Folding, Faulting, and Mountains Folding – Mount Kidd, Alberta, Canada – Figure 17.2 in text GLY 2010 – Summer 2013 - Lecture 13

Stress Stress is a force that is capable of greatly deforming rocks, and may result in folding or faulting of rock, and even to the building of mountains

Types of Stress There are three types of stress Compression Tension Shear Each type is discussed on next slides

Compression Opposing forces directed inward along a single line Compression shortens an object along the axis of compression, and thickens it in the directions perpendicular to the stress direction After Before

Tension Tension is the result of divergence, pulling an object in opposite directions along a common axis Tension lengthens an object along the axis of tension, and thins it in the perpendicular directions After Before

Tensional Cracking Tension can produce cracks in the direction perpendicular to the axis of tension Cracking develops

Tension Crack Pictures Left photo: Ground failure along North Deschutes Parkway showing lateral spread toward Capitol Lake, which is to the right of the photograph; view is to the north. (N47.040° W122.915°; 03/01/2001) Source: http://peer.berkeley.edu/nisqually/geotech/liquefaction/lateralspread/dcp_0207_s.jpg Right Photo: Lateral spreading of railroad embankment extending from Marathon Park (looking northeast). (N47.03723° W122.90963°; 02/28/2001) Photo Source: http://peer.berkeley.edu/nisqually/geotech/liquefaction/lateralspread/c03.jpg Nisqually Earthquake, 2/28/01, in Washington caused tension cracking.

Shear Opposing stress is created by two plates moving in opposite directions

Responses to Stress There are three responses to stress Elastic Plastic Rupture

Elastic Substances Behave elastically, stretch without breaking Snap back to their original position, when stress is removed Elastic limit: a limit beyond which substances cannot be stretched without breaking Example: Rubber band

Plastic Substances Slow deformation without breaking Plastically deformed substances do not return to their original shape when the stress is removed Rate of deformation is important - Stress applied quickly will cause rupture Rocks subjected to stress at high confining (load) pressures, and moderate to high temperatures, may deform plastically Example: Silly putty Movie from: http://vern.com/putty/creations/george.mpg Silly George, by Vern Hart Time-lapse slumping of silly putty. Notice movement in upper left corner.

Plastic Deformation The rate of plastic deformation makes a difference Silly putty breaks if pulled rapidly, stretches if pulled slowly Movie: ddx.avi, converted from ddx.avi

Rupture Elastic substances stretched beyond the elastic limit, or plastic substances deformed quickly, will rupture Rupture is called brittle failure

Deformation Rocks subjected to stress may: Deform by folding Rupture, with subsequent movement along the plane of rupture - this is called faulting Fold, then rupture

Folding Folds may be described in terms of two parameters: Axial Plane Limbs Axial Plane Limb Limb

Anticline If the fold is convex upward, it is called an anticline

Anticlinal Fold Rainbow Gap, Virginia Photo: Henry Johnson

Atlas Mountains Anticline One of the best exposures of a complexly folded mountain belt anywhere occurs in the Atlas Mountain system of northwest Africa

Domes Domes are anticlines that curve in three dimensions, like an upside down bowl Figure shows the Black Hills, South Dakota Diagram of dome – Figure 17.6, text

Eroded Dome, Sinclair, Wyoming

Syncline If the fold is convex downward, it is called a syncline

Syncline Photo Photo: Duncan Heron Synclinal fold exposed by roadcut

Anticline-Syncline Pair Anticline-Syncline pair in Devonian Old Red Sandstone. SW Wales, UK Note the different fold shapes

Basins Basins are syncline that curve in three dimensions, like a bowl Diagram: Figure 17.7 in text

Overturned Folds Overturned fold in lower center of picture

Recumbent Folds Recumbent folds are defined as folds with horizontal (<10° dip) axial surfaces Photo: Ron Perkins http://www.geo.duke.edu/Sched/Geopages/geo41/st.htm Photo # st036th.gif

Fold Diagram Diagram shows the major types of folds Figure 17.3 in text Diagram shows the major types of folds

Plunging Folds The axes of the folds may be tilted, creating a series of plunging folds Figure 17.4 in text

Folding Animation From Chapter 17, FoldingV2_PC.ppt

Joints Three joint sets (left photo) Video: Joints_&_Dikes,_Thunder_Hole,_Acadia.wmv from author Three joint sets (left photo) Joints and dikes, Acadia National Park video (right)

(Click picture to remove block) Faults A fault is a fracture along which definite movement has occurred (Click picture to remove block)

Strike and Dip The strike is any horizontal line drawn on an inclined surface. Strike-slip faulting is the result of shear forces. The strike-dip symbol, used on geologic maps, is shown - the long direction points in the horizontal direction, and the shorter side shows dip direction

Strike-slip Direction Strike-slip faults are further described as "right-lateral" or "left-lateral" depending if the block opposite the viewer moved to the right or left, respectively

Strike Slip Fault Photo: Arthur G. Sylvester. San Jacinto fault, Anza, Southern California

Right-Lateral Strike Slip Block is displaced to the right, looking across the fault Image: Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/rightlat.gif

Strike Slip Faults Right Lateral Near Coos Bay, Oregon

Left-Lateral Strike Slip Block is displaced to the left, looking across the fault Image: Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/leftlat.gif

Strike Slip Faults - Left Lateral Near Lillooet, British Columbia

Dip-slip Faults Dip direction is always perpendicular to the strike line

Fault Terminology Foot Wall and Hanging Wall are borrowed from mining terminology Ore veins are often deposited along faults

Normal Fault Normal faulting results from tensional forces Hanging wall moves down relative to the footwall (here, to the right) Places younger rocks on top of older Image: Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/normal.gif

Sevier Normal Fault Figure 17.8 in text

Death Valley Normal Faults photo: http://www.uoregon.edu/~millerm/DVN1.html

Reverse Fault Reverse faulting results from compressional forces Hanging wall moves up relative to the footwall (here, to the left) Places older rocks on top of younger Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/reverse.gif

Reverse Fault Reverse faults and associated fold http://www.uoregon.edu/~millerm/KlamT.html Near Klamath Falls, OR. Reverse faults and associated fold

Thrust Fault Thrust faults are low angle reverse faults They sometimes move large distances (tens of kilometers) Image: Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/thrust.gif

Lewis Overthrust Photo: http://www.uoregon.edu/~millerm/Lewis1.html Lewis Thrust fault. As viewed from Marias Pass, Glacier National Park, Montana. Looking N. Green arrow points to fault. There, Precambrian rocks of the Belt Supergroup lie directly on top Cretaceous shale and sandstone.

Explanation of Lewis Overthrust Image: chfsketch.jpg Chief Mountain was moved about forty kilometers and isolated by erosion Chief Mountain is much older (Precambrian) than the rock upon which it rests (Cretaceous)

Chief Mountain Older rock above younger, typical of thrust faults Glacier National Park, Montana

Oblique Slip Image: Source: http://www.gps.caltech.edu/~meltzner/wallacecreek/misc/images/oblique.gif Oblique-slip is a combination of vertical and horizontal movement

Horst and Graben Occur when there is offset along high-angle normal faults, so that one block (the graben) drops relative to the blocks (horsts) on either side. Tensional forces create these structures

San Andreas/Garlock Faults From Space

San Andreas Fault Pacific plate, left North America, right

San Andreas Offsetting Fence

Fault Animations From Chapter 17, FaultsV2_PC.ppt

Fault Diagram Summary Figure 17.9 in text

Orogenesis Tectonic forces often create mountains, a process called orogenesis There are several types of mountains Folded Faulted Upwarped Volcanic

Orogenesis by Folding Plate collisions involving continental plates can produce high mountains Examples: Himalayas (India, Tibet, China) Alps (Europe) Urals (Europe/Asia boundary) Appalachians

High peaks in the Himalayas Himalayan Mountains Mt. Everest High peaks in the Himalayas

Owens Valley and the Sierra Nevada Range

Orogenesis by Upwarping Formed when a large region of the earth’s crust is bent into a broad, regional uplift with little apparent deformation of the rocks Upwarping may be due to local vertical motion, rather than plate tectonic forces - often far from plate boundaries

Custer State Park, Black Hills, South Dakota

Volcanic Mountains

(Click picture to restore block) Faults A fault is a fracture along which definite movement has occurred (Click picture to restore block)