Crustal Deformation & Mountain Building Processes

Vocabulary flashcards covering rheological rock behavior, stress types, deformation structures (faults, joints, and folds), orientation measurements, orogenic mountain building, and isostatic compensation models.

Changes in the form and/or size of a rock body, involving displacement, rotation, or distortion.

Deformation

A component of deformation characterized by a change in the location of a rock body.

Displacement

A component of deformation characterized by a change in the orientation of a rock body.

Rotation

A component of deformation characterized by a change in the shape of a rock body.

Distortion

Deformation where atomic bonds break and stay broken, leading to the formation of permanent cracks or fractures.

Brittle deformation

Deformation where atomic bonds break but new bonds form quickly, allowing atoms to rearrange and grains to change shape without permanent cracks.

Ductile deformation

The force applied to a given area of rock.

Stress

A type of stress that shortens rock bodies horizontally and thickens them vertically.

Compressional stress

A type of stress that pulls rock apart, causing horizontal length to increase and rock bodies to thin vertically.

Tensional stress

A type of stress that slides one rock body past another along fault zones or by ductile flow.

Shear stress

A deformation structure consisting of fractures with displacement, movements along which cause most earthquakes.

Fault

A fault where the direction of movement of the blocks is parallel to the dip of the fault plane.

Dip-slip fault

A fault in which the hanging wall moves down relative to the footwall, accommodating crustal lengthening due to extensional forces.

Normal fault

A fault formed under compressional stress where the hanging wall moves up relative to the footwall with a dip

Reverse fault

A fault formed under compressional stress where the hanging wall moves up relative to the footwall with a dip angle

Thrust fault

A fault where the direction of movement or displacement is parallel to the strike of the fault, categorized as right-lateral or left-lateral.

Strike-slip fault

A large-scale strike-slip fault that cuts through the lithosphere to accommodate motion between two crustal plates.

Transform fault

A fault where the direction of movement or displacement is a combination of dip-slip and strike-slip displacements.

Oblique-slip fault

A roughly planar fracture in rock with no movement, typically developing in groups due to tensile stress, cooling and contraction, or decreases in overburden pressure.

Joint

A deformation structure formed by a series of wave-like rock undulations in response to compressional stress, shear stress, or metamorphism.

Fold

An arched fold of rock layers where the limbs dip away from the hinge, containing the oldest rocks in the center.

Anticline

A downfold of rock layers where the limbs dip toward the hinge, containing the youngest rocks in the center.

Syncline

A step-like fold structure in sedimentary strata that results from movement along buried faults.

Monocline

An upwarped circular outcrop structure shaped like an overturned bowl, displaying the oldest rock layers in the center.

Dome

A downwarped circular outcrop structure shaped like an upright bowl, displaying the youngest rock layers in the center.

Basin

The geographic orientation of a geologic formation relative to north (expressed as an azimuth or bearing).

Strike

The angle of inclination of a geologic formation relative to a horizontal plane.

Dip

The collective mountain-building processes that occur primarily along convergent plate margins.

Orogeny

A buoyant crustal block (such as an offshore volcanic arc, oceanic plateau, or microcontinent) that collides with and sutures to an overriding plate, adding new crust to a convergent-margin orogen.

Accreted terrane

A metamorphic facies characterized by low-temperature, high-pressure metamorphism that occurs during subduction at convergent plate margins.

Blueschist facies

The phenomenon in which Earth's crust floats on the denser mantle, thereby maintaining mechanical equilibrium.

Isostasy

An isostatic compensation model proposing that mountains project high above sea level because they are buoyed by a thick, low-density crustal root floating in denser mantle rock.

Airy Compensation model

An isostatic compensation model proposing that high mountains stand at higher elevations because they are composed of crustal rocks of lower density than adjacent lower regions.

Pratt Compensation model