Diastrophism

Diastrophism

is the dynamical forces generally tend to elevate the earths surface.

refers to the deformation of the earths crust and more specially the folding and faulting.

comes from the Gk word meaning twisting.

Types of Earth Movement

Uplift- is the movement of the earth wherein the earths crust rises.

Subsidence- a sinking or setting of a part of the earth crust with respect to the surrounding parts

Thrust- horizontal movement of the earths crust.

Theories of Diastrophism

Theory of Isostasy

from the Gk word meaning equal standing

states that as rock from higher region is removed by erosion and deposited on a lower region, the higher region slowly rises while the lower region becomes heavier and slowly sinks

Theory of Contraction

states that the earth is gradually shrinking.

Theory of Convection

which would account for the pushing and folding of rocks through convection

this process is true when it occurs under continental mass

Continental Drift Theory of Diastrophism

accounts for diastrophic movement and for the folding and faulting along the edges of the continents

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Theory of Expansion

states that the earth is gradually expanding.

expansion of the earth would change the continents position.

Structural Features of Earth Movement

Deformation of Rocks

the effects of diastrophism is more clearly seen in rocks, especially in sedimentary rocks.

any deformation of sedimentary rocks is shown in tilts, bends or break in the layer.

Folds

a bend or flexure in a rock can be likened to waves on the ocean.

each has a crust or upfold and a trough or downfold.

Dip and Strike

dip is the angle between the horizontal plane and structural surface

strike is the direction of a line along the edge of an inclined bed where it meets the horizontal plane

the strike is always at the right of the dip

Pitching Fold

folds whose axes slant downward at each end of an imaginary line running along the top of an anticline or along the bottom of a sycline are called the axes of the fold.

the angle between the axis and the horizontal is called pitch.

Joints and Fissures

a joint is a fracture or a little separation between the rock walls while fissures are cracks or actual gaps between the rocks wall.

Faulting

refers to the surface along which a rock body has been broken and has been displaced.

Three Types of Faulting

Thrust Fault- a low angle fault (45 degrees or less) in which the hanging wall is moved upward in relation to the footwall

normal fault- also called gravity fault, a dip-slip fault in which the hanging wall moves downward relative to the footwall

reverse fault- is the material above the fault plane that moves up in relation to the material below