Natural Resources

Structural Geology

Cleavage

The tendency of a rock to split along secondary, aligned fractures produced by deformation or metamorphism.

Cleavage

Steeply dipping, slaty cleavage, formed by pressure during folding, cuts across flat-lying beds of white sandstone and red shale in Freshwater Bay, Bonavista Bay.

Boudinage

A layer or planar feature, such as a dyke, that has been pulled apart into sausage-like pieces.

Boudinage

A stretched or boudinaged diabase dyke in volcanic rocks near Little Bay, Notre Dame Bay.

Folds

A bend, buckle or flexure in a rock due to compressional forces.

Folds

An example of very tight (isoclinal) folds in layered gneisses, near Postville, Labrador.

Different Types of Folds:

Folds Folds

Photo on the left shows large-scale, flat-lying fold in bedded Limestone and shale (sedimentary rocks) near Point-au-Mal, western Newfoundland.

Photo on the right shows angular or chevron folds in bedded sedimentary rocks of central Labrador.

Folds Folds

Photo on the left shows overprinting folds, which result in an eye-shaped interference pattern in metasedimentary gneiss, Charlottetown, southeast Labrador.

Photo on the right shows two folds (anticlines) juxtaposed along a fault (centre of the photograph to the right of the hammer) in the Long Island area, Placentia Bay. The syncline, which normally would separate two anticlines, has been faulted out.

Fault

A surface along which a rock body has been broken and displaced; the two parts have usually moved relative to each other.

Fault Fault Fault

The photo on the left is a major, linear fault called the Cape Ray Fault, shown by this pronounced topographic depression in southwestern Newfoundland.

The photo in the middle are bedded volcanic rocks that are offset or displaced (note the thin orange-weathering bed) along a fault (centre of photograph). The rocks to the left of the fault moved up relative to the rocks on the right. This photograph was taken in California.

The photo on the right is of a large-scaled folding and faulting in metasedimentary rocks. Example from Torngat Mountains, Saglek Fiord, Labrador.

Mylonite

A fine-grained rock formed by extreme crushing and pulverizing (rock powder) along a fault zone.

Mylonite

A streaky banding and rounded crystals in granite produced by crushing and rolling of grains (crystals) due to movement along the Dover Fault (Dover, Bonavista Bay).

 
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