Diastrophism

Diastrophism refers to deformation of the Earth's crust, and more especially to folding and faulting. Diastrophism can be considered part of geotectonics. Diastrophism comes from the Greek word meaning a twisting.

All processes that move, elevate or build up portions of the earth’s crust come under diastrophism. They include: (i) orogenic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust; (ii) epeirogenic processes involving uplift or warping of large parts of the earth’s crust; (iii) earthquakes involving local relatively minor movements; (iv) plate tectonics involving horizontal movements of crustal plates.

Diastrophism covers movement of solid (plastic) crust material, as opposed to movement of molten material which is covered by volcanism. Movement causes rock to be bent or broken. The most obvious evidence of disastrophic movement can be seen where sedimentary rocks have been bent, broken or tilted. Such non-horizontal strata provide visual proof of movement. Diastrophic movement can be classified as two types, folding and faulting, tilted beds usually are part of a larger syncline or anticline. Diastrophic movement is often called orogenic as it is associated with mountain building.

There are various theories of the cause of diastrophic movement such as being the result of pressures exerted by convection currents in the mantle or the rise of magma through the crust. Other deformations are caused by meteorite impact and combinations of gravity and erosion such as landslides and slumping.

The study of diastrophism encompasses the varying responses of the crust to tectonic stresses. These responses include linear or torsional horizontal movements (such as continental drift) and vertical subsidence and uplift of the lithosphere (strain) in response to natural stresses on Earth’s surface such as the weight of mountains, lakes, and glaciers. Subsurface conditions also cause subsidence or uplift, known as epeirogeny, over large areas of Earth’s surface without deforming rock strata. Such changes include the thickening of the lithosphere by overthrusting, changes in rock density of the lithosphere caused by metamorphism or thermal expansion and contraction, increases in the volume of the asthenosphere (part of the upper mantle supporting the lithosphere) caused by hydration of olivine, and orogenic, or mountain-building, movements.

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