Tectonic deformation and geologic structures

Mountain building Anatomy of a convergent mountain belt Valley & ridge Blue ridge

Mountain building Continental rift; opening of an ocean basin? Extensional horsts and grabens Horst Graben

Deformation Deformation: 1)translation 2) rotation 3) distortion (shape change) Deformation results from stress, Stress = force per unit area

Deformation - types of stress Compressive stress Tensional stress Lateral shear stress

Uniform pressure from all directions Deformation - tectonic Compression in a principal direction Extension in a principal direction Lateral shear

Brittle: shallow crust; with increased stress little change until failure (breaks) Ductile: deeper crust; with increased stress gradual change (squishes) Rock deformation: When does it fold and when does it fault? depends on rock type, crustal depth, rate

Products of deformation Faults Folds

Anticline: opens downward; oldest rocks in center Syncline: opens upward; youngest rocks in center Types of folds

Strike and dip measurements along the limbs of a fold Deformation - folds

domebasin Types of folds

fold appears to die out on ground surface Plunging folds

Types of faults Thrust faults: Compression HW up shallow dip Normal faults: Extension HW down steep dip

Types of faults Strike-slip faults: lateral shear no vertical change vertical dip

(map view) Thrust, strike-slip or normal faults?

Southern Appalachians - fold and thrust belt Cross-section through western Virginia Interrelated Folds & faults imbricate thrusts West Virginia Virginia North Mtn fault Staunton faultWaynesboro Blue Ridge Rockfish Valley CharlottesvilleGum Spring 10 km

Mountain building Richmond Basin = continental rift; related to opening of the Atlantic ocean Extensional horsts and grabens Richmond Richmond Basin Yorktown Chesapeake Bay Gum Spring Cape Charles 10 km Cross-section through eastern Virginia