Shearing of magma along a high-grade shear zone: Evolution of microstructures during the transition from magmatic to solid-state flow

Zibra, I.; Kruhl, Jörn H.; Montanini, Alessandra; Tribuzio, R.

doi:10.1016/j.jsg.2012.01.011

Cited by 39 publications

(49 citation statements)

References 47 publications

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“…Dynamic recrystallizations features define S 2 -C 3 structures and S 3 schistosities. The coexistence of quartz GBM to SGAR and feldspars kinked, SGR to GBM and amphibole SGR dynamic recrystallizations attest that shear zone emplaced under amphibolite to granulite conditions, ranging from 500 to 850 °C (Kurse et al, 2001;Passchier & Trouw, 2005;Stipp et al, 2002;Zibra, 2010Zibra, , 2012Zibra et al, 2012). P-T paths from the WCAFB define amphibolite to granulite conditions.…”

Section: Discussionmentioning

confidence: 95%

“…On the contrary, in typified blastomylonitic D 3 shear zones and from outer to inner zones, dynamic recrystallizations features range from quartz GBM to SGAR, feldspars SGR to GBM and amphibole SGR (Kurse et al, 2001;Passchier & Trouw, 2005;Stipp et al, 2002;Zibra, 2010Zibra, , 2012Zibra et al, 2012). D 3 folded S 0/1/2 and S 2 foliations in F 3 meso-and large-scale folds and emplaced shear zones in Central Africa from Ma (U/Pb-Zr, Toteu et al, 1994; Pb/Pb-Zr, Morin et al, 1991) to 1742 Ma in Cameroon (Ar/Ar-Bt, Owona, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…New and small grains with undulated boundaries disappeared for idiomorphic blasts with triple points replacing the old core minerals. Details of dynamic recrystallization stages and mechanisms can be consulted in Kurse et al (2001), Stipp et al (2002), Passchier and Trouw (2005), Zibra (2010Zibra ( , 2012, Zibra et al (2012). If these assertions are accepted, plastic recrystallizations define a reworked deformation affecting primary minerals such as porphyroclasts and porphyroblasts.…”

Section: Methodsmentioning

confidence: 99%

“…Since last decades, significant progress has been made in understanding the microstructural evolution of crystallizing or melting rocks in natural and numerical experiments and tectonic models (e.g. While, 1973While, , 1977Urai et al, 1986;Vernon, 2000;Hirth et al, 2001;Stipp et al, 2002;Passchier & Trouw, 2005;Zibra et al, 2010Zibra et al, , 2012Zibra, 2012). A close spatial and temporal relationship between pluton emplacement and shear zones has been documented in various geological settings (see Rosenberg, 2004 for a review; Weinberg et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

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Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

Owona¹,

Ondoa²,

Ekodeck³

2013

JGG

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The Paleoproterozoic is characterised by a global-scale period of crust formation, extensive mafic to granitic magmatism, crustal reworking and intracrustal partial melting. Since a dramatic strength drop is associated with the presence of melt in crystallising or melting rocks, Paleoproterozoic continental deformation is thought to have been largely accommodated by shearing of high-grade gneisses and syntectonic granitoids. The Paleoproterozoic Nyong complex, which is made up of volumetrically dominant granitoids, metapelites and granitic gneisses, quartzites and banded iron formations; has been affected by the Eburnean/Transamazonian polyphase ductile and brittle deformation responsible of S 1/2 foliation and S 2 schistosity, L 2 stretching and mineral lineations, F 3 meso-and large-scale folds, S 2 /C 3 structures and faults. Its shear zone strain anisotropies represent a natural laboratory to study the effect of crystal plastic deformation of felsic minerals and amphibole as predicted by numerical experiments and tectonic models. This paper describes the geometry of the deformation and focus on microstructural evidence of dynamic recrystallization features that were active under granulite conditions (>800 °C, >8.5 Kbar). These thermal conditions can be extended in similar Proterozoic worldwide shear zones.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

Owona¹,

Ondoa²,

Ekodeck³

2013

JGG

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“…The use of quartz recrystallization microstructures and CPO to estimate pressure and temperature conditions has been widely applied in different studies of mylonitic granites in shear zones (Tommasi et al, 1994;Stipp et al, 2002Stipp et al, , 2010Zibra et al, 2012). However, this approach has to be taken with caution because quartz microstructures are also sensitive to water content (Mancktelow and Pennacchioni, 2004;Menegon et al, 2011) and strain rate (Stipp et al, 2002).…”

Section: P T Fluid Conditions Of Deformationmentioning

confidence: 99%

Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

Viegas

Menegon

Archanjo³

2016

Solid Earth

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Abstract. The Pernambuco shear zone (northeastern Brazil)is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarsegrained (> 50 µm) feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 µm) localized in C' shear bands. Detailed microstructural observations and electron backscatter diffraction (EBSD) analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (∼ 1-2 mm) monomineralic veins transposed along the shear zone foliation or as thin ribbons (≤ 25 µm width) dispersed in the feldspathic mixture. The microstructure and c axis crystallographicpreferred orientation are similar in the thick monomineralic veins and in the thin ribbons, and they suggest dominant subgrain rotation recrystallization and activity of prism < a > and rhomb < a> slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the quartz monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 µm vs. 5 µm respectively). The fine-grained feldspar mixture has a weak crystallographic-preferred orientation interpreted as the result of shear zone parallel-oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Once C' shear bands were generated and underwent viscous deformation at constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate 1 order of magnitude faster than the monophase quartz monomineralic veins, as evidenced by applying experimentally and theoretically calibrated flow laws for dislocation creep in quartz and diffusion creep in feldspar. Overall, our data set indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase feldspathic material localized much of the strain. Extensive grain-size reduction and weakening of feldspars is attained in the East Pernambuco mylonites mainly via fracturing which would trigger a switch to diffusion creep and strain localization without a prominent role of metamorphic reactions.

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Midcrustal shearing and doming in aCenozoic compressive setting along theAilaoShan‐RedRiver shear zone

Zhang

Yin

Zhang

et al. 2017

Geochem Geophys Geosyst

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The Cenozoic Xuelong Shan antiformal dome is located along the northern segment of the Ailao Shan-Red River shear zone in Yunnan, China. Subhorizontal foliation in the gneiss core is recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike-slip shear zone. Microfabrics of crystallographicpreferred orientations (CPOs) in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust (300-5008C) in the mantling schist to the midcrust (15 km or more, 6508C) in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which range from garnet 1 amphibole 1 biotite 1 sillimanite 1 rutile 1 feldspar in the core to garnet 1 staurolite 1 biotite 1 epidote 1 muscovite within the limb units. The dome experienced the following deformation history: (1) a broad top-to-NE shear in the subhorizontal foliation of the gneiss core during the first stage of deformation (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2-D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The structural-thermal patterns suggest the antiformal dome formation was roughly coeval with top-to-NE ductile shearing in the midcrust of Tibet at 32 Ma or earlier. A major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike-slip deformation.

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Shearing of magma along a high-grade shear zone: Evolution of microstructures during the transition from magmatic to solid-state flow

Cited by 39 publications

References 47 publications

Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

Evidence of Quartz, Feldspar and Amphibole Crystal Plastic Deformations in the Paleoproterozoic Nyong Complex Shear Zones Under Amphibolite to Granulite Conditions (West Central African Fold Belt, SW Cameroon)

Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)

Midcrustal shearing and doming in aCenozoic compressive setting along theAilaoShan‐RedRiver shear zone

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