Mesoscopic Observations Research Articles

A 1251m-thick Deccan Flood Basalt Pile Recovered by Scientific Drilling in the Koyna Region, Western India

ABSTRACT A 1251 m thick succession of Deccan lava flows has been recovered by scientific drilling in the Koyna region, western part of the Deccan Volcanic Province (DVP). Forty-six lava flows, starting with the first flow overlying the granitic basement in the region, have been identified through mesoscopic studies of cores obtained from a 1500 m deep borehole KBH7 in Panchgani village of Patan sub-division. Mesoscopic observations supported by petrographic studies bring out the characteristics of the basaltic pile. The salient findings are as follows. The thickness of Deccan trap in the Panchgani area is 1251.20 m, comprising a succession of 40 simple lava flows and 6 compound lava flows. The contact with the underlying granitic basement occurs over a short span of 90 cm. Infra-trappean sediments are absent. Overall, ∼74% of the basaltic pile is constituted of massive basalt and ∼24% vesicular/amygdaloidal basalt. Red bole horizons are observed in 7 flows. Nine giant plagioclase basalt (GPB) flows are identified in the single vertical section. The long basalt core may serve as a model Deccan trap section for correlation with the flows exposed at the surface in the Koyna and surrounding region and support detailed investigations to constrain the duration of Deccan volcanism.

Armas de guerra ou de caça? Funcionalidade e proveniência das pontas de seta do Zambujal (Torres Vedras, Portugal)

Esta contribuição insere-se num trabalho mais vasto que temos vindo a desenvolver desde 2014 sobre a pedra lascada do Zambujal, focalizado na caracterização petrográfica, nas estratégias de aquisição e na gestão dos recursos siliciosos.
 O povoado fortificado do Zambujal assume-se como um caso de estudo privilegiado na Estremadura portuguesa, pelo elevado número de artefactos de sílex recuperados associados a um contexto cronoestratigráfico, em particular pela quantidade de pontas de seta proporcionalmente às restantes categorias líticas. Esta questão, juntamente com o facto de terem sido recolhidas naquele local (entre a primeira e a segunda linhas de defesa), reveste-se de grande importância, sugerindo a possibilidade de terem ocorrido conflitos armados entre estas populações ao longo do Calcolítico (3º milénio BCE).
 Neste estudo propomos testar a hipótese da existência de evidências de guerra no Calcolítico com base numa análise funcional (cálculo do índice de penetração - Ipn) e petrográfica (identificação de microfácies, génese e locais de aprovisionamento das litologias) das pontas de seta recolhidas no interior da barbacã da fortificação.
 Em conclusão, estes novos resultados, a partir de “velhos” dados, são o ponto de partida para identificar as estratégias de abastecimento e as fases iniciais das cadeias operatórias das pontas de seta do Zambujal, reconhecendo a existência de complexas redes de circulação de bens no Calcolítico que incluem, provavelmente, estratégias de controlo regional e inter-regional, reflectindo relações de estabilidade ou instabilidade entre as comunidades pré-históricas.

High‐Resolution Photography for Soil Micromorphology Slide Documentation

It is common practice today in soil micromorphology to scan slides with a flatbed scanner for slide documentation as well as for mesoscopic scale observation. However, the imagery produced by flatbed scanners often results in boundaries becoming diffuse when zooming in, a side effect of the continuously changing refraction of light caused by the moving scan head. This can be restricting or even unsatisfactory to specialists who rely on such imagery and while alternatives exist, their availability or suitability is not always guaranteed. This paper describes two variations on a static high‐resolution image acquisition method using a professional camera and common attributes of a standard photography studio. Minor postphotography processing too can be done with commonly used software packages. The presented method results in pictures with a resolution of 36 million pixels per image, providing high enough quality and resolution (approximately 4200 dpi) to allow the soil micromorphology practitioner to navigate the entire mesoscopic spectrum and as such offers a continuum of observation from the macroscopic scale to the optical microscopic observation at low (40×) magnification.

Environment induced entanglement in many-body mesoscopic systems

We show that two, non interacting, infinitely long spin chains can become globally entangled at the mesoscopic level of their fluctuation operators through a purely noisy microscopic mechanism induced by the presence of a common heat bath. By focusing on a suitable class of mesoscopic observables, the behaviour of the dissipatively generated quantum correlations between the two chains is studied as a function of the dissipation strength and bath temperature.

The occurrence of graphite-bearing fault rocks in the Atotsugawa fault system, Japan: Origins and implications for fault creep

Graphite in fault zones has received little attention even though it is a well-known solid lubricant that could affect frictional properties of faults dramatically. This paper reports the presence of abundant graphite in fault zones of the Atotsugawa fault system, central Japan. Mesoscopic and microscopic observations of fault rocks revealed two processes of carbon enrichment in fault zones. One is a pressure solution process or diffusive mass transfer in general which removes water-soluble minerals such as quartz and carbonates from rocks, resulting in the enrichment of insoluble minerals including carbon. The other process is precipitation of graphite from a high-temperature carbon-rich fluid, forming graphite filling fractures within cataclasitic fault zones. The two processes have led to the concentration, up to 12 wt% of graphite, in the Atotsugawa fault zones, compared to 0 to 3 wt% of carbonaceous materials in the host rocks. This concentration is high enough for graphite to affect frictional properties at wide range of slip rates. The presence of graphite may provide an explanation for the low resistivity, the patterns of microearthquakes and fault creep along the western part of the Atotsugawa fault system. Graphite should receive more attention as a weakening and stabilizing agent of faults.

Mass transfer and pressure solution in deformed shale of accretionary complex: Examples from the Shimanto Belt, southwestern Japan

This study investigates volume changes in the accretionary complex in southeastern Shikoku, Japan using mesoscopic and microscopic observations and chemical analyses of shale. Three types of deformation in shale were recognized: 1. coherent type (compacted), 2. type I mélange (less deformed), and 3. type II mélange (sheared). Pressure solution seams (PSS) are common and reflect large volume reductions for coherent type (13–50%) and type II mélange (17–54%). Positive correlations exist between PSS density and concentration of the immobile chemical component (TiO 2) and between PSS density and paleotemperature for type II mélange and coherent type. Under constant temperature conditions, the PSS density is higher for type II mélange than for coherent type, indicating more efficient generation of PSS for type II mélange. Based on the analysis of rheological equations, we conclude that generation of PSS may be controlled by differences in differential stress and/or the duration of deformation. The positive correlation between PSS density and TiO 2 concentration indicates that volume change in accretionary complexes can be described by a simple equation using PSS density.

Tourmaline nodules from Capo Bianco aplite (Elba Island, Italy): an example of diffusion limited aggregation growth in a magmatic system

The morphology of tourmaline nodules occurring in the Capo Bianco aplite (Elba Island, Italy) is studied. Outcrop features indicate that tourmaline nodules are the product of magmatic crystallization, as they are aligned along flow fields developed within the magmatic hosting mass. Mesoscopic observations indicate that nodule morphologies are very variable, from rounded to dendritic. Morphometric analyses show that tourmaline nodules are fractals and that fractal dimension quantifies their degree of irregularity. Numerical simulations of nodule growth are performed by using a Diffusion-Limited Aggregation process. The presence in natural samples of nodules with different morphologies is explained by considering a chaotic magmatic system characterized by a complex interplay between growth rate in different dynamical regions, latent heat of crystallization, and local convection dynamics. It is suggested that higher growth rates correspond to growth of tourmaline nodules in dynamical regions where the transfer of nutrients is very efficient. In such conditions, the latent heat released by the growing nodule is high, inducing strong local convection dynamics, destabilizing the nodule interface, and promoting the formation of dendritic morphologies. On the contrary, the growth of nodules in dynamical regions characterized by weak transfer of nutrients is inhibited leading to weak local convection dynamics and, consequently, to the formation of rounded morphologies.

Space-time thermodynamics and subsystem observables in a kinetically constrained model of glassy materials

In a recent article [M. Merolle et al., Proc. Natl. Acad. Sci. U.S.A. 102, 10837 (2005)], it was argued that dynamic heterogeneity in d-dimensional glass formers is a manifestation of an order-disorder phenomenon in the d+1 dimensions of space time. By considering a dynamical analog of the free energy, evidence was found for phase coexistence between active and inactive regions of space time, and it was suggested that this phenomenon underlies the glass transition. Here we develop these ideas further by investigating in detail the one-dimensional Fredrickson-Andersen (FA) model, in which the active and inactive phases originate in the reducibility of the dynamics. We illustrate the phase coexistence by considering the distributions of mesoscopic space-time observables. We show how the analogy with phase coexistence can be strengthened by breaking microscopic reversibility in the FA model, leading to a nonequilibrium theory in the directed percolation universality class.

Influence of deflection on a fold-to-fault progression: field evidence from near Marietta, South Carolina

Four periods of deformation (D1–D4) are recognized in the Lion Park Road borrow pit near Marietta, South Carolina. Although each period is characterized by distinct structures, D3 produced two structural styles (D3a, D3b) resulting from layer-parallel shortening. D3a is characterized by detachment folding at the tip of an underlying thrust. D3b is a fold-to-fault progression that was localized by east-dipping, quartz-filled gash fractures. The fold-to-fault progression demonstrates the influence of a mechanical anisotropy on ramp development. The early stages of D3b were formed by deflection of northwest-directed, layer-parallel shortening and active, down-section propagation of folds and thrusts. Following connection with a splay of basal detachment, later D3b stages resulted from up-section movement that produced kink folding and a throughgoing thrust. This up-section movement deformed and modified the geometries of older, down-section structures. Detailed mesoscopic field observations, integrated with a combination of current thrust fault models, are used to interpret the D3b fold-to-fault progression.

A record of pre-Variscan Barrovian regional metamorphism in the eastern part of the Slavonian Mountains (NE Croatia)

Petrological investigations and monazite dating are carried out on medium-grade metamorphic rocks (micaschist, gneiss and amphibolite) from the Kutjevacka Rijeka transect in the Slavonian Mts., Tisia Unit (NE Croatia). Field, mesoscopic and microstructural observations, as well as the preserved mineral chemistry, point to a single metamorphic event during peak assemblage growth reaching amphibolite facies conditions of ca. 600–650 °C and 8–11 kbar. Th, U and Pb contents of yttrium-rich accessory monazites indicate a pre-Variscan, i.e. Ordovician-Silurian age (444 ± 19 and 428 ± 25 Ma) for the medium-grade metamorphism of garnet-bearing micaschist.

Supersymmetric models for fermions on a lattice

AbstractWe investigate the large‐N behaviour of simple examples of supersymmetric interactions for fermions on a lattice. Witten's supersymmetric quantum mechanics and the BCS model appear just as two different aspects of one and the same model. For the BCS model, supersymmetry is only respected in a coherent superposition of Bogoliubov states. In this coherent superposition mesoscopic observables show better stability properties than in a Bogoliubov state.

Mesoscopic Approach to Energetic Material Sensitivity

ABSTRACT A background of some of the earliest mesoscopic phenomena observed in energetic material initiation is described together with newer results, an understanding of which provides a mesoscopic approach to energetic material sensitivity. Mesoscopic phenomena and observations include the formation of “initiation sites” at the atomic and molecular levels, and their propagation to form submicron “reaction sites,” which expand and coalesce to produce micron-scale “hot spots.” A physiochemical atomistic understanding for the observed phenomena is outlined and described.

Coarse-grained computations for a micellar system

We establish, through coarse-grained computation, a connection between traditional, continuum numerical algorithms (initial value problems as well as fixed point algorithms), and atomistic simulations of the Larson model of micelle formation. The procedure hinges on the (expected) evolution of a few slow, coarse-grained mesoscopic observables of the Monte Carlo simulation, and on (computational) time scale separation between these and the remaining "slaved," fast variables. Short bursts of appropriately initialized atomistic simulation are used to estimate the (coarse grained, deterministic) local dynamics of the evolution of the observables. These estimates are then in turn used to accelerate the evolution to computational stationarity through traditional continuum algorithms (forward Euler integration, Newton-Raphson fixed point computation). This "equation-free" framework, bypassing the derivation of explicit, closed equations for the observables (e.g., equations of state), may provide a computational bridge between direct atomistic/stochastic simulation and the analysis of its macroscopic, system-level consequences.

Reconstruction/Interpretation of Macroscopic Structures from Discontinuous Mesoscopic Observations: a Major Task of Field/Structural Geologists

Geologists face a difficult task when mapping metasedimentary rocks over large areas where outcrops are scarce: reconstruction/interpretation of the macroscopic structure from information gathered at isolated outcrops. Situations can range from very simple to very complex, but most have a unique solution. The basic technique derives from Shackleton's rule: to compare the stratigraphic (polarity) and geometric (angular relation between bedding and cleavage) criteria at each outcrop, to evaluate accordance - if they are accordant, the structure is very simple because antiforms (geometry) are anticlines (polarity) and synforms are synclines (upward facing folds); otherwise antiforms and synforms are, respectively, synclines and anticlines, and the macro-structure is more complex (downward facing folds). When studying, for instance, polyphase deformed metasedimentary rocks of accretionary wedges, the geologist often finds a second deformation phase with a concomitant cleavage, and he must be much more careful because first deformation phase criteria are modified by second phase folds. Still, solutions are possible if there are no second phase recumbent folds with plunging brows. When the geologist observes first phase overthrusts folded by a second deformation phase, the solutions are reasonably easier if the sense of shear of fault is known. Otherwise, solutions are similar to the ones of second phase folds. Here we propose new rules for these more complex cases. The most important rule is: first phase criteria are non-accordant in the inverted limbs of second phase folds, when vergences of first and second phases are in the same sense, and in the second phase normal limbs, when first and second phases show opposite vergences.

Diffusion Effects on Transformation and Deformation Behavior in Copper-Based Shape Memory Alloys

Experimental mesoscopic observations of the parent phase in Cu-based shape memory alloys, the associated martensitic transformation and the corresponding hysteresis cycle, are carried out. The coexistence effects between martensite and parent phase and the evolution of the transformation temperature (Ms), due to yearly effect on the parent phase, are determined. Several years of continuous measurements, mainly using Cu–Zn–Al alloys, establish: (A) The evolution of the transformation temperature with time and temperature in parent phase (amplitude close to 15% of the ambient temperature change). (B) The changes related with the coexistence among the phases (close to 5 K). (C) The existence of remnant after quench effects are also partially visualized via neutron diffraction. A model based on the experimental results describes the hysteresis cycle and the internal loops. The diffusion effects can be included in the model and the time evolution of Ms and of the hysteretic behavior can be well established. The simulated results allow predicting the damping performance of the material for long-term actions.

Distribution of fault rocks in the fracture zone of the Nojima Fault at a depth of 1140 m: Observations from the Hirabayashi NIED drill core

Abstract Characteristics of deformation and alteration of the 1140 m deep fracture zone of the Nojima Fault are described based on mesoscopic (to the naked eye) and microscopic (by both optical and scanning electron microscopes) observations of the Hirabayashi National Research Institute for Earth Science and Disaster Prevention (NIED) drill core. Three types of fault rocks; that is, fault breccia, fault gouge and cataclasite, appear in the central part of the fault zone and two types of weakly deformed and/or altered rocks; that is, weakly deformed and altered granodiorite and altered granodiorite, are located in the outside of the central part of the fault zone (damaged zone). Cataclasite appears occasionally in the damaged zone. Six distinct, thin foliated fault gouge zones, which dip to the south‐east, appear clearly in the very central part of the fracture zone. Slickenlines plunging to the north‐east are observed on the surface of the newest gouge. Based on the observations of XZ thin sections, these slickenlines and the newest gouge have the same kinematics as the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake), which was dextral‐reverse slip. Scanning electron microscopy observations of the freeze‐dried fault gouge show that a large amount of void space is maintained locally, which might play an important role as a path for fluid migration and the existence of either heterogeneity of pore fluid pressure or strain localization.

Internal structure of the Nojima Fault zone from the Hirabayashi GSJ drill core

Abstract The internal structures of the Nojima Fault, south‐west Japan, are examined from mesoscopic observations of continuous core samples from the Hirabayashi Geological Survey of Japan (GSJ) drilling. The drilling penetrated the central part of the Nojima Fault, which ruptured during the 1995 Kobe earthquake (Hyogo‐ken Nanbu earthquake) (M7.2). It intersected a 0.3 m‐thick layer of fault gouge, which is presumed to constitute the fault core (defined as a narrow zone of extremely concentrated deformation) of the Nojima Fault Zone. The rocks obtained from the Hirabayashi GSJ drilling were divided into five types based on the intensities of deformation and alteration: host rock, weakly deformed and altered granodiorite, fault breccia, cataclasite, and fault gouge. Weakly deformed and altered granodiorite is distributed widely in the fault zone. Fault breccia appears mostly just above the fault core. Cataclasite is distributed mainly in a narrow (≈1 m wide) zone in between the fault core and a smaller gouge zone encountered lower down from the drilling. Fault gouge in the fault core is divided into three types based on their color and textures. From their cross‐cutting relationships and vein development, the lowest fault gouge in the fault core is judged to be newer than the other two. The fault zone characterized by the deformation and alteration is assumed to be deeper than 426.2 m and its net thickness is > 46.5 m. The fault rocks in the hanging wall (above the fault core) are deformed and altered more intensely than those in the footwall (below the fault core). Furthermore, the intensities of deformation and alteration increase progressively towards the fault core in the hanging wall, but not in the footwall. The difference in the fault rock distribution between the hanging wall and the footwall might be related to the offset of the Nojima Fault and/or the asymmetrical ground motion during earthquakes.

Mesoscopic Scale Observations of Surface Alloying, Surface Phase Transitions, Domain Coarsening, and 3D Island Growth Pb on Cu(100)

Low energy electron microscopy (LEEM) is used to investigate the dynamics of Pb overlayer growth on Cu(100). By following changes in surface morphology during Pb deposition, the amount of Cu transported to the surface as the Pb first alloys into the surface during formation of the c(4x4) phase and subsequently de-alloys during conversion to the c(2x2) phase is measured. The authors find that the added coverage of Cu during alloying is consistent with the proposed model for the c(4x4) alloy phase, but the added coverage during de-alloying is not consistent with the accepted model for the c(2x2) phase. To account for the discrepancy, the authors propose that Cu atoms are incorporated in the c(2x2) structure. Island growth and step advancement during the transition from the c(2x2) to c(5{radical}2x{radical}2)R45{degree} structure agrees with this model. The authors also use the LEEM to identify the order and temperature of the two-dimensional melting phase transitions for the three Pb/Cu(100) surface structures. Phase transitions for the c(5{radical}2x{radical}2)R45{degree} and c(4x4) structures are first-order, but the c(2x2) transition is second order. They determine that rotational domains of the c(5{radical}2x{radical}2)R45{degree} structure coarsen from nanometer- to micron-sized dimensions with relatively mild heating ({approximately}120 C), whereas coarsening of c(4x4) domains requires considerably higher temperatures ({approximately}400 C). In studies of three-dimensional island formation, they find that the islands grow asymmetrically with an orientational dependence that is directly correlated with the domain structure of the underlying c(5{radical}2x{radical}2)R45{degree} phase.

Nature and origin of ‘carbon’ in the Archaean Witwatersrand Basin, South Africa

The nature and origin of the carbonaceous matter (‘carbon’) in the gold-bearing reefs of the Archaean Witwatersrand basin of South Africa has long been a subject of controversy and debate. The importance of the carbon results from its direct association with the gold grade. The studies reported here were directed at resolving the nature and origin of carbon. Techniques used include stope-scale (macroscopic) mapping, mesoscopic (hand specimen) examination, and microscopic studies incorporating the use of optical reflectance measurement. Macroscopic mapping has demonstrated the braided habit of carbon bodies over tens of square metres, with a close parallel to sedimentology. Mesoscopic observations, however, show the vein-like carbon seams are often cross-cutting sedimentary features, with the carbon occupying an anastomosing set of bed-parallel fractures. Microscopic observations show a globular form for the carbon and inclusions of uraninite particles. In seam carbon the globules are generally modified into elongated ‘spindles’ oriented perpendicular to bedding. Optical properties are dominated by generally high reflectance and anisotropy with a ‘swirling’ liquid crystal structure, classifying seam carbon as ‘carbonaceous mesophase’. It is this fine mesophase texture that has previously been wrongly attributed to plant (algal) morphology. Highly significantly, the optical anisotropy is bed perpendicular (rather than bed parallel as in normal sedimentary burial) indicating mesophase formation during fracture opening. Both reflectance and bireflectance of the seam mesophase show a range of values at all scales. No stratigraphic or depth trends were apparent, though geographic variation points to localization of the maximum temperature event(s). Given high anisotropies, maximum reflectance values in the 4–8% R o range and minima in the 1–2% R o range give arithmetic mean reflectance values of about 4.0% R o . Kinetic modelling equates these values with short term (50 000 years) temperature events of c. 400°C or burial temperatures of c. 280°C. Lower reflectance values of c. 2.0% R o obtained from the shales suggests thermal detachment of permeable and impermeable beds, a characteristic of pulsed hydrothermal flux. The included uraninite grains influence the orientation of the surrounding anisotropic mesophase demonstrating that uraninite predated the mesophase formation event. Regional palaeo-stress ‘frozen’ into the mesophase anisotropy indicates a NW–SE deviatoric stress. The combination of hydrocarbon, radiation and hydrothermal fluid flow marks Witwatersrand Basin pyrobitumens out as being different from conventional oil. Putative source rocks for the oil are identified in the intra-basinal Witwatersrand shale units. Lithological control in carbon seams is explained by the poro-perm and mechanical properties of the unconformity sequence of footwall, reef conglomerates and hanging wall quartzites favouring fracture along the unconformity surfaces. An overpressured oxidizing fluid created the fracture network that hosted the oil and also introduced uranium as uranyl ion. On meeting a reducing agent (oil), uraninite precipitated stabilizing the oil by polymerization. Further hotter hydrothermal flux then ‘coked’ the bitumen to often fibrous (spindle-shaped) mesophase. Continued flow deposited gold in the available pore spaces, most notably those formed by lateral contraction between mesophase spindles. The speculative role of methane in the reductive precipitation of gold is indicated by the presence of gold in any co-eval porosity largely independent of the mineral matrix.

Mesoscopic structure observation of egg white gel by small angle neutron scattering

The egg white sol becomes opaque gel by heat treatment, and the gel turns transparent on dehydration. In the present study, the structural change during the dehydration process was examined by small angle neutron scattering experiment; the data was fitted based on the Guinier and Ornstein-Zernike (O-Z) theories. The Guinier plot clarified the structure with the dimension of about 2.8 nm, which was almost independent of the water content. The correlation length derived from the O-Z plot became larger from 9.5 to 17.3 nm as the water content decreases.