Networking of shear zones at the brittle-to-viscous transition (Cap de Creus, NE Spain)

Fußeis, Florian; Handy, Mark R.; Schrank, Christoph

doi:10.1016/j.jsg.2006.03.022

Cited by 113 publications

(104 citation statements)

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“…13). This microstructural development is analogous to that of multi-scale shear zones at the frictional-viscous transition zones analyzed by Fusseis et al (2006) and Schrank et al (2008). With further increasing volume fraction of micro-shear zones, each of the quartz lenses became isolated, when they no longer behaved as a load-bearing framework, which led to a great reduction of differential stresses in them (Ss in stage 2 of Fig.…”

Section: Possible Large Degree Of Weakening By Coupled Micro-faultingmentioning

confidence: 51%

“…With further increasing shear deformation, the strain became more accommodated by pressure solution in micro-shear zones, and the quartz lenses were further sheared by the resultant stress concentration, leading to the increasing volume fraction of micro-shear zones (cf. Fusseis et al, 2006;Schrank et al, 2008). At this microstructural setting with plenty of mica, pressure solution pervasively occurred at the quartz-mica interface even under very low differential stresses driven by the electrical potential difference (Greene et al, 2009), which led to a complete obliteration of existing quartz c-axis fabrics in some quartz schist.…”

Section: Discussionmentioning

confidence: 88%

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Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Takeshita

El-Fakharani

2013

Journal of Structural Geology

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In the Sambagawa schist, southwest Japan, while ductile deformation pervasively occurred at D 1 phase during exhumation, low-angle normal faulting was locally intensive at D 2 phase under the conditions of frictional-viscous transition of quartz (c. 300 o C) during further exhumation into the upper crustal level. Accordingly, the formation of D 2 shear bands was overprinted on type I crossed girdle quartz c-axis fabrics and microstructures formed by intracrystalline plasticity at D 1 phase in some quartz schists. The quartz c-axis fabrics became weak and finally random with increasing shear, accompanied by the decreasing degree of undulation of recrystallized quartz grain boundaries, which resulted from the increasing portion of straight grain boundaries coinciding with the interfaces between newly precipitated quartz and mica. We interpreted these facts as caused by increasing activity of pressure solution: the quartz grains were dissolved mostly at platy quartz-mica interface, and precipitated with random orientation and pinned by mica, thus having led to the obliteration of existing quartz c-axis fabrics. In the sheared quartz schist, the strength became reduced by the enhanced pressure solution creep not only due to the reduction of diffusion path length caused by increasing number of shear bands, but also to enhanced dissolution at the interphase boundaries.

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Section: Possible Large Degree Of Weakening By Coupled Micro-faultingmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 88%

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Takeshita

El-Fakharani

2013

Journal of Structural Geology

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“…To develop this in detail, we interpret different quartz microstructures in our sample as representing different stages in a progressive evolution ("space for time"; see also Fusseis et al, 2006;Kilian et al, 2011). If the well-mixed polymineralic domains are the most mature parts of the studied ultramylonite, monomineralic quartz domains must be considered as relics of an original mylonitic fabric that has been captured in the process of disaggregation.…”

Section: A Model For Synkinematic Creep Cavitation By Different Mechamentioning

confidence: 99%

Hierarchical creep cavity formation in an ultramylonite and implications for phase mixing

et al. 2017

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Abstract. Establishing models for the formation of wellmixed polyphase domains in ultramylonites is difficult because the effects of large strains and thermo-hydro-chemomechanical feedbacks can obscure the transient phenomena that may be responsible for domain production. We use scanning electron microscopy and nanotomography to offer critical insights into how the microstructure of a highly deformed quartzo-feldspathic ultramylonite evolved. The dispersal of monomineralic quartz domains in the ultramylonite is interpreted to be the result of the emergence of synkinematic pores, called creep cavities. The cavities can be considered the product of two distinct mechanisms that formed hierarchically: Zener-Stroh cracking and viscous grain-boundary sliding. In initially thick and coherent quartz ribbons deforming by grain-size-insensitive creep, cavities were generated by the Zener-Stroh mechanism on grain boundaries aligned with the Y Z plane of finite strain. The opening of creep cavities promoted the ingress of fluids to sites of low stress. The local addition of a fluid lowered the adhesion and cohesion of grain boundaries and promoted viscous grain-boundary sliding. With the increased contribution of viscous grainboundary sliding, a second population of cavities formed to accommodate strain incompatibilities. Ultimately, the emergence of creep cavities is interpreted to be responsible for the transition of quartz domains from a grain-size-insensitive to a grain-size-sensitive rheology.

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“…Therefore, at larger strain, the layering always becomes favourably oriented for shear banding to occur. If layering is present at different scales in the medium, the rocks may go through cycles of hardening (folding) and weakening (shear banding), giving rise to anastomosing shear zone as was already pointed out by Ghosh and Sengupta (1987).…”

Section: Maximum Shear-stress Directions and The Orientation And Occmentioning

confidence: 72%

“…Betics (Platt and Vissers, 1980) and Aegean (Jolivet et al, 2010), strike-slip: e.g. Red River Fault (Leloup et al, 1995) and Cap de Creus (Fusseis et al, 2006)) and are known to exist at larger scale from seismic reflection data (Torvela et al, 2013). Focus has been put here on detachment zones because their footwalls exhibit exhumed rocks deformed at the brittle-ductile transition and also because we can use active analogues to calibrate strain rates in the models.…”

Section: Introductionmentioning

confidence: 99%

Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

et al. 2013

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Abstract.We have designed a series of fully dynamic numerical simulations aimed at assessing how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented.In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying initial dip of inherited layering in the footwall with regard to the orientation of simple shear applied at the rigid boundary simulating a rigid hanging wall, all scaling and rheological parameter kept constant. It appears that when MohrCoulomb plasticity is being used, shear bands are found to localise only when the layering is being stretched. This corresponds to early deformational stages for inital layering dipping in the same direction as the shear is applied, and to later stages for intial layering dipping towards the opposite direction of shear. In all the cases, localisation of the strain after only γ = 1 requires plastic yielding to be activated in the strong layer.The second parametric study shows that results are lengthscale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. However, decreasing or increasing strain rate is shown to reduce the capacity of the shear zone to localise strain. In the later case, the strain pattern resembles a mylonitic band but the rheology is shown to be effectively linear.Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but the strength cannot drop since the shear zone has a finite thickness.

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Networking of shear zones at the brittle-to-viscous transition (Cap de Creus, NE Spain)

Cited by 113 publications

References 52 publications

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan

Hierarchical creep cavity formation in an ultramylonite and implications for phase mixing

Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

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