Rocks: Records of Geologic Processes

1
RocksRecords of Geologic Processes
RocksRecords of Geologic Processes
2
Three types of rocks

• Igneous Rocks formed from the cooling and
  consolidation of magma.
• Sedimentary Rocks formed by the consolidation of
  fragments of previously existing rock or
  chemically precipitated from solution.
• Metamorphic Rocks whose original form has changed
  in the solid state due to increased temperature
  and/or pressure.

Which rocks are most abundant on the Earths
surface? Which rocks make up most of the Earth?
Sedimentary rocks
Metamorphic rocks
3
Major Rock Groups
4
Intrusive granite
Intrusive Granite
Fig. 3.2
5
Extrusive Basalt
Extrusive Basalt
6
Common minerals
7
Sedimentary rocks occurrence and change?

• Physical weathering reduction in size
• Chemical weathering change in composition

• Transportation
• Solid particles clastics by water, wind, ice
• Ions in solution .chemical

• Deposition
• Parallel layers, bedding
• Lithification through compaction

• From sediment to solid rock
• Compaction
• Cementation

Clastic sediments, deposited particles of sand,
silt and gravel
Chemical and biochemical sediments are
precipitated from seawater or made by organisms
8
Occurrence
Sedimentary rocks cover a large part of the
surface
Sedimments are difficult to preserve
9
Where does Metamorphism occur?
Regional Metamorphism
Contact Metamorphism
10
Metamorphism
High pressure, low temperature metamorphism
occurs in subduction zones
Ultra-high-pressure metamorphism occurs deep in
the crust
Regional metamorphism, elevated pressure and
temperature over large regions
Contact metamorphism, around magmatic intrusions
11
Outcrop
12
Coast outcrop
Oregon Sea Cliffs
Fred Hirschmann
13
Field outcrop
Fig. 3.8
Russ Kinne/ Comstock
14
Mountain outcrop
Fig. 3.9
Carr Clifton
15
Rock cycle, interaction of plate tectonic and
climate system
1. Subduction of an oceanic plate under a
continental plate creates a volcanic mountain
chain 2. Subducting plates dehydrates and melts
and infiltrates the overlying mantle wedge
causing melting 3. Magma cools to make igneous
rocks (volcanic and plutonic) 4. Uplifted
mountains force air to rise and loose their
moisture 5. Precipitation, freezing and thawing
creates loose material (sediments), erosion
strips it 6. Sediments are transported by rivers
to the ocean 7. Burial is accompanied by
subsidence and sinking 8. Along active tectonic
margins, continent collision, sediment gets
buried 9. As rocks are buried they undergo
metamorphism (extreme pressure and
temperature. 10. Further melting restarts the
cycle.