Date post: | 24-Dec-2015 |
Category: |
Documents |
Upload: | blaze-morrison |
View: | 223 times |
Download: | 0 times |
Types of MetamorphismRegional metamorphism
– Large scale – large volume of rock is affected– Associated with convergent plate margins and mountain
building– Folding and faulting increase thickness of the crust– Occurs over a range of temperatures and pressures– Fluids are also present– Low grade to high grade metamorphism– Will have zones of contact metamorphism
Regional Metamorphism
Metamorphic Grade
The following diagram illustrates the rock cycle. Match the lettered responses to the blank ovals on the diagram. (Note:
some letters are used more than once.)
Magma
Igneous rock
Sediment
5
3
1 2
8
7
4 6
• a) Cementation & Compaction (lithification)
• b) Heat and Pressure
• c) weathering, transportation, deposition
• d) Cooling and solidification
• e) Melting
Metamorphic rock
Sedimentary Rock
Rock Cycle
Geologic Structure
Rock Deformation
• Stress– Force applied to an area– Pressure– Differential stress – magnitude of stress is
greater in one direction
• Rock Strength– Rock’s resistance to deformation (stress)
Rock Deformation Cont.• Strain
– A rock’s response to stress
– Deformation resulting in change of shape or position
• Elastic deformation– Deformation is reversible, after stress is removed, materials
return to original shape, i.e. A rubber band
• Plastic deformation– Deformation is permanent
– Rock flow in response to stress
– Need high pressures and temperatures, generally deep in earth’s interior, i.e. Taffy
Rock Deformation Cont.• Brittle deformation
– Deformation is permanent– Rock break (fracture) or lose cohesion– Generally low temperature and low pressure,
common in shallow crust, i.e. Peanut brittle
Types of Stress
• Tensional (Extension) Stress• Compressional Stress• Shear Stress
Tension or Extensional Stress• Stress move away from each
other (pull apart)• Rock lengthens• Common in divergent
boundaries, but not sole locale
• Ductile deformation – stretching and thinning of rock
• Brittle deformation – fracturing and faulting
Compressional Stress• Stress presses (squeezes)
rock together• Rock shortens• Common at convergent
boundaries• Ductile deformation –
shortening and thickening of rock – rock folds
• Brittle deformation – fracturing and faulting
Shear Stress• Stress creates a
lateral shift in the rock
• Rock slides past other rock
• Common at transform boundaries
• Results in faults
Folds
• Ductile deformation
• Compressional stress
• Horizontal rocks are deformed
Fold Terminology• Limb – the sides of the fold• Axial plane (hinge plane) –
imaginary plane that divides the fold into two equal parts, marks location of maximum curvature
• Fold axis (hinge line) – the line formed by the intersection of the hinge plane and a bedding plane
Syncline
• A fold with the youngest beds in the middle
• Generally trough shaped, with limbs dipping toward the center
Anticline• A fold with the
oldest beds in the middle
• Generally arched shaped, with limbs dipping away the center
Monocline
• Folds with only one limb
• Often Associated with faults
Fold Symmetry
• Symmetrical fold – limbs of the fold dip at the same angle
• Asymmetrical fold – limbs of the fold dip at different angles
Overturned Fold
• Fold where one limb has been tilted beyond vertical
1 2Applied
to a 3causes
At low T & P or
high stress rateAt high T & P or
low stress ra
te54
The material
8
The material
6
9 10
Defined by oldest
rock in middle
Defined by youngest rock in middle
7no displacement
11
displacement
Each letter can be used only once, and it is possible that it will not be used.
Daily Exercise-Complete the concept map
Faults
• A results of brittle deformation
• Fractures in the Earth's crust where displacement has occurred
Fault Terminology
• Footwall – block that lies above the fault plane
• Hanging wall – block that lies below the fault plane
Classes of Faults• Dip-Slip
– Movement is primarily vertical
• Strike Slip– Movement is along strike
• Oblique-Slip– Movement is both
vertical and along strike
Dip-Slip Fault – Normal Fault
• Extensional Stress• Hanging wall moves
down with respect to footwall
FOOTWALLFOOTWALL HANGINGWALLHANGINGWALL
Normal Fault
• Horst – raised block of material bounded by two normal faults
• Graben – trough (valley) bounded by two normal faults
Dip-Slip Fault – Reverse Fault
• Compressional Stress• Hanging wall moves
up with respect to footwall
Dip-Slip Fault – Thrust Fault
• Compressional Stress• Low-angle reverse
fault (fault plane < 45o)
• Displacement can be 100’s km (~60 miles)
• Typically associated with folds
Strike-Slip Fault
• Shear Stress• No vertical movement• Movement parallel to
fault plane
Left-lateral strike-slip faults: movement of opposite plate is to the left
Right-lateral strike-slip faults: movement of opposite plate is to the right
Joints
• Brittle deformation at low pressure
• Tension fractures with NO DISPLACEMENT