Monoclinic and triclinic 3D flanking structures around elliptical cracks

Exner, Ulrike; Dąbrowski, Marcin

doi:10.1016/j.jsg.2010.08.002

Cited by 25 publications

(26 citation statements)

References 29 publications

(38 reference statements)

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“…The case of an irregular boundary for the flow s presently under estimated during magma emplacement (de Saint Blanquat et al, 1998), though it has been documented for shear zones (Jessup et al, 2006;Kuiper et al, 2007) and extrusion (Exner and Dabrowski, 2010;Fernàndez et al, 2013;Koyi et al, 2013). Folding is a consequence of the triclinicity, with the obvious development of sheath folds (Cobbold and Quinquis, 1980;Kuiper et al, 2007).…”

Section: Small Scale Vorticity Problemsmentioning

confidence: 99%

Textures and melt-crystal-gas interactions in granites

Vigneresse¹

2015

Geoscience Frontiers

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a b s t r a c tFelsic intrusions present ubiquitous structures. They result from the differential interactions between the magma components (crystal, melt, gas phase) while it flows or when the flow is perturbed by a new magma injection. The most obvious structure consists in fabrics caused by the interactions of rotating grains in a flowing viscous melt. New magma inputs through dikes affect the buk massif flow, considered as global within each mineral facies. A review of the deformation and flow types developing in a magma chamber identifis the patterns that could be expected. It determines their controlling parameters and summarizes the tools for their quantification. Similarly, a brief review of the rheology of a complex multiphase magma identifies and suggests interactions between the different components. The specific responses each component presents lead to instability development. In particular, the change in vorticity orientation, associated with the switch between monoclinic to triclinic flow is a cause of many instabilities. Those are preferentially local. Illustrations include fabric development, shear zones and flow banding. They depend of the underlying rheology of interacting magmas. Dikes, enclaves, schlieren and ladder dikes result from the interactions between the magma components and changing boundary conditions. Orbicules, pegmatites, unidirectional solidification textures and miarolitic cavities result from the interaction of the melt with a gaseous phase. The illustrations examine what is relevant to the bulk flow, local structures or boundary conditions. In each case a field observation illustrates the instability. The discussion reformulates instability observations, suggesting new trails for ther description and interpretation in terms of local departure to a bulk flow. A brief look at larger structures and at their evolution tries to relate these instabilities on a broader scale. The helical structures of the Rí cany pluton, Czech Republic and by the multiple granitic intrusions of Dolbel, Niger illustrate such events.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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Section: Small Scale Vorticity Problemsmentioning

confidence: 99%

Textures and melt-crystal-gas interactions in granites

Vigneresse¹

2015

Geoscience Frontiers

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“…In our three‐dimensional model, an initially circular frictionless slip surface embedded in a homogeneous, isotropic, linear viscous matrix is subjected to far‐field simple shear. The flow field around the slip surface is found with an adapted external Eshelby solution (Eshelby, 1959) for incompressible viscous materials in the limit of an elliptical and inviscid inclusion (Exner and Dabrowski, 2010). We use a Cartesian coordinate system, where shearing takes place in the x‐direction on the x‐y plane (Fig.…”

Section: Modelmentioning

confidence: 99%

“…Schlische, 1995), such as flanking structures (e.g. Exner and Dabrowski, 2010; Grasemann et al. , 2011).…”

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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“…7 ). The investigated isolated triclinic and monoclinic flanking structures formed by frictional slip but within ductile deforming host rocks and therefore the measured field data are additionally compared with a modified three-dimensional Eshelby solution for a viscous fluid modeling shearing of an elliptical crack oriented perpendicular to the flow direction (for derivations of relevant equations see Exner and Dabrowski, 2010 ). Fig.…”

Section: Monoclinic and Triclinic Flanking Structuresmentioning

confidence: 99%

“…Previous numerical, analytical and analogue studies of flanking structures treated the slip surface either as low viscosity inclusion embedded in a higher viscosity matrix or as a brittle fault (e.g. Grasemann and Stüwe, 2001 , Grasemann et al., 2003 , Grasemann et al., 2005 , Exner et al., 2004 , Kocher and Mancktelow, 2006 , Exner and Dabrowski, 2010 ). Many natural examples do not provide clear evidence for the existence of a weak material along the slip surfaces.…”

Section: Introductionmentioning

confidence: 99%

Displacement–length scaling of brittle faults in ductile shear

Grasemann

Exner

Tschegg

2011

Journal of Structural Geology

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Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow.

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Monoclinic and triclinic 3D flanking structures around elliptical cracks

Cited by 25 publications

References 29 publications

Textures and melt-crystal-gas interactions in granites

Textures and melt-crystal-gas interactions in granites

Sheath fold formation around slip surfaces

Displacement–length scaling of brittle faults in ductile shear

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