Paleostress
Encyclopedia
Paleostress is a subset of mechanical stress within geology. Variations in stress fields within the Earth's crust can result in a variety of mechanical responses:
Traditionally, deformation—either folding or fracturing—without dissolution
are collectively termed mechanical strain
.
Both macroscopic
and microscopic
strain may be elastic
, and only exist as long as differential stress
exists, or it may be inelastic -- that is the deformation due to a particular stress event remains even after the stress is removed. In the latter case, inelastic deformation, the stress field responsible for the deformation if it can be inferred, is, then, the paleostress.
Anderson's classic analysis of faulting serves as a simple application of paleostress analysis in terms of principal components of stress.
Zoback and Zoback's (1986) synthesis of contemporary stress measurements in North America was subsequently expanded to a global study (Zoback et al., 1989) which continues as the World Stress Project. Only a small subset of measurements in the WSP database qualify as paleostresses.
A number of regional studies of paleostresses has been undertaken, including Europe (Bergerat, 1987); North America (synthesized by Bird, 2002; Pilger, 2003), Australia (Pilger, 1982).
- Microscopic:
- CrystalCrystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
deformationDeformationIn materials science, deformation is a change in the shape or size of an object due to an applied force or a change in temperature...
, including twinningCrystal twinningCrystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
, - pressurePressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
solutionSolutionIn chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :... - Microfractures,
- Aligned fluid inclusionsFluid inclusionsthumb|250px|Trapped in a time capsule the same size as the diameter of a human hair, the ore-forming liquid in this inclusion was so hot and contained so much dissolved solids that when it cooled, crystals of halite, sylvite, gypsum, and hematite formed. As the samples cooled, the fluid shrank more...
. - Macroscopic:
- FoldingFoldingFold or folding may refer to:* Paper folding, the art of folding paper* Book folding, in book production* Skin fold, an area of skin that folds* Fold , in the game of poker, to discard one's hand and forfeit interest in the current pot...
- fracturing
- faulting (fracturing accompanied by offset of rock bodies on either side of the fracture surface)
Traditionally, deformation—either folding or fracturing—without dissolution
Dissolution
Dissolution or dissolve may refer to:* Dissolution , in law, means to end a legal entity or agreement such as a marriage, adoption, or corporation...
are collectively termed mechanical strain
Strain
Strain can refer to:* Strain , variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes* Strain , a chemical stress of a molecule...
.
Both macroscopic
Macroscopic
The macroscopic scale is the length scale on which objects or processes are of a size which is measurable and observable by the naked eye.When applied to phenomena and abstract objects, the macroscopic scale describes existence in the world as we perceive it, often in contrast to experiences or...
and microscopic
Microscopic
The microscopic scale is the scale of size or length used to describe objects smaller than those that can easily be seen by the naked eye and which require a lens or microscope to see them clearly.-History:...
strain may be elastic
Elasticity (physics)
In physics, elasticity is the physical property of a material that returns to its original shape after the stress that made it deform or distort is removed. The relative amount of deformation is called the strain....
, and only exist as long as differential stress
Differential stress
Differential stress is the difference between the greatest and the least compressive stress experienced by an object. For both the geological and civil engineering convention \sigma_1 is the greatest compressive stress and \sigma_3 is the weakest,...
exists, or it may be inelastic -- that is the deformation due to a particular stress event remains even after the stress is removed. In the latter case, inelastic deformation, the stress field responsible for the deformation if it can be inferred, is, then, the paleostress.
Anderson's classic analysis of faulting serves as a simple application of paleostress analysis in terms of principal components of stress.
Zoback and Zoback's (1986) synthesis of contemporary stress measurements in North America was subsequently expanded to a global study (Zoback et al., 1989) which continues as the World Stress Project. Only a small subset of measurements in the WSP database qualify as paleostresses.
A number of regional studies of paleostresses has been undertaken, including Europe (Bergerat, 1987); North America (synthesized by Bird, 2002; Pilger, 2003), Australia (Pilger, 1982).