Chapter 17
               Tectonics: Folds and Faults

             Physical Geology Illustrated Vocabulary        
Cochise College                                                     
Geology Home Page 
FOLDS and FAULTS 
Roger Weller, geology instructor
wellerr@cochise.edu  
copyright 2018-Roger Weller   3/24/18


folded sedimentary rocks, Santa Catalina Mountains, Pima County, Arizona   

Vocabulary
 

angular unconformity
-consists of a set of sedimentary layers deposited on an erosion
surface which is underlain by inclined sedimentary beds that are
truncated by the erosion surface and then capped with sedimentary
layers parallel to the erosion surface.
-Angular unconformity near Benson, Arizona 


anticline

-is a hill-shaped fold.

-Anticline near Tombstone, Arizona     
-anticline and syncline near Hayden, Arizona  
-anticline-Opal's Pals     

 

basin

-is a tectonic structure in which layers of sedimentary rock formed
into a circular depression. 
A basin is the opposite of a dome.
-Maps of the Michigan Basin 

 

basin and range faulting

-consists of a series of fault block mountains (horsts) separated
by basins formed by down-dropped blocks (grabens).

 

Basin and Range province

-refers to the southwest portion of the United States that is dominated
by basin and range faulting.

 

basin and range topography

-describes the resulting land surface of mountains separated by valleys
that is produced by basin and range faulting.

 

brittle

-refers to a material has a tendency to break or crush.  A brittle
material is not tough.

 

compression

-is a squeezing force that tends to flatten an object.

 

dip

-describes the angle by which an inclined plane, such as a sedimentary
bed or a fault surface, is tilted from the horizontal.

 

dip-slip fault

-is a type of fault in which the relative movement of the two fault blocks
is in the dip direction.

 

drag fold

-is a fold that is created when one sedimentary rock layer is dragged
across another during folding or faulting.

-drag fold in the Santa Catalina Mountains 

           

elastic

-is used to describe materials, which after being distorted, tend to snap
back to their original, pre-stressed condition.

 

fault
-is a break in the planet's crust along which there has been movement.

-turbidites cut by fault            

 

fault block

-is the large mass of rock located on one side of a fault.  Sometimes this term
refers to a single very large mass of rock surrounded on all sides by faults.

 

fault gouge

-consists of crushed and ground up rock along a fault zone.

 

fault zone

-is more complex than a single fault.  A fault zone consists of a series of
faults, all trending in the same direction and tectonically related to each other.

 

fold

-describes bent layers of rock.
-fold in the Huachuca Mountains

-folds in the Santa Catalina Mountains-1             

-folds in the Santa Catalina Mountains-2             

-folds in the Santa Catalina Mountains-4   
-Anticline and Syncline folds south of Tombstone    
-folds-Opal's Pals        

 

footwall fault block

-is the fault block underlying a dipping fault surface.

 

geologic map

-is a map that shows stratigraphic formations, folds, and faults.

-geologic map of the Whetstone Mountains, Southeastern Arizona     

 

headwall fault block

-is the fault block resting on top of an inclined fault surface.
 

joints

-are flat breaks along which there has been little or no movement.

-plants growing in joints in granite  *           

-joints in granite-1            

-joints in granite-2 

           

normal fault

-is a dip-slip fault where the headwall (upper) fault block slides down dip.

-normal fault cutting turbite beds    
-normal fault-Opal's Pals         

 

open folds

-are loose, uncompressed folds.
-open folds-Opal's Pals

 

plastic flow

-occurs when, under pressure, a material flows instead of breaking.

 

plunging folds

-are a series of folds whose fold axes are inclined to the horizontal.
-plunging folds-Opal's Pals

 

San Andreas Fault

Is a prominent strike-slip fault extending from near Yuma, Arizona, running
northeast of Los Angeles up through San Francisco.  The San Andreas Fault
separates the Pacific plate on the west from the North American plate to
the east.

-map of the Los Angeles area             

 

scarp

-is a small cliff formed through mass wastage as a slump or landslide or
through surface faulting associated with an earthquake.

-landslide scarp in Colorado            

 

shear

-is the type of stress where one block slides past another block. 
Materials caught between the two blocks are said to be undergoing shear.

 

slickensides

-consist of parallel scratches on the rocks on both sides of a fault surface. 
Slickensides are formed when the fault blocks rub
against each other during fault movement.

-slickensides with epidote 
-slickenside photos  
-slickensides-Opal's Pals         

 

strain

-represents the consequences of stress: folds, faults, joints, etc.

 

stress

-refers to the forces acting upon rocks: compression, tension, or shear

 

strike

-In order to describe the orientation of a dipping surface, such as a
fault or sedimentary layer, this term is applied to the compass direction
of the line created by the dipping plane intersecting a horizontal surface

 

strike-slip fault

-occurs when two fault blocks move horizontally past each other in
opposite directions along the direction of the strike line.
-strike slip fault-Opal's Pals

 

syncline

-is a valley fold where the dips of the two limbs of the fold point towards
each other.
-syncline-Sideling Hill, Maryland

-syncline near Tombstone, Arizona    
-syncline and anticline near Hayden, Arizona
-syncline-Opal's Pals         

 

tectonics

-refers to the folds, faults, and earthquakes within a region that indicate
the area is under stress or has been under stress.

 

tension

-is a force where objects are being pulled apart.

 

thrust fault

-is a low angle reverse fault where the headwall block moves up dip. 
This type of faulting is caused by horizontal compression.
-thrust Fault-Opal's Pals

 

tight folds

-consist of a series of folds so tightly compressed that the limbs of the
folds are nearly parallel to one another.

-tight fold  

-tight folds-Opal's Pals

 

topographic map

-is a map that indicates elevation of landforms with contour lines.

-raised topographic map of the Mule Mountains 

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