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Structural Geology

Structural geology caputures the dynamics of a geological setting.

Structural studies are probably the type of geological investigation that most often complements the indirect methods of geophysics. Together with seismic reflection and other geophysical data, structural studies contribute directly to an understanding of how continental crust has been thickened or thinned. This is determined by establishing the geometry and style of folding that has affected the rocks, and the geometry and nature of the faults that cut them, especially the amount and direction of displacement along them.
These structures include strain markers such as deformed pebbles, crystals, vesicles (irregularly shaped spaces in the rocks), fossils, and various kinematic indicators which show the degree and directions in which the rocks have been deformed. In turn, these observations permit some inference of the direction of paleostresses, that is the stresses on the rocks at the time they were being deformed. When combined with isotopic dating methods, such strain markers make it possible to establish the time at which movement took place and hence the age and duration of paleostresses. Estimates of the temperatures, pressures and hence depths at which rocks deformed in the crust, and sometimes even the magnitude of the stresses required, are possible when the rocks contain certain co-existing metamorphic mineral assemblages, for which equilibrium temperatures and pressures have been determined experimentally.

Here we see an interpretative diagram showing geological features of the Montreal - Val d'Or geotraverse (across the central Grenville corridor). Major terrane boundaries are indicated, and allochthonous slices (or packages of rocks which have been moved onto other rocks), as well as shear zones (along which movement took place) and intrusive complexes (plutons). The red lines show seismic lines along which data were acquired in 1993.

The collaborative interaction of structural geologists with seismologists that is planned for all transects is fundamental to achieving the most meaningful and complete interpretations of the seismic sections.

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