EART 3 Geology of National Parks 21804

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EART 3- Geology of National Parks 2/18/04

• OUTLINE
• Mountain Building and Deformation
• Metamorphism and Magmatism
• CONCEPTS
• Brittle versus ductile deformation faults and
  folds
• Metamorphic facies

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Accretionary Prism
Mountain Building or Orogeny involves rock
deformation and burial which includes
Faults
Deformation
Folds
Metamorphism
Burial
Magmatism
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Brittle versus Ductile Deformation

• Brittle deformation- involves the fracture or
  failure of material in response to force or
  stress (faulting).
• Ductile deformation- involves the flow of
  material in response to force or stress
  (folding).

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Factors that Control Brittle versus Ductile
Deformation

• Composition- quartz and olivine favor brittle
  deformation while calcite and micas favor ductile
• BUTTER vs. CHALK
• Temperature- low T favors brittle deformation
  while high T favors ductile
• Pressure- low P favors brittle deformation while
  high P favors ductile
• Rate Forces are Applied- fast rates favor brittle
  deformation while slow rates favor ductile

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Anticline
Syncline
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Normal Fault
Reverse Fault
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Normal Fault
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Normal Fault
Reverse Fault
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Reverse Fault
Hanging Wall
Foot Wall
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Metamorphism

• The process by which elevated temperatures and
  pressures within the Earth alter the mineral
  content and structure of solid rock without
  melting it.
• Temperature and pressure conditions required
• T gt 200 degrees C (400 degrees F)
• P gt 1 kilobar (1000 bars 1000 x pressure at
  surface)
• Pressure increases by 1 kilobar for every 3 km
  of depth
• Temperature increases by 25 degrees C per km of
  depth in shallow crust

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Metamorphic Rocks are classified on the basis of
texture (foliation) and the nature of the parent
rock (protolith)

• Foliation- rock texture due to parallel alignment
  of elongate minerals

Minerals grow with long axes perpendicular to
force.
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Foliated Metamorphic Rocks

• Protolith Rock Name
• Shale Slate
• Mudstone Phyllite
• Igneous rock Schist
• Gneiss

Specific minerals are stable at particular
pressures and temperatures
P and T
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Non-Foliated Metamorphic Rocks

• Protolith Name
• Limestone Marble
• Quartz rich Quartzite
• Sandstone

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Metamorphic Faciesname for particular group of
metamorphic minerals stable at specific pressure
and temperature conditions
Identifying mineral assemblages in a metamorphic
rock allows one to determine the P and T
conditions and therefore the environment in which
it formed.

• Hot shallow environment
• B. Normal burial conditions
• C. Cold deep environment

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Magmatism
Batholith- large irregularly shaped igneous
intrusion
Dike- tabular igneous intrusion that cross cuts
bedding
Sill- tabular igneous intrusion parallel to
bedding