Metamorphic Rocks and Conclusion of Sedimentary Rocks

1
Metamorphic Rocks and Conclusion of Sedimentary
Rocks
2
The deal with sedimentary rocks

• The bigger the grains, the higher the energy of
  the depositional environment in which it was
  formed.
• The smaller the grains, the quieter the
  environment in the rock formed.
• SEDIMENTARY ROCKS ARE SO USEFUL BECAUSE THEY
  RECORD THE EARTHS HISTORY. THEY TELL US WHAT
  KIND OF ENVIRONMENT WAS WHERE AND WHEN.

3
Stratification

• Since sedimentary rocks are formed by deposition
  of sediment, they form layers of rock.
• Stratification occurs when you get distinct
  layering in rocks (you deposit something
  different on top of something else).
• Principle of Uniformitarianism and Suposition
  each layer is uniform in composition, older
  layers are on bottom, newer layers on top.
• If there is discontinuity in the layers,
  geologists term it an unconformity.

4
How can you get an unconformity?

• Erosion of a layer just deposited.
• Faulting (normal or reverse)
• For reverse faulting, your older rocks would get
  pushed on top and mess up the order.

5
Cool Sed rock features

• Cross-bedding formed from changes in wind
  direction, or change in direction of water
  current.
• Ripple marks you can definitely tell which way
  water or wind moved
• Mudcracks formed when mud dries up and shrinks
• Geodes- water within sediments leaches into
  cavities of rocks precipitating calcite or quartz
  crystals

6
Metamorphic Rocks

• Metamorphism (in the geological sense)- the
  changing of one rock into another by inducing
  heat and/or pressure.
• Two types of metamorphism contact, and regional

7
Contact Metamorphism

• When rocks are changed by heat
• How this happens
• 1.) rocks that are subducted and come in contact
  with magma
• 2.) rocks happen to come into contact with magma
  that is migrating towards the surface (some new
  volcanism)

8
Regional Metamorphism

• Rock change because they undergo some kind of
  process that induces a lot of pressure
• How this happens
• 1.) rock in a subduction zone, the deeper you
  go, the more pressure you encounter
• 2.) rock in a fault zone (lots of pressure
  there)
• 3.) compressional forces via plate tectonics,
  isostatic adjustment, remember folding??????
  Ductile deformation?

9
Chemical Alteration

• Hydrothermal pretty much water eruptions- water
  comes into contact with magma, the magma boils it
  an sends it back to the surface enriched with
  chemicals from the subsurface and magma chamber

10
How you can tell if a rock is formed by contact
or regional metamorphism.

• One word FOLIATION
• Foliated rocks have visible parallel banding. A
  lot of the time these bands are wavy, warped,
  because after all, they were formed under
  pressure. So, FOLIATED ROCKS ARE FORMED BY
  REGIONAL METAMORPHISM.
• Non-foliated most of the time are rocks formed
  by contact metamorphism
• An example marble its a non foliated rock
  formed by regional metamorphism