Contrasting fluid evolution of granulite-facies marbles: implications for a high-T intermediate-P terrain in the Famatinian Range, San-Juan, Argentina

High-temperature, intermediate-pressure calc-silicate marbles occur in the granulite-facies terrain of the La Huerta Range in the Province of San Juan, NW-Argentina, in three bulk-compositional varieties: Type (1) dolomite-absent scapolite-wollastonite-grandite-clinopyroxene-quartz—calcite marbles; Type (2) diopside-forsterite-spinel-corundum—calcite marbles with dolomite exolution lamellae in calcite; Type (3) serpentinized forsterite-spinel-dolomite marbles. An isobaric cooling path from peak-metamorphic conditions of 860°C to 750°C at 6.5 kbar is inferred from scapolite-wollastonite-grandite reaction textures in Type (1) and is consistent with cooling after an advective heat input from related gabbroic and tonalitic intrusive bodies. Stable carbon and oxygen isotope geochemistry was used to decipher the fluid/rock evolution of the three marble types. An interpreted four-stage temperature-time-fluid flow path comprises: (1) infiltration of pre-peak-metamorphic fluids, depleted in δ¹⁸O, that caused a shift of primary sedimentary δ¹⁸O ratios to lower values (19.6–20.0); (2) syn-metamorphic fluid liberation from Type (1) marbles with evidence for processes close to batch devolatilization that caused a weak coupled ¹³C and ¹⁸O depletion during prograde metamorphism. A different devolatilization behaviour, close to Rayleigh fractionation, texturally associated with fold settings indicates that granulite-facies fluid flow was focused rather than pervasive; (3) H₂O-absent conditions were dominant when coronal grandite formed during incipient high-temperature isobaric cooling at the expense of scapolite and wollastonite in the Type (1) marbles; (4) intense post-peak- hydration of Type (2) and Type (3) marbles is the last recognizable metasomatic event. In combination, the three marble types record fluid infiltration both before and after the metamorphic peak.     

An analytical solution for the settlement of stone columns beneath rigid footings

This paper presents a new approximate solution to study the settlement of rigid footings resting on a soft soil improved with groups of stone columns. The solution development is fully analytical, but finite element analyses are used to verify the validity of some assumptions, such as a simplified geometric model, load distribution with depth and boundary conditions. Groups of stone columns are converted to equivalent single columns with the same cross-sectional area. So, the problem becomes axially symmetric. Soft soil is assumed as linear elastic, but plastic strains are considered in the column using the Mohr–Coulomb yield criterion and a non-associated flow rule, with a constant dilatancy angle. Soil profile is divided into independent horizontal slices, and equilibrium of stresses and compatibility of deformations are imposed in the vertical and horizontal directions. The solution is presented in a closed form and may be easily implemented in a spreadsheet. Comparisons of the proposed solution with numerical analyses show a good agreement for the whole range of common values, which confirms the validity of the solution and its hypotheses. The solution also compares well with a small-scale laboratory test available in the literature.     

Experimental simulation of melt migration in stromatic metatexite migmatites

Melting experiments on a gneissic protolith using the diamond trap technique produced an accumulation of crystals of biotite in the boundary of the diamond trap. Several hypotheses can be inferred to explain this feature, but textural evidence and calculations of the settling and drag velocities of the crystals suggest a model of extraction of melt due to a pressure gradient inside the capsule as the most likely origin of this biotite layer. This biotite layer and the trapped melt resemble the melanosome and leucosome, respectively, of stromatic metatexite migmatites. The melt extraction model developed is similar to the “filter pressing” model for migmatite formation. The diamond trap technique is a suitable method to develop migmatites experimentally.     

An ultrasonic method for the separation of carbonaceous material from schists for the determination of graphitization degree by X-ray diffraction

Previous studies have shown that the metamorphic grade of carbonaceous material (CM) can be quantified by an index known as the degree of graphitization. This index uses XRD to measure the interplaner d-spacings of graphitic material and to assess the degree of polymerization and ordering in the CM structure.

Traditional methods employ digestion of the silicate and oxide fractions by HF and HCl acid treatments. Unfortunately, this procedure often leaves behind insoluble residues of heavy minerals and fluorosilicate by-products. A new method was tried, taking advantage of the density difference between CM and the inorganic mineral phases prior to treatment with acids. Using ultrasonic disaggregation, separation is achieved by removing the low-density fraction that floats on top of a ground sample suspension after sedimentation. Subsequently this low-density fraction can be acid treated to concentrate CM. This paper is essentially a comparison of the two techniques for sample preparation with an examination of both pre- and post-treatment products by XRD and an evaluation of the graphitization index.     

The solar, exoplanet and cosmological lithium problems

We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li problem in planet hosting stars, which are claimed to be Li-poor when compared to field stars. Third, we discuss the cosmological Li problem, i.e. the discrepancy between the Li abundance in metal-poor stars (Spite plateau stars) and the predictions from standard Big Bang Nucleosynthesis. In all three cases we find that the “problems” are naturally explained by non-standard mixing in stars.     

Influence of geology in the geochemistry signature of Itacolomi State Park waters,Minas Gerais-Brazil

In all geological scenarios, mineral water reactions will affect the water chemistry. As such, water resources in different rocks commonly involve different hydrogeological compartments. The aim of this work is to evaluate the influence of geology in the geochemistry signature of Itacolomi State Park waters. To do so, a survey of the geological units in the area was carried out, a geological/stratigraphic division was made, and its correlation with the main geological events was determined. Using the advantages of GIS, all the catchments were delimited. Based on this division, near 30 stream and lake segments were chosen for analyses. In each point, all physiochemical properties of the water were measured, and samples were collected to determine the concentrations of major and trace elements by ICP–OES. The dynamics of the Itacolomi State Park rock-soil and stream water solutions suggest that mixing of drainage waters from different bedrock and soil sources regulates stream water physical–chemical parameters and solute concentrations. The analytical data showed a clear correlation between the chemical compositions of the solute and the geological characteristics of the catchment. Units that are covered by iron oxide hardpan (Manso unit) and iron-banded formations (Custódio unit) show a large amount of soluble elements, including high values of Fe and Mn. On the other hand, the presence of high values of Al and K (Itacolomi unit) are a direct consequence of the presence of quartzite associated with low pH values.     

The fresnel interferometric imager

The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 10⁵ to 10⁶ void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10^− 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10^− 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10^− 8 allows detection of objects at contrasts as high as than 10^− 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.     

Consolidation around stone columns. Influence of column deformation

A solution is presented for the radial consolidation around stone columns under constant surcharge load. The solution considers the influence of vertical and radial deformation of the column, either in elastic and elastoplastic regimes. The solution is in terms of the average excess pore pressure in the soil. It is based on previous solutions, initially developed for rigid column, or including only vertical deformation. For elastic column, the solution gives the variation of strains and stresses between the undrained and final states, for which it coincides with the existing elastic solutions. All the results are given in closed form, and both the elastic and plastic deformations of the column lead to an equivalent coefficient of consolidation for the radial flow, which enables the application of the existing methods of integration of the consolidation equation. A parametric study is presented, showing the influence of the main problem features. A design example is used to illustrate the application to practical cases. Copyright © 2008 John Wiley & Sons, Ltd.