A transmission electron microscope study of naturally deformed orthopyroxene

McLaren, A. C.; Etheridge, M. A.

doi:10.1007/bf00405223

Cited by 60 publications

(16 citation statements)

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“…The HRTEM image of the single dislocation (Figure 5b) generally shows a pair of dark areas and h00 lattice fringes between them, with the periodicity of a half (approximately 4.6 Å) of that in the surrounding Opx (approximately 9.2 Å). This feature is interpreted as the dissociation of the (100) [001] dislocation into two partial dislocations and formation of clinopyroxene (Cpx) between them, as proposed by several previous works (e.g., Coe and Kirby 1975;McLaren and Etheridge 1976). The Cs-corrected STEM-HAADF image of the dislocation confirmed the formation of Cpx (Figure 6).…”

Section: Resultssupporting

confidence: 69%

“…Furthermore, the presence of Cpx between the partial dislocations was also proposed (Coe and Kirby 1975;McLaren and Etheridge 1976;Nazé et al 1987). In the present study, STEM-HAADF imaging ( Figure 6) has clearly confirmed the presence of a Cpx structure.…”

Section: Dislocation Dissociation and Associated Chemical Heterogeneitymentioning

confidence: 71%

“…Many TEM works (e.g., Green and Radcliffe 1972;Kohlstedt and Vander Sande 1973;Coe and Kirby 1975;McLaren and Etheridge 1976;Van Duysen et al 1985;Nazé et al 1987;Steuten and Van Roermund 1989) indicated that dislocations (100) [001] of Opx are dissociated. Furthermore, the presence of Cpx between the partial dislocations was also proposed (Coe and Kirby 1975;McLaren and Etheridge 1976;Nazé et al 1987).…”

Section: Dislocation Dissociation and Associated Chemical Heterogeneitymentioning

confidence: 99%

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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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Section: Resultssupporting

confidence: 69%

Section: Dislocation Dissociation and Associated Chemical Heterogeneitymentioning

confidence: 71%

Section: Dislocation Dissociation and Associated Chemical Heterogeneitymentioning

confidence: 99%

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

et al. 2014

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“…Although the clino-to orthoenstatite transformation has been proposed as a deformation process in opx (Coe and Kirby 1975;Coe and Müller 1973;McLaren and Etheridge 1976;Raleigh, et al 1971), the paucity of clino-enstatite lamellae observed in our samples (mostly related to the dissociation of (100)[001] dislocations into two partials, see Fig. 7) as well as the very large elongation (shape ratio correspond to finite shear strain locally up to more than 20), imply that most of the deformation results from dislocation activity.…”

Section: Active Slip Systems In Opxmentioning

confidence: 99%

Crystal bending, subgrain boundary development, and recrystallization in orthopyroxene during granulite-facies deformation

Raimbourg¹,

Kogure

Toyoshima

2011

Contrib Mineral Petrol

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International audienceA prominent feature of a granulite-facies shear zone from the Hidaka Main Zone (Japan) is the folding of orthopyroxene (opx) porphyroclasts. Dislocation density estimated by transmission electron microscope (TEM) and chemical etching in homogeneously folded domains is too low to account for the amplitude of crystallographic bending, leading us to propose a model similar to "flexural slip" folding, where folded layers are micrometer-wide opx layers between thin planar clinopyroxene (cpx) exsolutions. Extension (compression) in the extrados (intrados) of the folded layer is accommodated by dislocations at the cpx-opx interfaces. Alternatively to distributed deformation, crystal bending also localizes in grain boundaries (GBs), mostly oriented close to the (001) plane and with various misorientation angles but misorientation axes consistently close to the b-axis. For misorientation up to a few degrees, GBs were imaged as tilt walls composed of regularly spaced (100)[001] dislocations. For misorientation angles of 7°, individual dislocations are no longer visible, but high-resolution TEM (HRTEM) observation showed the partial continuity of opx tetrahedral chains through the boundary. For 21° misorientation, the two adjacent crystals are completely separated by an incoherent boundary. In spite of these atomic-scale variations, all GBs share orientation and rotation axis, suggesting a continuous process of misorientation by symmetric incorporation of (100)[001] dislocations. In addition to the dominant GBs perpendicular to the (100) plane, boundaries at low angle with (100) planes are also present, incorporating dislocations with a component of Burgers vector along the a-axis. The two kinds of boundaries combine to delimit subgrains, which progressively rotate with respect to host grains around the b-axis, eventually leading to recrystallization of large porphyroclasts

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“…3A. However, it is difficult to assess how much of the observed structure resulted from post-metamorphic, especially weathering, processes (McLaren & Etheridge, 1980). Some recent high-resolution TEM across grain boundaries in metamorphic rocks suggests that they may be much tighter structures, similar to those found in metals and alloys (Veblen & Buseck, 1981).…”

Section: Discussionmentioning

confidence: 99%

The role of the fluid phase during regional metamorphism and deformation

Etheridge

Wall

Vernon

1983

Journal Metamorphic Geology

Self Cite

511

218

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Abstract. Evidence from rock microstructures, mass transfer and isotopic exchange indicates that substantial quantities of aqueous fluids are involved in low-and medium-grade regional metamorphism. Similar conclusions are drawn from many retrograde environments, whereas high-grade metamorphic fluids may be melt dominated. The mobile fluids play essential roles in metamorphic reactions, mass transport and deformation processes. These processes are linked by the mechanical consequences of metamorphic fluid pressures (Pr) generally being greater than or equal to the minimum principal compressive stress. Under such conditions metamorphic porosity comprises grain boundary tubules and bubbles together with continuously generated (and healed) microfractures. Deformation results in significant interconnected porosity and hence enhanced permeability. Lithologically and structurally controlled permeability variations may cause effective fluid channelling.Simple Rayleigh-Darcy modelling of a uniformly permeable, crustal slab shows that convective instability of metamorphic fluid is expected at the permeabilities suggested for the high Pf metamorphic conditions. Complex, largescale convective cells operating in overpressured, but capped systems may provide a satisfactory explanation for the large fluid/rock ratios and extensive mass transport demonstrated for many low-and medium-grade metamorphic environments. Such large-scale fluid circulation may have important consequences for heat transfer in and the thermal evolution of metamorphic belts.

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A transmission electron microscope study of naturally deformed orthopyroxene

Cited by 60 publications

References 15 publications

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

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

Crystal bending, subgrain boundary development, and recrystallization in orthopyroxene during granulite-facies deformation

The role of the fluid phase during regional metamorphism and deformation

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