Cathodoluminescence as a tracing technique for quartz precipitation in low velocity shear experiments

Two simulated gouges (a pure quartz and a quartz-muscovite mixture) were experimentally deformed in a ring shear apparatus at a constant low velocity under hydrothermal conditions favourable for dissolution–precipitation processes. Microstructural analysis using scanning electron microscope cathodoluminescence imaging and cathodoluminescence spectroscopy combined with chemical analysis showed that quartz dissolution and precipitation occurred in both experiments. The starting materials and deformation conditions were chosen so that dissolution–precipitation microstructures could be unambiguously identified from their cathodoluminescence signal. Precipitated quartz was observed as blue luminescent fracture fills and overgrowths with increased Al content relative to the original quartz. In the pure quartz gouge, most of the shear deformation was localized on a boundary-parallel slip surface. Sealing of fractures in a pulverized zone directly adjacent to the slip surface may have helped keeping the deformation localized. In the quartz-muscovite mixture, some evidence was observed of shear-accommodating precipitation of quartz in strain shadows, but predominantly in fractures, elongating the original grains. Precipitation of quartz in fractures implies that the length scale of diffusive mass transfer in frictional-viscous flow is shorter than the length of the quartz domains. Additionally, fracturing might play a more important role than generally assumed. Our results show that cathodoluminescence, especially combined with chemical analysis, is a powerful tool in microstructural analyses of experimentally deformed quartz-bearing material and visualizing quartz precipitation

Recrystallisation and Trace-Element Mobility in Zircons: Implications for U-Pb Dating

Complex microstructures of zircon recrystallisation have been discovered in igneous and metamorphic zircons from the Jack Hills Metasedimentary Belt in Western Australia, and the granitic injection complex of Harris in north-west Scotland. Cathodoluminescence (CL), electron backscatter diffraction (EBSD) and wavelength dispersive spectroscopy (WDS) analysis reveal that recrystallisation in the studied zircons is often characterised by (1) translation, bending and fading of the oscillatory zoning; (2) structural recovery of the zircon; (3) an enrichment in Hf and depletion in Y in recrystallised zircon; and (4) the formation of a recrystallisation interface with a minor (<2°) misorientation. A new, composite recrystallisation model in which trace element and dislocation migration occurs shortly after crystallisation during magmatic cooling and pipe diffusion along dislocation arrays formed by the accumulation of dislocations allows enhanced diffusion to enrich Hf and leach U, Pb and Y. After the recrystallisation event, subsequent metamictization of primary zircon (typically with oscillatory zoning) creates zones that can structurally recover through a diffusion-reaction re-equilibration mechanism, resulting in further trace-element mobility. These mechanisms can create complex microstructures in zircons, suggesting that a detailed understanding of the crystallisation and recrystallisation history of a zircon may be required to accurately interpret its U-Pb ages

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland — Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting (liquid-like layer along the grain boundaries) on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine-grained layers are about an order of magnitude higher than in the much coarser-grained layers. The dominant deformation mechanisms, based on the flow relation of Goldsby and Kohlstedt (2001), between the layers is also different, with basal slip rate limited by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the finer-grained layers, while GBS-limited creep and dislocation creep (basal slip rate limited by non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures (T>262 K), it is expected that the fine-grained layers deform at high strain rates, while the coarse-grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between impurity-rich and low-impurity ice can have important consequences for ice dynamics close to the bedrock

Інтертекстуальність та гіпертекстуальні трансформації в турецьких народних оповідях

In this paper, some of the Turkish minstrel tales are analyzed in the frame of Gérard Genette’s ‘palimpsests’ approach. In the transtextuality category; the minstrel tales demonstrate both intertextual relations and hypertextual transformations. In terms of intertextuality, the tales present self-conscious intertextual relations by referring to other texts. The paper focuses on that in terms of hypertextuality, the mistrel tales transform the other texts by the process of reduction, extension, amplification and so on. Because of this process, the structure, the plot and the meaning of the previous text is transformed. As a result, the Turkish minstrel tales, as oral literary texts, can actively have role in intertextual relations as hypertexts.Türk halk hikâyelerine Fransız anlatıbilimci Gérard Genette’in “palempsest” imgesi ile yaklaşıldığında, halk hikâyelerinin ötemetinsellik sınıflandırmasında “metinlerarasılık” ve “ana metinsellik” ilişkilerini yansıttıkları görülmektedir. Halk hikâyeleri, göndermeler yoluyla bir başka metni somut olarak içinde barındırarak metinlerarasılık ilişkisi kurmaktadır. Bunun yanında, diğer sözlü ve yazılı metinleri biçimsel ve izleksel ya da anlamsal olarak dönüştürerek anlatısını yeniden kompoze etmek noktasında ana metinsellik ilişkisini kurmaktadır. Bu çalışmada Türk halk hikâyelerinin ana metinsellik dönüşümleri biçimsel ve anlamsal dönüşümler yoluyla incelenecektir. Türk halk hikâyeleri odağında yapılan çalışmalarda, genellikle kaynak ve etki alanı arayışları ile karşılaştırmalı eleştiri yaklaşımından yararlanılmıştır. Türk halk hikâyelerine metinlerarasılık ile yaklaşmak, anlatıların anlamsal ve yapısal olarak nasıl katmanlaştığını görmek ve anlatıyı metin olarak çözümlemek açısından somut veriler sağlayan bir yöntemdir

The frictional strength and stability of spatially heterogeneous fault gouges

Along-fault lithological heterogeneity is observed in all fault zones that cross-cut compositional layering. Numerical modelling studies on fault rupture nucleation, propagation and arrest often assume that the fault mechanical behaviour is governed by either the rheologically weak phase or by a homogeneous gouge mixture of juxtaposing lithologies. However, the effects of spatial heterogeneity on fault gouge composition and hence its frictional behaviour are less known. In this study, we simulate a mixture of mechanically contrasting rheologies of claystones and sandstones in fault gouges by using lithologies available in the well-known Groningen gas field stratigraphy (Ten Boer and Slochteren members, respectively). Friction experiments were performed in a rotary shear configuration to accommodate the large displacements required to study mixing and clay smearing in faults with large offsets. A velocity stepping procedure was conducted to quantify the rate-dependence of friction and its evolution with displacement. A spatial heterogeneity was introduced by segmentation of the simulated gouge in claystone and sandstone patches. In contrast to previous studies, we show that Slochteren sandstone gouges can exhibit velocity-weakening behaviour related to strain-localization in a principal slip zone with reduced grain size. Our experiments on segmented gouges show displacement-dependent changes in the sliding friction and its rate-dependence. Clay smearing and shear localization on foliation planes cause weakening of the gouge and a shift from velocity-weakening to velocity-strengthening behaviour. Progressive shearing leads to juxtaposition of sandstone segments that are separated only by a thin clay smear. We propose that the associated increase in friction is caused by lithology mixing at the interfaces between the clay smear and the bulk Slochteren sandstone gouge, and by the disruption of continuous Y-shears. Progressive shearing does not lead to a decrease in the rate-sensitivity parameter (a-b). This observation suggests that shearing remains localized on phyllosilicate foliations, possibly accommodated by the increased width of the principal slip zone (PSZ) with displacement. Our results show that fault friction and its rate-dependence are not simply governed by the weakest lithology along a fault plane, nor that they can be simply represented by a homogeneous mixture of the juxtaposing lithologies. Detailed knowledge of the stratigraphic layering in combination with the fault offset is required to predict the macroscopic frictional behaviour of heterogeneous fault gouges

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modelling and analysed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighbouring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modelling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures

National EPOS initiatives and participation to the EPOS integration plan

European Plate Observing System (EPOS) is designed on a three-level architecture. The national research infrastructures (NRIs) constitute the backbone of the EPOS delivery framework, where data are generated, processed, analyzed and archived. These data are then integrated by thematic core services (TCS) and distributed through the centralized integrated core services (ICS). In this architecture, data provision from the NRIs is an essential element for the sustainable operation of the EPOS research infrastructure (RI). National EPOS initiatives in various countries in Europe are developed thanks to the increased awareness of the importance of FAIR (Findable, Accessible, Interoperable and Reusable) data management in science. As such, out of the 14 countries (13 members and one observer) that constitute the EPOS European Research Infrastructure Consortium (EPOS-ERIC), 11 have dedicated EPOS consortia established and included in the national roadmaps for research infrastructures. Moreover, there are in total 24 countries involved in the EPOS delivery framework where 10 are not yet members of EPOS-ERIC. However, the diversity of regulations and procedures adopted in different countries, hampers the development of dedicated EPOS consortia contributing to sustainability. In this paper, the national EPOS initiatives are discussed in order to emphasize synergies achieved and the shared efforts to build the EPOS RI during its life-cycle (the design, preparation, implementation, and pilot operational phases), tackling the challenge of sustainable operation.publishedVersio

Перебіг анемії вагітних у хворих на туберкульоз легень

В статье представлены данные течения анемии беременных и нарушения фетоплацентарного комплекса у 86 женщин, больных туберкулезом легких. Выявлено, что анемия на фоне туберкулезного процесса приводит к существенным функциональным и морфологическим нарушениям в плаценте. показано диагностическое значение оценки плацентарной дисфункции для профилактики и лечения анемии у данного контингента женщин.The article presents the data of course of pregnancy anemia and failures of fetoplacental complex in 86 women with pulmonary tuberculosis. It is found that anemia under tuberculous process leads to significant functional and morphological disturbances in placenta. Diagnostic significance of assessment of placental dysfunction for the prevention and treatment of anemia in this contingent of women is shown