Classroom presentations to accompany Understanding Earth, 3rd edition prepared by Peter Copeland and William Dupré University of Houston Chapter 10 Folds, Faults, and Other Records of Rock Deformation

Deformation of Rocks

Deformation of rocks Folds and faults are geologic structures. Structural geology is the study of the deformation of rocks and the effects of this movement.

Phil Dombrowski Fig Small-scale Folds

Small-scale Faults Tom Bean Fig. 10.2

Orientation of deformed rocks We need some way to describe the distribution of geologic structures. Strike Strike: bearing of a line defined by the intersection of the plane in question and the horizontal Dip Dip: acute angle between the plane and the horizontal, measured perpendicular to strike.

Fig. 10.4

Dipping Sedimentary Beds Chris Pellant Fig. 10.3

P.L. Kresan Cockscomb Ridge, S. Utah

Dip Strike P.L. Kresan

Geologic Map and Cross Section Fig. 10.5

Stress (force per unit area) Types of directed stresses include: Compression Extension Shear

Compression Action of coincident oppositely directed forces acting towards each other

Tension Action of coincident oppositely directed forces acting away from each other

Shear Action of coincident oppositely directed forces acting parallel to each other across a surface in a couple

Strength Ability of an object to resist deformation Compressive or tensile

Strain Any change in original shape or size of an object in response to stress acting on the object

Types of deformation Elastic Ductile (plastic) Brittle (rupture)

Elastic deformation Temporary change in shape or size that is recovered when the deforming force is removed

Ductile (plastic) deformation Permanent change in shape or size that is not recovered when the stress is removed Occurs by the slippage of atoms or small groups of atoms past each other in the deforming material, without loss of cohesion

Brittle deformation (rupture) Loss of cohesion of a body under the influence of deforming stress Usually occurs along sub-planar surfaces that separate zones of coherent material

Factors that affect deformation Temperature Pressure Strain rate Rock type The variation of these factors determines if a rock will fault or fold.

Effects of rock type on deformation Some rocks are stronger than others. competent: competent: rocks that deform only under great stresses incompetent: incompetent: rocks that deform under moderate to low stresses

Tectonic Forces and Resulting Deformation Fig. 10.6

Experimental Deformation of Marble M.S. Patterson Fig Brittle Deformation Ductile Deformation

Types of folds Types of folds (bent planar structures) anticline anticline: older rocks on the inside syncline syncline: older rocks on the outside (scale (scale - from mm to tens of km)

Anticlines and Synclines Fig. 10.9

Fold terms axial Plane: the plane of mirror symmetry dividing the fold into two limbs axis: line formed by the intersection of the axial plane and a bedding plane horizontal fold: where the fold axis is horizontal plunging fold: where the fold axis is not horizontal

Fold Terminology Fig

Bill Evarts Fig

Symmetrical, Asymmetrical and Overturned Folds Fig

Bill Evarts Axial plane Anticline Fig

Breck Kent Asymmetric Folds AntiformSynform

Phil Dombrowski Fig Overturned Folds

Overturned Syncline, Israel Geological Survey of Israel Fig

Map View of Plunging Folds Fig

Oil Field at crest of Plunging Anticline Kurt N. Coonstenius

Axial Trace of Plunging Anticline* * Note Landers Oil Field on crest of anticline Kurt N. Coonstenius

Valley and Ridge Province P. L. Kresan

J. Shelton, Geology illustrated Fig Plunging Folds in the Valley and Ridge

Valley and Ridge Province of the Appalachian Mountains Fig

Raplee Anticline, S.E. Utah

Raplee Anticline on the San Juan River, Utah

Domes and Basins Fig

John S. Shelton Fig Sinclair Dome, Wyoming

Syncline Fig

Drape Fold over Reverse Fault, WY George Davis

Columns Formed by Joint- controlled Weathering Terry Englander Fig

Joint-controlled Landscape, S.E. Utah

Faults Fractures in rocks created by earthquakes (hanging wall, footwall, displacement) Dip-slip faults — normal — reverse Strike-slip faults Oblique-slip faults

Faults may be "reactivated" History of a fault may be very long. Previously developed weakness is the most likely place to break. Reactivation may have opposite sense as before. Active = 10,000 to 100,000 years Very important for dams and reactors

Dip-slip faults Motion of the fault blocks, parallel to the dip direction.

Classification of Faults hanging wall footwall cross section

Classification of Faults hanging wall footwall cross section

Normal Fault footwall hanging wall cross section

Reverse Fault footwall hanging wall cross section

Thrust Fault footwall hanging wall cross section Thrust faults are low-angle reverse faults.

Fig

Fig a

Normal Dip-slip Fault

Fig b

Reverse Dip-slip Fault

Strike-slip faults Motion of the fault blocks, parallel to the strike direction.

Left-lateral Strike Slip Fault map view

Right-lateral Strike Slip Fault map view

Fig c

Gudmundar E. Sigvaldason Fig Strike- slip Fault

Fig d

Large-scale Overthrust Sheet Fig

Keystone Thrust Fault, S. Nevada John S..Shelton Fig Cambrian Limestone Jurassic Sandstone

Lewis Thrust, Sawtooth Range, Wyoming Kurt N. Coonstenius

French Thrust, Wyoming Cretaceous Shale Mississippian Limestone Kurt N. Coonstenius

Fig Rift Valley Formed by Extension

Wildrose Graben, Southern California

NASA/TSADO/Tom Stack Fig

Stages in the Development of the Basin and Range Province in Nevada and Utah Fig

Stages in the Development of the Basin and Range Province in Nevada and Utah Fig

1872 Fault Scarp, Southern California

1988 Armenian Earthquake Fault Scarp Fig Armando Cisternas

1992 Landers Earthquake Fault Scarp

Dating the order of deformation Use geometry: Inclusions Cross-cutting relationships Combine with fossils and radiometric dating