Shock-twinned zircon in ejecta from the 45-m-diameter Kamil crater in southern Egypt

2021 ◽  
Author(s):  
Aaron J. Cavosie ◽  
Luigi Folco
Keyword(s):  
High Pressure ◽  
Electron Backscatter Diffraction ◽  
Empirical Studies ◽  
Impact Craters ◽  
Deformation Features ◽  
Twin Formation ◽  
Dissociated Zircon ◽  
Shatter Cones ◽  
Backscatter Diffraction ◽  
Quartz Grains

ABSTRACT With an age of less than ~5000 yr and a diameter of 45 m, Kamil crater in Egypt is one of the youngest and smallest terrestrial impact craters known to date. Abundant evidence of shock-deformed sandstone has been reported from Kamil crater, including shatter cones, vesicular impact glass, high-pressure polymorphs of silica and car bon, planar deformation features (PDFs) and planar fractures (PFs) in quartz, dissociated zircon, melt veins, and intergranular melt, giving rise to a range of estimated shock pressures from ~20 to ~60 GPa. Here, we investigated shocked zircon from Kamil crater through characterization of microstructures in a centimeter-sized clast of shocked nonporous sandstone ejecta, previously described as containing quartz grains with PDFs and PFs, coesite, stishovite, diamond, and lechatelierite. Orientation analysis by electron backscatter diffraction (EBSD) showed that the quartz arenite consists of damaged detrital quartz grains surrounded by a matrix of either comminuted quartz or intergranular melt. Individual quartz grains are pervasively fractured (abundant PFs and PDFs); apparent isotropic crushing resulted in uniformly and highly dispersed orientation clusters on pole figures. Zircon grains are not abundant; however, four of 19 grains analyzed by EBSD contained {112} deformation twin lamellae, with individual lamellae ranging in length from 1 to 2 µm. Lengths of twin lamellae in Kamil zircon grains are anomalously short compared to those report-ed in shocked zircon from other impact structures, where individual lamellae are tens of micrometers long. Previous empirical studies have suggested that {112} twin lamellae in zircon form at ~20 GPa in non-porous target rocks, a finding supported by their coexistence, in some impactites, with high-pressure phases such as reidite. The only available experimental constraint, by diamond anvil cell, found {112} twins in zircon powder quenched at 20 GPa. The presence of coesite, stishovite, lechatelierite, and shocked quartz with PDFs in the studied sample is consistent with empirically derived pressure estimates of ~20 GPa for {112} twin formation in zircon in the ejecta sample from Kamil crater. Kamil thus represents the smallest and youngest impact structure where shock-twinned zircon has been reported. Given the apparent efficiency of {112} twin formation (21% of grains), shock-twinned zircon is here shown to provide a robust and readily identifiable record of shock deformation in a relatively common mineral at one of the smallest known terrestrial impact craters.

scholarly journals Deformation Features of Super-Deep Diamonds

Minerals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 18 ◽  
Author(s):  
Alexey Ragozin ◽  
Dmitry Zedgenizov ◽  
Vladislav Shatsky ◽  
Konstantin Kuper ◽  
Hiroyuki Kagi
Keyword(s):  
Internal Structure ◽  
Transition Zone ◽  
Lower Mantle ◽  
Electron Backscatter Diffraction ◽  
Growth Environment ◽  
Growth History ◽  
Deformation Features ◽  
Dynamic Growth ◽  
Growth Features ◽  
Backscatter Diffraction

The paper presents new data on the internal structure of super-deep (sublithospheric) diamonds from Saõ-Luiz river placers (Brazil) and from alluvial placers of the northeastern Siberian platform (Yakutia). The sublithospheric origin of these diamonds is supported by the presence of mineral inclusions corresponding to associations of the transition zone and lower mantle. The features of morphology and internal structure have been studied by optical and scanning electron microscopy (SEM), cathodoluminescence topography (CL), and electron backscatter diffraction (EBSD) techniques. Diamonds typically have complicated growth histories displaying alternating episodes of growth, dissolution, and post-growth deformation and crushing processes. Most crystals have endured both plastic and brittle deformation during the growth history. Abundant deformation and resorption/growth features suggest a highly dynamic growth environment for super-deep diamonds. High temperatures expected in the transition zone and lower mantle could explain the plastic deformations of super-deep diamonds with low nitrogen content.

An Investigation of Microtexture Evolution in an AlMgSi Alloy Processed by High-Pressure Torsion

2011 ◽  
Vol 702-703 ◽  
pp. 165-168 ◽  
Author(s):  
Aicha Loucif ◽  
Thierry Baudin ◽  
François Brisset ◽  
Roberto B. Figueiredo ◽  
Rafik Chemam ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Distribution Function ◽  
High Pressure Torsion ◽  
Electron Backscatter Diffraction ◽  
Orientation Distribution ◽  
Homogeneous Microstructure ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
Almgsi Alloy

This investigation uses electron backscatter diffraction (EBSD) to study the development of microtexture with increasing deformation in an AlMgSi alloy having an initial grain size of about 150 µm subjected to high pressure torsion (HPT) up to a total of 5 turns. An homogeneous microstructure was achieved throughout the disc sample at high strains with the formation of ultra-fine grains. Observations based on orientation distribution function (ODF) calculation reveals the presence of the torsion texture components often reported in the literature for f.c.c. materials. In particular, the C {001}<110> component was found to be dominant. Furthermore, no significant change in the texture sharpness was observed by increasing the strain.

Application of FIB-EBSD Tomography for Understanding Annealing Phenomena in a Cold Rolled Particle-Containing Nickel Alloy

2007 ◽  
Vol 558-559 ◽  
pp. 413-418 ◽  
Author(s):  
Wan Qiang Xu ◽  
Michael Ferry ◽  
Julie M. Cairney ◽  
John F. Humphreys
Keyword(s):  
Nickel Alloy ◽  
Focused Ion Beam ◽  
Electron Backscatter Diffraction ◽  
Ion Beam ◽  
Serial Sectioning ◽  
Dual Beam ◽  
Electron Backscatter ◽  
Cold Rolled ◽  
Twin Formation ◽  
Backscatter Diffraction

A typical dual-beam platform combines a focused ion beam (FIB) microscope with a field emission gun scanning electron microscope (FEGSEM). Using FIB-FEGSEM, it is possible to sequentially mill away > ~ 50 nm sections of a material by FIB and characterize, at high resolution, the crystallographic features of each new surface by electron backscatter diffraction (EBSD). The successive images can be combined to generate 3D crystallographic maps of the microstructure. A useful technique is described for FIB milling that allows the reliable reconstruction of 3D microstructures using EBSD. This serial sectioning technique was used to investigate the recrystallization behaviour of a particle-containing nickel alloy, which revealed a number of features of the recrystallizing grains that are not clearly evident in 2D EBSD micrographs such as clear evidence of particle stimulated nucleation (PSN) and twin formation and growth during PSN.

Texture Evolution of HPT-Processed Ni50Mn29Ga21

2011 ◽  
Vol 702-703 ◽  
pp. 169-172 ◽  
Author(s):  
Robert Chulist ◽  
Andrea Böhm ◽  
E. Rybacki ◽  
T. Lippmann ◽  
C.G. Oertel ◽  
...  
Keyword(s):  
High Pressure ◽  
Hydrostatic Pressure ◽  
Synchrotron Radiation ◽  
High Pressure Torsion ◽  
Electron Backscatter Diffraction ◽  
Texture Evolution ◽  
Residual Austenite ◽  
High Energy ◽  
Electron Backscatter ◽  
Backscatter Diffraction

The texture of polycrystalline Ni50Mn29Ga21alloys fabricated by high pressure torsion (HPT) was investigated with high-energy synchrotron radiation. HPT was performed at temperatures between 873K and 1173K under a hydrostatic pressure of 400 MPa. During HPT above 973K the initial cyclic fibre texture changes to a strong cube and a weak F component. Below 973K a strong rotated cube and weak F and C components develop. Additionally, electron backscatter diffraction reveals that samples deformed at low temperature do not completely transform to martensite giving rise to residual austenite.

Microstructural Analysis of Biomedical Co-Cr-Mo Alloy Subjected to High-Pressure Torsion Processing

2014 ◽  
Vol 616 ◽  
pp. 263-269
Author(s):  
Murat Isik ◽  
Mitsuo Niinomi ◽  
Ken Cho ◽  
Masaaki Nakai ◽  
Junko Hieda ◽  
...  
Keyword(s):  
High Pressure ◽  
Vickers Hardness ◽  
High Strain ◽  
High Pressure Torsion ◽  
Electron Backscatter Diffraction ◽  
Microstructural Analysis ◽  
Equivalent Strain ◽  
Ε Phase ◽  
Backscatter Diffraction ◽  
Equiaxed Grains

The effect of high-pressure torsion (HPT) processing on the microstructure and Vickers hardness of Co-Cr-Mo (CCM) alloys were investigated in this study. The microstructure of initial CCM alloy contains equiaxed grains with a grain diameter of approximately 50 μm and twins. The clear grain boundaries of equiaxed grains and twins disappear after HPT processing at a rotation number, N, of 10. The phase maps of initial CCM alloy and CCM alloy subjected to HPT processing at N = 5 measured by electron backscatter diffraction exhibit that the ratio of γ phase decreases from 93.5% to 34.1% and the ratio of ε phase increases from 6.5% to 65.9% by applying HPT processing. These results indicate that the ε phase is formed by high-strain, which is induced by the HPT processing. The Vickers hardness values on the surfaces of the CCM alloys subjected to HPT processing at N = 1, 5, and 10 increase with increasing the equivalent strain, εeq. These results suggest that an increase of Vickers hardness is correlated to an increase of the ratio of ε phase and the dislocation density, and grain refinement, which are caused by the high-strain induced by HPT processing.

scholarly journals Empirical constraints on progressive shock metamorphism of magnetite from the Siljan impact structure, Sweden

Geology ◽  
2021 ◽  
Author(s):  
Sanna Holm-Alwmark ◽  
Timmons M. Erickson ◽  
Aaron J. Cavosie
Keyword(s):  
Electron Backscatter Diffraction ◽  
Crystallographic Analysis ◽  
Hypervelocity Impact ◽  
Accessory Mineral ◽  
Shear Direction ◽  
Impact Structure ◽  
Shock Deformation ◽  
Deformation Features ◽  
Backscatter Diffraction ◽  
Impact Events

Little is known about the microstructural behavior of magnetite during hypervelocity impact events, even though it is a widespread accessory mineral and an important magnetic carrier in terrestrial and extraterrestrial rocks. We report systematic electron backscatter diffraction crystallographic analysis of shock features in magnetite from a transect across the 52-km-diameter ca. 380 Ma Siljan impact structure in Sweden. Magnetite grains in granitoid samples contain brittle fracturing, crystal-plasticity, and lamellar twins. Deformation twins along {111} with shear direction of &lt;112&gt; are consistent with spinel-law twins. Inferred bulk shock pressures for the investigated samples, as constrained by planar deformation features (PDFs) in quartz and shock twins in zircon, range from 0 to 20 GPa; onset of shock-induced twinning in magnetite is observed at &gt;5 GPa. These results highlight the utility of magnetite to record shock deformation in rocks that experience shock pressures &gt;5 GPa, which may be useful in quartz-poor samples. Despite significant hydrothermal alteration and the variable transformation of host magnetite to hematite, shock effects are preserved, which demonstrates that magnetite is a reliable mineral for preserving shock deformation over geologic time.

scholarly journals The Effects of Strain Annealing on Grain Boundary Distribution and Hardening in Superpure Nickel

1996 ◽  
Vol 28 (1-2) ◽  
pp. 71-79 ◽  
Author(s):  
C. B. Thomson ◽  
V. Randle
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Pure Nickel ◽  
Special Boundary ◽  
Special Boundaries ◽  
Commercially Pure ◽  
Electron Backscatter ◽  
Twin Formation ◽  
High Level ◽  
Backscatter Diffraction

Electron backscatter diffraction is applied to the study of texture and mesotexture in superpure nickel. Low level strain annealing is shown to influence the grain boundary population such that greater proportions of special boundaries exist. It is found that variations in the texture of a specimen are not reflected by characteristic changes in the grain boundary population, indicating that texture analysis cannot be applied to the prediction of special boundary densities. Mechanisms active during the evolution of special boundaries are discussed and compared to those involved under similar conditions in commercially pure nickel. It is shown that alnnealing twin formation need not be prevalent for a high level of special boundaries to form. Differences in the hardness of various boundary types are identified, such that low angle boundaries and ∑3 boundaries close to exact misorientation can be categorized separately to other boundaries, in that they show minimal hardening.

Peculiarities in the Texture Formation of Intermetallic Compounds Deformed by High Pressure Torsion

2014 ◽  
Vol 1760 ◽  
Author(s):  
Christine Tränkner ◽  
Aurimas Pukenas ◽  
Jelena Horky ◽  
Michael Zehetbauer ◽  
Werner Skrotzki
Keyword(s):  
High Pressure ◽  
High Pressure Torsion ◽  
Electron Backscatter Diffraction ◽  
High Energy ◽  
X Ray ◽  
Local Texture ◽  
Large Rotations ◽  
Electron Backscatter ◽  
Shear Strains ◽  
Backscatter Diffraction

ABSTRACTNiAl, YCu and TiAl polycrystals with B2 and L10 structure, respectively, have been deformed by high pressure torsion (HPT) at temperatures between 20°C and 500°C at a hydrostatic pressure of 8 GPa to high shear strains. Local texture measurements were done by diffraction of high-energy synchrotron radiation and X-ray microdiffraction. In addition, the microstructure was analyzed by electron backscatter diffraction (EBSD). Besides typical shear components an oblique cube component is observed with quite large rotations about the transverse direction. Based on the temperature dependence of this component as well as on microstructure investigations it is concluded that it is formed by discontinuous dynamic recrystallization. The influence of high pressure on recrystallization of intermetallics at low temperatures is discussed.

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