Sheath fold development with viscosity contrast: Analogue experiments in bulk simple shear

Marques, F.O.; Guerreiro, Susana; Fernandes, Ana Raquel

doi:10.1016/j.jsg.2008.07.001

Cited by 31 publications

(11 citation statements)

References 17 publications

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“…Another very similar example of coeval asymmetric folding and boudinage was observed in deformed quartz veins in a major shear zone by Pamplona et al (2014). The asymmetric folds in the amphibolite are generally in good correspondence with non-coaxial folds forming in simple shear and general strain regimes Holdsworth, 2006, 2007;Cobbold and Quinquis, 1980;Marques et al, 2008;Ridley, 1986). Folds and domino boudins both suggest non-coaxial deformation in the study area.…”

Section: Foldsmentioning

confidence: 61%

Multiphase boudinage: a case study of amphibolites in marble in the Naxos migmatite core

2018

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Abstract. In multiply deformed terrains multiphase boudinage is common, but identification and analysis of these is difficult. Here we present an analysis of multiphase boudinage and fold structures in deformed amphibolite layers in marble from the migmatitic centre of the Naxos metamorphic core complex. Overprinting between multiple boudinage generations is shown in exceptional 3-D outcrop. We identify five generations of boudinage, reflecting the transition from high-strain high-temperature ductile deformation to medium-to low-strain brittle boudins formed during cooling and exhumation. All boudin generations indicate E-W horizontal shortening and variable direction of bedding parallel extension, evolving from subvertical extension in the earliest boudins to subhorizontal N-S extension during exhumation. Two phases of E-W shortening can be inferred, the first associated with lower crustal synmigmatic convergent flow and the second associated with exhumation and N-S extension, possibly related to movement of the North Anatolian Fault.

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Section: Foldsmentioning

confidence: 61%

Multiphase boudinage: a case study of amphibolites in marble in the Naxos migmatite core

2018

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“…Passchier and Sokoutis, 1993), folding (e.g. Abbassi and Mancktelow, 1992;Rosas et al, 2002;Marques et al, 2008;Dell'Ertole and Schellart, 2013;Ramón et al, 2013), and boudinage (e.g. Zulauf et al, 2011;Marques et al, 2012).…”

Section: External Approachmentioning

confidence: 99%

A review of analogue modelling of geodynamic processes: Approaches, scaling, materials and quantification, with an application to subduction experiments

Schellart

Strak

2016

Journal of Geodynamics

132

105

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a b s t r a c tWe present a review of the analogue modelling method, which has been used for 200 years, and continues to be used, to investigate geological phenomena and geodynamic processes. We particularly focus on the following four components: (1) the different fundamental modelling approaches that exist in analogue modelling; (2) the scaling theory and scaling of topography; (3) the different materials and rheologies that are used to simulate the complex behaviour of rocks; and (4) a range of recording techniques that are used for qualitative and quantitative analyses and interpretations of analogue models. Furthermore, we apply these four components to laboratory-based subduction models and describe some of the issues at hand with modelling such systems. Over the last 200 years, a wide variety of analogue materials have been used with different rheologies, including viscous materials (e.g. syrups, silicones, water), brittle materials (e.g. granular materials such as sand, microspheres and sugar), plastic materials (e.g. plasticine), viscoplastic materials (e.g. paraffin, waxes, petrolatum) and visco-elasto-plastic materials (e.g. hydrocarbon compounds and gelatins). These materials have been used in many different set-ups to study processes from the microscale, such as porphyroclast rotation, to the mantle scale, such as subduction and mantle convection. Despite the wide variety of modelling materials and great diversity in model set-ups and processes investigated, all laboratory experiments can be classified into one of three different categories based on three fundamental modelling approaches that have been used in analogue modelling: (1) The external approach, (2) the combined (external + internal) approach, and (3) the internal approach. In the external approach and combined approach, energy is added to the experimental system through the external application of a velocity, temperature gradient or a material influx (or a combination thereof), and so the system is open. In the external approach, all deformation in the system is driven by the externally imposed condition, while in the combined approach, part of the deformation is driven by buoyancy forces internal to the system. In the internal approach, all deformation is driven by buoyancy forces internal to the system and so the system is closed and no energy is added during an experimental run. In the combined approach, the externally imposed force or added energy is generally not quantified nor compared to the internal buoyancy force or potential energy of the system, and so it is not known if these experiments are properly scaled with respect to nature. The scaling theory requires that analogue models are geometrically, kinematically and dynamically similar to the natural prototype. Direct scaling of topography in laboratory models indicates that it is often significantly exaggerated. This can be ascribed to (1) The lack of isostatic compensation, which causes topography to be too high.(2) The lack of erosion, which causes topography to be too high....

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“…However, Rosas et al. (2002) and Marques et al. (2008) have shown with analogue experiments that a relatively low strain of γ < 5 is sufficient to produce sheath folds.…”

Section: Discussionmentioning

confidence: 99%

“…Sheath folds are cone‐shaped structures with an opening angle of less than 90° (Ramsay, 1979; Skjernaa, 1989; Marques et al. , 2008).…”

Section: Introductionmentioning

confidence: 99%

Sheath fold formation around slip surfaces

2012

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Terra Nova, 24, 417–421, 2012 Abstract Sheath folds are associated with shear zones and have been used as high strain indicators. We present results from a three‐dimensional analytical study showing that the flow perturbation around a planar weakness acting as a slip surface, in simple shear leads to the formation of sheath folds at low shear strain. Closed traces of marker layers are exhibited in cross‐sections cut perpendicular to the shear direction in the vicinity of the slip surface tip. In cross‐sections cut parallel to the shear direction and normal to the shear plane, flanking folds are observed. Our model captures the first‐order observations of natural sheath folds, such as diversity of shapes and multiple eye‐structures. Natural equivalents of the planar weaknesses that we model include fractures, veins and rheologically weak layers. Flow perturbation around these zones of weaknesses is proposed as an alternative mechanism of sheath fold formation, which emphasizes the coeval operation of brittle and ductile processes in shear zones.

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Sheath fold development with viscosity contrast: Analogue experiments in bulk simple shear

Cited by 31 publications

References 17 publications

Multiphase boudinage: a case study of amphibolites in marble in the Naxos migmatite core

Multiphase boudinage: a case study of amphibolites in marble in the Naxos migmatite core

A review of analogue modelling of geodynamic processes: Approaches, scaling, materials and quantification, with an application to subduction experiments

Sheath fold formation around slip surfaces

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