Calculation of thermodynamic properties of hydrated borates by group contribution method

 General equations to correlate and predict the thermodynamic properties of hydrated borates were developed based on the experimental results according to their structural types. The thermodynamic properties (ΔH _f ⁰ and ΔG _f ⁰) of a hydrated borate phase are the sum of the contributions of the cations in aqueous solution, the borate polyanions, and the structural water to the corresponding thermodynamic properties. This method is called the group contribution method, and it is extensively used to calculate the thermodynamic properties of many kinds of inorganic compounds, such as silicates and clay minerals. Received: 23 November 1998 / Accepted: 11 October 1999     

A crystal-chemical investigation of Cr substitution in muscovite by XANES spectroscopy

 This work introduces a novel procedure to fit the scattering features of XANES spectra. The procedure was applied and validated on a chromium-containing muscovite for which structural and crystal-chemical characterization is available from literature. The simulation, which involved clusters formed by up to 90 atoms, proved to be effective in representing the Cr local environment, even if the system is characterized by a very low metal content, as demonstrated by the extremely good correspondence with experimental data. Received: 23 May 2002 / Accepted: 6 November 2002     

A supplemental sampling method for estuarine ichthyoplankton with emphasis on the atherinidae

A three-stage sampler, filtering water from the 0–5 cm, 5–25 cm, and 25–45 cm microhorizons was tested during conventional ichthyoplankton studies. The sampler was as much as 240X more efficient than 0.5 m nets in the collection of larval atherinids. The atherinids were found most abundantly in the 0–5 cm microhorizon, probably due to a positive phototaxic response.     

Alkali-reactivity problems with emphasis on Canadian aggregates

The “classical” form of alkali-aggregate reaction involves the disordered forms of silica particularly opal, chert and chalcedony. The alkali-carbonate reaction involves argillaceous dolomitic limestones and the alkali silicate reaction is found in some grey-wackes, phyllites and argillites.Concrete deterioration due to the alkali-silica reaction has been reported from nearly all major geographic regions of Canada. In the very far north expansive cherts were found on Ellesmere Island. On the Prairies chert is common in the gravels derived from various limestone formations in the Cordillera. These cherts seem to show a low level of alkali-expansivity but when this is combined with other forms of attack on concrete it may contribute to durability failure. Chert containing sands and gravels which show a lowlevel of alkali-expansivity are also known from Quebec. Siliceous limestones, some of whichcontain chalcedony, are known from Ontario and Quebec and in some instances, appear to be a major factor in concrete deterioration. The classical areas of alkali-carbonate reaction occur in Kingston and other parts of Ontario. Greywackes, phyllites and argillites associated with alkali-expansive reactions in concrete have been described particularly from the Maritime Provinces, from parts of the Canadian Shield and from the northern part of Ellesmere Island.     

Conductive cooling of spherical bodies with emphasis on the Earth

To explore planetary evolution, we provide conductive cooling profiles that account for planet size, phonon diffusivity and various internal heating scenarios. Our new analytical solution for simple cooling of spheres reveals that heat is removed from only Earth's outermost ~1000 km over geological time. Numerical models with decaying heat production show that any upward concentration of radionuclides causes high temperatures at shallow depths, forcing interior temperatures to increase with time while producing a thermal gradient that forbids lower mantle convection. Hence, differentiation drives upper mantle magmatism and tectonics, leaving a quiescent but hot deep interior, while slowly melting the core.     

花岗岩按照压力的分类

研究表明,中酸性火成岩大致按照Sr=400μg/g和Yb=2μg/g的标志可以划分为4种类型,即高Sr低Yb(Sr＞400×10-6,Yb＜2×10-6)、低Sr低Yb(Sr＜400×10-6,Yb＜2×10-6)、低Sr高Yb(Sr＜400×10-6,Yb＞2×10-6)和高Sr高Yb(Sr＞400×10-6,Yb＞2×10-6)型.其中,从低Sr高Yb型中还可以分出非常低Sr高Yb(Sr＜100×10-6,Yb＞2×10-6)的一类.着重探讨了这5类花岗岩形成的源区深度问题,指出按照残留相组成和花岗岩Sr、Yb含量,可以将花岗岩形成的压力分为3或4个级别:①高压下与石榴子石平衡的花岗岩具有高Sr低Yb的特征;②中等压力下,残留相为麻粒岩相(斜长石 石榴子石 角闪石 辉石),花岗岩具低Sr低Yb或高Sr高Yb的特点(取决于原岩成分);③低压下,残留相有斜长石无石榴子石的花岗岩为低Sr高Yb类型的;④与蛇绿岩有关的在洋壳剖面浅部由辉长岩部分熔融形成的M型花岗岩可能是非常低压(高温)条件下形成的.     

The analysis of zoning in magmatic crystals with emphasis on olivine

Many of the observed features of zoning in magmatic phenocrysts may be due to the orientation of the section rather than inherent properties of the crystals. An ideal section for the studying of zoning in magmatic crystals has two characteristics: it goes through the center of the crystal, and is perpendicular to one or more crystal faces. Using a model zoned olivine crystal, it is possible to construct accurate zoning profiles for different types of section (centered, symmetrical and skewed). The probability of obtaining a random section which passes within x% of the center of a crystal is shown to be P=0.0x, while the probability that a random section will be within A degrees of perpendicular to a given plane is P=sin(A). A systematic approach to the study of zoned crystals is outlined. In particular, it is suggested that composition be plotted against distance cubed, in order to correct for the volume versus size problem. A method of determining if a given section goes through (or near) the center of a zoned crystal is also presented. The reasoning in this work applies to other types of magmatic crystals such as pyroxenes and plagioclase.     

A contemporary appraisal of some key Fiskian concepts with emphasis on Holocene meander belt formation and morphology

Looking back five decades and reflecting on the contributions of Harold Fisk to Lower Mississippi Valley (LMV) geological knowledge, it is apparent that he was highly successful in making engineers aware of the critical role of glacial advance and retreat, sea level changes, valley slope and river gradient, and time in affecting geomorphic processes, sedimentary patterns, and river regimes. Perhaps his greatest contribution to river engineering was in recognizing and elaborating on the effects of bed and bank materials on stream meandering. Fisk, however, could only work within the prevailing geological theory and method of his time with regard to glacial chronology and stratigraphy and such matters as global structure and tectonics. Major advances in these areas with new concepts and techniques have shown his LMV glacial response model to be oversimplified and invalid in some respects. More cycles of valley filling and cutting are now known to be represented in the alluvial sequence and his concept of deep valley entrenchment as a direct response to sea level changes is untenable in light of substantial new data. The presence of a regional, rectilinear fracture pattern with a corresponding network of major fault zones has not been substantiated by subsurface data. The most widely known aspect of Fisk's work is his detailed interpretation and colorful depiction of the complex pattern of overlapping, cross cutting, and discontinuous Holocene meander belts and their hundreds of abandoned channels. However, it is now recognized that Fisk's elaborate chronological reconstruction is largely invalid both because of some incorrect basic assumptions and his lack of radiocarbon and other numerical dating techniques for precise control. A newly emerging model of meander belt formation is more generalized and relies heavily on archaeological evidence. It places emphasis on episodes of multiple active river courses (partial flow channels), frequent formation of distributary channels, and the significant influence of Mississippi River tributaries and minor basin drainage. Interesting regional variations over time in meander belt configurations and morphology may reflect climate changes, but at present broad-scale variations in the lithology of the Quaternary alluvial sequence appear to be the dominant control.     

High-pressure phase transitions of potassium aluminosilicates with an emphasis on leucite

Phase behaviors of kalsilite (KAlSiO₄), leucite (KAlSi₂O₆) and sanidine (KAlSi₃O₈) at high pressures and temperatures have been reviewed. New experimental data for leucite composition were obtained in a diamond-anvil press coupled with laser heating. At about 1,000° C, the leucite composition breaks down into an assemblage of kalsilite +kyanite+K₂Si₄O₉ (wadeite-type) in the range 60 to 120 kbar, of kalsilite+KAlSi₃O₈ (hollandite-type) in the range 120 to 150 kbar, and of KAlSi₃O₈ (hollandite-type) + KAlO₂ (?) at 170 kbar or above. The suggestion that kalsilite is the most appropriate potassium silicate in the anhydrous upper mantle needs to be revised. It is suggested that the wadeite-type K₂Si₄O₉ is the most appropriate host for potassium in the upper mantle at depths greater than about 150 km.     

Nature, origin and classification of peritidal tepee structures and related breccias

Distinctive peritidal tepee antiform structures, buckled margins of saucer-like megapolygons are common in marine vadose fenestral and pisolitic limestones and/or dolomites of carbonate platform sequences and occur in intertidal and supratidal carbonates ranging in age from Silurian to Holocene. These megapolygons commonly form and are sometimes truncated before the deposition of the next sedimentary layer. The megapolygons result from the expansion of surface sediments by as much as 15%. The expansion is caused by the following continuously repeated sequence of processes: (1) Desiccation and thermal contraction causing small fractures; (2) phases of wetting causing enlargement of fractures; (3) phases of crystallization of calcium carbonate and other minerals causing the enlargement, fill and cementation of the fractures. Precipitation is from brines and meteoric waters; (4) hydration of minerals, thermal expansion, breaking waves and faulting may add to this disruption. The development of the tepee fabric can be traced from an initially cemented subaerial fenestral crust, exhibiting expansion and compressional structures, to a completely disrupted and brecciated sediment riddled by a labyrinth of fractures and solution cavities. These spaces are filled by numerous phases of internal marine and fresh-water cement and sediment, the latter containing penecontemporaneous or younger marine faunas. Peritidal tepees are useful tools for geologic reconstruction and provide evidence of subaerial exposure; a tropical to subtropical climate; and back-beach or back-barrier deposition. Proper identification of tepees is of economic importance, because they provide good early porosity and permeability for petroleum entrapment and a site for mineralization. Aesthetically, tepee rocks are a fine kaleidoscopic decorative stone.     

Effects of groundwater flow on mineral diagenesis, with emphasis on carbonate aquifers

 This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural gas. Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology. This classification is applicable to all sedimentary basins. Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction, recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or completely stagnant systems that are geochemically "closed." Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due to extensive mineral precipitation. Received, April 1998 · Revised, July 1998 · Accepted, September 1998     

Assessment of in situ permeability with emphasis on packer testing in Kuwait

This paper discusses in situ permeability testing performed at two sites in bore holes drilled in an extensive hydrogeological exploration program in Kuwait. The testing program, comprising packer, falling and rising head tests, was carried out in calcareous and variedly textured cemented sand formed during post-depositional diagenetic processes with the colloquial name ‘Gatch’. The program was undertaken to assist in the design and construction of a pilot drainage scheme aimed at lowering of the groundwater table in Kuwait City and suburbs.

The results indicated that ‘Gatch’ is an almost impermeable soil. However, the hydraulic conductivity of the subsoils at the investigated sites is significantly influenced by the distribution and volume of macropores. These permeable zones act as preferential pathways for the movement of water bypassing the fine matrix and, thereby, improve markedly the overall drainage characteristics of the sites.

Various in situ test methods, including packer, compare results satisfactorily, to give the sites a variable hydraulic conductivity rating that straddles between very low and medium. The packer device, by faring well against other routine in situ tests, shows promises for use as a tool in the assessment of drainage parameters of cemented soils. Laboratory tests, performed in parallel, proved inadequate to characterize the permeability properties of the subsoils in Kuwait.     

A transmission electron microscopy analysis of secondary minerals formed in tungsten-mine tailings with an emphasis on arsenopyrite oxidation

Grains of naturally oxidized arsenopyrite [FeAsS] collected from the oxidation zone in W-mine tailings were investigated, primarily using transmission electron microscopy. The grains are severely pitted and are surrounded by secondary minerals. The pitted nature of the grains is related to mechanisms governing the electrochemical oxidation of sulfide minerals, with prominent cusp-like features occurring at cathodic regions of the surface, and pits occurring at anodic regions. In general, the oxidation of arsenopyrite leads to the formation of an amorphous (or nanocrystalline) Fe–As–O-rich coating that contains small amounts of Si, Ca, Cu, Zn, Pb and Bi; nanoscale variation in the As, Pb, Bi and Zn contents of the coating was noted. Secondary Cu sulfides, thought to be chalcocite [Cu₂S] and (or) djurleite [Cu₃₁S₁₆], occur as a layer (generally <500 nm thick) along the arsenopyrite grain boundary, and also within the coating as aggregates, and as layers that parallel the grain boundary. Although the precipitation of secondary Cu minerals along the grain boundary is a nanoscale feature, the process of formation is thought to be analogous to the supergene enrichment that occurs in weathered sulfide deposits. As the oxidation of arsenopyrite proceeds, layers and clusters of secondary Cu sulfides become isolated in the Fe–As–O coating. Secondary wulfenite [PbMoO₄] and an unidentified crystalline Bi–Pb–As–O mineral occur in voids within the coating, suggesting that these minerals precipitated from the local pore-water. Small and variable amounts of W, Ca, Bi, As and Zn are associated with the wulfenite, and Zn, Fe and Ca are associated with the Bi–Pb–As–O mineral. Some of the wulfenite is in contact with inclusions of molybdenite [MoS₂], suggesting that the oxidation of molybdenite in the presence of aqueous Pb(II) led to the formation of wulfenite. Mineralogical analyses at the nanoscale have improved the understanding of geochemical sources and sinks at this location. The results of this study indicate that the mineralogical controls on aqueous elemental concentrations at this tailings site are complex and are not predicted by thermodynamic calculations.     

A review of empirical orthogonal function (EOF) with an emphasis on the co-seismic crustal deformation analysis

Natural Hazards - An automatic, transparent, and regular way to investigate and analyze the spatiotemporal variations in a large, unstructured, and high-dimensional data set is highly desirable in...     

Reactivity and point defects of double oxides with emphasis on simple silicates

Heterogeneous solid-state reactions in quasibinary oxide systems are analyzed. As long as local thermodynamic equilibrium prevails, diffusion processes through the reaction product are rate-controlling. The diffusion coefficients are governed by point-defect concentrations. Point-defect thermodynamics allow calculation of relative point-defect concentrations as a function of the relevant thermodynamic variables, if the disorder type of the crystalline product is known. Disorder types in ternary ionic crystals are introduced. On this basis, several reactions leading to simple silicates of the form A ₂ BO ₄ are discussed in terms of ion mobilities and Gibbs energies of formation, and the possible reaction mechanisms are analyzed. Finally some remarks are included on the influence of the gas atmosphere on the reaction rate, on powder reactions and on phase boundary-controlled reaction rates.     

Dynamic modelling of retrogressive landslides with emphasis on the role of clay sensitivity

This paper presents a detailed numerical study of the retrogressive failure of landslides in sensitive clays. The dynamic modelling of the landslides is carried out using a novel continuum approach, the particle finite element method, complemented with an elastoviscoplastic constitutive model. The multiwedge failure mode in the collapse is captured successfully, and the multiple retrogressive failures that have been widely observed in landslides in sensitive clays are reproduced with the failure mechanism, the kinematics, and the deposition being discussed in detail. Special attention has been paid to the role of the clay sensitivity on each retrogressive failure as well as on the final retrogression distance and the final run‐out distance via parametric studies. Moreover, the effects of the viscosity of sensitive clays on the failure are also investigated for different clay sensitivities.     

Genetic classification of tectonic platform structures and paleotectonic reconstructions,from geophysical data on basement block structure

Geophysical expressions of the relatively mobile Cambrian-Sinian blocky layer of the platform, underlain by the relatively stable Precambrian base and overlain by sediments containing structures created by transfers of tensions from the blocky layer, are particularly well suitedfor structural regionalizations in Latvian Lithuanian territories and possibly elsewhere in the platform. Further testing and applications of the method are recommended. — V. P. Sokoloff.