scholarly journals Development of an intra-carbonate detachment during thrusting: The variable influence of pressure solution on deformation style, Khao Khwang Fold and Thrust Belt, Thailand

Geosphere ◽  
2021 ◽  
Author(s):  
C.K. Morley ◽  
S. Jitmahantakul ◽  
C. von Hagke ◽  
J. Warren ◽  
F. Linares
Keyword(s):  
Dominant Role ◽  
Clay Content ◽  
Line Length ◽  
Pressure Solution ◽  
Structural Development ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Detachment Zone ◽  
Indosinian Orogeny ◽  
Variable Influence

Classic detachment zones in fold and thrust belts are generally defined by a weak lithology (typically salt or shale), often accompanied by high over-pressures. This study describes an atypical detachment that occurs entirely within a relatively strong Permian carbonate lithology, deformed during the Triassic Indosinian orogeny in Thailand under late diagenetic-anchimetamorphic conditions. The key differences between stratigraphic members that led to development of a detachment zone are bedding spacing and clay content. The lower, older, unit is the Khao Yai Member (KYM), which is a dark-gray to black, well-bedded, clay-rich limestone. The upper unit, the Na Phra Lan Member (NPM), comprises more massive, medium- to light-gray, commonly recrystallized limestones and marble. The KYM displays much tighter to even isoclinal, shorter-wavelength folds than the NPM. Pressure solution played a dominant role throughout the structural development—first forming early diagenetic bedding; later tectonic pressure solution preferentially followed this bedding instead of forming axial planar cleavage. The detachment zone between the two members is transitional over tens of meters. Moving up-section, tight to isoclinal folds with steeply inclined axial surfaces are replaced by folds with low-angle axial planes, thrusts, and thrust wedging, bed-parallel shearing, and by pressure solution along bedding-parallel seams (that reduce fold amplitude). In outcrops 100–300 m long, reduction of line-length shortening on folds from >50% to <10% shortening upwards indicates that deformation in the NPM is being accommodated differently from the KYM, probably predominantly by shortening on longer wavelength and/or spacing folds and thrusts, given the low amount of strain observed within the NPM, which excludes widespread layer-parallel thickening

Partitioned tectonic shortening, with emphasis on outcrop-scale folding and flattening, Pindos fold-and-thrust belt, Peloponnese, Greece

2019 ◽  
Vol 56 (11) ◽  
pp. 1181-1201
Author(s):  
George H. Davis
Keyword(s):  
Earth Sciences ◽  
Layer Thickness ◽  
Line Length ◽  
Strain Partitioning ◽  
Progressive Deformation ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Thickness Variations ◽  
Pressure Dissolution ◽  
Transfer Mechanisms

Shortening estimates for fold–thrust belts seldom take into consideration outcrop-scale folding, especially folding related to prethrusting layer-parallel shortening (LPS) and flattening. The Pindos belt of the Peloponnese contains products of Maastrichtian to Paleocene tectonic shortening amenable to assessing strain partitioning. Shortening there initiated with LPS, including outcrop-scale folding, which was superseded by thrusting and macrofolding, with both macromechanisms producing additional outcrop-scale folding and (or) form-modification of initial LPS outcrop-scale folds. Skourlis and Doutsos (2003. International Journal of Earth Sciences, 92: 891–903) concluded that total shortening in this region was 68%, the summation of ∼15% LPS, ∼6% fault-related macrofolding, and ∼47% thrust–slip translation. But even this degree of shortening may be underestimated when outcrop-scale folding is considered. Two limestone-dominated Cretaceous formations and one Cretaceous–Eocene formation of limestone and mudstone display spectacular outcrop-scale folding produced by true multilayer behavior, internal buckling, and disharmonic quasi-flexural folding. Fold forms vary from chevron buckling of multilayers to more rounded folding of true multilayers to disharmonic flattened folds in pseudo-bedded limestone. Ramsay analysis of layer thickness variations across individual disharmonic folds underscores the disharmonic fold forms and intense degree of pressure dissolution generated fold flattening. Line-length shortening for well exposed “packages” of LPS outcrop-scale folding is as high as 30%, but overlying and underlying panels may be more modestly folded and (or) flattened, suggesting that shortening transfer mechanisms may have caused some sections to be bypassed. Achieving more meaningful shortening estimates of the outcrop-scale folding within an entire progressive deformation will require understanding of the partitioning of distribution of this folding regionally.

Pre-folding fracturing in a foredeep environment: insights from the Carseolani Mountains (central Apennines, Italy)

2021 ◽  
pp. 1-17
Author(s):  
Marco Mercuri ◽  
Luca Smeraglia ◽  
Manuel Curzi ◽  
Stefano Tavani ◽  
Roberta Maffucci ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Fracture Pattern ◽  
Pressure Solution ◽  
Fold Axis ◽  
Field Observations ◽  
Central Apennines ◽  
Structural Position ◽  
Deformation Structures ◽  
Thrust Belts ◽  
Belt System

Abstract Bedding-perpendicular joints striking parallel (longitudinal) and perpendicular (transverse) to both the axis of the hosting anticline and the trend of the foredeep-belt system are widely recognized in fold-and-thrust belts. Their occurrence has been commonly attributed to folding-related processes, such as syn-folding outer-arc extension, although they can also be consistent with a pre-folding foredeep-related fracturing stage. Here we report the pre-folding fracture pattern affecting the Pietrasecca Anticline, in the central Apennines (Italy), resolved by a detailed field structural analysis. Field observations, scan-lines and interpretation of virtual outcrops were used to study the intensity, distribution and the orientations of fracture pattern along the anticline. The fracture pattern of the Pietrasecca Anticline consists of longitudinal and transverse joints, oriented approximately perpendicular to bedding, and of a pre-folding longitudinal pressure-solution cleavage set, which is oblique to bedding regardless of the bedding dip. Cross-cutting relationships show that joints predated the development of the pressure-solution cleavage. Furthermore, joint intensity does not relate to the structural position along the anticline. Taken together, these observations suggest that jointing occurred in a foredeep environment before the Pietrasecca Anticline growth. Our work further demonstrates that joints striking parallel and orthogonal to the main fold axis do not necessarily represent syn-folding deformation structures.

The ecology of Sminthurus viridis (L.) (Collembola). I. Processes influencing numbers in pastures in Western Australia

1967 ◽  
Vol 15 (6) ◽  
pp. 1173 ◽  
Author(s):  
MMH Wallace
Keyword(s):  
Western Australia ◽  
Dominant Role ◽  
Clay Content ◽  
Early Death ◽  
Factors Affecting ◽  
Dead Bodies ◽  
Fat Bodies ◽  
Set Up ◽  
Content Support ◽  
Type 3

The changes in numbers of Sminthurus viridis (Collembola: Sminthuridae) in pastures in Western Australia were studied for 9 years on one site and for shorter periods on other sites. Five factors affecting numbers are described: (1) weather, (2) soil type (3) botanical composition of the pasture, (4) predation by Bdellodes lapidaria (Acarina: Bdellidae), and (5) eating of dead bodies by newly hatched nymphs. Weather is generally favourable for the active stages during autumn, winter, and spring. In the summer, the species is maintained by aestivating eggs. Dry periods during the winter months sometimes cause high mortalities. Soils containing a high silt-plus-clay content support higher numbers due mainly to increased oviposition. Flea densities increase more rapidly where there is a high proportion of broad-leaved plants, such as clover and capeweed in the pasture. Grassy areas are not favoured. Predation by B. lapidaria effectively reduces numbers. The presence of more than 20 B. lapidaria per square metre early in the winter prevents any outbreak of fleas later in the season. Bdellodes lapidaria numbers increase in response to an increase in flea numbers. An irregular predator-prey cycle is set up in this way. Density-induced mortality, resulting from the newly hatched nymphs eating the bodies of recently dead fleas, plays a dominant role at high densities. This process operates continuously though at decreased intensity at lower densities. When newly hatched nymphs feed upon dead nymphs and adults they ingest materials which cause early death. Sometimes this may lead to a dramatic collapse of the population. Fleas from high-density populations usually contain large quantities of uric acid in their "fat-bodies". It is suggested that death of the mature fleas at high densities is hastened through the storage of excessive amounts of waste material. Death of the young nymphs feeding upon the dead bodies may be brought about by the ingestion of these waste materials, although this has yet to be proven.

Anisotropy of magnetic susceptibility as strain indicator in a fold-and-thrust belt sandbox model above décollements with frictional contrast

2020 ◽  
Author(s):  
Thorben Schöfisch ◽  
Hemin Koyi ◽  
Bjarne Almqvist
Keyword(s):  
Magnetic Susceptibility ◽  
Complex Structure ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Low Friction ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Analogue Models ◽  
The Individual ◽  
Strain Indicator

<p>Magnetic fabric is used as strain indicator to provide further insights into different tectonic settings. Applying anisotropy of magnetic susceptibility (AMS) analysis on analogue models has shown to be a useful approach to understand details of deformation. Here we use this technique on shortened sandbox models to illustrate the relationship between rotation of grains and the influence of décollement friction in fold-and-thrust belts. Layers of sand were scraped to a thickness of 2.5 cm on top of high-friction sandpaper on one side and on low-friction fibreglass on the other side of the sandbox model. After shortening the model by 26%, samples were taken at the surface and at depth for measuring AMS. During shortening, above the high-friction décollement, a stack of imbricates was formed, which shows distinct clustering of the main principal magnetic susceptibility axes (k1 ≥ k2 ≥ k3) around the dip of the forethrusts. In contrast, AMS data above the low-friction décollement show a more heterogeneous AMS pattern due to complex structure development with box folds and fault bending. In general, the magnetic fabric can be differentiated between the initial model fabric in the foreland and a tectonic overprint within the hinterland. The AMS analysis show that strain increases with the development of structures towards the hinterland and additionally with depth, but differs between the two frictional décollements. At the transition zone between the two different frictional environments, a deflection zone developed where the trace of thrusts change trend causing additional rotation of sand grains within this zone perpendicular to main shortening direction, as reflected by the orientation of the k1 and k3 axes. Overall, the orientation of the AMS axes and shape of anisotropy depend on the structure geometry and movement, which are determined by the friction of the individual décollement beneath. Consequently, AMS in models indicates and describes the development of structures and reflects strain above different basal friction.</p>

The Barreme Basin and the Gevaudan diapir - an example of the interplay between compressional tectonics and salt diapirism

2020 ◽  
Author(s):  
Rod Graham ◽  
Adam Csicsek
Keyword(s):  
Foreland Basin ◽  
Finite Geometry ◽  
Driving Mechanism ◽  
Salt Diapirism ◽  
Sedimentary Evolution ◽  
Tectonic History ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
History Of

<p><strong>The Barreme Basin and the Gevaudan diapir - an example of the interplay between compressional tectonics and salt diapirism </strong></p><p><strong> </strong></p><p><strong>Adam Csicsek and Rod Graham</strong></p><p>Imperial College London</p><p><strong> </strong></p><p>Our understanding of the role of salt diapirism in determining the finite geometry of fold and thrust belts has grown apace in the last few years, but the interplay between the two remains a significant problem for structural interpretation. The Gevaudan diapir in the fold and thrust belt of the sub-Alpine chain of Haute Provence is well known and has been documented by numerous eminent alpine structural geologists. Graciansky, Dardot, Mascle, Gidon and Lickorish and Ford have all described and illustrated the geometry and evolution of the structure, and Lickorish and Ford’s interpretation is figured as an example of  diapirism  in a compressional setting by Jackson and Hudec in their text on salt tectonics. We review these various interpretations and present another.</p><p>The differences between the various interpretations say much about the complex interplay of salt diapirism and thin-skinned thrusting and have profound implications for the way we interpret the tectonic and sedimentary evolution of the Barreme basin which lies adjacent to the diapir</p><p>The Barreme basin is a thrust-top fragment of the Provencal foreland basin and has been described in detail from both sedimentological (e.g. Evans and Elliott, 1999) and structural (e.g. Antoni and Meckel, 1997) points of view. Here we make the case that it is also a salt related minibasin - a secondary minibasin developed on a now welded allochthonous Middle Cretaceous salt canopy.  We believe that within the basin it is possible to interpret successive depocentres which may record progressive salt withdrawal. We argue that though thrust loading must be the fundamental driving mechanism responsible for salt movement late in the tectonic history of the region, thrusting has not done much more than modify existing salt related geometry.    </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
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