Chemical etching of amphiboles and pyroxenes

Wegner, M. W.; Christie, J. M.

doi:10.1007/bf01046831

Cited by 8 publications

(4 citation statements)

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“…Microstructural feature of chemical etched deformed sample (a and c, BSD images and, b and d, InLens images). The sample was deformed at 505 °C and chemical etched followed the method proposed by Wegner and Christie (). (a) grain deformed in moderate sheared regions, only fractures at the grain contact are etched clearer; (b) close‐up image of the yellow rectangle in (a); (c) grain deformed in intensely sheared regions; (d) close‐up image of the yellow rectangle in (c).…”

Section: Discussionmentioning

confidence: 99%

“…The development of dislocations in their olivine particles has been observed to vary spatially within the grain and tend to be more concentrated in the vicinity of grain boundaries. To examine the occurrence of crystalline plasticity in our augite sample, we decorated the thin polished sections of deformed samples for SEM observation following the chemical etching method described by Wegner and Christie (1985), choosing a HF-HCl-citric mixture (#6 recipe in their methods) as the etchant. However, typical etch pits as indicators of dislocations were not observed by careful searching the grain surfaces in both intensely sheared zones and moderately sheared portions 10.1029/2018JB016456 (Figure 22).…”

Section: 1029/2018jb016456mentioning

confidence: 99%

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Velocity Weakening of Simulated Augite Gouge at Hydrothermal Conditions: Implications for Frictional Slip of Pyroxene‐Bearing Mafic Lower Crust

Tian

2019

JGR Solid Earth

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To understand the velocity-weakening behavior of pyroxene as a major constituent in mafic rocks under hydrothermal conditions, we employed augite (clinopyroxene, (Ca 0.577 Na 0.110 Mn 0.004 Mg 0.886 Fe 2+ 0.193 Fe 3+ 0.037 Al VI 0.173 Ti 0.019 )[Al IV 0.137 Si 1.863 O 6 ]) as simulated gouge sample material to run velocity stepping sliding tests at temperatures of 101-607°C, confining pressure of 127 MPa with 30 MPa pore pressure and axial loading rates of 0.04-1.0 μm/s. The friction coefficient was found to range from 0.71 to 0.73 with no systematic temperature dependence. Velocity-weakening behavior occurred at temperatures above 203°C, with low velocity dependence or (b-a) value around 0.0012, corresponding to b/a values of 1.15-1.18. Inferred b values in the rate and state friction laws exhibited an increasing trend with temperature increase from~0.0056 to~0.0098 up to 403°C, indicating activation of Arrhenius-type creep at the frictional contacts. Microstructural observations on deformed samples show ubiquitous precipitated particles suggesting intergranular pressure solution, and no evidence for deformation by crystalline plasticity was observed. This fact, together with the comparison between experimental data and model prediction, suggests that the process of intergranular pressure solution at frictional contacts may have governed the evolution effect for augite. The minor velocity weakening of augite combined with previous data on plagioclase is consistent with the modest velocity weakening seen in mafic rocks, such as quartz-free oceanic basalt. Such a minor velocity-weakening property tends to favor slow slip events on the downdip portion of the subduction interface below currently locked seismogenic zones, such as in southwestern Japan, northern Cascadia, and Mexico.

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Section: Discussionmentioning

confidence: 99%

Section: 1029/2018jb016456mentioning

confidence: 99%

Velocity Weakening of Simulated Augite Gouge at Hydrothermal Conditions: Implications for Frictional Slip of Pyroxene‐Bearing Mafic Lower Crust

Tian

2019

JGR Solid Earth

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“…Petrographic thin sections were prepared in the plane parallel to the shear direction and perpendicular to the foliation. The surfaces of the sections were polished with diamond paste then colloidal silica, and then chemical etching of the surface was carried out with hydrofluoric (HF) acid following the method described in Wegner and Christie (1985), the latter to enhance SEM imaging of SGBs and Ca-rich clinopyroxene (Cpx) lamellae exsolved in Opx along the (100) plane.…”

Section: Methodsmentioning

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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“…1A), while 40 elsewhere in the grain the rotation is more gradual, without visible contrast. To further unravel the grain internal microstructures, we carried out the chemical etching of polished surfaces, following the method described in Wegner and Christie (1985), which resulted in the preferential dissolution of (i) cpx lamellae parallel to the opx (100) planes and (ii) GBs, which appear as thin black lines (Fig. 2).…”

Section: Grain Foldingmentioning

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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Chemical etching of amphiboles and pyroxenes

Cited by 8 publications

References 6 publications

Velocity Weakening of Simulated Augite Gouge at Hydrothermal Conditions: Implications for Frictional Slip of Pyroxene‐Bearing Mafic Lower Crust

Velocity Weakening of Simulated Augite Gouge at Hydrothermal Conditions: Implications for Frictional Slip of Pyroxene‐Bearing Mafic Lower Crust

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

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