Intro to Geology Ch 15 Geologic Structures flashcards |

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Structural Geology

-the study of how rocks are deformed by Earth's force after lithification


-Force per unit area
~lb/cm squared


-Change in the shape & or size (volume) in response to stress

3 Types of Stress

-Compressional Stress
-Tensional Stress
-Shear Stress

Compressional Stress

-Forces push the rock together from opposite directions

Tensional Stress

-Forces pulling away from each other in an opposite direction

Shear Stress

-Stresses act parallel to a plane

3 Phases of Strain



-Deformed material that recovers its original shape after stress is reduced or removed


-Material will bend while under stress but will NOT return to its orginal shape after stress is removed


-Material fractures at stresses higher than the strength of that material

What is elastic limit?

-limit to how far something can bend w/o breaking

How Rocks Behave When Stressed

-Rocks response to stress depend on certain parameters

Parameters of Rock Stress

-Amount of stress applied
-Rate at which stress is applied
-The composition of the rock
-Temperature at which rock is strained
-Pressure at which rock is strained

Sedimentary Structures

-Features found within sedimentary rocks that form during or after deposition but before lithification

Deformation Structures

-Features that result from the deformation of the earth's crust after lithification

Tilted Beds have a Dip Measurement

-Angle that a bedding plane dips below the Earth's surface
-two components

2 components of tilted beds

-Angula (Tilt)
-Directional (Tilt)

Angular (Tilt)

-How many degrees below the horizontal

Directional (Tilt)

-What direction the bed dips

Tilted Beds have a Strike Measurement

-Compass direction ofa line formed by the intersection of an inclined bedding plane with a horizontal plane
-Perpendicular to the dip direction

2 Components to a Strike

-Angular (Strike)
-Directional (Stike)

Angular (Strike)

-How many degrees off of due North

Directional (Strike)

-Given in two directions

How to Measure a Strike & Dip

-Find an exposed outcrop
-Find a smooth surface or create one
-Use Brunton Compass


-Bends in layered rock

Components of a fold

-Hinge lines
-Axial Plane

Types of Folds

-Structural Domes
-Structural Basin


-Fold shaped like an arch
-Oldest rocks in the center (core) of the fold getting progressively younger toward the edge
-Beds dip away from hinge line


-Fold shaped like a trough
-Youngest rocks are in the core of the fold & get progressively older toward the edge
-Rock beds dip toward hinge line

Structural Domes

-Fold in which the beds dip away from a center point
-Olderst rocks are exposed at the core & get progressively younger toward the edge

Structural Basin

-Fold in which the beds dip toward a center point
-Youngest rocks are exposed at the core


-Fractures or cracks in a rock body in which no displacement has occured

3 Types of Joints

-Columnar Joints
-Sheet Joints
-Vertical Joints


-Fractures in rocks in along which sliding or displacement has occured

Drag Folds

-Minor folds produced by movement two fault blocks in opposite directions


-Polished & striated rock surface


-Zone of broken rock that was ground up by fault movement

Oblique-Slip Fault

-Dip-slip & strike-slip components of movement

Strike-Slip Fault

-Movement (slip) is parallel to the strike of the fault
-Horizontal or lateral faults
-Shear Stress
~ex: San Andreas Fault

Reverse Fault

-Hangingwall moves up relative to the footwall
-Compressional stress
-Thrust fault
~Low angle reverse fault
~less than 30 degrees

Normal Fault

-Hangingwall down relative to footwall
-Tensional stress

2 Types of Dip-Slip Faults

-Normal Fault
-Reverse Fault

Dip-Slip Faults

-Movement is parallel to dip direction

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