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