes
The Plate Tectonics Revolution
…Volcanoes (active, dormant and extinct)
The Plate Tectonics Revolution
http://shadow.eas.gatech.edu/~anewman/classes/geodynamics/misc/Worldmap.gif
…and mountain belts
Internal “guts”
of the Earth
Four Major “Geophysical” Layers
1) The Crust (rigid rock)
2) The Mantle (rigid, upper; ductile, lower)
3) The Outer Core (liquid metal; Fe/Ni)
4) The Inner Core (solid metal; Fe/Ni)
Heat exchange gives rise to
Convection Currents
The Plate Tectonics Mechanism
Rising convection currents stress the rigid outer layer
of the Earth.
Cooler
Hotter
The Plate Tectonics Mechanism
Rising convection currents stress the rigid outer layer
of the Earth. This layer consists of the crust and the
outer most mantle
Geophysical
layers
Cooler
Mantle
Hotter
The Plate Tectonics Mechanism
Collectively, the rigid outer most part of the Earth
(about 100 km thick) is called the Lithosphere
Tectonic
layers
Lithosphere:
Athenosphere:
Geophysical
layers
Cooler
Mantle
Hotter
The Plate Tectonics Mechanism
It is postulated that the convection currents can
eventually break up the lithosphere into separate plates
Tension
Cooler
Mantle
Hotter
The Plate Tectonics Mechanism
Hence the term “plate tectonics”
Tension
Asthenosphere
The Plate Tectonics Mechanism
Tectonic plates can interact in one of 3 ways
The Plate Tectonics Mechanism
Tectonic plates can interact in one of 3 ways
1) Move away from one another: Divergent Plate Boundary
The Plate Tectonics Mechanism
Tectonic plates can interact in one of 3 ways
1) Move away from one another: Divergent Plate Boundary
2) Move towards one another: Convergent Plate Boundary
The Plate Tectonics Mechanism
Tectonic plates can interact in one of 3 ways
1) Move away from one another: Divergent Plate Boundary
2) Move towards one another: Convergent Plate Boundary
3) Slide past one another: Transform Fault Plate Boundary
The Plate Tectonics Mechanism
Tectonic plates can interact in one of 3 ways
1) Move away from one another: Divergent Plate Boundary
2) Move towards one another: Convergent Plate Boundary
3) Slide past one another: Transform Fault Plate Boundary
Divergent Plate
Boundaries
Convergent Plate
Boundaries
San Andreas Fault
Transform Fault
Boundaries
Today’s Agenda
1.
Introduction to rocks
2. The Rock Cycle
Web notes 3:
Rocks
Rocks are naturally occurring solids containing one or
more minerals.
Rocks
Rocks are naturally occurring solids containing one or
more minerals.
They come in many, many, many different “flavors”
Rocks
Rocks are naturally occurring solids containing one or
more minerals.
e.g., Granite
Rocks
Rocks are naturally occurring solids containing one or
more minerals.
e.g., sandstone
Rocks
Rocks are naturally occurring solids containing one or
more minerals.
e.g., gneiss
Rocks
We recognize 3 major rock groups:
Rocks
We recognize 3 major rock groups:
1) Igneous (“born of fire”); originally molten
Rocks
We recognize 3 major rock groups:
1) Igneous (“born of fire”); originally molten
2) Sedimentary; originally particulate material or
produced from precipitation out of water
Rocks
We recognize 3 major rock groups:
1) Igneous (“born of fire”); originally
molten
2) Sedimentary; originally particulate
material or produced from
precipitation out of water
3) Metamorphic; pre-existing rocks
modified by pressure or temperature
Igneous Rocks
Can be either extrusive (volcanic) or intrusive (plutonic):
Igneous Rocks
Can be either extrusive (volcanic) or intrusive (plutonic):
Extrusive (volcanic) rocks
can be erupted as lava…
Igneous Rocks
Can be either extrusive (volcanic) or intrusive (plutonic):
Extrusive (volcanic) rocks
can be erupted as lava, or
as pyroclastic material
(e.g., ash)
Sedimentary Rocks
We recognize 4 major classes of sedimentary rocks:
Sedimentary Rocks
We recognize 4 major classes of sedimentary rocks:
1) Siliciclastic: composed of broken bits of silicate minerals;
Alluvial fan
Sedimentary Rocks
We recognize 4 major classes of sedimentary rocks:
1) Siliciclastic: composed of broken bits of silicate minerals
2) Biochemical: mostly composed of the remains of calcium
carbonate-secreting beasties
reef
Sedimentary Rocks
We recognize 4 major classes of sedimentary rocks:
1) Siliciclastic: composed of broken bits of silicate minerals
2) Biochemical: mostly composed of the remains of calcium
carbonate-secreting beasties
3) Chemical; formed through chemical precipitation alteration
Salt flat
Sedimentary Rocks
We recognize 4 major classes of sedimentary rocks:
1) Siliciclastic: composed of broken bits of silicate minerals
2) Biochemical: mostly composed of the remains of calcium
carbonate-secreting beasties
3) Chemical; formed through chemical precipitation alteration
4) Organic; formed from plant material
Peat bog
Metamorphic Rocks
We recognize 3 divisions of metamorphic rocks:
Metamorphic Rocks
We recognize 3 divisions of metamorphic rocks:
1) Foliated; display a prominent layering
schist
Metamorphic Rocks
We recognize 3 divisions of metamorphic rocks:
1) Foliated; display a prominent layering
2) Non-foliated; do not display layering
marble
Metamorphic Rocks
We recognize 3 divisions of metamorphic rocks:
1) Foliated; display a prominent layering
2) Non-foliated; do not display layering
3) Cataclastic; composed of broken up bits of rock
mylonite
The Rock Cycle
The Rock Cycle
The Rock Cycle
The Rock Cycle
Igneous
Loop
Metamorphic
Loop
Sedimentary
Loop
Today’s Homework
1. Download and read web notes 3
2. Organize your notes
Next Time
1) Quiz 2 (fill in the blank questions)
2) Basic Chemistry
GY 111: Physical Geology
Lecture 3: The Rock Cycle
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.