Structural Geology and Tectonics Flashcards

What is a décollement in fold-and-thrust belt geology?

Answer: A subhorizontal detachment surface along which thrust sheets slide

A décollement is a subhorizontal detachment zone, often in weak rock like evaporites or shale, along which thrust sheets are transported.

The critical taper model for accretionary wedges predicts that the wedge maintains a constant angle determined by what two factors?

Answer: Internal friction angle and basal friction angle

Critical taper theory (Coulomb wedge) shows that wedge geometry is controlled by the internal friction of the wedge and the friction along its base.

Which stress state produces normal faults according to Anderson's fault theory?

Answer: σ1 vertical, σ2 and σ3 horizontal

Anderson's theory states that normal faults form when the maximum principal stress σ1 is vertical (gravitational load exceeds horizontal stresses).

Passive continental margins are characterized by which structural feature?

Answer: Thick sedimentary wedges with listric normal faults

Passive margins develop on rifted continental edges with thick sedimentary prisms and listric normal faults formed during the rifting phase.

What is the term for the angle between a fold hinge line and horizontal?

Answer: Plunge

Plunge is the angle measured in a vertical plane between the fold hinge (axis) and the horizontal.

Mylonites are defined primarily by which characteristic?

Answer: Strong foliation and lineation from ductile shear zone deformation

Mylonites are ductilely deformed rocks with strong planar and linear fabrics formed by crystal-plastic flow in shear zones.

The supercontinent Pangaea is estimated to have begun breaking apart approximately how many million years ago?

Answer: 200 Ma

Pangaea began rifting approximately 200 million years ago during the Early Jurassic, eventually forming the modern continents.