Tectonics: Folds and Faults

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

plunging folds

-are a series of folds whose fold axes are inclined to the horizontal.

joints

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

open folds

-are loose, uncompressed folds.

tight folds

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

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.

basin and range faulting

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

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.

fault gouge

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

fold

-describes bent layers of rock.

dip

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

basin and range topography

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

fault

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

normal fault

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

drag fold

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

tension

-is a force where objects are being pulled apart.

anticline

-is a hill-shaped fold.

thrust fault

-is a low angle reverse fault where the headwall block moves up dip. This type of faulting is caused by horizontal compression.

topographic map

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

geologic map

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

scarp

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

compression

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

basin

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

dip-slip fault

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

syncline

-is a valley fold where the dips of the two limbs of the fold point towards each other.

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.

headwall fault block

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

footwall fault block

-is the fault block underlying a dipping fault surface.

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.

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.

elastic

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

strike-slip fault

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

plastic flow

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

brittle

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

tectonics

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

stress

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

Basin and Range province

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

strain

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

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.