The origin and development of kink‐bands in a foliated body

Dewey, John

doi:10.1002/gj.3350060206

Cited by 21 publications

(1 citation statement)

References 13 publications

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“…Each of these mechanisms should result in a characteristic deformation history, and a number of criteria have been described to discriminate between them. The inequality between the angles f and f K , which is found in most cases, and the corresponding volume change, have been used as a criterion to discard the hinge-migration mechanism (e. g. Dewey, 1969;Bhattacharya, 1977;Sharma and Bhola, 2005) and to infer rotation of the foliation (Anderson, 1964;Ramsay, 1967). Stewart and Alvarez (1991) have criticized this view, because in general they find that f ≠ f K in their experiments with cards, in which the existence of a widening of the kink bands during their development is shown.…”

Section: Introductionmentioning

confidence: 99%

On the development of kink-bands: A case study in the Westasturian-Leonese Zone (Variscan belt, NW Spain)

Aller

Bastida

Bobillo‐Ares

2020

BSGF - Earth Sci. Bull.

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A field analysis of kink bands developed in slates from three areas (Grandas, Boal and Luarca areas) of the Westasturian-Leonese Zone (Iberian Variscan belt) is presented. The analysis of the main parameters that characterize the geometry of the studied kink bands shows that those of the Grandas and Luarca areas exhibit a different evolution than those of the Boal area. In this latter area, the interlimb angle of the kink bands has lower values than those developed in the former areas and it involves rotation of the foliation inside and outside the band. In the areas with higher bulk shortening associated with the development of kink bands, chevron folds formed by juxtaposition of kink bands. Slip between folia and their rotation was probably the dominant mechanism in the formation of the kink bands, as deduced from the different values of the angle between the kink plane and the foliation inside (φK) and outside (φ) the band, and the occurrence of fractures along the kink planes and small steps between folia cross-cutting these fractures planes. The fractures along the kink planes prevented subsequent hinge migration. Geometrical analysis of kink bands formed by slip between folia and their rotation provides an estimation of the changes in area and thickness, and the strain inside the kink band. For angles of folia rotation ψ < 50°, the ratio between the strain ellipse axes is < 3 inside the band; this ratio is almost independent of the orientation of the kink planes with respect to the foliation outside the band (angle φ).

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Section: Introductionmentioning

confidence: 99%

On the development of kink-bands: A case study in the Westasturian-Leonese Zone (Variscan belt, NW Spain)

Aller

Bastida

Bobillo‐Ares

2020

BSGF - Earth Sci. Bull.

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Metamorphic textures and deformation: A new mechanism for the development of syntectonic porphyroblasts and its implications for interpreting timing relationships in metamorphic rocks

Wit

1976

Geological Journal

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interpreting timing relationships in metamorphic rocks M. J. de WitThe formation and growth of porphyroblasts is treated in detail, with particular reference to garnet. Previous eiplanations for included fabrics in porphyroblasts, and mechanisms of syntectonic growth leading to sigmoidal inclusion patterns, are shown to be based on invalid assumptions and are unacceptable. The following new mechanism for garnet porphyroblast growth is proposed. During deformation, fluid filled veins open, particularly where micaceous foliae open in folds associated with crenulation cleavages and kink bands. Garnet nucleates in these veins as they develop. The geometry of the veins depends on variability of strain rates, fluid diffusivity and the sequence of progressive deformation. In areas of low strain rate and high diffusivity, long and widaly spaced macroscopic garnet veins form. These may be buckled during the continuous deformation process. Conversely, where strain rates are high, and diffusivity is iow, short and closdly spaced microscopic garnet veins form. Buckling and shear may alter the vein shapes during their formation and sigmoidal veins can result. Veins join and coalesce to form single porphyroblasts, leaving a selvage of quartz and other minerals as an included fabric. The finite geometry of the included fabric ranges from helicitic to sigmoidal, which is interpreted to reflect the local deformation history during vein propagation. The fabric geometry is finalized when the veins fail to respond individually to the deformation due to their coalescence and formation into a single porphyroblast. Continuous vein propagation without significant deformation of the veins could lead to augen textures, whilst a process of continuous vein formation and rotation is shown to explain apparent syntectonic rotations of more than 180". This new hypothesis has the merit of being very simple, but it does require a new approach. This approach necessarily questions a number of previously well established "facts", such as pre-, syn-, and post-tectonic textures. it is argued that extreme care must be taken, when relating deformation episodes and metamorphic growth periods.

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Folds

Hills

1972

Elements of Structural Geology

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The origin and development of kink‐bands in a foliated body

Cited by 21 publications

References 13 publications

On the development of kink-bands: A case study in the Westasturian-Leonese Zone (Variscan belt, NW Spain)

On the development of kink-bands: A case study in the Westasturian-Leonese Zone (Variscan belt, NW Spain)

Metamorphic textures and deformation: A new mechanism for the development of syntectonic porphyroblasts and its implications for interpreting timing relationships in metamorphic rocks

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