Rock Basics: Background to
Understand Earth’s Landscapes
The Wave –
Western Australia
The Wave –
Utah
Composition of the Continental Crust
• O- Oxygen 47%
• Si- Silicon 28%
These together = 75% of continental crust
• Al- Aluminum 8.1%
• Fe- Iron 5.0%
•
•
•
•
Ca- Calcium 3.6% - nutrient
Na- Sodium 2.8% - nutrient
K - Potassium 2.6% - nutrient
Mg- Magnesium 2.1% - nutrient
Examples
Silicates: have Si as base, Quartz (Si02)
obvious 75%
Feldspars: have Si and Al, and when add (Ca, K, Na) =
Feldspars
Clay minerals stick to your boot and have layered
structures
Colorado & Minerals
Basic Rock Types
IGNEOUS
SEDIMENTARY
METAMORPHIC
Igneous (made by “fire”) - Solidified from molten rock (i.e., magma).
Sedimentary - Deposited (strata) and buried close to Earth’s surface.
Metamorphic (“changed form”) - Transformed from preexisting
rocks under high pressure, temperature & fluids.
Rock Types
Sedimentary
rocks are most
abundant near
Earth’s surface
Sediments
make up
75% surface
area
- poor preservation
Igneous and
Metamorphic
rocks make up
most of the
crustal volume
- limited exposure!
Sediments make
up only 5% by
volume
Details on Igneous Rocks
Entire classes on rock minerals…but for us…
•
Minerals crystallize from melt, derived from deep
within Earth’s crust or mantle
– High temperatures, 700° C & more
– Crystal size depends on cooling rate
• Small = rapid; large = slow (millions of years)
•
Intrusive rocks cool slowly within deep magma
chambers:
– Coarse, interlocking crystals
•
Extrusive rocks cool rapidly at (or near) the
surface of the earth:
– Fine-grained, often “glassy”
Igneous Rocks
Common in
volcanic areas &
plate boundaries
Basalt
Details on Sedimentary Rocks (strata)
•
Loose particles (sand, silt, marine shells)
accumulate on shorelines, basins, rivers, etc.,
– Clastic Sediments (clast = “little”)
•
Minerals precipitate from dissolved chemicals in
water
– Chemical & Biochemical Sediments
•
All are the products of Weathering—the breaking
apart & decaying processes, and Erosion—the
transportation processes from source to point of
deposition
Lithification
Shale
Conglomerate
Sandstone
Breccia
Large to Small
Details on Metamorphic Rocks
•
High temperatures and pressures at depth cause
changes in mineralogy, texture, and composition (very
complex…lots of ways to squish rocks)
– Changes take place in Solid State by recrystallization
and chemical reactions
– Temperatures greater than 250° C, less than 700° C
•
Regional Metamorphism - High pressures and
temperatures derive from regional collision,
deformation and mountain building (tectonics)
•
Contact Metamorphism - Locally high temperatures,
adjacent to intrusions
–
Igneous body touching & “cooking” surrounding area
Mafic & felsic minerals align…
Common at
convergent
plate
boundaries
Metamorphic Rocks
Notice alignment of
minerals = foliation
•
Metamorphic Rocks
Foliations - Planar fabric defined
by
– Alignment of platy minerals (micas
& clays)
– Alternating bands of mineral types
•
Indicative of high pressures and
deformation during formation
– Pressure-Temperature-time paths
Fig 4.6
•
Not
Foliated
•
Distinct
lowpressure
minerals
Typical Rock Types Seen by Geologic
Origin
Sedimentary Types
Metamorphic
Igneous Types
Clastic
Solution
(carbonate)
Foliated
NonFoliated
Intrusive
Coarse
Conglomerate
Breccia
Limestone &
Dolomite
Gneiss
Marble
Granite
Gabbro
Diorite
Medium
Sandstone
Siltsone
Limestone
& Dolomite
Schist
Phyllite
Quartzite
Fine
Shale
(Mudstone)
Calcareous
Mudstone
and Chert
Slate
Amphibolite
Grain
Aspects
Extrusive
Basalt
Rhyolite
Obsidian
The Rock
Cycle
-Melting & Intrusion
-Solidification of melt
-Mountain Building
-Uplift & Exposure
-Weathering
-Erosion
-Deposition & Burial
-Metamorphism
-Melting & Intrusion
Geologic
Time
Large blocks of time
represented by changes
in evolution
Animation about Geologic Time
Geologic Time as
Football Field:
click here to see
the animation
Plate Tectonics
Rearranging Earth’s Surface
Alfred Wegener and how a
scientific paradigm operates
“Scientists still do not appear to understand
sufficiently that all earth sciences must contribute
evidence toward unveiling the state of our planet
in earlier times, and that the truth of the matter
can only be reached by combing all this
evidence...It is only by combing the information
furnished by all the earth sciences that we can
hope to determine ‘truth’ here, that is to say, to
find the picture that sets out all the known facts in
the best arrangement and that therefore has the
highest degree of probability. Further, we have to
be prepared always for the possibility that each
new discovery, no matter what science furnishes it,
may modify the conclusions we draw.
Alfred Wegener. The Origins of Continents and Oceans
(4th edition)
Field work: Atlantic once closed
Shape Match
Rocks Match
Fossils Match
Lifetime of work
Theory of Continental Drift
Meteorologist proposes
to change geology
1st edition 1915
Until 1960s – Utter Rejection by
Geologists
Dr. Rollin T. Chamberlin of the University of Chicago said, “Wegener's
hypothesis in general is of the footloose type, in that it takes
considerable liberty with our globe, and is less bound by restrictions or
tied down by awkward, ugly facts than most of its rival theories.”
American Association of
Petroleum Geologists organized a
symposium specifically in
opposition to the continental drift
hypothesis.
“Utter, damned rot!”
W.B. Scott, President of the American
Philosophical Society
Today: We Map Tectonic Plates
Today: We accept that most Earthquakes
and Volcanoes occur along boundaries of
Tectonic Plates
See animation
See animation
Today: We Accept Plate Movement
Today: We Accept Pangaea
and its breakup
Why the Opposition & Shift?
• Opposition:
– An example of how a discipline can get “locked into” a
pathway of mental thinking for decades (paradigm)
– An example of how a discipline protects its “turf” –
rejecting the thoughts of a meteorologist
• Shift:
– Enough time for the opponents to die, and a bunch of
new geologists in the 1960s to challenge “the
establishment”
– Reminder throughout this class that ideas shift and
much depends on the mental framework of the
scientist
Structure of Earth allows continents to move
Wegener could not answer a
fundamental question of HOW
continents could move.
But geology advanced
to the point to begin to
understand Earth’s
internal structure &
how it allows
continental drift...
Earth’s Structure
Brittle Crust Floats on Flowing, Plasticlike Asthenosphere
Different Crusts: 5/6th submerged
(isostatic balance)
Ocean Crust
More Dense (sima)
Continental Crust
Less Dense (sial)
Isostacy
crust adjusts to
create a balance
(equilibrium)
Peep the ani...
Two continental
plates under Tibet
To reach isostatic
balance, Tibet
Plateau
rises
Too thick, so get uplift
Reason for Movement
(we think…)
Excess heat from
radioactive decay
creates liquid outer
core (and magnetic
field), and forces
mantle to have
convection
TYPES OF PLATE INTERACTION
Stream Systems on
Dynamic Earth
Type of Plate Interactions:
Divergent Boundaries
Mid-ocean
ridges are
places of
plate divergence
Mid-Atlantic Ridge is the Icon
Mid
Atlantic
Ridge
East
Pacific
Mid Indian
Ridge
Rise
Sea Floor Spreading:
Key to Rejecting the Old Ways
• “Plate Tectonics” = continental drift + seafloor spreading
• Rename the theory with new evidence:
1. Potassium-Argon dating
2. Paleomagnetism
Age of the Ocean Crust
Animation
showing ages
of ocean crust
getting older
away from
spreading
Always New Details Being Added
Submarine Volcano erupting!
Paleomagnetism
Animations – Click on the Pictures
Visualizing reversals of magnetic
field and how this creates a
mirror image on the two sides of
a spreading center
Lava has
minerals that
“record” the
magnetic field
Paleomagnetism in Symmetry
Conclusion
was that
sea floors
spreading
apart
Don’t Worry!
Hollywood movie
“The Core” – silly
It will take thousands
of years to shift that
extreme
Source for Latest Info:
Website
Obvious question:
With making new sea floor, why isn’t
Earth expanding?
Old ocean plates undergo “subduction”
Type of Plate Interactions:
Convergent Boundaries
Oceanic-Continental Convergence
Denser Oceanic Crust Subducts
Trench Forms
Volcanoes Form
Lithosphere Subducts Into Asthenosphere
Earthquakes Common All Along Boundary
Cartoon
Andes
Nazca plate collide
with South
American Plate
Latest Research from Nature
Ocean – Continent
Convergence
in Pacific
Northwest
Oc-Co Convergence...
Island Arcs from Ocean – Ocean
Convergence
Oc-Oc Converg ani...
Continent – Continent Collision
Example of Himalaya
Himalaya Formation
Formation of Appalachian
Mountains resulted from the
collision of the African and
European Plates with North
American Plate prior to 300
million years ago.
Ural Mountains
Formation of the Ural Mountains related to collision tectonics prior to 300 Ma ago.
Convergence &
Tsunami
Effects Of Plate Locking
EQ (or landslide or volcanic eruption) Movement
Generates the Wave that travels about 500
mph
Animations
Shows how Tsunami can
be made from subduction
Shows time sequence in
Tsunami destroying coastal
city in Alaska
Mega-Quake
set off 2004
Tsunami & will
happen again
Energy ripple
Sri Lanka
Sumatra Uplift
Type of Plate Interactions:
Transform Boundaries
Side-by-side motion
along San Andreas zone
Transform motion of the San Andreas Fault can be seen by offset of streams
that cross the fault zone.
California Won’t Fall into the Ocean
Continent is 5/6ths
submerged, so it is
anchored very tight
Other Transform
Boundaries
Hot Spots
Focus here on Hawaii & Yellowstone
Often in the middle of a plate
Hawaiian Hotspot
Animation of Hawaii as moves over Hot Spot
Trail of the Hot Spot
Note change in direction 43 myr ago
Change in direction 43 myr ago
Alternative
Hypothesis
Yellowstone Hot Spot