Strain analysis and rheology contrasts in polymictic conglomerates: An example from the Seine metaconglomerates, Superior Province, Canada

Czeck, Dyanna M.; Fissler, Darlene A.; Horsman, Eric; Tikoff, Basil

doi:10.1016/j.jsg.2009.08.004

Cited by 19 publications

(6 citation statements)

References 54 publications

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“…Effectively passive and deformable pebbles in deformed conglomerates are the most important and thus most widely investigated, as their shape fabrics can be used for strain analysis and rheology studies (e.g., Gay, 1968;Lisle et al, 1985;Treagus and Treagus, 2002;Czeck et al, 2009). In our simulations, for a given Rη, an increasing C enhances the aspect ratios (R f ) of pebbles but reduces their rotation (Figs.…”

Section: Pebble Deformationmentioning

confidence: 91%

High-strain deformation of conglomerates: Numerical modelling, strain analysis, and an example from the Wutai Mountains, North China Craton

Ran

Bons

Wang

et al. 2018

Journal of Structural Geology

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Conglomerates have been widely used to investigate deformation history and rheology, strain, vorticity and viscosity. Previous studies reveal that several factors, such as pebble shapes and concentrations, as well as material properties, affect conglomerate deformation. However, how pebble concentration and interaction between pebbles affect deformation is not understood very well. We use the 2D numerical modelling platform ELLE coupled to the full field crystal visco-plasticity code (VPFFT) to simulate the deformation of conglomerates with various viscosity contrasts between pebbles and matrix and different pebble concentrations, with both linear (stress exponent n=1) and power-law (n=3) viscous rheologies, under simple shear conditions up to a shear strain of ten. Pebbles can behave as effectively passive, deformable or effectively rigid. An increase in pebble concentrations/viscosity contrasts enhances pebble deformation, but reduces their rotation. A mean aspect ratio (R f ) -orientation (φ) plot is proposed to gain an estimate of pebble deformation behaviour and the amount of bulk strain.Closely spaced rigid or deformable pebbles can form clusters that mechanically act as single inclusions. Rigid clusters rotate and survive for only short strain increments, whereas the more stable deformable ones keep on elongating with minor rotation. We provide a natural example of deformed conglomerates from the Wutai Mountains, North China Craton. These consist of banded-iron-formation (BIF) pebbles embedded in a schistose matrix. Using the mean R f -φ plot, a finite strain of ~6 under simple shear could be determined. The viscosity of the pebbles is estimated at about 5 to 8 times that of the matrix for a linear rheology (n=1), or 2 to 5 times if a power-law rheology with n=3 is assumed. 1． IntroductionConglomerates have received particular attention in structural geology for studies on strain analysis, deformation process, rheology and tectonic

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Section: Pebble Deformationmentioning

confidence: 91%

High-strain deformation of conglomerates: Numerical modelling, strain analysis, and an example from the Wutai Mountains, North China Craton

Ran

Bons

Wang

et al. 2018

Journal of Structural Geology

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“…Unfortunately, clasts and their surrounding matrix rarely deform in a passive manner, due to competency or ductility contrasts between the marker and the host rock. This competency contrast is inherently linked to the viscosity contrast between different clast types and the matrix (Ramsay, 1967;Gay, 1968aGay, ,b, 1969Lisle, 1985b;Freeman, 1987;Freeman and Lisle, 1987;Treagus, 2002;Mulchrone and Walsh, 2006;Czeck et al, 2009). Gay (1968a) pointed out that clasts with a low viscosity deform faster than the bulk rock strain ellipse, while clasts with high viscosities resisted deformation and deformed slower than the bulk rock strain ellipse.…”

Section: Non-passive Deformationmentioning

confidence: 99%

Determining finite strain: how far have we progressed?

McCarthy

Meere

Mulchrone

2019

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One of the main aims in the field of structural geology is the identification and quantification of deformation or strain. This pursuit has occupied geologists since the 1800s, but has evolved dramatically since those early studies. The quantification of strain in sedimentary lithologies was initially restricted to lithologies of known initial shape, such as fossils or reduction spots. In 1967, Ramsay presented a series of methods and calculations, which allowed populations of clasts to be used as strain markers. These methods acted as a foundation for modern strain analysis, and have influenced thousands of studies. This review highlights the significance of Ramsay's contribution to modern strain analysis. We outline the advances in the field over the 50 years since publication of Folding and Fracturing of Rocks, review the existing limitations of strain analysis methods and look to future developments.

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“…Competency contrasts between clasts and matrix can result in heterogeneous strain patterns at the thin section and outcrop scale (e.g., Sanderson, 1982;Yonkee, 2005;Holyoke and Tullis, 2006;Yonkee et al, 2013). Experiments and studies of naturally deformed rocks have shown that quartz clasts isolated within a micaceous matrix often exhibit a lower elongation magnitude compared to the matrix (e.g., Tullis and Wenk, 1994;Treagus and Treagus, 2002;Czeck et al, 2009;Yonkee et al, 2013). The data set of Long et al (2011c) from GH and TH rocks on the Shemgang transect illustrates higher strain magnitudes accommodated by schist and phyllite (median X/Z ratio of 3.0) compared to quartzite (median X/Z value of 1.6), indicating that relative differences in elongation magnitudes between quartz-and mica-rich lithologies are recorded by plastic elongation of quartz clasts.…”

Section: Three-dimensional Finite Strain Of Quartz Porphyroclastsmentioning

confidence: 99%

Distributed north-vergent shear and flattening through Greater and Tethyan Himalayan rocks: Insights from metamorphic and strain data from the Dang Chu region, central Bhutan

2017

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In several places in the Himalaya, there are debates over the location of and defining criteria for the South Tibetan detachment (STD) system. Here, we attempt to resolve this debate in central Bhutan by interpreting temperature, pressure, finite strain, and shear-sense data from an 11-km-thick structural transect through the Dang Chu region. Raman spectroscopy on carbonaceous material and garnet-biotite thermometry define a gradual, structurally upward decrease from 600-700 °C to 400-500 °C, and structural data indicate pure shear-dominant (W m ≤0.4), layer-normal flattening strain and north-vergent shearing distributed through most of the section. Our data, when combined with published data from central Bhutan, define gradual, structurally upward cooling and an upright pressure gradient that is 1.2-2.4 times lithostatic distributed between 0 and 11 km above the Main Central thrust (MCT). Transport-parallel lengthening varies between ~20%-110% at 2-5 km above the MCT and between ~5%-55% at 5-11 km above the MCT, and north-vergent shearing is distributed between 2 and 11 km above the MCT. These data rule out the presence of a discrete, normal-sense shear zone and instead illustrate distributed structural thinning accommodated by north-vergent shearing. The strain data allow for ~85 km of distributed north-vergent displacement, which may be related to differential southward transport during MCT emplacement. Alternatively, distributed shear may have been translated northward into the STD system in northern Bhutan. Timing constraints for shearing on the MCT and STD allow for both possibilities. Central Bhutan provides a case study for largescale, distributed structural thinning, and highlights the diverse range of processes that accommodate tectonic denudation during orogenesis.

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Strain analysis and rheology contrasts in polymictic conglomerates: An example from the Seine metaconglomerates, Superior Province, Canada

Cited by 19 publications

References 54 publications

High-strain deformation of conglomerates: Numerical modelling, strain analysis, and an example from the Wutai Mountains, North China Craton

High-strain deformation of conglomerates: Numerical modelling, strain analysis, and an example from the Wutai Mountains, North China Craton

Determining finite strain: how far have we progressed?

Distributed north-vergent shear and flattening through Greater and Tethyan Himalayan rocks: Insights from metamorphic and strain data from the Dang Chu region, central Bhutan

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