Petrological Applications Research Articles

Influences of kinetics and mechanism in metamorphism: a study of albite crystallization

The kinetics and mechanisms of reactions: 1. (I) Analcite + Quartz = Albite + H 2O. 2. (II) Jadeite + Quartz = Albite. have been studied at 300–500°C. P(fluid) = 1 kbar, in aqueous solutions 0.1 M NaCl and 0.05 M Na 2Si 2O 5 (NaDS). Albite is the only phase to form, with the exception that at 300°C reaction II in NaCl forms metastable analcite with an Al 2O 3 SiO 2 ratio of 1:6. All reaction occurs by solution-precipitation mechanisms. The effects of the two solutions are opposed; reaction I in NaDS solution is faster than in NaCl, whereas reaction II proceeds more quickly in NaCl. The kinetics of reaction I can be substantially described by: X Ab = K · t 3 2 (X Ab = mole fraction of product albite, t = time of reaction and K is a rate constant). Reaction II appears to behave according to: X Ab = K' · t 1 2 . In both reactions nucleation appears to be kinetically negligible. Oxygen isotope fractionation between albite and water at 350–500°C is described by: 1000 In α Ab- H 2 O = 2.81 ± 0.11 × 10 6 T −2 −3.50 ± 0.23. The temperature dependencies of the rate constants for reaction I can be described by the functions: K NaCl = 1.2 × 10 11 ± 50 · exp(−44.5 ± 5.6 kcal/ RT) K NaDs = 7.1 × 10 17 ± 10 · exp(−60.8 ± 3.0 kcal/ RT). Basic problems in petrological applications of these rate equations are differing rate controlling mechanisms in natural and experimental situations and the complexities of metamorphic kinetic controls. Extrapolations of the Arrhenius equations suggest that the kinetics of reaction I would not perturb its occurrence at equilibrium in regional (burial) metamorphism [except, perhaps, when P(H 2O) < P(load)]. However, in contact metamorphism ‘overshooting’ of equilibrium may occur, leading to partial reaction in outermost zones of metamorphism and attenuation of thermal aureoles.

Petrographic Constituent Analysis of Coal and Property of Macerals

Author described the method of petrographic constituent analysis, some property of macerals and the application of coal petrology for fundamental research or industry.The methods of microscopical measurement for the macerals and reflectance of coal are now studying at the Japanese Committe on coal petrology in the Japan Iron and Steel Federation for the Japanese Industrial Standard (JIS).Research on the property of macerals of Japanese coal and imported coal is specially important for a prameter both coal rank and caking property in coke industry.

Carbonation and melting reactions in the system CaO?MgO?SiO2?CO2 at mantle pressures with geophysical and petrological applications

Bowen's petrogenetic grid was based initially on a series of decarbonation reactions in the system CaO-MgO-SiO2-CO2 with starting assemblages including calcite, dolomite, magnesite and quartz, and products including enstatite, forsterite, diopside and wollastonite. We review the positions of 14 decarbonation reactions, experimentally determined or estimated, extending the grid to mantle pressures to evaluate the effect of CO2 on model mantle peridotite composed of forsterite(Fo)+orthopyroxene(Opx)+clinopyroxene(Cpx). Each reaction terminates at an invariant point involving a liquid, CO2, carbonates, and silicates. The fusion curves for the mantle mineral assemblages in the presence of excess CO2 also terminate at these invariant points. The points are connected by a series of reactions involving liquidus relationships among the carbonates and mantle silicates, at temperatures lower (1,100–1,300° C) than the silicate-CO2 melting reactions (1,400–1,600° C). Review of experimental data in the bounding ternary systems together with preliminary data for the system CaO-MgO-SiO2-CO2 permits construction of a partly schematic framework for decarbonation and melting reactions at upper mantle pressures. The key to several problems in the peridotite-CO2 subsystem is the intersection of a subsolidus carbonation reaction with a melting reaction at an invariant point near 24 kb and 1,200°C. There is an intricate series of reactions between 25 kb and 35 kb involving changes in silicate and carbonate phase fields on the CO2-saturated liquidus surfaces. Conclusions include the following: (1) Peridotite Fo+Opx+Cpx can be carbonated with increasing pressure, or decreasing temperature, to yield Fo+Opx+Cpx+Cd (Cd=calcic dolomite), Fo+Opx+Cd, Fo+Opx+Cm (Cm=calcic magnesite), and finally Qz+Cm. (2) Free CO2 cannot exist in subsolidus mantle peridotite with normal temperature distributions; it is stored as carbonate, Cd. (3) The CO2 bubbles in peridotite nodules do not represent free CO2 in mantle peridotite along normal geotherms. (4) CO2 is as effective as H2O in causing incipient melting, our preferred explanation for the low-velocity zone. (5) Fusion of peridotite with CO2 at depths shallower than 80 km produces basic magmas, becoming more SiO2-undersaturated with depth. (6) The solubility of CO2 in mantle magmas is less than about 5 wt% at depths to 80 km, increasing abruptly to about 40 wt% at 80 km and deeper. (7) Deeper than 80 km, the first liquids produced are carbonatitic, changing towards kimberlitic and eventually, at considerably higher temperatures, to basic magmas. (8) Kimberlite and carbonatite magmas rising from the asthenosphere must evolve CO2 at depths 100-80 km, which contributes to their explosive emplacement. (9) Fractional crystallization of CO2-bearing SiO2-undersaturated basic magmas at most pressures can yield residual kimberlite and carbonatite magmas.

New data in experimental studies of the K2O-Al2O3-SiO2-H2O system at high pressures and their petrological applications

New data in experimental studies of the K₂O-Al₂O₃-SiO₂-H₂O system at high pressures and their petrological applications

Les impuretés de substitution isomorphe et la formation de radicaux libres dans les minéraux (centres à électrons et centres à trous)

As far as trace elements are concerned, all natural minerals are solid solutions. Substitutional impurities (and interstitial impurities and vacancies) are point defects that capture electrons or holes during natural or artificial irradiation. A great number of centers were found in minerals by using paramagnetic electronic resonance (PER). The models of these centers are definitely elucidated. The centers are widely present in rock forming minerals : feldspars, quartz, zircon, phenacite, topaz, euclase, kyanite, beryl, sodalite, lazurite, danburite, datolite, tourmaline, apatite, amblygonite, anhydrite, barytite, celestite, calcite, aragonite, etc. Periodical systems of these centers in minerals and inorganic coumpounds are proposed. A review of the models of centers and of their petrological application is given.

Melting Relationships in the System CaO-MgO-CO2-H2O, with Petrological Applications

Phase relationships on the vapor-saturated liquidus surface in the system CaO-MgO-CO_2-H_2O have been deduced from data in the systems CaO CO_2-H_2O, CaO-MgO-CO_2, and MgO-CO_2-H_2O, and from preliminary experiments in the quaternary system. These are illustrated in composition tetrahedra, and in isobaric sections through the petrogenetic model. The univariant PT curve for the beginning of melting lies between 625° C and 600° C in the pressure range 10 bars to 4 kilobars, in the presence of a vapor phase rich in H_2O. The curve is divided into three sections by two invariant points, each section having a different primary magnesian phase involved in the melting reaction. Periclase occurs on the low-pressure section (less than about 1 kilobar), and with increasing pressure first brucite and then dolomite become stable on the liquidus. The pressure of the second invariant point, above which dolomite is stable on the liquidus, is not known. The effect of FeO as an additional component is considered. Processes of crystallization resulting from changes in temperature, in pressure, and in the composition of the vapor phase are discussed. These processes are applied to the crystallization and differentiation of carbonatite magmas, and the reverse processes involving fusion are applied to the metamorphism of dolomites. Crystallization differentiation of a carbonatite magma could produce the sequence of intrusion observed at some carbonatite complexes: calcitic sovite, followed by ankeritic sovite, and finally sideritic carbonatite. Partial melting may occur during the thermal metamorphism of dolomites, but melting is unlikely during regional metamorphism.

Recent Advances in Geology and Geophysics: ABSTRACT

No wholly new exploration techniques have evolved during the past 10 years. However, geologists and geophysicists have learned that there is more to discovering oil fields than the detection of closed structures and the selection of sites where rocks have sufficient porosity to hold oil. They have realized that oil fields are located only in favorable geological settings characterized by certain large-scale geological features. They also have realized that it is possible, using geology and geophysics, End_Page 1563------------------------------ to analyze geological information intelligently, including well cuttings, surface samples, surface and subsurface geological maps, seismic records, gravity information, and magnetic information in order to determine whether or not the local geological environment is conducive to oil accumulation. Modern exploration techniques make possible the localization of potential oil reservoirs in such sedimentary features as limestone reef complexes, deltas, beaches, etc. The most difficult aspects of this modern exploration concept are the correlation of geological and geophysical data and the reduction of geophysical data into meaningful geology. The past decade has witnessed a rebirth of sedimentary petrology in oil-finding. This renaissance involves the study of Recent sediments as a key to the past and the application of geochemistry, paleontology, and petrology to the definition of sedimentary depositional patterns. During the past 10 years, geophysicists not only have improved their equipment for better measurements of the properties of sediments but also have made significant progress in developing methods of presenting geophysical data in geological form. End_of_Article - Last_Page 1564------------

Phase-Equilibrium Relations in the System Nepheline-Albite-Water at 1,000 kg/cm2

Phase-equilibrium relations have been determined in the system NaAlSiO4-NaAlSi3O8-H2O at a water-vapor pressure of 1,000 kg/cm2. The minimum melting temperature in this system is 835° C. at a composition of 27 weight per cent nepheline and 73 weight per cent albite. Lattice parameters of pure sodium nephe-line and of nepheline solid solutions in this system have been determined and are discussed in terms of three hypotheses proposed by Smith and Tuttle (1957). The petrologic applications of the experimentally determined system are considered with reference to certain undersaturated alkaline rocks, and it is concluded that crystal ⇌ liquid equilibria have been involved in the genesis of these rocks.

Development of Clay Mineral Zones During Deltaic Migration

An understanding of the origin of clay mineral zones in coastal plain sediments is a prerequisite for the effective stratigraphic application of clay petrology. One common type of clay mineral zone is developed by the occasional migration of a major delta lying near the margin of two clay-petrologic provinces. As an active delta migrates from place to place along a coast, the magnitude of its detrital contribution to any location will vary between a maximum and a minimum. By this process the regressive deltaic phase sediments may alternate with transgressive marine zones in which locally derived or longshore drift material is relatively more prominent. If the major stream is supplying a clay mineral suite which differs from the longshore current-borne and locally derived clay (i.e., from local weathering, reworking of older beds, small river influx, etc.), a series of correlative regressive-transgressive clay mineral zones will be built up. This process is illustrated by comparing clay mineral variations in cores from the eastern Mississippi Delta area with the known deltaic history of the region. The abandoned St. Bernard Subdelta, which the Mississippi occupied from 1,700 to 2,800 years ago, has a clay mineral zone sequence similar to that in the sediments of interdeltaic Mississippi Sound which lies 40 miles east. This similarity allows the two sections to be correlated across facies boundaries so that the Recent chronology of the two areas can be related.

Petrological application of the low-power binocular microscope

In carrying out a petrological examination of pebbles collected by Mr. F. Gossling from the Lower Greensand of Surrey and west Kent, the writer has found a low-power dissecting binocular microscope an extremeIy useful piece of apparatus. The instrument, by Watson, is fitted with two pairs of objectives on a rotating nosepiece, and with two pairs of eyepieces, so that it commands the choice of four different magnifications.The pebbles are treated in a uniform manner. After the preliminary examination of a ‘bag’ of pebbles, those selected for study are ground flat on one side, finishing on the fine carborundum plate as if for section making. Each one is then mounted on the usual 3 by 1 inch glass slide, taking care not to over-cook the balsam. If the pebbles are treated systematically in batches of six, a dozen pebbles can be mounted in less than an hour, so that the gain of time over section-making is very considerable.