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Questions and Answers
What is defined as a foliation in geology?
What is defined as a foliation in geology?
What does the term ‘boudinage’ refer to in geological terms?
What does the term ‘boudinage’ refer to in geological terms?
How do plunging anticlines differ from synclines?
How do plunging anticlines differ from synclines?
What is the significance of the 'stem of the Y symbol' in geology?
What is the significance of the 'stem of the Y symbol' in geology?
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What characterizes a mélange in geological terms?
What characterizes a mélange in geological terms?
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What does the axial plane represent in a fold?
What does the axial plane represent in a fold?
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What typically occurs in accretionary wedges?
What typically occurs in accretionary wedges?
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What happens when rocks are overturned in a geological formation?
What happens when rocks are overturned in a geological formation?
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Study Notes
Fabric
- Fabric is a general term for the geometric arrangement of material within a rock.
- A foliation is a planar fabric in a rock.
- Folds and slaty cleavage are examples of foliation.
Boudinage
- Boudinage forms when a rigid bed is stretched amidst less rigid beds.
- The rigid bed breaks up, forming sausage-shaped boudins.
- The less rigid beds deform without breaking.
Plunging Folds
- Plunging anticlines/synclines occur when the hinge is not horizontal.
- Layers ‘close out’ at one end.
- In anticlines, the end they close on is the direction the fold plunges; synforms are opposite.
Fold Terminology
- Hinge: region of maximum curvature
- Limbs: relatively straight sides of the fold
- Axial Plane: surface that bisects the fold
- Fold Axis: intersection of axial plane and the folded surface
- Axial Plane Trace: intersection of the axial plane and the ground
Younging Direction
- Younging direction indicates the order strata were deposited.
- The stem of the Y symbol points in the younging direction.
- Way up indicators help determine younging direction (e.g. graded bedding, ripples, flame structures, mud cracks).
Folding and Younging
- If younging direction is unknown, use synform and antiform to determine the oldest rocks.
- If the oldest rocks are on the bottom, use syncline and anticline.
- If rocks are overturned, the oldest rocks are on top.
Accretionary Wedge
- An accretionary wedge is a mélange where material is scraped off the underlying plate and compressed into a wedge.
- Volcanic arcs are dominated by igneous processes that build mountains on and within the crust above a subduction zone.
- Thrust belts can develop behind arcs that experience significant compression.
- Thrust belts are associated with retro-arc foreland basin systems (characterized by thrust faults).
Mélange
- Mélange is a large-scale breccia with a lack of continuous bedding.
- Fragments of rock of all sizes are included in a fine-grained, deformed matrix.
- Mélange typically consists of a jumble of large blocks of varied lithologies.
- Mélange is commonly formed in the accretionary wedge above a subduction zone.
- Mélange broadly means "a varied mixture."
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Description
This quiz covers key concepts related to geological fabrics, including definitions and examples of foliation, boudinage, plunging folds, and important fold terminology. Test your knowledge on how these structures form and what they indicate about geological processes.
