In geology , a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than 2 km (1.2 mi) or 5 km (3.1 mi) above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the overriding plate in active subduction zones. Nappes form when a mass of rock is forced (or "thrust" ) over another rock mass, typically on a low angle fault plane. The resulting structure may include large-scale recumbent folds , shearing along the fault plane, imbricate thrust stacks , fensters and klippes .
15-514: The term stems from the French word for tablecloth in allusion to a rumpled tablecloth being pushed across a table. Nappes or nappe belts are a major feature of the European Alps , Dinarides , Carpathians and Balkans . Since the 19th century many geologists have uncovered areas with large-scale overthrusts. Some of these were substantiated with paleontological evidence. The concept
30-420: A decollement plane. Evaporites are also often related the decollement and thrust planes. Evaporites are strongly prone to shear deformation and therefore preferred planes of detachment. Behavior of thrust sheets is currently explained on the model of the orogenic wedge , which is dependent on the internal wedge taper θ. Gravitational sliding is movement generated by the movement down an inclined plane under
45-574: A salt glacier . Differential loading causes salt deposits covered by overburden ( sediment ) to rise upward toward the surface and pierce the overburden, forming diapirs (including salt domes ), pillars, sheets, or other geological structures. In addition to Earth-based observations, diapirism is thought to occur on Neptune's moon Triton , Jupiter's moon Europa , Saturn's moon Enceladus , and Uranus's moon Miranda . Diapirs commonly intrude buoyantly upward along fractures or zones of structural weakness through denser overlying rocks. This process
60-654: A nappe is called a decollement , detachment plane or sole of thrust. The root area is an area where the nappe is completely separated from its substratum. It is often compressed and reduced, even underthrust below the surrounding tectonic units, resulting in a specific structure called a suture . A nappe whose root area is unknown, is called a rootless nappe . Areas with a nappe structure often contain two types of geological features: According to petrographical composition, two basic types of nappes are known: Nappes are generally considered as compressional structures, however some exceptions could be found especially among
75-740: A significant risk when trying to drill through them. There is an analogy to a Galilean thermometer . Rock types such as evaporitic salt deposits, and gas charged muds are potential sources of diapirs. Diapirs also form in the Earth's mantle when a sufficient mass of hot, less dense magma assembles. Diapirism in the mantle is thought to be associated with the development of large igneous provinces and some mantle plumes . Explosive, hot volatile rich magma or volcanic eruptions are referred to generally as diatremes . Diatremes are not usually associated with diapirs, as they are small-volume magmas which ascend by volatile plumes, not by density contrast with
90-478: Is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor instability structures in regions with low tectonic stress such as in the Gulf of Mexico to narrow dikes of material that move along tectonically induced fractures in surrounding rock. The term
105-418: Is known as diapirism . The resulting structures are also referred to as piercement structures . In the process, segments of the existing strata can be disconnected and pushed upwards. While moving higher, they retain many of their original properties, e.g. pressure; their pressure can be significantly different from the pressure of the shallower strata they get pushed into. Such overpressured "floaters" pose
120-572: The plastic and viscous behavior of solid rock necessary to move along low angle faults. It is considered that such characteristics may be achieved at significantly less extreme conditions in the clayey rocks or evaporites , which can then act as tectonic lubricants . The process, which significantly reduces the frictional resistance, is the fluid overpressure, which acts against the normal pressure, thereby reducing high lithostatic pressures and allowing fracturation , cataclasis and formation of tectonic breccia or fault gouge that could act as
135-544: The Wikimedia System Administrators, please include the details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 258433881 Upstream caches: cp1108 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 11:05:31 GMT Diapirism A diapir ( / ˈ d aɪ . ə p ɪər / ; from French diapir [djapiʁ] , from Ancient Greek διαπειραίνω ( diapeiraínō ) 'to pierce through')
150-422: The action of gravity . Gravitational spreading, possibly accompanied by an initial phase of diapirism , is generated by large heat flow that causes detachment in a hinterland . Other mechanisms, such as push from behind, action of tangential compressive forces, and shortening of the basement, are essentially variations of the previous mechanisms. Tablecloth Too Many Requests If you report this error to
165-460: The gravitational slides along low angle faults. Gravitational forces could even be important in certain cases during emplacement of compressional thrusts. The movement of huge masses of rock may be influenced by several forces, forces that may act together or sequentially. These forces frequently result in high temperature and pressure metamorphism and strong deformation of nappe rocks. At shallower depths, low pressures and temperatures can't cause
SECTION 10
#1732791931627180-458: The ideas of nappes to the Carpathians . Nappe can be qualified in a number of ways to indicate various features of a formation. The frontal part in the direction of movement, is called the leading edge of a nappe; numerous folds and secondary thrusts and duplexes are common features here and are sometimes called digitations . The surface of a thrust fault which caused movement of
195-440: The surrounding mantle. Diapirs or piercement structures are structures resulting from the penetration of overlaying material. By pushing upward and piercing overlying rock layers, diapirs can form anticlines (arch-like shape folds ), salt domes (mushroom/ dome-shaped diapirs), and other structures capable of trapping hydrocarbons such as petroleum and natural gas . Igneous intrusions themselves are typically too hot to allow
210-624: Was developed by Marcel Alexandre Bertrand , who unraveled the complex tectonic history of the Alps and identified the feature as nappe de charriage . He reinterpreted earlier studies by Arnold Escher von der Linth and Albert Heim in the Glarus Alps . His work in Switzerland influenced Escher and Maurice Lugeon . Several years later, nappe structure was investigated in northwestern Scotland by Charles Lapworth . Lugeon later transferred
225-433: Was introduced by Romanian geologist Ludovic Mrazek , who was the first to understand the principle of salt tectonics and plasticity . The term diapir may be applied to igneous intrusions , but it is more commonly applied to non-igneous, relatively cold materials, such as salt domes and mud diapirs. If a salt diapir reaches the surface, it can flow because salt becomes ductile with a small amount of moisture, forming
#626373