Навлака

Уколико сте тражили протетску надокнаду, погледајте чланак Круница (стоматологија).

Навлака у Ћиљен шан, Кина. Старија (лево, плава и црвена) навлака преко млађе (десно, смеђа).

Гленкул навлака у Ејрд да Лоху, Асинт у Шкотској. Неправилна сива маса стене формирана је од архејских или палеопротерозојских Луисијанских комлекса који су провучени по добро обложеном камбријском кварциту, дуж врха од млађе јединице.

Навлаке представљају реверсне раседе, са благим, скоро хоризонталним падом раседне површи, и амплитудом кретања стена од више километара.

За навлачења од неколико десетина, па до више од стотину километара, користи се назив шаријаж.

Геометрија и номенклатура навлака

Мала навлака на литицама у Лилсток беј, Сомерсет, Енглеска; померање од око два метра

Diagram of the evolution of a fault-bend fold or 'ramp anticline' above a thrust ramp, the ramp links decollements at the top of the green and yellow layers

Diagram of the evolution of a fault propagation fold

Development of thrust duplex by progressive failure of ramp footwall

Antiformal stack of thrust imbricates proved by drilling, Brooks Range Foothills, Alaska

Расед

Ова навлака је тип раседа који је потонуо са 45 степени или мање.

Ако је угао равни раседа нижи (често мањи од 15 степени од хоризонтале) а померање прекривајућег блока је велико (често у распону километара), расед се назива расед превртања. Ерозија може да уклони део горњег блока, стварајући фенстер (или прозор) - када је доњи блок изложен само на релативно малом простору. Када ерозија уклани већину горњег блока, остављајући остатке налик на острва на доњем блоку, остаци се називају клипен.

Blind thrust faults

Главни чланак: Blind thrust earthquake

If the fault plane terminates before it reaches the Earth's surface, it is referred to as a blind thrust fault. Because of the lack of surface evidence, blind thrust faults are difficult to detect until they rupture. The destructive 1994 earthquake in Northridge, Los Angeles, California, was caused by a previously undiscovered blind thrust fault.

Because of their low dip, thrusts are also difficult to appreciate in mapping, where lithological offsets are generally subtle and stratigraphic repetition is difficult to detect, especially in peneplain areas.

Fault-bend folds

Thrust faults, particularly those involved in thin-skinned style of deformation, have a so-called ramp-flat geometry. Thrusts mostly propagate along zones of weakness within a sedimentary sequence, such as mudstones or halite layers, these parts of the thrust are called decollements. If the effectiveness of the decollement becomes reduced, the thrust will tend to cut up the section to a higher stratigraphic level until it reaches another effective decollement where it can continue as bedding parallel flat. The part of the thrust linking the two flats is known as a ramp and typically forms at an angle of about 15°–30° to the bedding. Continued displacement on a thrust over a ramp produces a characteristic fold geometry known as a ramp anticline or, more generally, as a fault-bend fold.

Fault-propagation folds

Fault-propagation folds form at the tip of a thrust fault where propagation along the decollement has ceased but displacement on the thrust behind the fault tip is continuing. The continuing displacement is accommodated by formation of an asymmetric anticline-syncline fold pair. As displacement continues the thrust tip starts to propagate along the axis of the syncline. Such structures are also known as tip-line folds. Eventually the propagating thrust tip may reach another effective decollement layer and a composite fold structure will develop with characteristics of both fault-bend and fault-propagation folds.

Thrust duplex

Duplexes occur where there are two decollement levels close to each other within a sedimentary sequence, such as the top and base of a relatively strong sandstone layer bounded by two relatively weak mudstone layers. When a thrust that has propagated along the lower detachment, known as the floor thrust, cuts up to the upper detachment, known as the roof thrust, it forms a ramp within the stronger layer. With continued displacement on the thrust, higher stresses are developed in the footwall of the ramp due to the bend on the fault. This may cause renewed propagation along the floor thrust until it again cuts up to join the roof thrust. Further displacement then takes place via the newly created ramp. This process may repeat many times, forming a series of fault bounded thrust slices known as imbricates or horses, each with the geometry of a fault-bend fold of small displacement. The final result is typically a lozenge shaped duplex.

Most duplexes have only small displacements on the bounding faults between the horses and these dip away from the foreland. Occasionally the displacement on the individual horses is greater, such that each horse lies more or less vertically above the other, this is known as an antiformal stack or imbricate stack. If the individual displacements are greater still, then the horses have a foreland dip.

Duplexing is a very efficient mechanism of accommodating shortening of the crust by thickening the section rather than by folding and deformation.

Тектонско окружење

Главни чланак: Thrust tectonics

An example of thin-skinned deformation (thrusting) in Montana. Note that the white Madison Limestone is repeated, with one example in the foreground and another at a higher level to the upper right corner and top of the picture.

Large overthrust faults occur in areas that have undergone great compressional forces. These conditions exist in the orogenic belts that result from either two continental tectonic collisions or from subduction zone accretion. The resultant compressional forces produce mountain ranges. The Himalayas, the Alps, and the Appalachians are prominent examples of compressional orogenies with numerous overthrust faults.

Thrust faults occur in the foreland basin which occur marginal to orogenic belts. Here, compression does not result in appreciable mountain building, which is mostly accommodated by folding and stacking of thrusts. Instead thrust faults generally cause a thickening of the stratigraphic section. When thrusts are developed in orogens formed in previously rifted margins, inversion of the buried paleo-rifts can induce the nucleation of thrust ramps.

Foreland basin thrusts also usually observe the ramp-flat geometry, with thrusts propagating within units at a very low angle "flats" (at 1–5 degrees) and then moving up-section in steeper ramps (at 5–20 degrees) where they offset stratigraphic units. Thrusts have also been detected in cratonic settings, where "far-foreland" deformation has advanced into intracontinental areas.

Thrusts and duplexes are also found in accretionary wedges in the ocean trench margin of subduction zones, where oceanic sediments are scraped off the subducted plate and accumulate. Here, the accretionary wedge must thicken by up to 200% and this is achieved by stacking thrust fault upon thrust fault in a melange of disrupted rock, often with chaotic folding. Here, ramp flat geometries are not usually observed because the compressional force is at a steep angle to the sedimentary layering.

Издвајање потисног раседа

Историја

Thrust faults were unrecognised until the work of Arnold Escher von der Linth, Albert Heim and Marcel Alexandre Bertrand in the Alps working on the Glarus Thrust; Charles Lapworth, Ben Peach and John Horne working on parts of the Moine Thrust Scotland; Alfred Elis Törnebohm in the Scandinavian Caledonides and R. G. McConnell in the Canadian Rockies. The realisation that older strata could, via faulting, be found above younger strata, was arrived at more or less independently by geologists in all these areas during the 1880s. Geikie in 1884 coined the term thrust-plane to describe this special set of faults. He wrote:

By a system of reversed faults, a group of strata is made to cover a great breadth of ground and actually to overlie higher members of the same series. The most extraordinary dislocations, however, are those to which for distinction we have given the name of Thrust-planes. They are strictly reversed faults, but with so low a hade that the rocks on their upthrown side have been, as it were, pushed horizontally forward.

Литература

• „Earthquake Glossary - blind thrust fault”. USGS. 2012-07-24. Архивирано из оригинала 2016-01-15. г. Приступљено 2016-02-01. 
• Pratt, Thomas L.; Shaw, John H.; Dolan, James F.; Christofferson, Shari A.; Williams, Robert A.; Odum, Jack K.; Plesch, Andreas (2002). „Shallow seismic imaging of folds above the Puente Hills blind-thrust fault, Los Angeles, California” (PDF). Geophysical Research Letters. 29 (9): 18—1. Bibcode:2002GeoRL..29.1304P. ISSN 0094-8276. doi:10.1029/2001GL014313 . Архивирано из оригинала (PDF) 5. 3. 2005. г. Приступљено 2016-02-01. CS1 одржавање: Формат датума (веза)
• Shaw, John H.; Suppe, John (1996). „Earthquake hazards of active blind-thrust faults under the central Los Angeles basin, California”. Journal of Geophysical Research. 101 (B4): 8623. Bibcode:1996JGR...101.8623S. ISSN 0148-0227. doi:10.1029/95JB03453. 
• Shaw, John H. (1999-03-05). „An Elusive Blind-Thrust Fault Beneath Metropolitan Los Angeles”. Science. 283 (5407): 1516—1518. Bibcode:1999Sci...283.1516S. PMID 10066170. S2CID 21556124. doi:10.1126/science.283.5407.1516. 
• Perlman, D. (2001-08-23). „L.A. moves with water table / Changing water table moves L.A. / City rises and falls with annual pumping from ground storage”. SFGate. Архивирано из оригинала 4. 2. 2015. г. Приступљено 2. 2. 2016. CS1 одржавање: Формат датума (веза)
• Shiner, P (2004). „Thin-skinned versus thick-skinned structural models for Apulian carbonate reservoirs: constraints from the Val d'Agri Fields, S Apennines, Italy”. Marine and Petroleum Geology. 21 (7): 805. doi:10.1016/j.marpetgeo.2003.11.020. 
• Hatcher, R. D. (2007). „Confirmation of Thin-skinned Thrust Faulting in Foreland Fold-Thrust Belts and Its Impact on Hydrocarbon Exploration: Bally, Gordy, and Stewart” (PDF). Bulletin of Canadian Petroleum Geology, 1966(First in the AAPG History of Petroleum Geology Series on Papers Having a Major Impact on Petroleum Geology: A contribution of the AAPG History of Petroleum Geology Committee). 
• Butler, R. W. H., S. Mazzoli, S. Corrado, M. De Donatis, D. Di Bucci, R. Gambini, G. Naso, C. Nicolai, D. Scrocca, P. Shiner, and V. Zucconi (2004). K. R. McClay, ур. „Applying thick-skinned tectonic models to the Apennine thrust belt of Italy—Limitations and implications” (PDF). Thrust tectonics and hydrocarbon systems: AAPG Memoir 82. стр. 647—67. CS1 одржавање: Употреба параметра аутори (веза)
• Timothy Briggs Byrne; Char-Shine Liu (2002). Geology and Geophysics of an Arc-continent Collision, Taiwan. Special Paper 358. Geological Society of America. ISBN 978-0-8137-2358-7. 

Спољашње везе

• Appalachian folding, thrusting and duplexing Архивирано на сајту Wayback Machine (12. јануар 2010)
• Rob Butler's webpage on thrusts
• Contraction: Chapter 16; A complementary resource to Chapter 16 of the textbook "Strukturgeologi" by Haakon Fossen & Roy Gabrielsen