Academic literature on the topic 'Shortening and vergence'

The 3D kinematic evolution of thrust systems, in which vergence changes along strike, is poorly understood. This study uses 3D seismic data from Big Piney-LaBarge field, Wyoming, to examine the geometry and kinematics of two faults at the leading edge of the Hogsback thrust sheet, the frontal thrust of the Late Cretaceous Sevier fold-thrust belt. These thrusts lie along strike of each another and share an east-vergent detachment within the Cretaceous Baxter Shale. The two thrusts verge in opposite directions: The southern thrust verges eastward forming a frontal ramp consistent with major thrusts of the Sevier belt, whereas the northern thrust verges westward to form a type 1 triangle zone with the Hogsback thrust. The thrusts have strike lengths of 5 km (3.1 mi) and 8 km (5.0 mi), respectively, and they are separated by a transfer zone of less than 0.5 km (0.3 mi) wide. Strata in the transfer zone appear to be relatively undeformed, but reflections are less coherent here, which suggests small offsets unresolved by the seismic survey. Retrodeformable cross sections and a structure contour map on the Cretaceous Mesaverde Group indicate that shortening varies along strike, with a pronounced minimum at the transfer zone and greater shortening across the northern, west-vergent thrust (610 m [2000 ft]) than across the southern, east-vergent thrust (230 m [755 ft]). Mapping of these thrusts suggests that they propagated laterally toward each other to form a type 1 antithetic fault linkage in the transfer zone. Spatial patterns expressed in seismic attributes in and near the detachment horizon, which include waveform classification and spectral decomposition, suggest that stratigraphic variations may have pinned the detachment, thus localizing the transfer zone. Thickness variations in the thrust sheet also may have influenced the thrust geometry. Our study provides an analog for analysis of similar complex contractional belts around the world.

Several deformation models have been proposed for the Paraguay Belt, which primarily differ in the number of phases of deformation, direction of vergence and tectonic style. Structural features presented in this work indicate that the tectonics was dominated by low dip thrust sheets in an initial phase, followed by two progressive deformation phases. The first phase of deformation is characterized by a slate cleavage and axial plane of isoclinal recumbent folds with a NE axial direction, with a recrystallization of the minerals in the greenschist facies associated with horizontal shear zones with a top-to-the-SE sense of movement. The second stage shows vergence towards the NW, characterized by crenulation cleavage axial plane to F2 open folds over S0 and S1, locally associated with reverse faults. The third phase of deformation is characterized by subvertical faults and fractures with a NW direction showing sinistral movement, which are commonly filled by quartz veins. The collection of tectonic structures and metamorphic paragenesis described indicate that the most intense deformation at the deeper crustal level, greenschistfacies, occurred during F1, which accommodated significant crustal shortening through isoclinal recumbent folds and shear zones with low dip angles and hangwall movement to the SE, in a thin-skinned tectonic regime. The F2 deformation phase was less intense and had a brittle to ductile behavior that accommodated a slight shortening through normal open subvertical folds, and reverse faults developed in shallower crustal level, with vergence towards the Amazonian Craton. The third phase was less pervasive, and the shortening was accommodated by relief subvertical sinistral faults.

In the deep seated gravity-driven deformation systems of the Gulf of Mexico contemporaneous extension and contraction of the overburden is favored by mechanical decoupling from the basement along thick salt sequences (up to 4 km). The updip extension is located inland, on the continental shelf of northeast Mexico, and is characterized by extensional listric faults and roll-overs; the downdip shortening zone is located at the deep waters and is characterized by a fold and thrust belt detached above the salt layer. Two physical experiments are used to discuss some aspects of these gravity-driven systems. The experimental setup includes a motor-driven experimental table, an inclined brittle basement (1°), a silicone layer simulating the salt sequences, and sand layers simulating the pre-kinematic Jurassic-Cretaceous strata before Laramide shortening. Deformation resulted in further tilting of the basement (3° to 4°). After the onset of deformation, thin sand layers were added at regular time intervals simulating the syntectonic sedimentation. The experiments reproduced the geometry of the deformation at the frontal ramp characterized by a seaward vergent thrust and its associated deformed region (the Perdido fold belt). The fold and thrust belt localization was favored by the change in basement inclination (a built-in slope change). Key elements interpreted in one available section of the area were reproduced in the model: a) the presence of an antithethic roll-over in the extensional zone and, b) the basinward vergence of folds and thrusts observed in the downdip shortening zone in the mexican Perdido fold belt.

AbstractThe presence of a set of well-known turbidite successions, deposited in progressively E-migrating foredeep basins and subsequently piled up with east vergence, makes the Northern Apennines of Italy paradigmatic of the evolution of deepwater fold-and-thrust belts. This study focuses on the early Apenninic collisional stage, early Miocene in age, which led to the accretion of the turbidites of the Trasimeno Tectonic Wedge (TTW), in the central part of the Northern Apennines. Based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing, we present a detailed tectonic reconstruction of the TTW. In the study area, the TTW is characterized by a W-dipping shaly basal décollement located at a depth of 1–5 km. The tectonic wedge is c. 5 km thick at its central-western part and tapers progressively eastwards to c. 1 km. The total shortening, balanced along a 33 km long cross-section, is c. 60 km, including 20 km (40%) of internal imbrication, c. 23 km of horizontal ENE-wards translation along the basal décollement and c. 17 km of passive translation caused by the later shortening of footwall units. Deformation balancing, constrained through upper Aquitanian – upper Burdigalian (c. 21–16 Ma) biostratigraphy, provides an average shortening rate of c. 8.6 mm a–1. Internal shortening of the TTW shows an average shortening rate of c. 4 mm a–1 for this period.

Abstract. Within the Northern Calcareous Alps (NCA) fold-and-thrust belt of the Eastern Alps, multiple pre-shortening deformation phases have contributed to the structural grain that controlled localization of deformation at later stages. In particular, Jurassic rifting and opening of the Alpine Tethys led to the formation of extensional basins at the northern margin of the Apulian plate. Subsequent Cretaceous shortening within the Northern Calcareous Alps produced the enigmatic Achental structure, which forms a sigmoidal transition zone between two E–W-striking major synclines. One of the major complexities of the Achental structure is that all structural elements are oblique to the Cretaceous direction of shortening. Its sigmoidal form was, therefore, proposed to be a result of forced folding at the boundaries of the Jurassic Achental basin. This study analyses the structural evolution of the Achental structure through integrating field observations with crustal-scale physical analogue modelling to elucidate the influence of pre-existing crustal heterogeneities on oblique basin inversion. From brittle–ductile models that include a weak basal décollement, we infer that oblique shortening of pre-existing extensional faults can lead to the localization of deformation at the pre-existing structure and predicts thrust and fold structures that are consistent with field observations. Consequently, the Achental low-angle thrust and sigmoidal fold train was able to localize at the former Jurassic basin margin, with a vergence opposite to the controlling normal fault, creating the characteristic sigmoidal morphology during a single phase of NW-directed shortening.

Extraocular muscle (EOM) myofibers do not fit the traditional fiber typing classifications normally used in noncranial skeletal muscle, in part, due to the complexity of their individual myofibers. With single skinned myofibers isolated from rectus muscles of normal adult rabbits, force and shortening velocity were determined for 220 fibers. Each fiber was examined for myosin heavy chain (MyHC) isoform composition by densitometric analysis of electrophoresis gels. Rectus muscle serial sections were examined for coexpression of eight MyHC isoforms. A continuum was seen in single myofiber shortening velocities as well as force generation, both in absolute force (g) and specific tension (kN/m2). Shortening velocity correlated with MyHCIIB, IIA, and I content, the more abundant MyHC isoforms expressed within individual myofibers. Importantly, single fibers with similar or identical shortening velocities expressed significantly different ratios of MyHC isoforms. The vast majority of myofibers in both the orbital and global layers expressed more than one MyHC isoform, with up to six isoforms in single fiber segments. MyHC expression varied significantly and unpredictably along the length of single myofibers. Thus EOM myofibers represent a continuum in their histological and physiological characteristics. This continuum would facilitate fine motor control of eye position, speed, and direction of movement in all positions of gaze and with all types of eye movements—from slow vergence movements to fast saccades. To fully understand how the brain controls eye position and movements, it is critical that this significant EOM myofiber heterogeneity be integrated into hypotheses of oculomotor control.

Abstract The NW Borneo deep-water fold-and-thrust belt, offshore Sabah, southern South China Sea, contains a structurally complex region of three to four seafloor ridges outboard of the shelf-slope break. Previous studies have suggested the seafloor ridges formed either above shale diapirs produced by mass movement of overpressured shales (i.e., mobile shale) or above an imbricate fold-and-thrust array. Here, we performed tectonostratigraphic analyses on a petroleum industry three-dimensional (3-D) seismic volume that imaged the full growth stratal record. We show fold growth history, deformation styles, along-strike structural variabilities, and synkinematic sedimentation during triangle zone–style fold growth. Nine seismic horizons within growth strata were mapped and correlated to petroleum industry seismostratigraphy. Synkinematic sedimentation interactions with growing folds and near-surface strains were analyzed from seismic attribute maps. We interpret that the seafloor structures were formed by imbricate thrusts above multiple detachments. We estimate ∼8 km minimum shortening since the late Miocene ca. 10 Ma. The folds show oversteepened fold forelimbs, back-rotated backlimbs, and forward-vergent (NW to NNW) “blind” thrust ramps that terminate within the growth strata. Fold cores show evidence of internal shear. Immature folds show detachment fold geometries, whereas mature folds show forelimb break thrusts, type I triangle zones, and rotated forward-vergent roof thrusts. Thrust linkages spaced ∼10 km apart were exploited as thrust top synkinematic sedimentation pathways; the linkages also partition near-surface strains. Our comprehensive, three-dimensional documentation of triangle zone fold growth and sedimentation in a deep-water fold belt highlights internal shear, multiple detachments, and opposite thrust vergence; mobile shales are not required to explain the deformation.

Cambro-Ordovician continental-margin rocks of the Humber zone of the Quebec Appalachians were mainly deformed during the Taconian orogeny (Middle Ordovician to Early Silurian). Two Taconian deformational events are recorded west of the Sutton–Notre-Dame mountains anticlinorium axis. They are characterized, respectively, by northwest-directed faulting and synmetamorphic folding (D1−2) and by southeastward back-thrusting motion (D3); the latter deformation has previously been poorly documented in the Quebec Appalachians. This duality of structural vergence is probably induced by the progressive tectonic wedging of basement rocks during a nearly constant northwest–southeast Taconian shortening. In correlative higher grade metamorphic rocks of New England, back-thrusting structures (D3) have not been described and are most probably absent because their root zone is located well above the present-day erosional surface of that part of the Appalachian belt.

Geological traverse between the town of Jabbri and Rupper, southeast Hazara delineates the stratigraphic and structural element of the area presented by high resolution geological map and cross section of the area. Oldest rocks in this section is Precambrian Hazara formation which is disconformably overlain by a Jurassic to Eocene sequence including Samana Suk, Chichali, Lumshiwal, Kawagarh, Hangu, Lockhart, Patala, Margalla-hill-limestone, Chorgali and Kuldana formations. Located in Lesser Himalayas, under the influence of main boundary thrust (MBT), this area developed several thrust systems from north to south including Hazara thrust, Haro thrust, Sangoda thrust, Rupper thrust. The main regional Hazara thrust has Precambrian rock in its hanging wall thrusted over the Jurassic Samna Suk formation. In lower detachment, there are several local thrust systems within Jurassic-Eocene strata.These thrusts trends in NE-SW direction indicating NW-SE compressional regime with the hanging wall Drag folds showing southward vergence. The stereographic plot of mesoscopic scale folds shows at least three folding events and varying plunging directions between the range of 240° and 290°. Most of the folds are plunging towards west and this is yet another indicator of east-west compressional forces. These folds orientations suggest transpressional deformation rather than pure compression. The balanced restore section shows that there is about 2.5 km shortening along 15 km restored section which makes about 16% shortening along the section.

AbstractDuctile shear zones with dextral transpressive deformation separate the Ljusdal lithotectonic unit from the neighbouring units (Bothnia–Skellefteå and Bergslagen) in the 2.0–1.8 Ga Svecokarelian orogen. Sedimentation steered by regional crustal extension at c. 1.86–1.83 Ga was sandwiched between two separate phases of ductile strain with crustal shortening and predominantly high-grade metamorphism with plutonic activity. Metamorphism occurred under low-pressure, medium- to high-temperature conditions that locally reached granulite facies. The earlier shortening event resulted in the accretion of outboard sedimentary and c. 1.89 Ga volcanic rocks (formed in back- or inter-arc basin and volcanic arc settings, respectively) to a continental margin. Fabric development (D1), the earlier phase of low-pressure and variable temperature metamorphism (M1) and the intrusion of a predominantly granitic to granodioritic batholith with rather high εNd values (the Ljusdal batholith) occurred along this active margin at 1.87–1.84 Ga. Thrusting with westerly vergence, regional folding and ductile shearing (D2–3), the later phase of low-pressure and variable temperature metamorphism (M2), and the subsequent minor shear-related intrusion of granite, again with relatively high εNd values, prevailed at 1.83–1.80 Ga. Mineral deposits include epithermal Au–Cu deposits hosted by supracrustal rocks, V–Fe–Ti mineralization in subordinate gabbro and norite bodies inside the Ljusdal batholith, and graphite in metasedimentary rocks.

Cette thèse, par une approche multidisciplinaire, propose un nouveau modèle d'orogène à double vergence pour les Andes Centrales du Nord, expliquant l'épaississement crustal et la topographie actuelle. Une nouvelle synthèse structurale et stratigraphique à travers l'avant-arc et la Cordillère Occidentale a permis de révéler la présence d'un chevauchement majeur à vergence Ouest. Pour la première fois, la construction d'une coupe équilibrée traversant toutes les Andes Centrales du Nord, combinée à des données thermochronologiques, illustre un modèle orogénique à double vergence se propageant de façon synchrone depuis ~30 Ma avec un raccourcissement total de 158 km. Une modélisation numérique de l'évolution tectono-climatique de l'orogénèse nous montre le contrôle tectonique sur le climat régional des Andes avec l'accélération de l'aridification du versant Ouest à ~15 Ma et au Pliocène, ainsi que le soulèvement tardif et la formation d'un équivalent de l'Altiplano, qui aurait été incisé et vidangé récemment par la rivière du Marañón
Using a multidisciplinary approach, this thesis proposes a new double-verging orogen model for the Northern Central Andes, which can explain the crustal thickening and the current topography interacting with a complex climate. A new structural and stratigraphic synthesis across the forearc and the Western Cordillera revealed the presence of a major western vergence thrust. For the first time, the construction of a balanced cross-section through the whole Northern Central Andes, combined with thermochronological data, illustrates a double verging orogenic model propagating synchronously since ~30 Ma, with a total shortening of 158 km. Numerical modeling of the tectono-climatic evolution of the Andean orogeny shows the acceleration of the aridification in its western flank at ~ 15 Ma and during the Pliocene, as well as the late uplift and the formation of an equivalent of the Altiplano, which would have been incised and emptied recently by the Marañón River

Les orogènes à double vergence sont classiquement définis comme deux prismes critiques opposés (pro et retro) qui évoluent ensemble. Les études récentes montrent que les rétro-prismes et leurs bassins d’avant-pays associés se comportent différemment des pro-prismes. Cependant, ni les facteurs qui mènent un orogène à devenir doublement vergent, ni la relation entre le pro- et rétro-prisme ne sont bien compris. Le but de cette étude est d'améliorer notre connaissance 1) de la relation entre le pro- et le rétro-prisme pendant l'orogénèse, 2) des facteurs contrôlant l'évolution d'un orogène à double vergence, et 3) d’un lien dynamique possible entre le pro- et le rétro-prisme. Répondre à ces questions nécessite une connaissance améliorée de l'évolution d'un orogène à double vergence. Nous nous sommes concentrés sur les Pyrénées Orientales, en raison de la grande quantité de données disponibles. Nous avons effectué une étude de terrain tectono-stratigraphique détaillée à l’est du Massif de Saint Barthelemy et dans l’avant-pays autour de Lavelanet (plaque Européenne). Notre interprétation d’une coupe restaurée intègre une configuration crustale pré-orogenique en tant qu'une marge hyper-amincie. Nous relions l'évolution détaillée du rétro-prisme à celle du pro-prisme (plaque Ibérique), afin de mieux contraindre la dynamique à l'échelle crustale. Nous subdivisons l'évolution des Pyrénées Orientales en quatre phases. La première phase (Crétacé Supérieur) est caractérisée par la fermeture d'un domaine de manteau exhumé entre les plaques et l'inversion synchrone d'un système de rift riche en sel et thermiquement déséquilibré. Le raccourcissement était distribué de façon égale entre les deux marges pendant cette première phase d’inversion. Une phase de quiescence (Paléocène), limitée au rétro-prisme, enregistre la transition entre l'inversion et la phase de collision. La phase de collision principale (Éocène) enregistre le taux de raccourcissement le plus élevé, et était principalement accommodé dans le pro-prisme. Pendant la phase finale (Oligocène) le rétro-prisme était largement inactif et le raccourcissement du pro-prisme a ralenti. Cela démontre que la relation entre le pro- et rétro-prisme change avec le temps. Nous avons utilisé des modèles numériques 2D thermomécaniques à l'échelle lithosphérique pour simuler l'évolution d'un orogène à double vergence s'initie après avec un rift. Nos résultats montrent un modèle évolutif similaire à celui observé dans les Pyrénées Orientales avec une phase d'inversion du rift approximativement symétrique suivie d'une phase de collision asymétrique. L'héritage du rift est essentiel pour permettre le développement d’un orogène à double vergence. Des autres facteurs, comme les processus de surface et la déformation de la couverture, ont un effet significatif sur la structure crustale et la répartition du raccourcissement entre les deux prismes. Un niveau de décollement (sel) à la base de la couverture favorise la formation d'un empilement antiformal d’écailles crustales, similaire à la géométrie observée dans la Zone Axiale des Pyrénées, en formant un prisme à faible pente qui force la déformation crustale à se concentrer dans l'arrière-pays. Enfin, nous montrons que l'évolution des pro- et rétro-prismes est inextricablement liée : des événements ou des conditions d'un côté de l'orogène ont un effet direct sur l'autre côté de l'orogène. Ceci est clairement démontré dans nos modèles par des variations constantes des taux de raccourcissement du pro- et rétro-prisme en réponse à l'accrétion dans le pro-prisme. Le Haut Atlas (Maroc) et Pyrénées peuvent être respectivement considérés comme des exemples d'inversion de rift symétrique et de phases de collision asymétrique ultérieures
The doubly vergent nature of some natural orogens is classically understood as two opposing thrust wedges (pro and retro) that comply with critical taper theory. The evidence that retro-wedges and their associated basins behave differently from their pro-wedge counterparts has been steadily increasing over the past few decades. However, what causes an orogen to become doubly vergent is currently not well understood. Nor is the relationship between the pro- and retro-wedge during the evolution of a doubly vergent orogen. It is the aim of this work to improve our understanding of: 1) how the pro- and retro-wedges relate to each other during the orogenic process, 2) what factors control the evolution of a doubly vergent orogen and 3) a possible link between the pro- and retro-wedge. Answering these questions requires an improved knowledge of the evolution of a doubly vergent orogen. We focussed on the Eastern Pyrenees as a type example of a doubly vergent orogen, due to the large amount of available data. We performed a detailed tectonostratigraphic study of the retro-foreland of the Eastern Pyrenees (European plate), updating the interpretation based on recent insights into its hyperextended rift origins. We link the evolution of the retro-foreland to that of the pro-foreland (Iberian plate) in order to derive insight into the crustal scale dynamics. Based on cross section restoration, reconstructed shortening rates and subsidence analysis, we subdivide the East Pyrenean evolution into four phases. The first (Late Cretaceous) phase is characterised by closure of an exhumed mantle domain between the European and Iberian rifted margins, and simultaneous inversion of a salt-rich, thermally unequilibrated rift system. Shortening was distributed roughly equally between both margins during this early inversion phase. Following inversion, a quiescent phase (Paleocene) was apparently restricted to the retro-foreland. This phase may record the period of transition between inversion and full collision in the Eastern Pyrenees. The main collision phase (Eocene) records the highest shortening rates, which was predominantly accommodated in the pro-wedge. Retro-wedge shortening rates were lower than during the rift inversion phase. During the final phase (Oligocene) the retro-wedge was apparently inactive and shortening of the pro-wedge slowed. This demonstrates that the relationship between the pro- and retro-wedges changes through time. We used lithosphere-scale thermo-mechanical numerical models to simulate the evolution of a doubly vergent orogen. Our results show a similar evolutionary pattern as observed in the Pyrenees: A roughly symmetrical rift inversion phase is followed by an asymmetric collision phase. Rift inheritance was found to be essential for enabling double vergence. Other factors, such as surface processes and thin-skinned deformation, were found to have a significant effect on the crustal structure and strain partitioning between both wedges. A salt décollement layer in the sedimentary cover promotes the formation of a crustal antiformal stack such as observed in the Pyrenees and Alps by forming a wide and low-taper thin-skinned fold-and-thrust belt that forces crustal deformation to focus in the hinterland. Finally, we show that the evolution of the pro- and retro-wedges is inextricably linked: events or conditions on one side of the doubly vergent orogen have an immediate effect on the other side of the orogen. This is clearly demonstrated in our models by constant variations in shortening rates of the pro- and retro-wedge in response to accretion of new pro-wedge thrust sheets. The High Atlas (Morocco) and Pyrenees can be seen as examples of symmetric rift inversion and later asymmetric collision phases, respectively

ABSTRACT Discrimination between gravity slides and tectonic fold-and-thrust belts in the geologic record has long been a challenge, as both have similar layer shortening structures resulting from single bed duplication by thrust faults of outcrop to map scales. Outcrops on uplifted benches within the Miocene to Pliocene Misaki accretionary unit of Miura-Boso accretionary prism, Miura Peninsula, central Japan, preserve good examples of various types of bedding duplication and duplex structures with multiple styles of folds. These provide a foundation for discussion of the processes, mechanisms, and tectonic implications of structure formation in shallow parts of accretionary prisms. Careful observation of 2-D or 3-D and time dimensions of attitudes allows discrimination between formative processes. The structures of gravitational slide origin develop under semi-lithified conditions existing before the sediments are incorporated into the prism at the shallow surfaces of the outward, or on the inward slopes of the trench. They are constrained within the intraformational horizons above bedding-parallel detachment faults and are unconformably covered with the superjacent beds, or are intruded by diapiric, sedimentary sill or dike intrusions associated with liquefaction or fluidization under ductile conditions. The directions of vergence are variable. On the other hand, layer shortening structure formed by tectonic deformation within the accretionary prism are characterized by more constant styles and attitudes, and by strong shear features with cataclastic textures. In these structures, the fault surfaces are oblique to the bedding, and the beds are systematically duplicated (i.e., lacking random styles of slump folds), and they are commonly associated with fault-propagation folds. Gravitational slide bodies may be further deformed at deeper levels in the prism by tectonism. Such deformed rocks with both processes constitute the whole accretionary prism at depth, and later may be deformed, exhumed to shallow levels, and exposed at the surface of the trench slope, where they may experience further deformation. These observations are not only applicable in time and space to large-scale thrust-and-fold belts of accretionary prism orogens, but to small-scale examples. If we know the total 3-D geometry of geologic bodies, including the time and scale of deformational stages, we can discriminate between gravitational slide and tectonic formation of each fold-and-thrust belt at the various scales of occurrence.

ABSTRACT The Bighorn uplift, Wyoming, developed in the Rocky Mountain foreland during the 75–55 Ma Laramide orogeny. It is one of many crystalline-cored uplifts that resulted from low-amplitude, large-wavelength folding of Phanerozoic strata and the basement nonconformity (Great Unconformity) across Wyoming and eastward into the High Plains region, where arch-like structures exist in the subsurface. Results of broadband and passive-active seismic studies by the Bighorn EarthScope project illuminated the deeper crustal structure. The seismic data show that there is substantial Moho relief beneath the surface exposure of the basement arch, with a greater Moho depth west of the Bighorn uplift and shallower Moho depth east of the uplift. A comparable amount of Moho relief is observed for the Wind River uplift, west of the Bighorn range, from a Consortium for Continental Reflection Profiling (COCORP) profile and teleseismic receiver function analysis of EarthScope Transportable Array seismic data. The amplitude and spacing of crystalline-cored uplifts, together with geological and geophysical data, are here examined within the framework of a lithospheric folding model. Lithospheric folding is the concept of low-amplitude, large-wavelength (150–600 km) folds affecting the entire lithosphere; these folds develop in response to an end load that induces a buckling instability. The buckling instability focuses initial fold development, with faults developing subsequently as shortening progresses. Scaled physical models and numerical models that undergo layer-parallel shortening induced by end loads determine that the wavelength of major uplifts in the upper crust occurs at approximately one third the wavelength of folds in the upper mantle for strong lithospheres. This distinction arises because surface uplifts occur where there is distinct curvature upon the Moho, and the vergence of surface uplifts can be synthetic or antithetic to the Moho curvature. In the case of the Bighorn uplift, the surface uplift is antithetic to the Moho curvature, which is likely a consequence of structural inheritance and the influence of a preexisting Proterozoic suture upon the surface uplift. The lithospheric folding model accommodates most of the geological observations and geophysical data for the Bighorn uplift. An alternative model, involving a crustal detachment at the orogen scale, is inconsistent with the absence of subhorizontal seismic reflectors that would arise from a throughgoing, low-angle detachment fault and other regional constraints. We conclude that the Bighorn uplift—and possibly other Laramide arch-like structures—is best understood as a product of lithospheric folding associated with a horizontal end load imposed upon the continental margin to the west.

Recent tectonic reinterpretations of the Late Paleozoic Southwest Laurentian margins recognize widespread Late Paleozoic deformation as a critical component in the boundary region development. Overprinted late Paleozoic structures record repeated shortening events in both northern and southern Nevada, but spatial and temporal data are currently lacking to resolve the evolution of this margin. The Timpahute Range, south-central Nevada, bridges part of the spatial gap between previous detailed studies of Late Paleozoic deformation. The purpose here is to (1) evaluate structures in the area that do not appear to fit with recognized Sevier hinterland structures (the Central Nevada thrust belt [CNTB]) and (2) consider whether these contractional structures may be Late Paleozoic and possibly link, or not, structures to the north and south. New mapping in the Timpahute Range documents four geometrically or kinematically distinct sets of structures: Tempiute Ridge folds, Schofield Pass fault zone (SPFZ), structures of the CNTB, and Cenozoic extensional faults. The first three are interpreted to represent separate shortening events based on cross-cutting relations and differences in orientations of the Tempiute Ridge folds and SPFZ (north [N]), and structures of the CNTB (northwest [NW]). The Tempiute Ridge folds represent the oldest event, D1. These folds are large, trend N and verge east (E). The SPFZ is west (W)-vergent, cuts across the limb of a D1 fold and represents D2. The SPFZ is interpreted to be older than the CNTB structures, D3, based on positions of fault cut offs, and differences in footwall and hangingwall facies. All of the shortening events predate the newly dated 102.9 ± 3.2 Ma Lincoln stock and its contact metamorphic aureole. New and previous correlations suggest that a belt of Permian deformation extends from southeast (SE) California northward at least to the Timpahute Range. The Tempiute Ridge folds and SPFZ have the same distinctive geometries, styles, and kinematics as structures in the Nevada National Security Site. The mountain-size, E-vergent Tempiute Ridge folds and the W-vergent SPFZ correlate to structures associated with the Belted Range thrust and the W-vergent CP thrust, respectively. The Belted Range thrust previously has been correlated southward into the Death Valley region. Thus, convergence created large-amplitude folds and thrusts for ~200 km along strike. Structures of this age are exposed in northern Nevada but are smaller. These new relations fill a data gap and suggest differences in the size and structural style of Permian structures along strike and corresponding variations in the plate boundary configuration.