Crustal Deformation

Crustal Deformation Types of Deformation Folds Faults & Joints Subduction & Mountain Building Collisional Mountain Belts

Terms Dip angle Angle of tilt away from horizontal

GEOL131: Crustal Deformation Types of Deformation

Elastic Rock bends but snaps back to original shape Elastic limit GEOL131: Crustal Deformation: Types of Deformation Elastic Rock bends but snaps back to original shape Earthquakes Elastic limit Capacity of rock for elastic deformation If elastic limit exceeded, deformation is permanent

GEOL131: Crustal Deformation: Types of Deformation Brittle Rock breaks Colder, harder, and shallower rock tends to be brittle

Ductile Rock bends permanently GEOL131: Crustal Deformation: Types of Deformation Ductile Rock bends permanently Deeper, hotter, weaker rock tends to be ductile

GEOL131: Crustal Deformation Folds

Folded Rocks Product of ductile deformation GEOL131: Crustal Deformation Folded Rocks Product of ductile deformation Form at deep crustal levels Rock is warmer

GEOL131: Crustal Deformation: Folds Basic Fold Anatomy Axis Limb Limb

Anticlines & Synclines GEOL131: Crustal Deformation: Folds Anticlines & Synclines

GEOL131: Crustal Deformation: Folds Domes

GEOL131: Crustal Deformation: Folds Basins

GEOL131: Crustal Deformation: Folds Monoclines

Fold Orientations Symmetrical Asymmetrical GEOL131: Crustal Deformation: Folds Fold Orientations Symmetrical Both limbs have same dip angle Asymmetrical Limbs have different dip angles

Fold Orientations Overturned Recumbent GEOL131: Crustal Deformation: Folds Fold Orientations Overturned One limb tilted more than 90 degrees Recumbent Both limbs horizontal

Fold Orientations Upright Plunging Fold axis not tilted GEOL131: Crustal Deformation: Folds Fold Orientations Upright Fold axis not tilted Plunging Fold axis is tilted

Recognizing folds in map view GEOL131: Crustal Deformation: Folds Recognizing folds in map view What patterns do folds make on the Earth’s surface? There is usually no cross-section view available to geologists

Recognizing folds in map view GEOL131: Crustal Deformation: Folds Recognizing folds in map view Upright anticline Upright syncline Oldest layer Youngest layer

Recognizing folds in map view GEOL131: Crustal Deformation: Folds Recognizing folds in map view Upright anticline Upright syncline Oldest layer at center Youngest layer at center

Recognizing folds in map view GEOL131: Crustal Deformation: Folds Recognizing folds in map view Oldest layer at center Youngest layer at center Arrows show direction of fold axis tilt

Recognizing folds in map view GEOL131: Crustal Deformation: Folds Recognizing folds in map view Dome: oldest layer at center Basin: youngest layer at center

GEOL131: Crustal Deformation Faults & Joints

Basic Fault Anatomy Hanging Wall Footwall GEOL131: Crustal Deformation: Faults & Joints Basic Fault Anatomy Hanging Wall Footwall

Dip-Slip Faults Normal faults Reverse faults Thrust faults GEOL131: Crustal Deformation: Faults & Joints Dip-Slip Faults Normal faults Reverse faults Thrust faults

Dip-Slip Faults: Normal GEOL131: Crustal Deformation: Faults & Joints Dip-Slip Faults: Normal

Fault Block Mountains Tensional stress Normal faulting GEOL131: Crustal Deformation: Faults & Joints Fault Block Mountains Tensional stress Normal faulting

Fault Block Mountains GEOL131: Crustal Deformation: Mountain Building Grand Tetons

Dip-Slip Faults: Reverse GEOL131: Crustal Deformation: Faults & Joints Dip-Slip Faults: Reverse

Dip-Slip Faults: Thrust GEOL131: Crustal Deformation: Faults & Joints Dip-Slip Faults: Thrust

Dip-Slip Faults: Summary GEOL131: Crustal Deformation: Faults & Joints Dip-Slip Faults: Summary Normal faults Tensional stress Hanging wall moves down Reverse faults Compressional stress Hanging wall moves up Thrust faults Footwall moves up Lower angle than reverse faults

Strike-Slip Faults Left-lateral Right-lateral Caused by shear stress GEOL131: Crustal Deformation: Faults & Joints Strike-Slip Faults Left-lateral Right-lateral Caused by shear stress

Strike-Slip Faults (Right-lateral) GEOL131: Crustal Deformation: Faults & Joints Strike-Slip Faults (Right-lateral)

Joints Fractures with no movement Cause accelerated weathering GEOL131: Crustal Deformation: Faults & Joints Joints Fractures with no movement Cause accelerated weathering Weathered joints in southern Utah

GEOL131: Crustal Deformation Mountain Building

Types of Mountain Building Fault-block Andean Collisional Cordilleran Alpine

Fault Block Mountains GEOL131: Crustal Deformation: Mountain Building Grand Tetons

Andean-Type Mountain Building GEOL131: Crustal Deformation: Subduction & Mountain Building Andean-Type Mountain Building First stage Development of continental volcanic arc Emplacement of igneous plutons Development of accretionary wedge

Andean-Type Mountain Building GEOL131: Crustal Deformation: Subduction & Mountain Building Andean-Type Mountain Building Second stage Subduction stops Uplift and erosion of igneous plutons Uplift of accretionary wedge

Collisional Mountain Belts GEOL131: Crustal Deformation Collisional Mountain Belts

Cordilleran-Type Mountain Building GEOL131: Crustal Deformation: Collisional Mountain Belts Cordilleran-Type Mountain Building Accretion of multiple volcanic island arcs onto a continent

Alpine-Type Mountain Building GEOL131: Crustal Deformation: Collisional Mountain Belts Alpine-Type Mountain Building Collision of two continents

Alpine-Type Mountain Building GEOL131: Crustal Deformation: Collisional Mountain Belts Alpine-Type Mountain Building Continental escape: blocks of continental crust are pushed away from a continental collision zone

End of Chapter