Thrust is one of the types of discontinuous displacements of rock layers. Represents the pushing of one mass of rocks over another along an inclined fault [1] . Thus, the layers lying on the upper side of the fault are shifted up, and from the bottom - down. The first block is called hanging , the second - lying . In this case, the fault is inclined to the horizon at a slight angle - otherwise the object is called not thrust, but throw up . The boundary between them is usually drawn by the angle of 45 ° (less often 60 °) [2] [3] [4] . In some thrusts, this angle is almost zero [1] .
Overthrusts are formed during compression of the earth's crust. Often they develop from lying folds [1] . In this case, the plastic deformation that formed the fold can be replaced by a rupture, chipping, and the appearance of a thrust [1] [3] .
A very gentle (including horizontal) thrust on a large scale (with a thickness of the upper block of hundreds of meters and a displacement of several kilometers) is called “ scoop ”, “tectonic cover”, “tectonic overlap”, “alpinotype thrust”, “pillowcase” (and the latter term has other meanings) [5] [6] [7] .
Types of Thrusts
Some types of thrusts have special names [3] :
- thrust alpinotypic - the same as thrust (very gentle large thrust);
- thrust of squeezing (stretching) - associated with the squeezing of especially highly plastic rocks of the fold wing . Only slightly inclined to the stratification surfaces of the layers that it covers. Its inclination approximately corresponds to the inclination of the fold wing;
- formation thrust (consonant, ground) - occurring along a fault passing between layers of rocks of increased plasticity more or less parallel to these layers;
- post - erosion thrust - emerging on the earth's surface and developing under the conditions of erosion . A characteristic feature is a sharp decrease in the slope in the upper part;
- regional thrust - located on the border of large structural elements ( anticlinoria , synclinoria , etc.). Extends to many tens, and sometimes hundreds of kilometers. Can cross folds, and then is secant (see below);
- shear thrust - occurring along a fault crossing the rock layers at a significant angle;
- shear thrust - formed independently of folding. It can cross both horizontal and creased layers.
See also
- Autochton (geology)
- Paraautochton
Notes
- ↑ 1 2 3 4 Thrust // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
- ↑ Overthrow // Geological Dictionary: in 2 volumes / K.N. Paffengoltz et al. - Edition 2, rev. - M .: Nedra, 1978. - T. 1. - S. 100.
- ↑ 1 2 3 Thrust // Geological Dictionary: in 2 volumes / K.N. Paffengoltz et al. - Edition 2, rev. - M .: Nedra, 1978. - T. 2. - S. 7–8.
- ↑ Flinging // Great Soviet Encyclopedia : [in 30 vol.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
- ↑ Sharyazh // Geological Dictionary: in 2 volumes / K.N. Paffengoltz et al. - Edition 2, rev. - M .: Nedra, 1978. - T. 2. - S. 415-416.
- ↑ Tectonic cover / Khain V.E. // Great Soviet Encyclopedia : [30 t.] / Ch. ed. A.M. Prokhorov . - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.