scholarly journals How the presence of a salt décollement in the sedimentary cover influences the behavior of subsalt thrusts in fold-and-thrust belts

2017 ◽  
Vol 188 (6) ◽  
pp. 37 ◽  
Author(s):  
Bruno C. Vendeville ◽  
Tang Pengcheng ◽  
Fabien Graveleau ◽  
Huang Shaoying ◽  
Xin Wang
Keyword(s):  
Sedimentary Cover ◽  
Critical Surface ◽  
Thrust Belt ◽  
Surface Slope ◽  
Deformation Front ◽  
Low Viscosity ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Analogue Experiments ◽  
Free Domain

We conducted a series of analogue experiments on shortening of a brittle cover (dry sand) above a deep, thin, frictional detachment (glass microbeads). In some experiments, the cover was homogeneous, entirely brittle. In others, there was a thin viscous silicone layer (representing salt) embedded at mid height into the cover, and initially located in the foreland of the fold-and-thrust belt. Our goal was to determine whether or not the presence of such a décollement in the cover could have an impact on the mechanics and kinematics of the underlying subsalt thrusts. Results confirm that, once the front of the foldbelt reached the hinterland salt pinch out, the kinematics of the deeper belt changed drastically: its front stopped propagating forward, and most of the subsequent shortening was accommodated by a larger-than-normal slip along the foremost and youngest deep thrust, while, above the salt décollement, the deformation front propagated very fast, creating a very low surface slope. We hypothesize that it is the gentle sub-critical surface slope associated with rocksalt’s low viscosity that prevents the build-up of an overall surface slope steep enough to allow the underlying, deep foldbelt to continue propagating forward. Finally, one experiment in which only one half of the width of the model comprised an interbedded viscous décollement has shown that the kinematics of the deep thrust was affected even in the adjacent salt-free domain.

The crustal structure in the transition from the on land fold-and-thrust belt to the offshore accretionary prism in the Taiwan arc-continent collision

2020 ◽  
Author(s):  
Joaquina Alvarez-Marrón ◽  
Dennis Brown ◽  
Juan Alcalde ◽  
Ignacio Marzán ◽  
Hao Kuo-Chen
Keyword(s):  
Continental Margin ◽  
Seismic Tomography ◽  
Accretionary Prism ◽  
Crustal Thickening ◽  
Accretionary Wedge ◽  
Thrust Belt ◽  
Deformation Front ◽  
Coast Line ◽  
Transition Area ◽  
Fold And Thrust Belt

<p>The region of Taiwan is undergoing active, oblique arc-continent colision between the Luzon Arc on the Philippine Sea Plate and the continental margin of Eurasia. The Fold-and-Thrust Belt (FTB) in Taiwan passes southwards into a submarine accretionary wedge at the Manila subduction zone. The aim of this contribution is to examine how an on land FTB changes into a marine accretionary prism in the context of an oblique arc-continent collision. The Miocene pre-orogenic sediments of the continental margin are widespread in the FTB ca. 23° latitude while the offshore wedge is built up dominantly by Pliocene to recent syn-orogenic sediments. In the transition area from the marine accretionary wedge ca. 21° latitude to the on land FTB, the thrust wedge is climbing up the slope of the Eurasian continental margin. The deformation front is at sea floor depth of ca. 4 km in the south to less than 1 km as it reaches the coast line. Here we use the island surface geology, marine reflection seismic profiles, and seismic tomography models to construct contour maps of the basal thrust and the depth to the Moho across a transition area from near 23° to near 21° latitude. In this zone, the deformation front draws a convex curvature as the wedge widens from ca. 50 in the north and south, to more than 130 km near 22° latitude. The basal thrust surface shows a scoop shape as its dip changes from southeast near the coast line to east southward. The basal thrust reaches over 7 km deep beneath the rear of the FTB before ramping into de basement and merging into the Chaochou fault at 10 km depth. Offshore, it shows a gentler dip from 7 km to c. 10 km depth before getting steeper towards the east below the Hengchung Ridge. The basal cuts laterally along-strike through the margin’s sedimentary cover to incorporate thicker Miocene pre-orogenic sediments onto its hanging wall as it passes from the offshore wedge to the on land FTB.</p><p>In the offshore area, the Moho (we use a Vp proxy of 7.5 km/s extracted from the seismic tomography) shallows southeastward, from near 25 km depth below the shelf slope break to less than 17 km depth below the offshore wedge near 21.5° latitude before it starts to deep east towards beneath the Taiwan coast. The Moho dips northeast from near 25 km depth below the coast near Kaohsiung, to near 40 depth below the rear of the FTB at 23.5°, latitude. This complex morphology of the Moho may be related to the changes in crustal thickness and the obliquity of the collision. Because of this, crustal thickening is less pronounced beneath southern Taiwan where the thinner part of the margin is colliding with the arc.</p><p>This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency from the Ministry of Science Innovation and Universities of Spain.</p>

scholarly journals Control of 3D tectonic inheritance on fold-and-thrust belts: insights from 3D numerical models and application to the Helvetic nappe system

2019 ◽  
Author(s):  
Richard Spitz ◽  
Arthur Bauville ◽  
Jean-Luc Epard ◽  
Boris J. P. Kaus ◽  
Anton A. Popov ◽  
...  
Keyword(s):  
3D Model ◽  
Swiss Alps ◽  
Thrust Belt ◽  
First Order ◽  
Tectonic Inheritance ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Model Configuration ◽  
Fold And Thrust Belts ◽  
Half Graben

Abstract. Fold-and-thrust belts and associated tectonic nappes are common in orogenic regions. They exhibit a wide variety of geometries and often a considerable along-strike variation. However, the mechanics of fold-and-thrust belt formation and the control of the initial geological configuration on this formation are still incompletely understood. Here, we apply three-dimensional (3D) thermo-mechanical numerical simulations of the shortening of the upper crustal region of a passive margin to investigate the control of 3D laterally variable inherited structures on the fold-and-thrust belt evolution and associated nappe formation. We consider tectonic inheritance by applying an initial model configuration with horst and graben structures having laterally variable geometry and with sedimentary layers having different mechanical strength. We use a visco-plastic rheology with temperature dependent flow laws and a Drucker-Prager yield criterion. The models show the folding, detachment and horizontal displacement of sedimentary units, which resemble structures of fold and thrust nappes. The models further show the stacking of nappes. The detachment of nappe-like structures is controlled by the initial basement and sedimentary layer geometry. Significant horizontal transport is facilitated by weak sedimentary units below these nappes. The initial half-graben geometry has a strong impact on the basement and sediment deformation. Generally, deeper half-grabens generate thicker nappes and stronger deformation of the neighboring horst while shallower half-grabens generate thinner nappes and less deformation in the horst. Horizontally continuous strong sediment layers, which are not restricted to inital graben structures, cause detachment folding and not overthrusting. The amplitude of the detachment folds is controlled by the underlying graben geometry. A mechanically weaker basement favors the formation of fold nappes while stronger basement favors thrust sheets. The applied model configuration is motivated by the application of the 3D model to the Helvetic nappe system of the French-Swiss Alps. Our model is able to reproduce several first-order structural features of this nappe system, namely (i) closure of a half-graben and associated formation of the Morcles and Doldenhorn nappes, (ii) the overthrusting of a nappe resembling the Wildhorn and Glarus nappes and (iii) the formation of a nappe pile resembling the Helvetic nappes resting above the Infrahelvetic complex. Furthermore, the finite strain pattern, temperature distribution and timing of the 3D model is in broad agreement with data from the Helvetic nappe system. Our model, hence, provides a first-order 3D reconstruction of the tectonic evolution of the Helvetic nappe system based on thermo-mechanical deformation processes.

From Fold-and-Thrust Belts on Salt to Salt Deposition and Tectonics in a Fold-and-Thrust Belt, Sivas, Turkey

2015 ◽  
Author(s):  
Jean-Claude Ringenbach* ◽  
Etienne Legeay ◽  
Charlie Kergaravat ◽  
Jean-Paul Callot
Keyword(s):  
Thrust Belt ◽  
Salt Deposition ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Fold And Thrust Belts

The Role of Isostasy in the Evolution of Thin-Skinned Fold and Thrust Belt

2021 ◽  
Author(s):  
Youseph Ibrahim ◽  
Patrice Rey
Keyword(s):  
Numerical Experiments ◽  
Basal Layer ◽  
Structural Evolution ◽  
Geological Model ◽  
Thrust Belt ◽  
Isostatic Adjustment ◽  
Flexural Response ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Fold And Thrust Belts

<p>The stacking of thrust sheets and mass transfer of sediment during fold and thrust belt accretion imposes a load on the basement and underlying mantle. This load induces an isostatic adjustment through a flexural response, which may also contribute to the overall architecture of the fold and thrust belt. Whereas plate kinematics imposes its tempo to evolving fold and thrust belts, the rheology of the mantle controls the tempo of the isostatic flexure. Using two-dimensional high-resolution numerical experiments, we explore how the interplay between the tectonic compressional rate and the isostatic flexural rate influences the structural evolution and final architecture of fold and thrust belts. </p><p>We run a suite of numerical experiments using the well-tested code Underworld. Our geological model is mapped over a 42 km by 16 km numerical grid, with a cell resolution of 80 m. The geological model consists from top to bottom of  ‘sticky air’, 4 km of sediment that alternates in competence at 500 m intervals, a 3 km thick basement, and a basal layer which - in combination with a basal kinematic boundary condition - controls the amount of isostatic flexure. Materials have a mechanical behavior that results from elasto-visco-plastic rheology. The pressure at the base of the model is held constant, and the vertical velocity is updated at each timestep. The amount of material entering or exiting the model at each point along the base scales with the density of the basal layer, which is used to control the isostatic rate. Sedimentation and erosion are self-consistent through mechanical erosion and a hillslope diffusion law. Our models show that as the ratio between tectonic and flexural rates decreases (i.e. flexure gets faster), fold and thrust belts become narrower, lower in elevation, and structurally more complex. We compare these results with natural analogs including the Cordilleran and Jura fold and thrust belts.</p>

scholarly journals Mechanical Influence of Inherited Folds in Thrust Development: A Case Study from the Variscan Fold-and-Thrust Belt in SW Sardinia (Italy)

Geosciences ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 276
Author(s):  
Fabrizio Cocco ◽  
Antonio Funedda
Keyword(s):  
Ductile Deformation ◽  
Mechanical Anisotropy ◽  
Thrust Belt ◽  
External Zone ◽  
Layer Cake ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Vertical Variations ◽  
Stratigraphic Succession

Fold-and-thrust belts have a high variability of structural styles, whose investigation provides continuous updates of the predictive models that try to better approximate the geometries recognized in the field. The majority of studies are focused on the geometry and development of folds and thrust surfaces and the amount of displacement, taking into account the role played by the involved stratigraphic succession assumed as a layer cake. We present a case study from the external zone of the Variscan fold-and-thrust belt in SW Sardinia, where it was possible to investigate the lateral and vertical variations of the mechanical properties of the involved succession, how they related to previous folding, control thrust geometry, and kinematics. In this case, the superposition of two fold systems acted as a buttress that induced extensive back-thrusting. We found that there is a close connection between the attitude of the bedding and the geometry of back thrust surfaces, shear strength during thrust propagation, and variation in the shortening amount, depending on which part of the folds were cut across. The folding-related mechanical anisotropy also seems to have induced a ductile deformation in the footwall of back-thrusts. Although the case study considers the development of back-thrust, the relations between thrust and not-layer cake geometries could also be applied to fore-thrust development.

The Amer Belt: remnant of an Aphebian foreland fold and thrust belt

1986 ◽  
Vol 23 (12) ◽  
pp. 2012-2023 ◽  
Author(s):  
Judith G. Patterson
Keyword(s):  
Normal Faults ◽  
Lake Area ◽  
Thrust Belt ◽  
East Side ◽  
Progressive Deformation ◽  
The West ◽  
Polyphase Deformation ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Stratigraphic Model

Aphebian supracrustal sequences occur as outliers throughout the northwestern portion of the Churchill Structural Province of the Canadian Shield. In the Amer Lake area, medium- to high-grade, polydeformed Archean rocks are unconformably overlain by the Amer supracrustal sequence, which comprises quartzite, carbonate, mafic volcanic, and meta-arkose and meta-pelitic units. This supracrustal sequence is interpreted as having been deposited under miogeoclinal conditions, transitional to exogeoclinal.The Amer sequence crops out in a broad, west-southwest-plunging synclinorium and contains evidence of polyphase deformation that includes the following: (1) Folds plunging gently to the west-southwest and west-southwest-striking thrust faults, transected by oblique tear faults. Thrust vergence is northerly to northwesterly, onto the Archean craton. Because of the orientation of the synclinorium, there is a down plunge view of the thrusts at the eastern end of the belt. (2) Younger, localized cross folds, probably representative of progressive deformation. (3) Late, northwest-trending normal faults, with east side down.The stratigraphic elements and family of structures in the Amer Belt are similar to those found in the foreland fold and thrust belts of major Phanerozoic and Proterozoic orogens. The Amer Belt is interpreted as being a remnant of a once extensive foreland fold and thrust belt.Some workers have considered the northwestern Churchill Structural Province a large cratonic foreland of the Trans-Hudson Orogen. However, remnants of a foreland fold and thrust belt, a major batholithic complex, and profound geophysical breaks interpreted as being possible sutures are incorporated into a new tectono-stratigraphic model that proposes that a cryptic Aphebian orogen exists in the northwestern Churchill Structural Province.

scholarly journals The Saint-Ursanne earthquakes of 2000 revisited: evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt

2022 ◽  
Vol 115 (1) ◽  
Author(s):  
Federica Lanza ◽  
Tobias Diehl ◽  
Nicholas Deichmann ◽  
Toni Kraft ◽  
Christophe Nussbaum ◽  
...  
Keyword(s):  
Template Matching ◽  
Sedimentary Cover ◽  
Mechanism Analysis ◽  
Thrust Belt ◽  
Northern Switzerland ◽  
Thrust Faulting ◽  
The North ◽  
Fold And Thrust Belt ◽  
New Findings ◽  
Mont Terri

AbstractThe interpretation of seismotectonic processes within the uppermost few kilometers of the Earth’s crust has proven challenging due to the often significant uncertainties in hypocenter locations and focal mechanisms of shallow seismicity. Here, we revisit the shallow seismic sequence of Saint-Ursanne of March and April 2000 and apply advanced seismological analyses to reduce these uncertainties. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which is currently evaluated as a possible site for the development of a deep geothermal project. Template matching analysis for the period 2000–2021, including data from mini arrays installed in the region since 2014, suggests that the source of the 2000 sequence has not been persistently active ever since. Forward modelling of synthetic waveforms points to a very shallow source, between 0 and 1 km depth, and the focal mechanism analysis indicates a low-angle, NNW-dipping, thrust mechanism. These results combined with geological data suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the Saint-Ursanne sequence. Together with two other more recent shallow thrust faulting earthquakes near Grenchen and Neuchâtel in the north-central portion of the Jura fold-and-thrust belt (FTB), these new findings provide new insights into the present-day seismotectonic processes of the Jura FTB of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely < 0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement.

scholarly journals Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt

Geosciences ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 254
Author(s):  
Ali Yaghoubi ◽  
SeyedBijan Mahbaz ◽  
Maurice B. Dusseault ◽  
Yuri Leonenko
Keyword(s):  
Stress State ◽  
Sedimentary Cover ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fault System ◽  
Reverse Fault ◽  
Thrust Belt ◽  
Dezful Embayment ◽  
State Of Stress ◽  
Fold And Thrust Belt

This study focuses on determining the orientation and constraining the magnitude of present-day stresses in the Dezful Embayment in Iran’s Zagros Fold and Thrust Belt. Two datasets are used: the first includes petrophysical data from 25 wells (3 to 4 km deep), and the second contains 108 earthquake focal mechanisms, mostly occurring in blind active basement faults (5 to 20 km deep). Formal stress inversion analysis of the focal mechanisms demonstrates that there is currently a compressional stress state ( in the basement. The seismologically determined SHmax direction is 37° ± 10°, nearly perpendicular to the strike of most faults in the region. However, borehole geomechanics analysis using rock strength and drilling evidence leads to the counterintuitive result that the shallow state of stress is a normal/strike-slip regime. These results are consistent with the low seismicity level in the sedimentary cover in the Dezful Embayment, and may be evidence of stress decoupling due to the existence of salt layers. The stress state situation in the field was used to identify the optimally oriented fault planes and the fault friction coefficient. This finding also aligns with the prediction Coulomb faulting theory in that the N-S strike-slip basement Kazerun Fault System has an unfavorable orientation for slip in a reverse fault regime with an average SW-NE SHmax orientation. These results are useful for determining the origin of seismic activity in the basin and better assessing fault-associated seismic hazards in the area.

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