Competence (geology) - Misplaced Pages

Degree of resistance of rocks to deformation in terms of mechanical strength For other uses, see Competence (disambiguation).

In geology, competence refers to the degree of resistance of rocks to deformation or flow. In mining, 'competent rocks' are those in which an unsupported opening can be made. More competent rock weathers slower than less competent rock.

Characteristics

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Competent rocks are more commonly exposed at outcrops as they tend to form upland areas and high cliffs, or headlands where present on a coastline. Incompetent rocks tend to form lowlands and are often poorly exposed at the surface. During deformation, competent beds tend to deform elastically by either buckling, or faulting and fracturing. Incompetent beds tend to deform more plastically, although it is the competence contrast between different rocks that is most important in determining the types of structure that are formed. The relative competence of rocks may change with temperature, such as in metamorphosed limestones, which are relatively competent at low metamorphic grade, but become highly incompetent at high metamorphic grade.

Most sedimentary and volcanic sequences show layering between different lithologies. When affected by deformation, the response of the sequence depends on the competence of the various layers.

Crystal plasticity becomes more important as the temperature increases, and the relative deformability of individual minerals controls the competence of particular rock units.

References

Fossen, H. (2010). Structural Geology. Cambridge University Press. p. 430. ISBN 978-0-521-51664-8. Retrieved 1 April 2011.
Cristescu, N. (1989). Rock rheology. Mechanics of elastic and inelastic solids. Vol. 7. Springer. p. 1. ISBN 978-90-247-3660-7. Retrieved 1 April 2011.

v t e Structural geology
Underlying theory	Deformation mechanism Lamé's stress ellipsoid Mohr–Coulomb theory Mohr's circle Overburden pressure Rock mechanics Strain Strain partitioning Stress Stress field Tension
Measurement conventions	Brunton compass Inclinometer Orthographic projection Rake Stereographic projection Strike and dip
Large-scale tectonics	Accretionary wedge Allochthon Autochthon Back-arc basin Continental collision Convergent boundary Décollement Divergent boundary Extensional tectonics Fault block Fenster Fold and thrust belt Fold mountains Foreland basin Graben Half-graben Horse Horst Horst and graben Intra-arc basin Inversion Klippe List of tectonic plate interactions Mélange Mountain formation Nappe Obduction Orogeny Passive margin Plate tectonics Pull-apart basin Rift valley Rift Saddle Strike-slip tectonics Structural basin Suture Syneclise Terrane Thick-skinned deformation Thin-skinned deformation Thrust tectonics
Fracturing	Columnar jointing Dike Exfoliation joint Fissure Joint Vein
Faulting	Asperity Cataclasite Cataclastic rock Detachment fault Disturbance Fault friction Fault mechanics Fault scarp Fault trace Thrust fault Transfer zone Transform fault
Foliation and lineation	Cleavage Compaction Crenulation Fissility Oblique foliation Pressure solution Rock microstructure Slickenside Stylolite Tectonic phase Tectonite
Folding	Anticline Chevron Detachment fold Dome Homocline Monocline Syncline Vergence
Boudinage	Competence
Kinematic analysis	3D fold evolution Paleostress inversion Paleostress Section restoration
Shear zone	Mylonite Pure shear Shear
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