Polygonal Texture Research Articles

Genesis of honeycomb buildups in the Permian Zechstein Group, Southern North Sea

Seismic interpretation has revealed a hitherto unreported honeycomb pattern of carbonate buildups within the Orchard Platform (Southern North Sea). The Z2 Stassfurt Halite Fm. onlaps the southern margin of the Orchard Platform and is also found infilling Z2 intra-platform lagoons to form salt lakes. Post Z2 evaporation, the deeper Z3 water column drowned the Orchard Platform inhibiting the platform recovery attempted by the Z3 Plattendolomit Fm. The palaeobathymetric variability of the drowned Orchard Platform was sufficient to bring parts of the seafloor into the photic zone allowing for the sporadic growth of the Z3 Plattendolomit Fm. However, the palaeobathymetric lows remained beneath the photic zone ensuring an incomplete regeneration of the Orchard Platform with the creation of a high-frequency network of intra-platform lagoons which mimic the polygonal texture of a honeycomb. Whilst previously accepted as collapse structures or karst systems, this study correlates the development of the honeycomb buildups to variations in seafloor palaeobathymetry which in turn mimic the structural lineaments of the Zechstein subcrop. Syn-depositional instability in the Zechstein subcrop caused the topsets of the Z2 salt lakes to become warped. The warped halite provided seed points for Z3 Plattendolomit Fm. growth which allowed for linear ridges of carbonate to traverse the Z2 salt lakes and eventually connect with the honeycomb buildups. Deposition in the Mesozoic lead to loading of the Zechstein. Halite-filled Z3 lagoons accommodated this loading, which caused a pinching effect on the Z3 honeycomb buildups. The sedimentological understanding provided by this study not only de-risks frontier exploration but also provides insight into carbonate growth in restricted platform recovery scenarios.

The petrogenesis of orbicular granites in the Diana’s Pool area, Zimbabwe

Abstract This paper assesses a poorly studied outcrop of orbicular granite from the Matopos granite batholith in the Diana’s Pool area, Zimbabwe. Historical samples from Diana’s Pool exhibit closely packed orbicules in a granitic matrix. They are 9 to 14 cm in diameter and are characterised by different types of orbicules containing coarse-grained felsic cores, fine-grained and alternating ferromagnesian and feldspathic shells, and a coarse-grained matrix. The orbicules are generally spherical to ellipsoidal in shape, however, some appear to be abraded and deformed. The compositions and grain sizes of cores and the matrix are comparable. Both the matrix and the cores are medium- to coarse-grained and dominated by plagioclase (the matrix probably in slightly lesser proportions), microcline (in variable proportions, and seemingly absent in some cores), quartz, biotite and accessory hornblende and magnetite. Contrary to the cores and matrix, shells are fine-grained and exhibit polygonal textures. In addition to this, the shells are dominated by biotite and magnetite; however, they do not contain hornblende. Plagioclase shows an almost complete overlap of An contents, x¯ = 26 ± 2.3 (core), x¯ = 24 ± 0.9 (shell) and x¯ = 25 ± 2.0 (matrix). Biotite composition in the shells is significantly less magnesian (x¯ = 16 ± 2.4) than in core (x¯ = 27 ± 2.2) and matrix (x¯ = 25 ± 2.2), whose compositions overlap. Average initial 87Sr/86Sr ratios from plagioclase in all the analysed shells (x¯ = 0.70226) are slightly more radiogenic than in the matrix (x¯ = 0.70193) and cores (x¯ = 0.70187). Cores are autoliths, which are plagioclase-rich, cumulate, or rim fragments reworked by new magma inputs or injections. Heterogeneous nucleation leading to the formation of orbicular shells around the cores is attributed to adiabatic decompression of magma pulses ascending in dykes, leading to superheating and resorption of early solids, and volatile exsolution, inducing undercooling, supersaturation, and shell crystallisation. The coarse-grained matrix crystallised later, after the orbicules formed, creating the groundmass and locking the orbicules in place. The deformation of shells and cores suggests that the orbicules continued to evolve in the presence of a melt (matrix material). As part of the Matopos Hills World Heritage Site, the Diana’s Pool orbicular granites present a unique and noteworthy petrogenesis, which should be preserved as part of the region’s important geoheritage.

Ground subsidence and polygon development due to thermokarst in the Lena-Aldan interfluve, eastern Siberia, revealed by satellite remote sensing data

Thermokarst development is a topographic change in the landscape that is commonly associated with permafrost degradation in ice-rich permafrost regions. The Lena-Aldan interfluvial area in Central Yakutia in eastern Siberia has undergone extensive thermokarst development in the last three decades, particularly in the vicinity of settlements. Despite the negative effects of thermokarst development on the inhabitants of these settlements, no quantitative observation methods have been developed to investigate the surface displacement due to thermokarst development over entire towns. This study utilized interferometric synthetic aperture radar to reveal ground-surface displacement associated with thermokarst near the settlements of selected towns. The findings showed that significant subsidence was detected in disturbed areas (farming and abundant arable land) near the towns. The magnitude of subsidence in the Tyungyulyu and Mayya areas was less than that in Churapcha and Amga. Polygon density in a defined area in each town was examined using high-resolution optical images. The polygon density in Churapcha was considerably lower than that in Mayya, whereas polygonal texture in some areas in Tyungyulyu and Amga was unclear. Spatial frequency analysis using satellite optical images showed clear differences in averaged spectrum models between well-developed and less-developed polygons, which may reflect trough depths and density of vegetation between polygons. Satellite-based subsidence maps and statistics describing polygon development may be useful for evaluating both initial and subsequent stages of thermokarst development.

Paleoproterozoic hydration of gabbronorite from the Mesoarchean Lechana layered complex, eastern Botswana

Amphibole in mafic rocks of Archean layered complexes could be magmatic, metamorphic or metasomatic in origin. In this study, we use a combined field, petrography, mineral chemistry, phase equilibria modeling and 40Ar/39Ar geochronology approach to characterize amphibole in gabbronorites from the Mesoarchean Lechana layered complex in eastern Botswana. To get a better understanding of the overprint events, the characteristics of amphibole in the spatially associated amphibolite are also included. The gabbronorite preserves magmatic cumulate texture, with brownish amphibole replacing pyroxene as widespread thin (up to 80 μm) rims. In comparison, the greenish amphibole in amphibolite form part of granoblastic polygonal texture. Amphibolite preserve evidence for anatectic and metasomatic overprints, while the gabbronorite only exhibit effects of the later. Phase equilibria modeling provide P-T conditions and H2O content for the amphibole formation in the gabbronorite. The 40Ar/39Ar geochronology gave an age of 2037 ± 27 Ma for this process. We relate the Paleoproterozoic hydration to form amphibole in gabbronorite to the residual aqueous fluids expelled during crystallization of an anatectic melt in the spatially associated amphibolite. The results highlight an example of the formation of amphibole in Archean layered mafic rocks via a post-magmatic hydration event.

Earth's Earliest Phaneritic Ultramafic Rocks: Mantle Slices or Crustal Cumulates?

AbstractWhen plate tectonics initiated remains uncertain, partly because many signals interpreted as diagnostic of plate tectonics can be alternatively explained via hot stagnant‐lid tectonics. One such signal involves the petrogenesis of early Archean phaneritic ultramafic rocks. In the Eoarchean Isua supracrustal belt (Greenland), some phaneritic ultramafic rocks have been dominantly interpreted as subduction‐related, tectonically‐exhumed mantle slices or cumulates. Here, we compared Eoarchean phaneritic ultramafic rocks from the Isua supracrustal belt with mantle peridotites, cumulates, and phaneritic ultramafic samples from the Paleoarchean East Pilbara Terrane (Australia), which is widely interpreted to have formed in non‐plate tectonic settings. Our findings show that Pilbara samples have cumulate and polygonal textures, melt‐enriched trace element patterns, relative enrichment of Os, Ir, and Ru versus Pt and Pd, and chromite‐spinel with variable TiO2 and Mg#, and relatively consistent Cr#. Both, new and existing data show that cumulates and mantle rocks potentially have similar whole‐rock geochemical characteristics, deformation fabrics, and alteration features. Geochemical modeling results indicate that Isua and Pilbara ultramafic rocks have interacted with low‐Pt and Pd melts generated by sequestration of Pd and Pt into sulphide and/or alloy during magmatism. Such melts cannot have interacted with a mantle wedge. Correspondingly, geochemical compositions and rock textures suggest that Isua and Pilbara ultramafic rocks are not tectonically‐exhumed mantle peridotites, but are cumulates that experienced metasomatism by fluids and co‐genetic melts. Because such rocks could have formed in either plate or non‐plate tectonic settings, they cannot be used to differentiate early Earth tectonic settings.

Exploring the relationships between shear zones and granites: field and microstructural data for contrasting case studies of the Borborema Province (NE Brazil)

We discuss meso- and microstructural features of granites closely related to strike-slip shear zones in the Borborema Province, NE Brazil. The Riacho do Icó stock is an en-cornue intrusion aged at ca. 607 Ma. Magmatic fabric is recorded in the core of the granite, whilst increasing deformation is marked by the development of mylonitic fabrics towards the Afogados da Ingazeira shear zone, including magmatic foliation and lineation rotation. Early recrystallization of quartz and K-feldspar crystals is widespread as a fabric with well-developed granoblastic polygonal textures and lobate subgrain boundaries, heterogeneously deformed lenses and ameboid quartz ribbons, typical of igneous rocks submitted to deformation in deep crustal levels. On the other hand, the Espinho Branco-Santa Luzia leucogranitic belt is hosted along the Patos Lineament, aged between the ca. 575 – 565 Ma interval. These rocks show discordant relationships with the host migmatites and the main deformational fabric is characterized by a dominant magmatic foliation that is locally overprinted by structures that are typical of solid-state flow. Quartz melt pockets and interstitial quartz grains filling fractures in feldspar clasts are common. Such characteristics are compatible with granites that were injected in the continental crust along planar anisotropies (i.e., shear zones) formed during the late-stage partial melting events that originated the migmatites of the area. The case studies are proxies in the understanding of different episodes of magma emplacement along shear zones in this part of West Gondwana.

Phase behaviors of classic liquid crystal dimers and trimers: Alternate induction of smectic and twist-bend nematic phases depending on spacer parity for liquid crystal trimers

A new heliconical mesophase without apparent molecular positional ordering, which was discovered in achiral bent molecules [i.e., the twist-bend nematic (NTB) phase], has become a hot topic of research in the field of liquid crystals (LCs). In this study, a series of classic LC trimer homologs, namely 4,4′-bis[ω-(4-cyanobiphenyl-4′-yloxy)alkoxy]biphenyls (CBOnOBOnOCB; n = 4–11), was synthesized, and their phase transitions and mesophase structures were evaluated in detail, to reinvestigate their elusive monotropic mesophases. Polarized optical microscopy (POM) observations revealed that below the nematic (N) phases, even-n homologs exhibited the fan-shaped and polygonal textures of the layered smectic (Sm) phase, while odd-n homologs displayed the blocky and striped textures associated with the recently discovered heliconical NTB phase. X-ray diffraction analyses of CBOnOBOnOCB (n = 10 and 11) revealed that their mesophases exhibited the cybotactic N phase property, and suggested that the monotropic mesophase observed for odd CBO11OBO11OCB was the pseudo-layered heliconical NTB phase rather than the layered Sm phase. Therefore, it was suggested that the Sm and NTB phases were alternately induced, depending on the spacer parity of classic LC trimer homologs CBOnOBOnOCB. This could be ascribed to the steric interactions associated with different molecular geometries, which are largely governed by the imposed spacer parity, and possess parallelly and obliquely located mesogenic biphenyl moieties for the even-n and odd-n homologs, respectively. In addition, the phase-transition behavior of a homologous series of ether-linked cyanobiphenyl-based LC dimers (CBOnOCB; n = 3–12) was investigated. POM observations shows that odd-n CBOnOCB homologs (n = 5, 7, 9, and 11) exhibited the monotropic N–NTB phase transition, which was only observed in the small supercooled N domains. Even-n CBOnOCB homologs exhibited only the N phase and did not exhibit Sm phases below the temperature of the N phase upon cooling. Hence, alternate induction of the Sm and NTB phases depending on n parity was observed only in the LC trimer homologs.

Biomimicry of iridescent, patterned insect cuticles: comparison of biological and synthetic, cholesteric microcells using hyperspectral imaging.

Biological systems inspire the design of multifunctional materials and devices. However, current synthetic replicas rarely capture the range of structural complexity observed in natural materials. Prior to the definition of a biomimetic design, a dual investigation with a common set of criteria for comparing the biological material and the replica is required. Here, we deal with this issue by addressing the non-trivial case of insect cuticles tessellated with polygonal microcells with iridescent colours due to the twisted cholesteric organization of chitin fibres. By using hyperspectral imaging within a common methodology, we compare, at several length scales, the textural, structural and spectral properties of the microcells found in the two-band cuticle of the scarab beetle Chrysina gloriosa with those of the polygonal texture formed in flat films of cholesteric liquid crystal oligomers. The hyperspectral imaging technique offers a unique opportunity to reveal the common features and differences in the spectral-spatial signatures of biological and synthetic samples at a 6-nm spectral resolution over 400 nm-1000 nm and a spatial resolution of 150 nm. The biomimetic design of chiral tessellations is relevant to the field of non-specular properties such as deflection and lensing in geometric phase planar optics.

Novel cholesterol-based liquid crystalline dimers: the α-cyanostilbene group served as a photofluorophore and mesogenic moiety

ABSTRACT Cyanostilbene units are vigorous candidates for chromophores and mesogens. Therefore, a series of dimer liquid crystals based on cyanostilbene and cholesterol were synthesised and characterised. The structure conforms to the molecular design and its physicochemical properties are stable. With the growth of the inner spacer flexible carbon chain, the mesomorphic properties are greatly different: not only the odd–even effect of the clearing points (/clearing enthalpies) is caused but also the samples exhibit increasingly complex enantiotropic mesophases, including SmC*, SmA and N* phases. Corresponding textures of these phases were observed, such as polygonal textures, focal-conic textures with dechiralisation lines and oily streaks textures, etc., and phase structures were further verified using variable-temperature XRD. Through the combined use of UV and fluorescence emission spectrometers, it was found that the increase of water content caused the enhancement of fluorescence intensities and the redshift of UV absorptions, which confirmed the fascinating aggregation-induced emission enhancement (AIEE) effect of the ChM-CN molecules.

Mineralogical and geochemical constraints on the origin and evolution of albitites from Dmytrivka at the Oktiabrski complex, Southeast Ukraine

Albitites from Dmytrivka quarry form veins like bodies within fenitized alkali granites of the Oktiabrski complex. They are mainly composed of albite, and subordinately K-feldspar, zircon, aegirine, astrophyllite, pyrochlore and ilmenite. Albitites are characterized by high alkalies (Na2O + K2O) content coupled with low MgO, CaO, and SiO2 concentrations relative to host alkali granites. They show inversion of REE patterns (negative slopes for LREE and positive slopes for HREE), enrichment in HFSE (i.e. Zr, Nb, Ta), and strong Eu anomalies. The existence of rare composite of M-type and W-type REE tetrad effect in albitites indicates their complex genesis, i.e. formation during the coexistence of the melt with aqueous phase, later being superimposed by further alterations with hydrothermal solutions. The magmatic origin of albitites (evolved from highly differentiated A-type magma and emplaced at shallow depths) is documented by the presence of flow and snowball textures, zircon-aegirine glomerocrysts, no traces of replacement interfaces and reaction zones between K-feldspar and albite as well as no smooth, gradual changes in bulk-rock compositions between alkali granite, fenite vs albitite. On the contrary, the strong influence of pervasive, post-magmatic high-temperature (381–392 °C evidenced by CM geothermometer), and highly-oxidizing alkaline-bearing metasomatizing fluids on albitites is revealed by the occurrence of polygonal textures of albite laths, red CL luminescence of feldspars typical of fenitized rocks as well as crystallization of astrophyllite at the expense of arfvedsonite. Additionally, the presence of fluid-mineral interactions is evidenced by the development of secondary porosity and patchy zoning within zircon crystals coupled with the presence of blue (Dy3+-Tb3+-activated) and yellow (SiO4-Tb3+-activated) domains within them. All these textural, mineralogical and geochemical features observed in albitites from Dmytrivka suggest complex, magmatic-hydrothermal nature of the rocks.

Application of 3D EBSD Technique to Study Crystallographic Texture in Heavily Cold-Rolled and Recrystallized Modified 9Cr–1Mo Steel

Automated electron backscatter diffraction (EBSD) technique in a dual-beam field emission gun scanning electron microscope has been successfully used to obtain three-dimensional (3D) orientation mapping of grains in modified 9Cr–1Mo after severe plastic deformation and recrystallization. In this technique, the microstructure and micro-texture across several sections of the material were studied by means of the state-of-the-art “slice and view” methodology using grazing incidence high-energy Ga+ focused ion beam for slicing and electron beam for viewing and EBSD analysis. By combining the data from each slice, a 3D texture map could be generated by means of image reconstruction technique. The orientation map thus generated provided volumetric microstructural and micro-textural information. The 3D EBSD studies on the heavily deformed mod-9Cr–1Mo steel (cold-rolled 88%) revealed that rolled grains were elongated like plates with thickness ≤ 200 nm. Analysis of the fiber texture components in rolled specimen across the sections showed near equal preference for all fiber texture components with some enhancement of the α-fiber texture. However, by recrystallizing at 1023 K for 1 h, elongated grains along rolling direction with large diameters (~ 40 to 100 µm) were observed together with finer (size ~ 0.5 to 2 µm) polygonal grains and γ-fiber texture component dominated over other texture components.

Twist bend nematic liquid crystals prepared by one-step condensation of 4-(4-Pentylcyclohexyl) benzoic acid and alkyl diol

ABSTRACTTwist bend nematic (NTB)-forming 9OCCHP5 and 11OCCHP5 dimers were synthesised by one-step condensation of 4-(4-pentylcyclohexyl) benzoic acid and alkyl diol with yields as high as 80%. Although each dimer formed the NTB phase only during the cooling process in a narrow temperature width as large as 4°C, their equiweight mixture formed an NTB phase during both the heating and cooling processes, displaying elliptical polygonal domains and rope-like optical texture. The NTB temperature range became wider by 29–38°C and reduced the orientational order parameter significantly from 0.39 to 0.29 with decreasing temperature.

U-Pb, Re-Os, and Ar/Ar Geochronology of Rare Earth Element (REE)-Rich Breccia Pipes and Associated Host Rocks from the Mesoproterozoic Pea Ridge Fe-REE-Au Deposit, St. Francois Mountains, Missouri

Rare earth element (REE)-rich breccia pipes (600,000 t @ 12% REO) are preserved along the margins of the 136 Mt Pea Ridge magnetite-apatite deposit, within Mesoproterozoic (~1.47 Ga) volcanic-plutonic rocks of the St. Francois Mountains terrane in southeastern Missouri, USA. The breccia pipes cut the rhyolite-hosted magnetite deposit, and contain clasts of nearly all local bedrock and mineralized lithologies. Grains of monazite and xenotime were extracted from breccia pipe samples for SHRIMP U-Pb geochronology; both minerals were also dated in one polished thin section. Monazite forms two morphologies: (1) matrix granular grains composed of numerous small (<50 μm) crystallites intergrown with rare xenotime, thorite, apatite, and magnetite; and (2) coarse euhedral, glassy, bright yellow grains similar to typical igneous or metamorphic monazite. Trace element abundances (including REE patterns) were determined on selected grains of monazite (both morphologies) and xenotime. Zircon grains from two samples of host rhyolite and two late felsic dikes collected underground at Pea Ridge were also dated. Additional geochronology done on breccia pipe minerals includes Re-Os on fine-grained molybdenite and 40Ar/39Ar on muscovite, biotite, and Kfeldspar. Ages (± 2-sigma errors) obtained by SHRIMP U-Pb analysis are as follows: (1) zircon from the two host rhyolite samples have ages of 1473.6 ± 8.0 and 1472.7 ± 5.6 Ma; most zircon in late felsic dikes is interpreted as xenocrystic (age range ca. 1522-1455 Ma); a population of rare spongy zircon is likely of igneous origin and yields an age of 1441 ± 9 Ma; (2) pale yellow granular monazite—1464.9 ± 3.3 Ma (no dated xenotime); (3) reddish matrix granular monazite—1462.0 ± 3.5 Ma and associated xenotime—1453 ± 11 Ma; (4) coarse glassy yellow monazite—1464.8 ± 2.1, 1461.7 ± 3.7 Ma, with rims at 1447.2 ± 4.7 Ma; and (5) matrix monazite (in situ) —1464.1 ± 3.6 and 1454.6 ± 9.6 Ma, and matrix xenotime (in situ) —1468.0 ± 8.0 Ma. Two slightly older ages of cores are about 1478 Ma. The young age of rims on the coarse glassy monazite coincides with a Re-Os age of 1440.6 ± 9.2 Ma determined in this study for molybdenite intergrown with quartz and allanite, and with the age of monazite inclusions in apatite from the magnetite ore (Neymark et al., this volume). A 40Ar/39Ar age of 1473 ± 1 Ma was obtained for muscovite from a breccia pipe sample. Geochronology and trace element geochemical data suggest that the granular matrix monazite and xenotime (in polygonal texture), and cores of coarse glassy monazite precipitated from hydrothermal fluids during breccia pipes formation. The second episode of mineral growth at ca. 1443 Ma may be related to faulting and fluid flow that rebrecciated the pipes. The ca. 10 m.y. gap between the ages of host volcanic rocks and breccia pipe monazite and xenotime suggests that breccia pipe mineral formation cannot be related to the felsic magmatism represented by the rhyolitic volcanic rocks, and hence is linked to a different magmatic-hydrothermal system.

A multi-analytical approach for determining the origin of the marbles in Temple-A from Laodicea ad Lycum (Denizli-Western Anatolia, Turkey)

Abstract Laodicea ad Lycum is the major and most important Hellenistic city in the Lycos Valley. The ancient city is located at 6 km northeast of Denizli and the most contemporary and significant archaeological site in southwestern Turkey. A large marble temple complex, which is simply named Temple-A, is a remarkable structure. The marbles of Temple-A can be classified into four groups, based on color, crystal size, crystal boundaries and foliation status. These groups are identified as (i) lilac-purple-veined, (ii) white, (iii) gray-veined and (iv) gray-blackish marbles. Microscopically, the lilac-purple veined, gray-veined and gray-blackish marbles display heteroblastic mosaic texture, and the white marbles display a homoeoblastic polygonal texture. The marble groups chiefly consist of calcite + dolomite ± augite (lilac-purple veined), calcite (white), calcite + dolomite ± quartz ± muscovite ± opaque minerals (gray-veined) and calcite ± quartz ± pyroxene ± zircon (gray-blackish). The minero-petrographic, geochemical and C–O stable isotope results reveal that most of the marbles sampled Temple-A at Laodicea share the same characteristics and composition of the marbles exploited in the ancient quarries of Hierapolis and Domuzderesi.

Fluid-present deformation aids chemical modification of chromite: Insights from chromites from Golyamo Kamenyane, SE Bulgaria

Chemical signatures of chromitites are commonly used to track the evolution of the Earth's mantle. However, chemical modification during deformation may have important implications for the interpretation of chromites' signatures. Here, we describe the details of how deformation promotes chemical modification in chromite. Physicochemical characteristics of the chromites were quantified by measuring crystallographic orientation relationships using Electron Back-Scattered Diffraction (EBSD) and electron microprobe analysis (EMP). Chromites show porphyroclastic textures with coarse-grained porphyroclasts (ca. 0.2–5mm) and fine-grained neoblasts (<200μm). Coarse-grained chromites are chemically zoned in terms of major elements from core to rim, preserving this initial igneous feature in the cores, while the outer rims reveal a metamorphic signature. Large chromite grains are characterized by local crystal-plastic deformation, exhibiting distinct inter-crystalline deformation including continuous crystal bending and subgrain boundaries as well as chemical modification in their outer, deformed parts. Two types of fine-grained chromite, F1 and F2, are present. While F1 exhibits a well-developed polygonal texture, straight grain boundaries and low intercrystal misorientation (<1°), F2 shows low-angle boundaries and significant intercrystalline misorientation (2–8°). Both F1 and F2 have higher Fe3+ and Cr and lower Mg# values than the cores of large grains. We interpret F1 and F2 to represent chromite recrystallized by heterogeneous nucleation and subgrain rotation recrystallization, respectively. Crystallographic preferred orientation (CPO) and misorientation data on the well-developed low-angle (subgrain) boundaries in coarse grains and F2 grains indicate that deformation in chromite was accommodated mainly by dislocation creep with the dominant activation of the {111}<100> slip system. The retrograde P–T exhumation path predicted by thermodynamic and chemical modeling suggests that these fine-grained chromites were produced when the initial chromitites reacted with oxidizing fluids during retrograde metamorphism (~1.0GPa and 500–700°C). Our results show that deformation in the dislocation-creep regime in a chemically open system has induced chemical modification and homogenization within chromite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of chromites, utilizing their microstructurally controlled variation or lack thereof.

Minero-petrographic and isotopic characterization of two antique marble quarries in the Deni̇zli̇ region (western Anatolia, Turkey)

Abstract The marbles are widely used rock types in the structures of today and ancient world. In this study, two ancient marble quarries named as Hierapolis and Domuzderesi in Denizli region, have been examined. The marble samples from these quarries can be grouped into three types, based on color, crystal size, crystal boundaries and foliation status. These groups are identified as white, gray veined and gray marbles. In terms of microscopic features, heteroblastic polygonal (white marbles in Hierapolis, gray veined and gray marbles in Domuzderesi) and homeoblastic polygonal textures (white marbles in Domuzderesi) have been defined. The mineral compositions of all marble groups are quite similar. They are consisting predominantly of carbonate minerals (calcite, dolomite) and, as accessory minerals quartz, muscovite, pyroxene and ferric iron oxides. These results are also supported by the XRD studies. According to the geochemical analyses, protoliths of Hierapolis and Domuzderesi marbles are limestone. In Hiearapolis marble quarry, the δ13C and δ18O values change between 0.63 - 3.52 ‰ and (-9.55) - (-1.21) ‰, in turn. The δ13C and δ18O values of Domuzderesi marble quarry range from (-1.44) ‰ and 3.41 ‰, -13.26 ‰ and (-5.3) ‰, respectively. Minero-petrographic, geochemical and C-O stable isotope results reveal that Hierapolis and Domuzderesi ancient quarries have similar characteristics which have orginated from a same protolith.

EXTRACTING SEMANTICALLY ANNOTATED 3D BUILDING MODELS WITH TEXTURES FROM OBLIQUE AERIAL IMAGERY

Abstract. This paper proposes a method for the reconstruction of city buildings with automatically derived textures that can be directly used for façade element classification. Oblique and nadir aerial imagery recorded by a multi-head camera system is transformed into dense 3D point clouds and evaluated statistically in order to extract the hull of the structures. For the resulting wall, roof and ground surfaces high-resolution polygonal texture patches are calculated and compactly arranged in a texture atlas without resampling. The façade textures subsequently get analyzed by a commercial software package to detect possible windows whose contours are projected into the original oriented source images and sparsely ray-casted to obtain their 3D world coordinates. With the windows being reintegrated into the previously extracted hull the final building models are stored as semantically annotated CityGML ”LOD-2.5” objects.

The Construction of the Dupin Cyclides in a Smectic A Polygonal Texture

We report experimental observations with optical microscopy of the usual so-called polygonal texture. We have made simulations of the Dupin cyclides in one small region of the sample.

Bouligand Structures Underlie Circularly Polarized Iridescence of Scarab Beetles: A Closer View

The iridescent metallic green beetle, Chrysina gloriosa, selectively reflects left circularly polarized light, and exhibits iridescence. The exoskeleton of C. gloriosa is decorated by a polygonal texture: hexagonal cells (∼10 micron) coexist with pentagons and heptagons. We find that the fraction of pentagons and heptagons computed using Voronoi analysis increase with an increase in curvature, implying that it is energetically favorable to create disordered patterns for higher curvature surfaces. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the size of the core and spatial distribution of color changes when the angle of incoming incident light is varied. Using confocal microscopy, we observe that these cells consist of nearly concentric, nested arcs that lie on surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. In this paper, we describe in detail how the microstructure referred to as Bouligand structure provides the basis for the morphogenesis, and for generating the intricate optical response of the exoskeleton of the beetle.

Variability of rock texture and morphology correlated with the clay‐bearing units at Mawrth Vallis, Mars

AbstractThe clay units at Mawrth Vallis have been well‐characterized in hyperspectral data; however, a similar study of high spatial resolution High Resolution Imaging Science Experiment (HiRISE) data has not been previously conducted. Here the textures of the clay units are described and related to mineralogy across the central Mawrth Vallis region. The nontronite‐bearing rocks appear tan in HiRISE COLOR data and are polygonally fractured with polygons 2–5 m across. In some cases, the fractures appear wider and/or have darker fill or the rocks are a darker brown. The montmorillonite‐bearing rocks appear blue with regular polygons 0.5–1.5 m across; sometimes, there are larger polygons surrounded by regular polygons, a square fracture pattern, or the color appears yellow or mottled blue‐yellow. Kaolinite‐rich rocks are the brightest outcrops and are nonpolygonally fractured. Regions with spectra consistent with hydrated silica or the ferrous mineral component do not have unique textures. Hydrated silica‐bearing rocks appear yellow or mottled with a regular polygonal texture or yellow with hummocky appearance with no polygons. It is also possible that dust/sand on the surface alters the montmorillonite spectrum to appear like that of hydrated silica. The ferrous component may be expressed as mottled coloring or as a bright fracture fill. The nontronite‐ and montmorillonite‐bearing units have remarkably consistent textures in this region, allowing them to be uniquely identified in the Mawrth Vallis region in nonhyperspectral data sets such as CTX and HiRISE. The morphology of the polygons in these two units suggests that their formation is likely dominated by desiccation and controlled by composition.