Rocks: Records of Geologic Processes

1
Rocks Records of Geologic Processes

• Rock Families
• Igneous Rocks
• Sedimentary Rocks
• Metamorphic Rocks
• The Rock Cycle

2
All a Geologist wants to do is

• 1. To figure out how all the rocks every- where
  were formed
• 2. And understand all these processes
• 3. So that we can understand
• Earths history,
• Find fuel mineral resources,
• Solve environmental problems
• Protect ourselves from natural hazards!

3
Rock

• A naturally-occurring solid aggregate of
  minerals.
• It can be made of just 1 mineral (mono-mineralic)
• - marble, limestone
• Or of many minerals (poly-mineralic)
• - granite, sandstone, slate

4
Rocks are identified by

• 1. TEXTURE - grain size shape
• Fine grained - can not see individual grains
• Coarse grained - can see individual grains
• Grain shape - rounded or angular
• Grain arrangement - floating, inter-locked, etc.
• 2. COMPOSITION - chemistry
• Percent SiO2
• Mg/Fe, Na/K, presence of H2O, etc.

5
(No Transcript)
6
Rock Cycle and the Earth System
7
Three Families of Rocks
8
Igneous Rocks - born of fire

• Rocks formed by the crystallization of magma
• Cool below the surface - INTRUSIVE/PLUTONIC -
  slow cooling

Cool at surface - EXTRUSIVE/VOLCANIC - fast
cooling
9
Igenous Rocks - formed from the crystallization
of magma
10
Sedimentary Rocks

• Rocks formed by
• consolidation of pieces of previously existing
  rocks
• chemical precipitation from solution
• Material is deposited in BEDs, buried
  compacted/cemented to form rock

11
Weathering, Erosion, Transportation, Deposition,
Burial, Lithification.
12
Sedimentary rocks

• 5 by volume of the upper crust
• 75 by area of continents
• Often the only record of geologic events
• e.g. Himalaya will someday be sandstone

13
Metamorphic Rocks

• Rocks formed by the transformation of
  previously-existing rocks in the solid state due
  to increased temperature pressure and fluids.

14
Kinds of Metamorphism, etc.

• All rock families can be altered
• Change is in mineralogy texture in the solid
  state!
• Foliation recrystallization
• Thermal range is between 250 - 7000 C
• Kinds are CONTACT REGIONAL
• Regional metamorphism is progressive so earlier
  assemblages are overprinted by later ones
• Contact is related to the size of the intrusion

15
(No Transcript)
16
Proportions of the Rock Types
17
We see bedrock in outcrops drilled cores.
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
The end