Dynamic Recrystallization in a Naturally Deformed Albite

Gerald, J. D. Fitz; Etheridge, M. A.; Vernon, R. H.

doi:10.1155/tsm.5.219

Cited by 39 publications

(8 citation statements)

References 21 publications

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“…This process is based on two distinct steps: (1) initial formation of the new grain and (2) its growth. Such recrystallization by nucleation has been observed in albite, magnesium, and quartz (Knipe and White 1979;Fitz Gerald et al 1983;Urai et al 1986;Drury and Urai 1990). This produces grains in which their compositions reflect the thermodynamically favorable composition at the time of nucleation and growth.…”

Section: Plastic Deformation Mechanisms Of Grain Size Reductionmentioning

confidence: 82%

Brittle-ductile microfabrics in naturally deformed zircon: Deformation mechanisms and consequences for U-Pb dating

Piazolo

Austrheim

Whitehouse

2012

American Mineralogist

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We present an electron backscatter diffraction, cathodoluminescence, and radiogenic U-Pb dating study of large zircon grains (0.8-1.5 mm) that show evidence of intracrystalline deformation, fracturing, grain size reduction and a large spread in U-Pb ages. The samples are from an amphibolite facies deformation zone within granulite facies anorthositic rocks (Bergen Arc, Norway). Large zircon grains show three main lattice distortion types: (I) distortions with rotations around <001> and an orientation change of ∼0.3 °/µm subparallel to (100); (II) highly distorted, half circular shaped zones located at grain edges with at least 0.8-1°/µm distortions; and (III) low-angle boundary networks forming deformation zones up to 100 µm wide. Types II and III distortions exhibit significant disturbances of the otherwise homogeneous CL signature.Crystal plastic deformation with the slip system [010](100) resulted in type I distortions. Stress concentrations at grain contacts between rheologically hard grains caused localized crystal plastic deformation with minor amount of microfracturing forming type II distortions. Type III distortions formed by crystal plastic deformation often associated with inclusions using several slip systems. Distortions of types I and II show minor and moderate resetting of the original ca. 900 Ma zircon grains, respectively, due to enhanced pipe diffusion along dislocation walls. In type II distortions, accelerated lattice diffusion through the highly distorted crystal lattice, combined with exceptionally high boundary to volume ratio, caused significant chemical disturbance and age resetting to 410 Ma. Fine-grained aggregates contain grains with low internal deformation and an oscillatory zoned CL signature (Z-grains) or high internal deformation and a disturbed CL signature (D-grains). Z-and Dgrains are interpreted to have formed by heterogeneous nucleation and growth, and fracturing along strain-hardened low-angle boundaries present within types I and II, respectively. Z-grains show a clustered chemical signature with a 437 ± 11 Ma age interpreted to directly date the Caledonian amphibolite facies reworking.

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Section: Plastic Deformation Mechanisms Of Grain Size Reductionmentioning

confidence: 82%

Brittle-ductile microfabrics in naturally deformed zircon: Deformation mechanisms and consequences for U-Pb dating

Piazolo

Austrheim

Whitehouse

2012

American Mineralogist

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“…Usually, geometric control of macroscopic kinematic frame on deformation microstructures imply their genetic relationship (Reddy and Buchan 2005;Kaczmarek et al 2011). Therefore, PDBs could be a result of shearing at high differential stress and high strain rates that induced energetically preferable slip in zircon; high temperatures in the vicinity of pseudotachylytes facilitated dislocation creep (e.g., Hobbs 1968;White 1973White , 1976Fitz Gerald et al 1983;Ranalli 1995). Scenario 3 implies formation of pseudotachylytes, followed by frictional heating of the surrounded rocks and by shearing that resulted in PDBs formation in zircon.…”

Section: Characterization Of Planar Deformation Bandsmentioning

confidence: 99%

Planar microstructures in zircon from paleo-seismic zones

Kovaleva

Klötzli

Habler

et al. 2015

American Mineralogist

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Pseudotachylytes resulted from frictional melts associated with ultramylonites in high-grade metapelitic rocks from the Ivrea-Verbano zone in the Southern Alps (Northern Italy) were studied with focus on the deformation microstructures in zircon. The aims were to investigate the characteristics of zircon deformation in seismic zones, and to recognize specific microstructures generated in zircon during earthquakes, which could be useful for mineral dating of paleo-seismic events; helps to understand how seismic energy is released at depth and interacts with metamorphic processes.The interior of polished zircon grains ranging from 30 to 150 mm in length were investigated with optical microscope and scanning electron microscope (SEM) techniques, including secondary electron (SE), backscattered electron (BSE), forward scattered electron (FSE), cathodoluminescence (CL) imaging, and crystallographic orientation mapping by electron backscatter diffraction analysis (EBSD). Grains were studied in situ and as separated fractions embedded in epoxy disks. Among different cataclastic and crystal-plastic deformation microstructures in zircon we identified characteristic planar deformation bands (PDBs), planar fractures (PFs), and curviplanar fractures (CFs).Planar deformation bands in zircon are crystallographically controlled planar lattice volumes with misorientation from the host grain, which varies from 0.4° to 2.7°. PDBs are usually parallel to {100} crystallographic planes, have width from 0.3 to 1 mm and average spacing of 5 mm in 2D sections. Planar deformation bands appear as contrast lamellae in orientation contrast images and in EBSD maps, and in rare cases can be observed with the optical microscope. PDBs form in specifically oriented grains due to high differential stresses, high temperatures, and high strain rates generated in seismically active environment and/or due to shearing in the vicinity of frictional melts. Discovered structures represent a result of crystal-plastic deformation of zircon grains with operating dislocations having <100>{010} glide system and <001> misorientation axis, therefore, they can be classified as a new type 4 lattice distortion pattern, according to the existing classification for zircon (Piazolo et al. 2012;Kovaleva et al. 2014).We have demonstrated that formation of planar fractures in zircon takes place not only during impacts, but also in seismically active zones. We observe at least two cases of formation of PFs with {100} orientation: (1) as a result of evolution of PDBs and (2) as micro-cleavage.This study demonstrates that planar microstructures in terrestrial zircon do not exclusively form during impact events, but also as a result of seismic events at depth due to unusually high differential stress, strain rate, and temperature. According to the new findings, PDBs in zircon from the deep-crust are supposed to represent newly recognized evidence of seismicity.

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“…One possible mechanism for the grain size reduction is the formation of subgrain boundaries (SGBs) and their evolution into general GBs with progressive misorientation angles between the two sides of the SGBs. From the observation of recrystallization textures, the transition from SGBs with regular arrays of dislocations within a single crystal to GBs incoherently separating two distinct crystals is often associated with a misorientation angle of 10°to 15°(e.g., Poirier and Nicolas 1975;White 1977;Guillopé and Poirier 1979;White and Mawer 1988), although for plagioclase, Fitz Gerald et al (1983) proposed critical misorientation values below 5°. The general idea is that above a certain critical misorientation angle, dislocations should be too closely spaced for coherent crystal to be present between them (Read 1953).…”

Section: Introductionmentioning

confidence: 99%

Subgrain boundary analyses in deformed orthopyroxene by TEM/STEM with EBSD-FIB sample preparation technique

et al. 2014

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High-resolution structure analyses using electron beam techniques have been performed for the investigation of subgrain boundaries (SGBs) in deformed orthopyroxene (Opx) in mylonite from Hidaka Metamorphic Belt, Hokkaido, Japan, to understand ductile deformation mechanism of silicate minerals in shear zones. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analysis of Opx porphyroclasts in the mylonitic rock indicated that the crystal orientation inside the Opx crystals gradually changes by rotation about the b-axis by SGBs and crystal folding. In order to observe the SGBs along the b-axis by transmission electron microscopy (TEM) or scanning TEM (STEM), the following sample preparation protocol was adopted. First, petrographic thin sections were slightly etched with hydrofluoric acid to identify SGBs in SEM. The Opx crystals whose b-axes were oriented close to the normal of the surface were identified by EBSD, and the areas containing SGBs were picked and thinned for (S) TEM analysis with a focused ion beam instrument with micro-sampling system. High-resolution TEM imaging of the SGBs in Opx revealed various boundary structures from a periodic array of dissociated (100) [001] edge dislocations to partially or completely incoherent crystals, depending on the misorientation angle. Atomic-resolution STEM imaging clearly confirmed the formation of clinopyroxene (Cpx) structure between the dissociated partial dislocations. Moreover, X-ray microanalysis in STEM revealed that the Cpx contains a considerable amount of calcium replacing iron. Such chemical inhomogeneity may limit glide motion of the dislocation and eventually the plastic deformation of the Opx porphyroclasts at a low temperature. Chemical profiles across the high-angle incoherent SGB also showed an enrichment of the latter in calcium at the boundary, suggesting that SGBs are an efficient diffusion pathway of calcium out of host Opx grain during cooling.

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Dynamic Recrystallization in a Naturally Deformed Albite

Cited by 39 publications

References 21 publications

Brittle-ductile microfabrics in naturally deformed zircon: Deformation mechanisms and consequences for U-Pb dating

Brittle-ductile microfabrics in naturally deformed zircon: Deformation mechanisms and consequences for U-Pb dating

Planar microstructures in zircon from paleo-seismic zones

Subgrain boundary analyses in deformed orthopyroxene by TEM/STEM with EBSD-FIB sample preparation technique

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