Confining pressures within the earth are caused by the weight of the overlying rock pushing downward and from all sides. Drillers experience great problems with confining pressure. This is known as brittle deformation. This is known as ductile deformation and the rock is said to behave plastically. Rocks deep within the crust under high confining pressures deform by folding. In brittle deformation, a continuous, force is applied to a rock.
As the force is gradually increased, little change occurs in the rock until suddenly it fractures. In ductile deformation, a gradually increasing force will cause the rock to undergo smooth and continuous plastic deformation. The rock will contort and change shape without fracturing. The type of rock also determines the type of deformation. Under similar confining pressures, halite rock salt is more susceptible to ductile deformation than is granite, which will more likely fracture.
Igneous and metamorphic rocks tend to be stronger and thus resist deformation to a greater extent than sedimentary rocks. The strike of a surface is the direction of a line formed by the intersection of a rock layer with a horizonal surface. The strike is described in terms of direction such as N 10 o W.
The dip is measured at right angles to the strike and is a measure of the angle at which the surface tilts relative to a horizontal surface. The dip is indicated in terms of angle and direction e.
Layered rocks folded into arches are called anticlines whereas troughs are referred to as synclines. Figures The two limbs come together to form an imaginary line called the fold axis. The direction in which the fold axis points indicates the strike of the fold. Rock bands appearing on one side of the fold axis are duplicated on the other side. For basins and domes, strata exposed at the surface form concentric circles around a central point Figure Rock exposures become progressively younger towards the axis of synclines.
Rock layers dip away from the fold axis in anticlines, but dip toward the fold axis in synclines. The axial plane divides a fold as symmetrically as possible. The line formed by the intersection of the axial plane with the beds define the fold axis. If the axis is not horizontal, the structure is said to be a plunging fold. Time Tables. Advertisement Remove all ads. Distinguish Between. Solution Show Solution Folding Faulting Folds are bends in the rocks that are due to compressional forces.
Faults are formed due to tensional forces along which displacement of rock takes place. Folding occurs when compressional force is applied to rocks that are ductile or flexible Faults occur when force operating in opposite direction leads to tension and as a result rocks develop cracks on the fissure. Rocks that lie deep within the crust and are therefore under high pressure are generally ductile and particularly susceptible to folding without breaking. Rock layers that are near the earth's surface and not under high confining pressures are too rigid to bend into folds, but if tectonic forces are large, rocks break.
Folding leads to the development of fold mountains. For e. Faulting results in the formation of block mountains like black forest mountains etc. Report Error Is there an error in this question or solution? Chapter 1: Earth Movements - Exercise [Page 14].
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