What is Structural Geology?

Structural geology is about deformation structures in rocks, about their geometry, history, about the reason why they developed and how. Structural geologists study rock deformation structures and mechanisms to understand the evolution of the Earth. They do this, for example, to understand the origin of mountain ranges, or, to make money by unraveling the present-day structure of, ore deposits, or oil and gas reservoir rocks. Some structural geologists are involved in understanding Earth quake mechanisms.

For a more elaborate and well written introduction to Structural Geology goto:
Earth Structure. An Introduction to Structural Geology and Tectonics (by Ben van der Pluijm)

At geological time-scale, the Earth is not a rigid sphere like a pebble. Its interior is in motion, the continents move, they are pulled apart, sheared, compressed and deformed. Rocks deform as if they would consist of toothpaste. The result of this can be seen in cross sections through mountain ranges, such as e.g. through the Glarus Alps:

Geological profile through the Glarus Alps by Martin Burkhard, from Burkhard, M. (1990) Aspects of the large.scale deformation in the most external parts of the Swiss Alps (Subalpine Molasse to Jura fold belt) Eclogae geol. Helv. 83 (3), 559-583.

Here are some simple drawings from simple geological deformation structures.

Examples of geological deformation structures

You can find movies of numerical folding simulations on the homepage of Stephan Schmalholz.

Examples of deformation microstructures

Much nicer examples of microstructures can be found at the homepage of the Microstructure & Deformation Group in Basel.
And here are some advanced drawings from microstructures made by Albert Heim in 1878.

Some more small scale structures.

Collection of structural geology slides on the web

Structural Geology Slide Set (UBC Canada)
Structural Geology Lecture Slides (UBC Canada)
Geological structures ... in deformed rocks (University of Newcastle, Austraila)
Structure slides ... from the Introductory Geology WebPages at Duke University
Photo index of a variety of geological features (University of Oregon)
Structural Geology Photo Gallery (Rick Almendinger, Cornell University)
Images of Active Tectonics
Macro- to micro-scale structures in the Assynt region of the Moine thrust belt (Geoff Lloyd)
The Moine thrust belt (Rob Butler)
Subalpine Field Excursion (Rob Butler)
Strike Slip Faults (Arthur Sylvester)
Microtextures of metamorphic rocks (Index of Minerals in Thinsection)
Microstructures Online (Monash)
Slide set and notes Deformation Mechanisms & Microstructures Oct. 1998 (J. Tullis, C. Teyssier, H. Stünitz

See also

Structural Geology on the Web (by Kevin Smart)
Structural Geology and Metamorphic Petrology on the WWW (by Jürgen Kraus)

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November 2002