Download Plate Tectonics

From Brian Gilligan
Methods of Thermal Energy Transfer
3. RADIATION
Heated objects radiate energy as well.
Methods of Thermal Energy Transfer
Convection is the most important mechanism for
geologic processes.
Rock Types and the Rock Cycle
ROCK - a naturally occurring aggregate of minerals
formed within the Earth.
Basaltic Dike
Acadia Nat’l Park,
Maine
Delicate Arch, Arches Nat’l Park, UT
Rock Types and the Rock Cycle
A MINERAL is a
naturally occurring, inorganic solid,
consisting of either a single element or compound,
with a definite chemical composition (or varies within
fixed limits),
and a systematic internal arrangement of atoms.
Pyrite
FeS2
Diamond
C
Beryl
Be3Al2(Si6O18)
Rock Types and the Rock Cycle
Three types of rocks.
These are present in the crust and at the
Earth’s surface.
Each have fundamentally different origin.
IGNEOUS
SEDIMENTARY
METAMORPHIC
Igneous Rocks
- Cooled and solidified from MOLTEN material.
- Formed either at or beneath the Earth’s surface.
- MELTING of pre-existing rocks required.
Granite
Basaltic
Lava
Sedimentary Rocks
- Pre-existing rocks are weathered and broken down
into fragments that accumulate and are then
compacted or cemented together.
- Also forms from chemical precipitates or organisms.
Metamorphic Rocks
- Form when pre-existing Earth materials are subjected
to heat, pressure and/or chemical reactions
and change the mineralogy, chemical
composition and/or structure of the material.
Gneiss
Coal
Slate
Any rock type can become any other rock type given time and
processes acting on them.
These changes are reflected in the ROCK CYCLE.
Time and Geology
For most geologic processes a great deal a time
is needed.
Earth is 4.6 billion years old.
Time is available for these processes to operate very
slowly.
Geologists measure time in two ways:
1. RELATIVE AGE DATING
2. ABSOLUTE AGE DATING
Time and Geology
Relative Age Dating:
- Determined by spatial relationships between adjacent
rock bodies and one another.
- Provides relative age, no numbers involved.
- Makes use of:
Principle of Superposition
Principle of Cross-Cutting Relationships
Principle of Inclusions
Principle of Original Horizontality
Time and Geology
Relative Age Dating:
Time and Geology
Absolute Age Dating:
- Determine actual age of the rock or structure.
- Provides absolute age, actual numbers of years
are involved and applied.
- Places rocks and events in Geologic Time Scale.
- Makes use of:
Radiometric techniques
Tree-Ring Dating (Dendrochronology)
Fission Track Dating
Lichenometry
Time and Geology
Absolute Age Dating:
GEOLOGIC TIME SCALE
- Subdivided into Era, Periods and Epochs
- Based on fossil evidence, initially.
- Actual years added using techniques mentioned
earlier.
The Theory of Plate Tectonics
Underlying unifying principle of geology.
Evolved in the late 1960s, early 1970s.
Realization that certain parts of the Earth were more
affected by earthquakes and volcanoes.
Also noted that large mountainous regions occur on
margins of continents.
Changes in sea level were related to these events.
Was not a random occurrence.
Distribution of major volcanoes and earthquakes
The Theory of Plate Tectonics
Many hypotheses presented to answer these questions.
None answered all the questions at all localities.
Led to hypothesis of PLATE TECTONICS.
Became widely accepted in a few short decades.
The Theory of Plate Tectonics
Steps in Development
1. Benjamin Franklin (late 1700s)
Recognized that crust of Earth was a shell.
Surface could be broken and parts moved about.
2. Alfred Wegener (1912)
German meteorologist-geophysicist
Proposed theory of Continental Drift.
Proposed continents float on a denser
underlying interior of the Earth.
CONTINENTS periodically break up and
DRIFT apart.
The Theory of Plate Tectonics
Wegener believed all continents were joined together.
Supercontinent of Pangaea existed about 200 myBP.
Pangaea covered 40% of the Earth’s surface.