Rock Deformation II

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Rock Deformation II -More Excursions
in Structural Geology
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Folds

• Warps in rock strata due to ductile deformation
• Generally indicate horizontal compression

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Simple physical model of folding in rocks
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• Folds are described by
• The strike of their hinge line
• The hinge line is the intersection of the hinge
  plane with the folded layer
• Hinge lines may be inclined in a plunging fold
• The angle of dip of their limbs

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• Three simple fold forms exist
• Synclines warp downward
• Anticlines warp upward
• Monoclines dip in one direction

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Recall this? Itll help!
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Anticlines Synclines

• Sequence of ages of strata indicate the geologic
  structure in folds
• Anticlines oldest layers exposed at the center
  of the fold
• Synclines youngest strata exposed along the
  center of the fold

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Anticline in its natural environment -oldest
rocks in the core of fold
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Syncline youngest rocks in core of fold
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anticline
syncline
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Folds occur as sets Fold Belts
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Fold Belts

• Orogenic belts consist of long linear series of
  folds
• Fold geometry is not overly complex
• Pattern of outcrops may appear complex
• Complex folds may develop as folds are
• Re-folded
• Cut by thrust faults

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Orogenic belt with complex folding
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• Folds can be complex
• Multiple folding events
• Complex forms are created

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• Plunging folds when the folds axis is dipping
  or plunging
• Asymmetric Fold one limb dips more steeply than
  the other
• Overturned and Recumbent folding is so extreme
  that beds are turned upside-down

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Plunging Fold
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Complex Folds

• Domes Basins
• Generally occur in continental interiors
• Broadly warped regions
• Roughly circular pattern of outcrops

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• Diapirs
• Less dense salt layers may rise up
• Some overlying strata may be pierced
• Salt diapir has an inverted teardrop shape
• Strata above diapir are domed upward

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Folding (and Faulting) occurs at multiple scales