Structural Geology II
Orienting Planes and Lines
Faults
Folds
Orienting Planes in Space
Strike
The compass direction of a horizontal line which lies in the plane of interest
The compass direction of the line formed by the intersection of a horizontal plane with the
plane of interest
Orienting Planes in Space
Dip
The angle from the horizontal down to the plane of interest, measured in the vertical plane
perpendicular to strike
Dip Direction
General compass direction, perpendicular to strike, in which the plane slopes downward
Strike & Dip on a Map
Experimental Method
Testing Rocks
General Principles
Basic Fault Information
Dip-slip faults
Motion is parallel to the dip
Motion is best seen in cross section
Normal or reverse faults
Strike-slip faults
Motion is parallel to the strike—horizontal
Motion is best seen in map view
Right-lateral or left-lateral strike-slip faults
Dip-slip Fault Terminology
Normal Fault
Hanging wall moves down relative to footwall
Reverse Fault
Hanging wall moves up relative to footwall
Thrust—Reverse fault that dips < 45°
Normal Fault
Normal Faults
Normal Faults
Reverse Faults
Reverse Faults
Strike-Slip Faults
Strike-Slip Faults
Joints
Planar fractures along which there is no evidence of sliding motion
Motion is perpendicular to the plane
Joints represent tensile failure
Causes of joints
Unloading
Cooling
Tectonic strain release
Joints
Due to unloading
Removal of overlying material by erosion
Rocks expand upward
Produces sheet joints
Spacing between joints increases with depth
Joints
Due to release of tectonic strain
Rocks first expand in direction of least stress
Next expand in direction of intermediate stress
Produces orthogonal joint sets
T intersections allow determination of age
Folds
Folds
Anticlines
Convex upward
Beds dip away from each other & the core of the fold
Oldest bed in the core of the fold
Synclines
Concave upward
Beds dip toward each other and the core of the fold
Youngest bed in the core of the fold
Parts of a Fold
Non-Plunging Folds
Plunging Folds
Plunging Folds
Fold Profiles
Monocline
Monocline
Dome
Upheaval Dome
Basin