Quantitative characterization of plastic deformation of zircon and geological implications

The deformation-related microstructure of an Indian Ocean zircon hosted in a gabbro deformed at amphibolite grade has been quantified by electron backscatter diffraction. Orientation mapping reveals progressive variations in intragrain crystallographic orientations that accommodate 20° of misorientation in the zircon crystal. These variations are manifested by discrete low-angle (<4°) boundaries that separate domains recording no resolvable orientation variation. The progressive nature of orientation change is documented by crystallographic pole figures which show systematic small circle distributions, and disorientation axes associated with 0.5–4° disorientation angles, which lie parallel to rational low index crystallographic axes. In the most distorted part of the grain (area A), this is the [100] crystal direction. A quaternion analysis of orientation correlations confirms the [100] rotation axis inferred by stereographic inspection, and reveals subtle orientation variations related to the local boundary structure. Microstructural characteristics and orientation data are consistent with the low-angle boundaries having a tilt boundary geometry with dislocation line [100]. This tilt boundary is most likely to have formed by accumulation of edge dislocations associated with a 〈001〉{100} slip system. Analysis of the energy associated with these dislocations suggest they are energetically more favorable than TEM verified 〈010〉{100} slip. Analysis of minor boundaries in area A indicates deformation by either [01¯0] (001) edge, or [100](100) and [001](100) screw dislocations. In other parts of the grain, [11¯0] cross slip on (111), (111¯) and (112) planes seems likely. These data provide the first detailed microstructural analysis of naturally deformed zircon and indicate ductile crystal-plastic deformation of zircon by the formation and migration of dislocations into low-angle boundaries. Minimum estimates of dislocation density in the low-angle boundaries are of the order of ∼3.1010 cm−2. This value is sufficiently high to have a marked effect on the geochemical behavior of zircon, via enhanced bulk diffusion and increased dissolution rates. Therefore, crystal plasticity in zircon may have significant implications for the interpretation of radiometric ages, isotopic discordance and trace element mobility during high-grade metamorphism and melting of the crust

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized

Defining the mechanism for compaction of the CV chondrite parent body

The Allende meteorite, a relatively unaltered member of the CV carbonaceous chondrite group, contains primitive crystallographic textures that can inform our understanding of early Solar System planetary compaction. To test between models of porosity reduction on the CV parent body, complex microstructures within ~0.5-mm-diameter chondrules and ~10-µm-long matrix olivine grains were analyzed by electron backscatter diffraction (EBSD) techniques. The large area map presented is one of the most extensive EBSD maps to have been collected in application to extraterrestrial materials. Chondrule margins preferentially exhibit limited intragrain crystallographic misorientation due to localized crystal-plastic deformation. Crystallographic preferred orientations (CPOs) preserved by matrix olivine grains are strongly coupled to grain shape, most pronounced in shortest dimension &lt; a &gt;, yet are locally variable in orientation and strength. Lithostatic pressure within plausible chondritic model asteroids is not sufficient to drive compaction or create the observed microstructures if the aggregate was cold. Significant local variability in the orientation and intensity of compaction is also inconsistent with a global process. Detailed microstructures indicative of crystal-plastic deformation are consistent with brief heating events that were small in magnitude. When combined with a lack of sintered grains and the spatially heterogeneous CPO, ubiquitous hot isostatic pressing is unlikely to be responsible. Furthermore, Allende is the most metamorphosed CV chondrite, so if sintering occurred at all on the CV parent body it would be evident here. We conclude that the crystallographic textures observed reflect impact compaction and indicate shock-wave directionality. We therefore present some of the first significant evidence for shock compaction of the CV parent body

A nonvolatile phase-change metamaterial color display

This is the final version. Available from Wiley via the DOI in this record.Chalcogenide phase-change materials, which exhibit a marked difference in their electrical and optical properties when in their amorphous and crystalline phases and can be switched between these phases quickly and repeatedly, are traditionally exploited to deliver nonvolatile data storage in the form of rewritable optical disks and electrical phase-change memories. However, exciting new potential applications are now emerging in areas such as integrated phase-change photonics, phase-change optical metamaterials/metasurfaces, and optoelectronic displays. Here, ideas from these last two fields are fused together to deliver a novel concept, namely a switchable phase-change metamaterial/metasurface resonant absorber having nonvolatile color generating capabilities. With the phase-change layer, here GeTe, in the crystalline phase, the resonant absorber can be tuned to selectively absorb the red, green, and blue spectral bands of the visible spectrum, so generating vivid cyan, magenta, and yellow pixels. When the phase-change layer is switched into the amorphous phase, the resonant absorption is suppressed and a flat, pseudowhite reflectance results. Thus, a route to the potential development is opened-up of nonvolatile, phase-change metamaterial color displays and color electronic signage.Engineering and Physical Sciences Research Council (EPSRC

Surface morphology and structural types of natural impact apographitic diamonds

External and internal morphologies of natural impact apographitic diamonds (paramorphoses) have been studied.Вивчено зовнішню і внутрішню морфологію природного імпактного апографітового алмазу – параморфоз.Изучена внешняя и внутреняя морфология природного импактного апографитового алмаза – параморфоз

Phase-change meta-photonics

We combine phase-change materials and metamaterial arrays (metasurfaces) to create new forms of dynamic, tuneable and reconfigurable photonic devices including ‘perfect’ absorbers, infra-red light modulators, optical beam steerers and enhanced phase-change optoelectronic displays

Boom boom pow: Shock-facilitated aqueous alteration and evidence for two shock events in the Martian nakhlite meteorites

Nakhlite meteorites are ~1.4 to 1.3 Ga old igneous rocks, aqueously altered on Mars ~630 Ma ago. We test the theory that water-rock interaction was impact driven. Electron backscatter diffraction demonstrates that the meteorites Miller Range 03346 and Lafayette were heterogeneously deformed, leading to localized regions of brecciation, plastic deformation, and mechanical twinning of augite. Numerical modeling shows that the pattern of deformation is consistent with shock-generated compressive and tensile stresses. Mesostasis within shocked areas was aqueously altered to phyllosilicates, carbonates, and oxides, suggesting a genetic link between the two processes. We propose that an impact ~630 Ma ago simultaneously deformed the nakhlite parent rocks and generated liquid water by melting of permafrost. Ensuing water-rock interaction focused on shocked mesostasis with a high density of reactive sites. The nakhlite source location must have two spatially correlated craters, one ~630 Ma old and another, ejecting the meteorites, ~11 Ma ago

Actively forming Kuroko-type volcanic-hosted massive sulfide (VHMS) mineralization at Iheya North, Okinawa Trough, Japan

Modern seafloor hydrothermal systems provide important insights into the formation and discovery of ancient volcanic-hosted massive sulfide (VHMS) deposits. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 drilled five sites in the Iheya North hydrothermal field in the middle Okinawa Trough back-arc basin, Japan. Hydrothermal alteration and sulfide mineralization is hosted in a geologically complex, mixed sequence of coarse pumiceous volcaniclastic and fine hemipelagic sediments, overlying a dacitic to rhyolitic volcanic substrate. At site C0016, located adjacent to the foot of the actively venting North Big Chimney massive sulfide mound, massive sphalerite-(pyrite-chalcopyrite ± galena)-rich sulfides were intersected (to 30.2% Zn, 12.3% Pb, 2.68% Cu, 33.1 ppm Ag and 0.07 ppm Au) that strongly resemble the black ore of the Miocene-age Kuroko deposits of Japan. Sulfide mineralization shows clear evidence of formation through a combination of surface detrital and subsurface chemical processes, with at least some sphalerite precipitating into void space in the rock. Volcanic rocks beneath massive sulfides exhibit quartz-muscovite/illite and quartz-Mg-chlorite alteration reminiscent of VHMS proximal footwall alteration associated with Kuroko-type deposits, characterized by increasing MgO, Fe/Zn and Cu/Zn with depth. Recovered felsic footwall rocks are of FII to FIII affinity with well-developed negative Eu anomalies, consistent with VHMS-hosting felsic rocks in Phanerozoic ensialic arc/back-arc settings worldwide. Site C0013, ∼100 m east of North Big Chimney, represents a likely location of recent high temperature discharge, preserved as surficial coarse-grained sulfidic sediments (43.2% Zn, 4.4% Pb, 5.4% Cu, 42 ppm Ag and 0.02 ppm Au) containing high concentrations of As, Cd, Mo, Sb, and W. Near surface hydrothermal alteration is dominated by kaolinite and muscovite with locally abundant native sulfur, indicative of acidic hydrothermal fluids. Alteration grades to Mg-chlorite dominated assemblages at depths of >5 mbsf (metres below sea floor). Late coarse-grained anhydrite veining overprints earlier alteration and is interpreted to have precipitated from down welling seawater as hydrothermal activity waned. At site C0014, ∼350 m farther east, hydrothermal assemblages are characterized by illite/montmorillonite, with Mg-chlorite present at depths below ∼30 mbsf. Recovered lithologies from distal, recharge site C0017 are unaltered, with low MgO, FeO and base metal concentrations. Mineralization and alteration assemblages are consistent with the Iheya North system representing a modern analogue for Kuroko-type VHMS mineralization. Fluid flow is focussed laterally along pumiceous volcaniclastic strata (compartmentalized between impermeable hemipelagic sediments), and vertically along faults. The abundance of Fe-poor sphalerite and Mg-rich chlorite (clinochlore/penninite) is consistent with the lower Fe budget, temperature and higher oxidation state of felsic volcanic-hosted hydrothermal systems worldwide compared to Mid Ocean Ridge black smoker systems

Measurement of the mass difference m(D-s(+))-m(D+) at CDF II

We present a measurement of the mass difference m(D-s(+))-m(D+), where both the D-s(+) and D+ are reconstructed in the phipi(+) decay channel. This measurement uses 11.6 pb(-1) of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D-s(+))-m(D+)=99.41+/-0.38(stat)+/-0.21(syst) MeV/c(2)