Large Overthrusts Research Articles

Evolution of structures, pressure and temperature in the footwall of large scale overthrusts - Oman’s passive continental margin during obduction orogeny

Evolution of structures, pressure and temperature in the footwall of large scale overthrusts - Oman’s passive continental margin during obduction orogeny

Imbricate thrust structure of the Northwestern Caucasus

Many geologists suggest a determinative role of folding in the formation of the Northwestern Caucasus structure. Mapped or drilled thrusts are considered minor structures complicating steep fold limbs. Moreover, they are often described as reverse or even normal faults. In accordance with the generally accepted concept of overthrusts as subordinate structures relative to faulting, they are shown as short unlinked segments, which do not extend beyond anticlinal folds [1, 4, and others]. However, as will be shown below, this concept is erroneous and inconsistent with factual data. Actually, the genesis, morphology, and position of folds in plan view are completely controlled by overthrusts, which define the general tectonic style of the Northwestern Caucasus. The considered region adjacent to the Western Kuban marginal trough is divided into the Psebeps‐ Goitkh anticlinorium in the axial part, the Novorossiisk‐Lazarevsk synclinorium in the south, and Soberbash‐Gunai synclinorium in the north. The tectonic zones mentioned above are bordered by large regional overthrusts. The most important of them is the Akhtyr overthrust, which separates the Caucasus fold belt from the adjacent Western Kuban marginal trough in the north. The overthrust initiated at the orogenic stage separated terranes of different geodynamic settings during the subsequent evolution of the region. The Western Kuban marginal trough was significantly buried beneath allochthonous structures of the Soberbash‐ Gunai synclinorium as a result of the northward displacement and overthrusting of rock masses on its southern flank. Therefore, the trough has a distinct asymmetrical structure with the axis inclined to the thrust front. The complex imbricate Akhtyr thrust consists of smaller thrusts. Therefore, its main surface, which is marked by major tectonic displacements, can be taken as the northern boundary of the Soberbash‐Gunai synclinorium. Its front passes through the Dzhiginka‐UstChekup‐Adagum‐Kesler‐Kudak‐Kievsk areas. Smaller thrusts that splay off from the main thrust to the north control the North Varenikov, North Adagum, and North Krymsk anticlines among others. The Soberbash‐Gunai synclinorium and Psebeps‐ Goitkh anticlinorium are in tectonic contact along the thrust fault, the front of which marks high-amplitude local uplifts (South Krymsk, Damansk, Gladkov, Verkhnii Chekup, and others). The anticlines have a linear shape, with short northern (near-thrust) limbs but gentler and wider southern limbs. Tectonic doubling of sections, brecciation zones, and slickensides are recorded in boreholes. To the south-southwest, the thrust fault surface becomes gentler with depth. In plan view, its front represents a slightly curved rather than straight line, which consists of smaller arc-shaped thrusts concave to the north-northeast.

Overthrusts due to easy-slip/poor-slip transitions at the bed: the mathematical singularity with non-linear isotropic viscosity

AbstractThere are several cases in which large overthrusts and sub-horizontal faults appear to have occurred in temperate or cold glaciers. As a contribution to solving the problem of their origin, the stress field when there is an abrupt change in the bottom boundary conditions is determined, assuming ice to be isotropic, third-power-law viscous. Deviatoric stresses vary with the distance r to the singularity as r−1/4, and strain rates as r−3/4. They are computed numerically to a multiplicative factor, which is determined by the conditions at a large distance, but not computed here. Although the apparent viscosity varies as r1/2 times a function of the polar angle, the stress field around the singularity is not essentially different from that obtained assuming a constant viscosity. Some considerations on the apparition of faults follow, but at the scale of the microrelief the adopted model becomes oversimplified.

Shattered Rock and Precarious Rock Evidence for Strong Asymmetry in Ground Motions during Thrust Faulting

Recent thrust faulting models, both physical and numerical, have indicated very high ground motions on the hanging wall and relatively low motions on the footwall of thrust faults. In this article, recent field evidence supporting this strong asymmetry is described. Earlier field observations of objects thrown in the air also suggest that ground motions must have exceeded 1 g and 100 cm/sec. New shattered rock evidence on the hanging wall of thrust faults in Southern California supports the occurrence of intense ground motions. On the other hand, the lack of shattered rock and the presence of precariously balanced rocks on the footwall of two thrust faults in Southern California indicate relatively low ground motions, thus indicating strong asymmetry in ground motions near the fault trace for thrust faults. Some current ground-motion attenuation curves and hazard maps may give too low values on the hanging wall and too high values on the footwall. This could be of critical importance to estimating earthquake hazard from potentially large thrust fault earthquakes in the Los Angeles Basin and elsewhere in the world. The new evidence also supports the idea that dynamic inertial detachment of the hanging wall from the footwall occurs in nature in the manner suggested by some recent physical and numerical models. If such detachment occurs, it could also have important implications for understanding thrust fault rupture mechanics, for example, the paradox of large overthrusts and the heat flow paradox for thrusts.

Particle motions in a physical model of shallow angle thrust faulting

A physical model of thrust faulting has been constructed out of elastic foam rubber. The thrust wedge has an angle of 25°., and is forced from the back by a steel-hydraulic system of effectively infinite rigidity, analogous to the force exerted by tectonic plates. The observed particle motions show many features different from those commonly assumed in dislocation models of subduction thrusts. Interface waves associated with fault opening propagate along the thrust plane (from the back) and temporarily decouple the overlying hanging wall plate from the foot wall. Because of the geometry of the reflecting fault boundary, and the free surface (also reflecting), energy is trapped in the wedge and, as a consequence, the particle motions and energy in the hanging wall are much greater than in the foot wall. The interface wave and the energy trapped in the upper plate propagate up the wedge and break out at the toe of the thrust with a spectacular increase in motions. If this model is analogous to the real earth, it suggests that some common assumptions in dislocation modeling may be incorrect. The model may explain apparent missing energy radiated to teleseismic distances, the anomalously low number of empirical Green’s functions needed to model teleseismicp waves, and the evidence of intense shaking on the hanging wall toe of some thrust fault earthquakes. The results support the suggestion that interface waves may explain the lack of high frictional heat generation from thrust faults, and may explain the ‘paradox of large overthrusts’. The results also suggest that the seismic hazard of great subduction thrust earthquakes and continental shallow angle thrust faults might in some cases be seriously underestimated.

Rupture mechanism and interface separation in foam rubber models of earthquakes: a possible solution to the heat flow paradox and the paradox of large overthrusts : Brune, J N; Brown, S; Johnson, P A TectonophysicsV218, N1/3, Feb 1993, P59–67

Rupture mechanism and interface separation in foam rubber models of earthquakes: a possible solution to the heat flow paradox and the paradox of large overthrusts : Brune, J N; Brown, S; Johnson, P A TectonophysicsV218, N1/3, Feb 1993, P59–67

Rupture mechanism and interface separation in foam rubber models of earthquakes: a possible solution to the heat flow paradox and the paradox of large overthrusts

Spontaneous stick-slip along the interface between stressed foam rubber blocks is a simple analog of earthquake rupture and stick-slip. Results from this model are used to elucidate the role of normal stress variations along the interface in the stick-slip process. Observations indicate significant normal interface vibrations and separation during slip, suggesting that dynamic changes in normal stress (rather than a drop in the coefficient of friction) may control stick-slip, as suggested, for example, by Tolstoi, Oden and Martins and Brune and co-workers. Observations of particle trajectories indicate that stick-slip shear motion is associated with various degrees of fault separation. For an asymmetric model, the motion is consistent with slipping motion of the type suggested by Schallamach and Price. For a symmetric model, the motion is similar to that suggested by Comninou and Dundurs. If interface waves of this type, involving separation during slip, occur in earthquakes, they may be a solution to the heat flow paradox, since a major part of the slip occurs during separation and during low normal stress. Thus frictional heat generation is reduced. Normal interface vibrations during stick-slip may explain the high corner frequency of P wave spectra and the generally high levels of P wave spectra beyond the corner frequency. Schallamach-Comninou type waves are consistent with the partial stress drop-abrupt locking-self healing models of Brune and Heaton.

The mechanical paradox of large overthrusts: Alternative interpretation and reply

The mechanical paradox of large overthrusts: Alternative interpretation and reply

The mechanical paradox of large overthrusts

Research Article| December 01, 1988 The mechanical paradox of large overthrusts RAYMOND A. PRICE RAYMOND A. PRICE 1Geological Survey of Canada, Department of Energy, Mines and Resources, Ottawa K1A 0E4 Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (1988) 100 (12): 1898–1908. https://doi.org/10.1130/0016-7606(1988)100<1898:TMPOLO>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation RAYMOND A. PRICE; The mechanical paradox of large overthrusts. GSA Bulletin 1988;; 100 (12): 1898–1908. doi: https://doi.org/10.1130/0016-7606(1988)100<1898:TMPOLO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The mechanical paradox of large overthrusts originates with a fallacious assumption in the conceptual model upon which mechanical analyses of overthrust faulting have been based. The notion that the maximum width of a sheet of rock that may be displaced along an overthrust fault can be determined by using the Mohr-Coulomb failure criterion to compare the strength of the rocks with the stress required to overcome the total frictional resistance to slip (and the total cohesion or adhesion?) over the entire fault surface tacitly assumes that slip is initiated, and occurs, simultaneously over the entire fault surface. This unstated and untenable assumption, which is incompatible with what is known about real faults, is the real explanation for the "mechanical paradox."A realistic model for overthrust faulting must be compatible with the nature of real overthrust faults, and particularly with the way in which displacements, including earthquake displacements, occur on real faults. Most large overthrusts are discrete shear surfaces within a coherent mass of rock that is physically continuous around their ends. Total displacement clearly varies from place to place over these discrete shear surfaces and, moreover, must be the cumulative result of many relatively small incremental displacements that also varied from place to place over the finite part of the fault surface on which they occurred. Each increment began as a local shear failure and propagated along the fault as a "smeared-out" (Somigliana) dislocation at a velocity that was small considering the time required for propagation over the total area of the fault. During any individual displacement "event," whether a megathrust earthquake or a creep event, only a small part of the fault surface was in relative motion at any one time. Fault displacements may appear to occur simultaneously across laboratory specimens that are very small relative to the velocity of propagation of displacement because the transit time is so short. When the linear scale is expanded over six orders of magnitude to encompass an entire surface of a large overthrust fault, however, the transit time is much longer because the velocity of propagation is very small relative to the area of the fault surface, and the displacement clearly involves only a very small part of the fault surface at any one time.The shape and size of overthrust faults result from the propagation of dislocations, and this process is controlled by the strength heterogeneity and anisotropy of the rock mass as well as by variations in the regional stress field, but not by the frictional resistance to sliding integrated over the entire fault surface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Large Variscan overthrusts beneath the Paris Basin

The ECORS project is devoted to the deep geophysical investigation of the continental and oceanic crust in France through the study of fundamental problems such as the formation of basins, mountain belts and continental margins. The first of the profiles completed is the ‘Nord de la France’, which is mainly devoted to the survey of the major units of the Northern Hercynian Belt and of the deep crust below the Mesozoic Paris basin. The deep geophysical investigations undertaken on this profile have led tothe acquisition of diverse information, such as vibroseismic, wide-angle reflection, refraction and magnetotelluric data. The main results presented here show evidence of large overthrusts in the Variscan chain which is currently buried beneath the thin Mesozoic cover of the Paris basin. They show a differentiation of structural units in the upper crust, their link with the lower crust, and the depth and geometry of the Moho. They also give rise to some speculations regarding the nature of various gravimetric and magnetic anomalies such as the large ‘anomalie magnetique du Bassin de Paris’ (AMBP).

The southeastern Canadian Cordillera: Thrust faulting, tectonic wedging, and delamination of the lithosphere

Displacement of tectonic wedges, bounded above and below by zones of thrust faulting with opposing vergence, has produced tectonic delamination at various stratigraphic levels and times in the Rocky Mountain fold and thrust belt of Canada. The ‘triangle zone’, along the eastern edge of the belt, comprises an easterly tapering wedge of imbricate thrust-slices and delaminated Upper Cretaceous molasse deposits. The Porcupine Creek anticlinorium is a fan fold resulting from the insertion of a wedge of Proterozoic rocks along a zone of delamination at the base of the Lower Paleozoic shale succession. In the Selkirk fan structure, which involves the metamorphic infrastructure of the Cordillera, delamination has occurred as the result of the insertion of an apparently allochthonous mass (a ‘suspect terrane’) between the detached parautochthonous supracrustal rocks and the autochthonous basement complex. The diagnostic feature of tectonic wedging and delamination is a reversal in vergence between the bottom and the top of the wedge. Conspicuous tectonic overprinting (‘polyphase folding’) characteristically occurs above the wedge, and is commonly described as ‘backfolding’ and ascribed to polyphase orogeny. Tectonic wedging and delamination are widepread in compressional fold belts of various ages. Examples occur in the Cordilleran tectonic collage of accreted terranes and in early Proterozoic (Wopmay Orogen), Paleozoic (Caledonide-Appalachian) and Cenozoic (Alps) mountain belts. Moreover, tectonic wedging and delamination occur over the whole spectrum of scales from the microscopic to the lithospheric. They are an inherent feature of ‘flake tectonics’ and of the development of large overthrusts such as crystalline basement sheets and obducted ophiolites, all of which comprise a strong upper layer that has been delaminated from the rest of one lithospheric plate, and has overlapped another lithospheric plate that has been wedged beneath it. Geometric and kinematic relationships discernible in well-documented natural prototypes of tectonic wedging and delamination on a small scale provide a basis for elucidating relationships that are more difficult to establish directly on a large scale.

Stereo and Mosaic Aerial Photo Study of Central Ouachita Mountain System in Oklahoma and Arkansas: ABSTRACT

A careful study of stereo aerial photographs of a central part of the Ouachita Mountains in Oklahoma and Arkansas, followed by a related study of photo-index sheets of a much larger area in the Ouachitas, yields the following tentative conclusions: 1. The earliest structural dislocations of field dimensions are a series of approximately parallel bedding faults in the Stanley Shale, increasing in numbers downward in the section. A slight schistosity, also nearly parallel with bedding, may likewise increase downward. Some large overthrusts may have formed at this time. The prime source of this deformation was probably an underthrusting basement moving northward. 2. The next recognizable tectonic movements were uplifts of three main anticlinoria, although these could have followed episode 3. At this time the Ouachitas began to shed much coarse and finer clastic sediments toward the west and probably in other directions. 3. The next major episode seems to be steep faulting probably involving the basement and overlying sediments, producing semi-fault-block structures with tight broken anticlines; this was followed by a collapse of the sediments into deep synclines. Most of the high synclinal and more complicated ranges have straight or gently curved bordering faults in the adjacent lowlands. 4. The Mid-Continent regional uplift which included the Ouachitas must have produced a flood of coarse clastics adjacent to the mountains. These tectonic conglomerates have been removed by subsequent deep erosion, but their distal equivalents--the Garber, Duncan-San Angelo, and Whitehorse sands--are present in the Lower and Middle Permian of western Oklahoma and the western part of north-central Texas. 5. The nearly vertical Big Cedar fault extends nearly 200 mi from near Big Cedar, Oklahoma, to Jacksonville, Arkansas, northeast of Little Rock. It probably was formed during a period of relaxation or tension in Jurassic or Cretaceous time, and roughly parallels other faults in the coastal plain in southwest Arkansas. The Big Cedar fault touches 9 or 10 separate local structures along its length. End_of_Article - Last_Page 422------------

Rocks of the alpine ophiolitic suite: Discussion on the paper “the origin of ultramafic and ultrabasic rocks” by P.J. Wyllie

Abstract Based on petrologic and geologic investigations, anew conception of the origin of the ophiolitic suite in the Pennine-Austroalpine border region of the eastern Swiss Alps is offered which might be applied to other Alpine-type mountain ranges. During both the Jurassic and Cretaceous, the upper mantle buckled upwards in the region between the Pennine eugeosyncline and the Austroalpine miogeosyncline. Here oceanic conditions must have prevailed with the extrusion of basic volcanics. During the following compression phase, the rise formed an ideal glide surface for the large overthrusts with which large ultrabasic rock masses from the buckled mantle were carried along.

Tectonic convergence of facies in large overthrusts

Tectonic convergence of facies in large overthrusts

Ein experimenteller beitrag zur deutung grosser überschiebungen

Some experiments as a basis for discussing large overthrusts Limestone cylinders cut diagonally at 30° to the axis with a single crystal interlayer of gypsum of halite some 0.1 mm thick have been subjected to triaxial compression. The condition for sliding has been determined at confining pressures corresponding to a thickness of the overthrust block between 2,500 and 4,000 m. The coefficient of sliding friction is about 0.1. The reason for the low friction is the crystal plasticity. For areas where minerals able to translation like gypsum, halite, but also calcite or mica occur at the base of the overthrust slice, a model is suggested which allows for overthrust distances of even 100 km. Diagonal unter einem Winkel von 30° zur Achse geteilte Kalksteinzylinder wurden mit einer einige Zehntel Millimeter dicken Zwischenlage aus Gips oder Steinsalz (Einkristalle) in einer Hochdruckapparatur dreiachsial beansprucht. Bei Manteldrucken, die einer Deckenmächtigkeit von 2.500 bis 4.000 m entsprechen, wurde die Gleitbedingung bestimmt. Der ermittelte Reibungskoeffizient liegt um 0,1. Ursache der geringen Reibung ist die Kristallplastizität. Für Gebiete mit translationsfähigen Mineralien an der Basis der Überschiebungsmasse (Gips, Steinsalz, aber auch Calcit, Glimmer) wird ein Modell vorgestellt, mit dem sich sogar Deckenüberschiebungsweiten von 100 km mechanisch begründen Hessen.

Crystalline Klippen in the Index District, Cascade Range, Washington

At Mt. Baring, Gunn Peak, and Merchant Peak in the Cascade Range 40 miles east of Seattle, two klippen of hornblende-rich migmatitic rocks overlie a sequence of weakly metamorphosed argillites, quartzites, greenstones, and Permian marbles. The klippen are composed of schistose amphibolites which underwent partial static granitization into migmatites. During and after their tectonic emplacement, the migmatites were extensively sheared and brecciated. The underlying sedimentary and volcanic rocks are here described as the Gunn Peak Formation (restricted) and the Barclay Creek Formation, a new formation of possible Permian age. These rocks were metamorphosed in the greenschist facies; then, during cataclastic metamorphism, slabs of Barclay Creek argillite became tectonically intercalated between blocks of migmatite. Small ultramafic intrusions were emplaced near and at the base of the klippen. Emplacement of the klippen probably preceded deposition of the Late Cretaceous and Paleocene Swauk Formation. After cataclastic metamorphism, both migmatites and underlying rocks underwent contact metamorphism ranging from greenschist to pyroxene-hornfels facies; this is attributed to the intrusion of two Tertiary quartz diorite batholiths east and west of the klippen. Similar hornblende-rich, coarse crystalline bodies occur in association with weakly metamorphosed and unmetamorphosed rocks along a 175-mile zone west of the Mesozoic crystalline core of the northern Cascades. These crystalline rocks, like the ultra-mafic rocks, may be shreds of pre-Middle Devonian basement dragged up from deeper levels of the crust during the emplacement of one of several large Cretaceous overthrusts which formed west of the Cordilleran plutonic belt.

Structural Evolution of Part of Southeastern Arizona: ABSTRACT

The structural evolution of southeastern Arizona has been dominated by the differential vertical uplift of the Precambrian and Triassic-Jurassic granites. Most of the ranges are complex anticlines with Precambrian or Triassic-Jurassic granites in their core. Some uplifts exceed 25,000 feet. Many of the ranges began to rise in Triassic-Jurassic time and have continued to rise intermittently in essentially the same position at least through Miocene time. This conclusion is supported by: (1) truncation of Paleozoic strata on the flanks of the present ranges in pre-Lower Cretaceous time, (2) depositional thinning of Cretaceous strata down the flanks of the present ranges and the development of Cretaceous basins adjacent to and parallel with incipient ranges rising in Cretaceo s time, (3) high-angle Laramide reverse faults which define the flanks of present ranges and uplift the granite cores with respect to the schist which underlies the range flanks, and (4) Basin-and-Range type faulting which further developed uplifts already in existence. Most of the previous investigators of the structural geology of southeastern Arizona have described intensive and extensive overthrusting. Overthrusting has probably been overemphasized, primarily because of a failure to discriminate between large overthrusts and detached blocks which have moved down the flanks of large anticlines under the influence of gravity. This conclusion is based on recognition of a possible source and an available declivity, and, in particular, on a study of the internal structures of the detached blocks which has often shown that the blocks moved down the mountain flank rather than out of the valley onto the uplifted mountain block. Of interest to the petroleum geologist are the structural and stratigraphic variations along the flanks of the intermittently rising anticlines and the comparatively simple structure which may exist in the intervening valleys. End_of_Article - Last_Page 413------------

Petroleum Geology of Colombia, South America: ABSTRACT

As a petroleum producing country, Colombia ranked 8th in world production in 1940. Of the South American countries, Colombia is second to Venezuela, whose output is nearly ten times as great, and slightly ahead of Argentina. At least six petroliferous provinces may be recognized in Colombia. They are the Magdalena Valley, the southwestern basin area of Lake Maracaibo, the plains or llanos area in the southeastern part of the country, the coastal area of the Caribbean, the Goajira Peninsula and the Pacific coast region. The most important producing areas at present are the middle Magdalena Valley and the southwestern Lake Maracaibo area. Travel in the country is difficult except in the uplands where most of the roads are located. The native language is Spanish, English b ing spoken only sparingly. Pre-Cretaceous rocks are known to occur in the Cordilleras Oriental and Central and also in the Llanos area, but are of no importance in the production of petroleum. Cretaceous limestones and shales are extensively developed east of the Central Cordillera and are highly petroliferous. Cenozoic deposits are found in the intermontane valleys, in the Llanos area and along the Caribbean coast. In the middle Magdalena Valley, there are important reservoir beds of petroleum. Large overthrusts are characteristic features of the Magdalena Valley. They are also known to occur in the Llanos area in the valley west of the Cordillera Central and in the southwestern Lake Maracaibo basin area. In the Magdalena Valley and in the southwestern Lake Maracaibo area petroleum occurs on faulted anticlines. In the coastal region sharp anticlines, with some faulting, are known. Oil and gas seepages and mud volcanoes are of common occurrence. Little is known of the structure of the Goajira Peninsula and the Pacific Coast areas. Production comes from Oligocene and Eocene sands in the middle Magdalena Valley. Two structures, Infantas and La Cira, produced all the oil of this region up to about 1943. Two new fields have been added to the above producers. The Barco area, located in the southwestern Lake Maracaibo basin, obtains its oil from the Cretaceous and Tertiary on faulted anticlines. In the Cesar Valley, located in the lower Magdalena Valley area, production of high gravity oil from Oligocene limestone has been reported in new wells. End_of_Article - Last_Page 1778------------