Oblate Grains Research Articles

Effects of grain shape on packing and dilatancy of sheared granular materials.

A granular material exposed to shear shows a variety of unique phenomena: Reynolds dilatancy, positional order and orientational order effects may compete in the shear zone. We study granular packing consisting of macroscopic prolate, oblate and spherical grains and compare their behaviour. X-ray tomography is used to determine the particle positions and orientations in a cylindrical split bottom shear cell. Packing densities and the arrangements of individual particles in the shear zone are evaluated. For anisometric particles, we observe the competition of two opposite effects. On the one hand, the sheared granules are dilated, on the other hand the particles reorient and align with respect to the streamlines. Even though aligned cylinders in principle may achieve higher packing densities, this alignment compensates for the effect of dilatancy only partially. The complex rearrangements lead to a depression of the surface above the well oriented region while neighbouring parts still show the effect of dilation in the form of heaps. For grains with isotropic shapes, the surface remains rather flat. Perfect monodisperse spheres crystallize in the shear zone, whereby positional order partially overcompensates dilatancy effects. However, even slight deviations from the ideal monodisperse sphere shape inhibit crystallization.

Optical constants of refractory oxides at high temperatures

Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300 K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. A high-temperature-high-pressure-cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum (alpha-Al$_2$O$_3$), spinel (MgAl$_2$O$_4$), and alpha-quartz (SiO$_2$), temperature-dependent optical constants were measured from 300 K up to more than 900 K. Small particle spectra were also calculated from these data. All three examined oxides show a significant temperature dependence of their mid-IR bands. For the case of corundum, we find that the 13$\mu$m emission feature - seen in the IR spectra of many AGB stars - can very well be assigned to this mineral species. The best fit of the feature is achieved with oblate corundum grains at mean temperatures around 550 K. Spinel remains a viable carrier of the 13$\mu$m feature as well, but only for T < 300 K and nearly spherical grain shapes. Under such circumstances, spinel grains may also account for the 31.8$\mu$m band that is frequently seen in sources of the 13$\mu$m feature and which has not yet been identified with certainty.

Androecium development in the bromeliad Dyckia pseudococcinea L.B.Sm. (Pitcairnioideae-Bromeliaceae), an endangered species endemic to Brazil: implications for conservation

Dyckia pseudococcinea L.B.Sm. is endemic to the restingas of Maricá, State of Rio de Janeiro, in southeastern Brazil. However, since this area is under intense ecological stress, D. pseudococcinea is considered an endangered plant species. An important step toward the conservation of this species is establishing the developmental stage most favorable to in vitro propagation. Accordingly, the present study analyzed the androecium to establish the developmental stages of anthers, emphasizing anther wall development, androsporogenesis and androgametogenesis. The relationships between the size of flowers and anthers were also studied. Anther wall development follows the basic-type, while the tapetum, which is originated from the subepidermal layer (inner secondary parietal layer 2 and archesporial initials), follows the secretory-type. Androsporogenesis is successive and originates isobilateral and decussate tetrads. The oblate and monosulcate pollen grains exhibit microreticulate exine and are dispersed at the bicellular stage. At the vacuolated stage, the androspore (microspore) is still proliferating and not yet completely differentiated. Therefore, since the androspore has not yet lost its embryonic capacity, we suggest the preferential use of this developmental stage, which is present in flower buds 6.4–7.1mm in length, in conservation protocols focused on the androgenesis of D. pseudococcinea.

Infrared emission from the composite grains: effects of inclusions and porosities on the 10 and 18 μm features

In this paper we study the effects of inclusions and porosities on the emission properties of silicate grains and compare the model curves with the observed infrared emission from circumstellar dust. We calculate the absorption efficiency of the composite grain, made up of a host silicate oblate spheroid and inclusions of ice/graphite/or voids, in the spectral region 5.0-25.0$\mu m$. The absorption efficiencies of the composite spheroidal oblate grains for three axial ratios are computed using the discrete dipole approximation (DDA). We study the absorption as a function of the volume fraction of the inclusions and porosity. In particular, we study the variation in the $10\mu m$ and $18\mu m$ emission features with the volume fraction of the inclusions and porosities. We then calculate the infrared fluxes for these composite grains at several dust temperatures (T=200-350K) and compare the model curves with the average observed IRAS-LRS curve, obtained for circumstellar dust shells around oxygen rich M-type stars. The model curves are also compared with two other individual stars. The results on the composite grains clearly indicate that the silicate feature at 10$\mu m$ shifts with the volume fraction of graphite inclusions. The feature does not shift with the porosity. Both the features do not show any broadening with the inclusions or porosity. The absorption efficiencies of the composite grains calculated using DDA and Effective Medium Approximation (EMA) do not agree. The composite grain models presented in this study need to be compared with the observed IR emission from the circumstellar dust around a few more stars.

Role of fine-scale layering and grain alignment in the electrical anisotropy of marine sediments

Electrical resistivities of seafloor sediments determined by controlled source electromagnetic (CSEM) surveys have been found to be significantly greater than those measured by electrical well logging, in some instances by a ratio of as much as 5:1. Because borehole logging techniques invariably measure electrical resistivity using currents circulating in horizontal planes and CSEM surveys are sensitive to the currents circulating in vertical planes, a possible cause of this discrepancy is strong electrical anisotropy of the sediments. We have examined electrical log data from vertical exploration and appraisal wells and deviated production wells in the North Sea. By correlating the same sedimentary units between wells, we are able to compare resistivities measured at different borehole inclination angles. As the inclination angle changes, the amount of vertical and horizontal resistivity contributing to the resistivity changes. Hence we can estimate the electrical anisotropy in the sediments. Results indicate that anisotropy ratios of 1:5 and greater are present within the shale-dominated units. We show that fine-scale horizontal layering can make only a relatively small contribution to this anisotropy, but that a model of horizontal alignment of highly oblate spheroidal grains can account for most or all of it.

A new species of Polygala (Polygalaceae) from ultramafic soils in Sekhukhuneland, South Africa, with notes on its ecology

Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk (Polygala; section Polygala; subsection Heterolophus), a new species with a restricted range in Sekhukhuneland, South Africa, is described, illustrated and compared with other members of the genus. It is a dwarf shrub that can be distinguished by its much-branched habit, sparsely flowered inflorescences, pink alae with darker pink veins, brown to black seed testa, and oblate pollen grains with pronounced opercula. Geographically, P. sekhukhuniensis is confined to heavily eroded localized sites, a natural geomorphological feature of some of the highly water-dispersible soils derived from ultramafic rocks in the valleys of the Steelpoort River and its tributaries in the Sekhukhuneland Centre of Plant Endemism. P. sekhukhuniensis is a calciotrophic excluder of heavy metals that accumulates Ca in its leaves. It is ecologically compared with co-occurring species of Polygala on ultramafic-derived soil.

Microfabric characteristics and rheological significance of ultra‐high‐pressure metamorphosed jadeite‐quartzite and eclogite from Shuanghe, Dabie Mountains, China

AbstractQuantitative analysis of the structural evolution of jadeite‐quartzite, a rare ultra‐high pressure (UHP) rock type from the Dabie Mountains of eastern China, sheds light on the formation and evolution of UHP orogenic belts worldwide. Geological mapping of the Shuanghe area, where jadeite‐quartzites crop out, was carried out to determine the spatial relationships between different UHP rocks within this orogen. The deformation mechanisms of jadeite‐quartzite, geodynamical parameters (stress, strain, strain rate), and microstructure including lattice preferred orientation (LPO) were determined from six jadeite‐quartzite samples from the Shuanghe area. LPOs of clinopyroxene (jadeite and omphacite), garnet, rutile and quartz from these jadeite‐quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the Shuanghe area. Microstructural LPOs of jadeite, omphacite, garnet, rutile and quartz were determined using electron backscattered diffraction (EBSD) analysis. Quartz fabrics were largely recrystallized during late, low‐grade stages of deformation, whereas garnet shows no strong LPO patterns. Rutile fabrics show a weak LS fabric along [001]. Jadeite and omphacite show the strongest eclogite facies LPO patterns, suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust. Microstructural data show that the jadeite LPO patterns are similar to those of omphacite and vary between L‐ and S‐types, which correlate with prolate and oblate grain shape fabrics (SPO); quartz LPOs are monoclinic. Microstructural analysis using TEM shows that the dominant slip systems of jadeite in one sample are (100)[001], (110)[001] and (1 1 0)1/2[110], while in another sample, no dislocations are observed. Abundant dislocations in quartz were accommodated by the dominant slip system (0001)[110], indicating basal glide and represents regional shearing during the exhumation process. This suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under UHP conditions. The protoliths of jadeite‐quartzite, metasedimentary rocks from the northern passive continental margin of the Yangtze craton, experienced the same deep subduction and were deformed under similar rheological conditions as other UHP eclogite, marble and paragneiss. Experimental UHP deformation of quartzo‐feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite–stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths. The resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km (24 GPa). Thus, processes of deep continental subduction may be better‐understood through understanding the rheology and mechanical behaviour of jadeite. Jadeite‐quartzites such as those from the Shuanghe may be exhumed remnants of deeply‐subducted slabs of continental crust, other parts of which subducted past the ‘depth of no return’, and remain in the deep mantle.

Near-infrared imaging polarimetry of young stellar objects in ρ Ophiuchi

The results of a near-infrared (J H K LP) imaging linear polarimetry survey of 20 young stellar objects in ρ Ophiuchi are presented. The majority of the sources are unresolved, with K band polarizations, PK 20% are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K band core polarizations >6% are only observed in Class I YSOs. A 3-dimensional Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the ρ Oph young stellar objects with extended nebulae. A ρ / r 1.5 power law for the density is applied throughout the envelopes. The large scale centrosymmetric polarisation structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned nonspherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually 610%, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes 61.05 � m.

Morfologia polínica das espécies arbóreas de Apocynaceae do Estado de Santa Catarina, Brasil

Foi analisada no presente trabalho a morfologia polínica de sete espécies pertencentes a três gêneros da família Apocynaceae ocorrentes no Estado de Santa Catarina, Brasil. Os grãos de pólen das três espécies de Aspidosperma [A. australe Muell. Arg. A. pyricollum Muell. Arg. e A. ramiflorum Muell. Arg.] correspondem a um mesmo tipo polínico e não apresentam características morfológicas específicas. O mesmo fato ocorre com as três espécies do gênero Peschiera (Peschiera cf. australis (Muell. Arg.) Miers, Peschiera catharinensis (DC) Miers e Peschiera aff. histrix (Stend.) DC. Rauvolfia sellowii Muell. Arg. apresenta uma morfologia polínica característica por meio de grãos de pólen oblatos e brevicolpados. Característico para todas as espécies examinadas é a formação de um vestíbulo na área apertural dos grãos de pólen.

Recrystallization of high-purity aluminium during equal channel angular pressing

Aluminium with 5N purity were deformed at room temperature by equal channel angular pressing following Route A up to three passes. The microstructure and the crystallographic texture were investigated by orientation imaging microscopy and electron backscatter diffraction, respectively. The microstructure showed complete recrystallization after the first ECAP pass onwards. The grain size decreased slightly with increasing number of passes. The corresponding texture consisted of an oblique cube component. The oblate grains and the cube texture were rotated anticlockwise about the transverse direction. The inclination of grains with respect to the direction of ECAP was dependent on the distance from the top of the billet and changed from pass to pass. The mechanism of formation of the microstructure and texture is discussed in the light of the physical phenomena involved.

Analytical study of spheroidal dust grains in plasma

Using the modified spheroidal equations, the potential of a spheroidal conducting grain, floated in a plasma, is calculated. The electric field and capacitance for both prolate and oblate spheroidal grains are investigated. The solutions, obtained up to the second-order approximation, show that the plasma screening causes the equipotential surfaces around the grain to be more elongated or flattened than the potential spheroids of the Laplace equation. This leads to the variation of the plasma concentration around the grain.

Oblique Cube Texture Formation in High Purity Aluminum during Equal Channel Angular Pressing

Aluminum of 5N purity has been deformed at room temperature by equal channel angular pressing using three passes of route A. The microstructure and texture have been investigated by electron back-scattering and neutron diffraction. The microstructure from the first pass on is totally dynamically recrystallized. The recrystallization texture consists of an oblique cube component. The oblate grains and the cube texture are anticlockwise rotated about the transverse direction. The inclination with respect to the extrusion direction depends on the distance from the top of the extruded bar and changes from pass to pass. The mechanism of ormation of the recrystallization microstructure and texture is discussed.

High-resolution imaging polarimetry of HL Tau and magnetic field structure

We present high quality near infrared imaging polarimetry of HL Tau at 0.4 to 0.6 arcsec resolution, obtained with Subaru/CIAO and UKIRT/IRCAM. 3-D Monte Carlo modelling with aligned oblate grains is used to probe the structure of the circumstellar envelope and the magnetic field, as well as the dust properties. At J band the source shows a centrosymmetric pattern dominated by scattered light. In the H and K bands the central source becomes visible and its polarisation appears to be dominated by dichroic extinction, with a position angle inclined by � 40 ◦ to the disc axis. The polarisation pattern of the environs on scales up to 200 AU is consistent with the same dichroic extinction signature superimposed on the centrosymmetric scattering pattern. These data can be modelled with a magnetic field which is twisted on scales from tens to hundreds of AU, or alternatively by a field which is globally misaligned with the disc axis. A unique solution to the field structure will require spatially resolved circular polarisation data. The best fit Monte Carlo model indicates a shallow near infrared extinction law. When combined with the observed high polarisation and non-negligible albedo these constraints can be fitted with a grain model involving dirty water ice mantles in which the largest particles have radii slightly in excess of 1 µm. The best fit model has an envelope structure which is slightly flattened on scales up to several hundred AU. Both lobes of the bipolar outflow cavity contain a substantial optical depth of dust (not just within the cavity walls). Curved, approximately parabolic, cavity walls fit the data better than a conical cavity. The small inner accretion disc observed at millimetre wavelengths is not seen at this spatial resolution.

Rock texture and magnetic lineation in dykes: a simple analytical model

We develop two simple models for simulating the combination of magnetic sub-fabrics related to magma flow in dykes. The basic assumptions are (i) the petrofabric is representative of the flow fabric, and (ii) the petrofabric is composed of S/C-type structures related to flow. The first model consists of summing the magnetic tensors of two identical sub-fabrics, differing solely by their relative rotation. This model accounts for the possible change of the macroscopic magnetic lineation from a flow-related fabric to a lineation situated at the geometric intersection between the two sub-fabrics. Such a result is obtained in the case of oblate to highly oblate sub-fabric ellipsoids. The second model integrates the effect of very oblate grains of variable orientations into calculating the shape controlled magnetic tensor of each sub-fabric, and emphasizes the possible under-estimation of fabric superposition due to microscopic disordering. The magma fluxes along the East Greenland volcanic margin are illustrated by the flow pattern within the major dyke swarm. The magmatic flow vectors inferred from the imbrication of magnetic foliation at the dyke margins are primarily horizontal. The classic use of magnetic lineation can lead to contradictory results, giving flow vectors perpendicular to the flow directions. The magnetic lineation is situated close to the zone axis of magnetic foliation planes over a wide range of scales throughout the dyke swarm, suggesting that the contradiction may arise from the association of several textural domains at the sample scale. Forward modelling of macroscopic magnetic fabrics using the first model yields good agreement with the measured magnetic fabric of the East Greenland dykes. Our results, which are applicable to strained sedimentary rocks, highlight the possible misuse of the magnetic lineation due to combination of magnetic textures. The exchange between a microscopic lineation, i.e. mineralogical lineation, and a macroscopic lineation, i.e. intersection lineation, is particularly expected for dykes that generally bear oblate magnetic textures.

Multiple scattering of polarized radiation by non-spherical grains: First results

We present the first numerical radiative transfer simulation of multiple light scattering in dust configurations containing aligned non-spherical (spheroidal) dust grains. Such models are especially important if one wants to explain the circular polarization of light, observed in a variety of astronomical objects. The optical properties of the spheroidal grains are calculated using the method of separation of variables developed by Voshchinnikov & Farafonov ([CITE]). The radiative transfer problem is solved on the basis of the Monte Carlo method. Test simulations, confirming the correct numerical implementation of the scattering mechanism, are presented. As a first application, we investigate the linear and circular polarization of light coming from a spherical circumstellar shell. This shell contains perfectly aligned prolate or oblate spheroidal grains. We investigate the dependence of the results on the grain parameters (equivolume radius, aspect ratio) and the shell parameters (inner/outer radius, optical thickness). The most remarkable features of the simulated linear polarization maps are so-called polarization null points where the reversal of polarization occurs. They appear in the case when the grain alignment axis is perpendicular to the line of sight. The position of these points may be used for the estimation of grain shape and geometrical structure of the shell. The origin of null points lies in the physics of light scattering by non-spherical particles and is not related to the cancellation of polarization as was discussed in previous models. The maps of circular polarization have a sector-like structure with maxima at the ends of lines inclined to the grain alignment axis by .

Crystallographic fabrics of omphacite, rutile and quartz in Vendée eclogites (Armorican Massif, France). Consequences for deformation mechanisms and regimes

This study aims at further understanding of the mechanisms how lattice-preferred orientations (LPO) develop during deformation in the main eclogite minerals. Microstructures and textures of deformed eclogites from the Les Essarts complex (Western France) were investigated using optical microscopy and electron backscatter diffraction (EBSD) in the scanning electron microscope. Microfabric analyses of eclogite-facies minerals are used to identify their deformation mechanisms, which define the rheology at high-pressure metamorphic conditions. Mechanisms of intracrystalline deformation by dislocation movement (dislocation creep) result usually in a non-linear flow law (typically power law), while diffusive processes (diffusion creep) correspond to linear flow laws. General microstructural observations may suggest intracrystalline deformation (dislocation creep) of omphacite. The omphacite LPO vary between S- and L-type and correlate with oblate or prolate grain shape fabrics, respectively. Until now, these LPO types have not been understood by plasticity models based on dislocation glide on the known slip systems in clinopyroxene. An alternative interpretation is given in terms of anisotropic growth and dissolution, with grain boundary diffusion as the rate controlling process. There are further indications suggesting diffusion creep with concomitant anisotropic growth and dissolution as a main deformation mechanism in omphacite. In omphacite around a hollow garnet, crystallographic and shape fabrics align with the c[001] axes parallel to the grain elongations defining the mineral lineation, which rotates locally with the inferred flow direction. In this part, the grain sizes of omphacite and rutile are larger than in the surrounding matrix. The geometry of both the shape and crystallographic fabrics is interpreted to represent the local stress regime (directions and ratios of the principal stresses). The LPO of rutile duplicate the LPO of omphacite and a similar distinction between S- and L-type was used. Rutile deformation mechanisms probably involve dislocation creep as well as diffusion creep. Quartz mainly occurs as an interstitial phase with weak LPO patterns interpreted as random. No representative obliquity of the LPO in omphacite nor rutile with respect to foliation and lineation was observed to be used as potential shear sense criteria. However, the rutile LPO was slightly rotated relative to the omphacite LPO consistently in most samples. The results suggest that diffusion processes are strongly involved in the deformation of eclogites. A linear flow law should be taken into account in tectonic models where eclogites are incorporated.

The temperature of nonspherical circumstellar dust grains

The temperatures of prolate and oblate spheroidal dust grains in the envelopes of stars of various spectral types are calculated. Homogeneous particles with aspect ratios a/b≤10 composed of amorphous carbon, iron, dirty ice, various silicates, and other materials are considered. The temperatures of spherical and spheroidal particles were found to vary similarly with particle size, distance to the star, and stellar temperature. The temperature ratio T d(spheroid)/T d(sphere) depends most strongly on the grain chemical composition and shape. Spheroidal grains are generally colder than spherical particles of the same volume; only iron spheroids can be slightly hotter than iron spheres. At a/b≈2, the temperature differences do not exceed 10%. If a/b≥4, the temperatures can differ by 30–40%. For a fixed dust mass in the medium, the fluxes at wavelengths λ≥100 are higher if the grains are nonspherical, which gives overestimated dust masses from millimeter observations. The effect of grain shape should also be taken into account when modeling Galactic-dust emission properties, which are calculated when searching for fluctuations of the cosmic microwave background radiation in its Wien wing.

Particle Shapes and the 2175 A Feature

The Galactic interstellar extinction curve exhibits a pronounced feature at 2175 ?. The most striking characteristic of this feature is the relatively fixed nature of its central wavelength, while the width of the feature may vary. Small graphite particles are often proposed as the carrier of this UV bump. However, graphite grains of a single size and shape cannot reproduce the observed width and peak characteristics simultaneously. Here, we investigate to what extent these characteristics may be reproduced by invoking a shape distribution of prolate and oblate graphite particles. The graphite constants calculated by Draine and Lee do not yield the narrowest 2175 ? features that have been observed. We have recalculated the dielectric function of astronomical graphite such that a spherical grain of radius 50 ? produces a feature with a peak at x0 = 4.6 ?m-1 and a width ? = 0.8 ?m-1. Using grains in the Rayleigh approximation, we have calculated extinction curves for combinations of prolate, spherical, and oblate grain shapes and successfully reproduce the stationary nature of the peak. In addition, such shape variations do give a standard deviation in the width of the feature of ~1/2 the observed standard deviation. However, the absolute values of the calculated widths fall short by ~10% compared with observed widths. The observed lack of correlation between peak position and width is not reproduced by the shape variations considered here.

Inelastic dissipation in a freely rotating body: application to cosmic dust alignment

Motivated by a recent study by Lazarian and Draine, which showed that a high degree of grain alignment of the paramagnetic dust is achievable if the rates of internal relaxation are controlled by the Barnett relaxation process, we undertake a study of an alternative mechanism of internal dissipation, namely, the inelastic dissipation of energy in oblate dust grains. We find that deformations at double frequency that were disregarded in earlier studies dominate the inelastic relaxation. Our results indicate that for sufficiently oblate grains, e.g. for grains with a 4:1 axis ratio, or/and grains formed by agglomeration, inelastic relaxation dominates the Barnett relaxation within large (a > 0.1 μm) grains. For grains with an axis ratio less than 1:2, the inelastic relaxation is dominant for suprathermally rotating grains.

Volume loss, fluid flow, and coaxial versus noncoaxial deformation in retrograde, amphibolite facies shear zones, northern Malawi, east-central Africa

Two retrograde, amphibolite facies shear zones were studied to explore the relationship between retrograde mineral reactions, volume strain, fluid flow, mylonitization, and coaxial versus noncoaxial deformation. The two shear zones are the contractional Mafwewu Hills shear zone and the transcurrently displacing Mkamasa River shear zone of northern Malawi. In general, shear-zone formation is characterized by the breakdown of feldspar and biotite and the formation of sillimanite, quartz, and water. Silica, alkali, and alkali earth elements were mobile. Mass-balance calculations, based on major- and trace-element geochemistry, indicate as much as 50%–60% volume loss in mylonite. Fluid to rock ratios estimated from the calculated depletions of silica are as much as 200–400, indicating that the initiation and activity of the shear zones were accompanied by large amounts of fluids that infiltrated the shear zones. These fluids caused an almost complete loss of alkalies within the shear zone, leading to the development of almost “dry” and sheet-silicate–free mylonite. It is proposed that the associated destabilization of micas destroyed the pathways for fluid circulation and ultimately caused the cessation of shearing. In the Mafwewu Hills shear zone, shear-zone–related stretching lineations are oriented parallel to tectonic transport. In the Mkamasa River shear zone, the stretching lineations curve from a subhorizontal attitude in the wall rock into a subvertical attitude in mylonite characterized by large volume loss. Shear bands in the Mkamasa River shear zone indicate a sinistral sense of shear. A synoptic analysis of mesoscale S and Z asymmetric folds indicates that the orientation of the stretching lineations in mylonite characterized by large volume loss is subperpendicular to the regional tectonic transport direction. Aspect ratios of feldspar and quartz in XZ sections (X ≥ Y ≥ Z, principal axes of finite-strain ellipsoid) show oblate grain shapes and show a positive correlation with volume strain. Mean kinematic vorticity numbers are 0.26–0.44 in the wall rock and 0.57–0.79 in mylonite. In mylonite, small kinematic vorticity numbers correlate with large volume loss. The transport-perpendicular orientation of the stretching lineations in strongly volume-deficient mylonite is thought to be the result of a pronounced component of shortening normal to the shear zone; the resulting higher degree of coaxial deformation controlled the final orientation of the stretching lineations.