Quartz c-axes parallel to stretching directions in very low-grade metamorphic rocks

Stallard, Aaron; Shelley, David

doi:10.1016/0040-1951(95)00040-t

Cited by 38 publications

(23 citation statements)

References 17 publications

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“…The rock sampled, however, is a lowmetamorphic-grade phyllite and has not experienced temperatures in the range of those expected to favour prism [c] slip. Similar unexpected patterns have been noted in lowmetamorphic-grade slates and phyllites in New Zealand where they are interpreted to reflect mechanical rotation of grains elongate in the c axis direction parallel with the stretching direction (Stallard and Shelly, 1995). Such an interpretation is consistent with the sparse evidence of dynamic recrystallization in the matrix quartz.…”

Section: Quartz Crystallographic Fabric Interpretationsupporting

confidence: 71%

“…However, c axis orientations consistent with slip in the rhomb and prism a directions indicate that there was some dynamic modification of the crystal lattice in response to deformation. As suggested by Stallard and Shelly (1995), physical rotation of the clasts may have occurred preferentially in the matrix grains surrounded by phyllosilicate-rich layers, into which strain was preferentially partitioned. The matrix quartz grains that occur in areas with less abundant phyllosilicate may have accommodated more of the strain directly through dislocation slip resulting in the development of the prism a and rhomb/basal a c axis orientations observed in the crystallographic fabric.…”

Section: Quartz Crystallographic Fabric Interpretationmentioning

confidence: 99%

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Microscale strain partitioning? Differential quartz crystallographic fabric development in Phyllite, Hindu Kush, Northwestern Pakistan

Larson

Faisal

2014

Solid Earth

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Abstract. Spatially referenced quartz c axis fabrics demonstrate the preservation of multiple, distinct fabrics in a specimen collected from northwestern Pakistan. The overall fabric yielded by the specimen is dominated by a single population of quartz grains, while the fabric signatures of two other unique, spatially distinct populations are overwhelmed. It is these minor fabrics, however, that provide information on temperature of deformation (403 ± 50 • C), differential stress (8.6 + 2.6/−1.5 MPa to 15.0 +3.8/−2.5 MPa), strain rate (10 −16 s −1 to 10 −15 s −1 ), and strain partitioning recorded by the specimen.

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Section: Quartz Crystallographic Fabric Interpretationsupporting

confidence: 71%

Section: Quartz Crystallographic Fabric Interpretationmentioning

confidence: 99%

Microscale strain partitioning? Differential quartz crystallographic fabric development in Phyllite, Hindu Kush, Northwestern Pakistan

Larson

Faisal

2014

Solid Earth

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“…Quartz c-axes concentrated along the mineral lineation may be associated with two processes (Gapais & Barbarin 1986): oriented growth (Shelley 1980(Shelley , 1993Stallard & Shelley 1995); or prism ,c. slip Mainprice et al 1986;Schmid & Casey 1986). Preferred growth of quartz along the c-axis is documented for both high-temperature conditions during magma crystallization (Gapais & Barbarin 1986), as well as for lower temperatures such as during crack-seal processes (Cox & Etheridge 1983;Hippert 1994).…”

Section: Primary Quartz Fabricsmentioning

confidence: 99%

Pegmatite mylonites: origin and significance

Gapais

Boundi

2014

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International audiencePegmatites generally behave as resistant objects compared to their host rocks during solid-state deformation. They usually show folding or boudinage within their host rocks, features observed from low-grade to high-grade deformations, up to upper-amphibolite metamorphic conditions. Here we describe mylonitic pegmatite veins emplaced within S-C fabric-bearing two-mica granites. Pegmatites consist mainly of feldspar and quartz ribbons, with remnants of coarse-grained Kfs phenocrysts. Quartz ribbons are made of large grains elongated in the shearing direction, with evidence of dynamic recrystallization involving grain boundary migration. Ribbons show very strong lattice-preferred orientations of c-axes at low angles to the stretching lineation. From these, we propose that quartz ribbons are formed by oriented growth during syn-shearing crystallization of the pegmatite. Subsequent syn-shearing solid-state deformation involved grain size reduction accompanied by prism slip. The occurrence of pegmatite mylonites within granitoid intrusions should be considered as a univocal argument for synkinematic emplacement

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“…Furthermore, this c axis CPO is observed in grains that are strongly misoriented with respect to the host (up to 70°in misorientation profiles; Figures 6d and 6e) and does not appear to be inherited from the host grains population (Figure 7e). Strong c axis CPOs have been documented in quartz aggregates deformed at low to very low metamorphic grade, for example, in slates and schists (Stallard & Shelley, 1995;Takeshita & Hara, 1998), phyllonites (Hippertt, 1994), and veins (Cox & Etheridge, 1983). These authors explained the presence of c axis CPOs oriented parallel to the stretching lineation as a result of competitive growth during dissolution and precipitation with quartz grains growing faster along the c axis and hence showing a tendency to mark the stretching direction (Bons & den Brok, 2000;Frondel, 1962;Hippertt, 1993;Stallard & Shelley, 1995).…”

Section: Role Of Fluids and Dynamic Recrystallization In Shear Band Dmentioning

confidence: 99%

Fluid‐Assisted Strain Localization in Quartz at the Brittle/Ductile Transition

Papeschi

Musumeci

2019

Geochem Geophys Geosyst

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A mylonitic quartzite with conjugate and synthetic shear bands was investigated by Electron Backscatter Diffraction and optical microscopy to obtain insights on recrystallization mechanisms and strain localization in quartz at plastic to semibrittle conditions close to the brittle‐ductile transition. The mylonitic quartzite deformed during late Miocene thrusting coeval with contact metamorphism in the high‐strain domains of the Calamita Schists (Elba Island, Italy). Mylonitic deformation occurred from amphibolite to lower greenschist facies conditions during cooling of the aureole. Dynamic recrystallization, dominated by the activity of dislocation creep by prism slip, produced recrystallized quartz layers mantling relic large quartz porphyroclasts. Under decreasing temperature and fluid‐rich conditions, quartz porphyroclasts acted as relatively rigid bodies and fractured along synthetic and conjugate C′ shear bands. Shear bands developed along kinematically favored orientations, just locally assisted by weak crystallographic planes in quartz. Fracturing along shear bands was assisted by cataclasis and fluid infiltration enhancing fracture propagation and healing by recrystallization and authigenesis of new quartz and phyllosilicate grains. The process enhanced the propagation of and strain localization in shear bands, with the development of bands of weak phyllosilicates. Furthermore, we observed the development of a c axis preferred orientation (CPO) related to dissolution and precipitation of new grains with their c axis oriented parallel to shear bands. This study highlights the importance of the interplay between brittle and crystal‐plastic processes and fluid ingress in the semibrittle regime to understand deformation partitioning and strain localization.

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Quartz c-axes parallel to stretching directions in very low-grade metamorphic rocks

Cited by 38 publications

References 17 publications

Microscale strain partitioning? Differential quartz crystallographic fabric development in Phyllite, Hindu Kush, Northwestern Pakistan

Microscale strain partitioning? Differential quartz crystallographic fabric development in Phyllite, Hindu Kush, Northwestern Pakistan

Pegmatite mylonites: origin and significance

Fluid‐Assisted Strain Localization in Quartz at the Brittle/Ductile Transition

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