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.

Coeval sedimentation, magmatism, and fold-thrust belt development in the Trans-Hudson Orogen: geochronological evidence from the Wekusko Lake area, Manitoba, Canada

1999 ◽  
Vol 36 (2) ◽  
pp. 293-312 ◽  
Author(s):  
Kevin M Ansdell ◽  
Karen A Connors ◽  
Richard A Stern ◽  
Stephen B Lucas
Keyword(s):  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Lake Area ◽  
Thrust Belt ◽  
Fold And Thrust Belt ◽  
Minimum Age ◽  
Flin Flon ◽  
Felsic Volcanic

Lithological and structural mapping in the east Wekusko Lake area of the Flin Flon Belt, Trans-Hudson Orogen, suggested an intimate relationship between magmatism, fluvial sedimentation, and initiation of fold and thrust belt deformation. Conventional U-Pb geochronology of volcanic rocks in fault-bounded assemblages provides a minimum age of 1876 ± 2 Ma for McCafferty Liftover back-arc basalts, and ages of between 1833 and 1836 Ma for the Herb Lake volcanic rocks. A rhyolite which unconformably overlies Western Missi Group fluvial sedimentary rocks has complex zircon systematics. This rock may be as old as about 1856 Ma or as young as 1830 Ma. The sedimentary rocks overlying this rhyolite are locally intercalated with 1834 Ma felsic volcanic rocks, and yield sensitive high resolution ion microprobe (SHRIMP) U-Pb and Pb-evaporation detrital zircon ages ranging from 1834 to 2004 Ma. The Eastern Missi Group is cut by an 1826 ± 4 Ma felsic dyke, and contains 1832-1911 Ma detrital zircons. The dominant source for detritus in the Missi Group was the Flin Flon accretionary collage and associated successor arc rocks. The fluvial sedimentary rocks and the Herb Lake volcanic rocks were essentially coeval, and were then incorporated into a southwest-directed fold and thrust belt which was initiated at about 1840 Ma and active until at least peak regional metamorphism.

scholarly journals Thrust tectonics in the central part of the External Hellenides, the case of the Gavrovo thrust

2017 ◽  
Vol 47 (2) ◽  
pp. 540
Author(s):  
E. Kamberis ◽  
S. Sotiropoulos ◽  
F. Marnelis ◽  
N. Rigakis
Keyword(s):  
Structural Deformation ◽  
Thrust Belt ◽  
Seismic Profiles ◽  
The West ◽  
Thrust Faulting ◽  
Fold And Thrust Belt ◽  
Thrust Tectonics ◽  
Extensional Faulting ◽  
Surface Geology ◽  
Flat Geometry

Thrust faulting plays an important role in the structural deformation of Gavrovo and Ionian zones in the central part of the ‘External Hellenides’ fold-and-thrust belt. The Skolis mountain in NW Peloponnese as well as the Varassova and Klokova mountains in Etoloakarnania are representative cases of ramp anticlines associated with the Gavrovo thrust. Surface geology, stratigraphic data and interpretation of seismic profiles indicate that it is a crustal-scale thrust acted throughout the Oligocene time. It is characterized by a ramp-flat geometry and significant displacement (greater than 10 km). Out of sequence thrust segmentation is inferred in south Etoloakarnania area. Down flexure and extensional faulting in the Ionian zone facilitated the thrust propagation to the west. The thrust emplacement triggered halokenetic movement of the Triassic evaporites in the Ionian zone as well as diapirisms that were developed in a later stage in the vicinity of the Skolis mountain.

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.

Mid-crustal detachment beneath southern Timor-Leste: seismic evidence for Australian basement in the Timor collision complex (and implications for prospectivity)

2021 ◽  
Author(s):  
T. R. Charlton
Keyword(s):  
Seismic Data ◽  
Passive Margin ◽  
Petroleum Exploration ◽  
Seismic Survey ◽  
Normal Faults ◽  
Thrust Belt ◽  
Collision Complex ◽  
Fold And Thrust Belt ◽  
Timor Leste ◽  
Seismic Sections

Seismic data originally acquired over SW Timor-Leste in 1994 shows two consistent seismic reflectors mappable across the study area. The shallower ‘red’ reflector (0.4-1s twt) deepens southward, although with a block-faulted morphology. The normal faults cutting the red marker tend to merge downward into the deeper ‘blue’ marker horizon (0.5-2.8s twt), which also deepens southward. Drilling intersections in the Matai petroleum exploration wells demonstrate that the red marker horizon corresponds to the top of metamorphic basement (Lolotoi Complex), while the blue marker horizon has the geometry of a mid-crustal extensional detachment. We see no indications for thrusting on the seismic sections below the red marker horizon, consistent with studies of the Lolotoi Complex at outcrop. However, surficial geology over much of the seismic survey area comprises a thin-skinned fold and thrust belt, established in 8 wells to overlie the Lolotoi Complex. We interpret the fold and thrust belt as the primary expression of Neogene arc-continent collisional orogeny, while the Lolotoi Complex represents Australian continental basement underthrust beneath the collision complex. In the seismic data the basal décollement to the thrust belt dips southward beneath the synorogenic Suai Basin on the south coast of Timor, and presumably continues southward beneath the offshore fold and thrust belt, linking into the northward-dipping décollement that emerges at the Timor Trough deformation front. The same seismic dataset has been interpreted by Bucknill et al. (2019) in terms of emplacement of an Asian allochthon on top of an imbricated Australian passive margin succession. These authors further interpreted a subthrust anticlinal exploration prospect beneath the allochthon, which Timor Resources plan to drill in 2021. This well (Lafaek) will have enormous significance not only commercially, but potentially also in resolving the long-standing allochthon controversy in Timor: i.e., does the Lolotoi Complex represent ‘Australian’ or ‘Asian’ basement?

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