Water and magmas; a mixing model

A model for the mixing of H₂O and silicate melts has been derived from the experimentally determined effects of H₂O on the viscosity (fluidity), volumes, electrical conductivities, and especially the thermodynamic properties of hydrous aluminosilicate melts. It involves primarily the reaction of H₂O with those O^?2 ions of the melt that are shared (bridging) between adjacent (Al, Si)O₄ tetrahedra to produce OH^? ions. However, in those melts that contain trivalent ions in tetrahedral coordination, such as the Al³⁺ ion in feldspathic melts, the model further involves exchange of a proton from H₂O with a non-tetrahedrally coordinated cation that must be present to balance the net charge on the AlO₄ group. This cation exchange reaction, which goes essentially to completion, results in dissociation of the H₂O and is limited only by the availability of H₂O and the number of exchangeable cations per mole of aluminosilicate.In the system NaAlSi₃O₈-H₂O, upon which this thermodynamic model is based, there is 1 mole of exchangeable cations (Na⁺) per mole (GFW) of NaAlSi₃O₈, consequently ion exchange occurs for H₂O contents up to a 1:1 mole ratio (X^m_w = mole fraction H₂O = 0.5). For mole fractions of H₂O greater than 0.5, no further exchange can occur and the reaction with additional bridging oxygens of the melt produces 2 moles of associated OH^? ions per mole of H₂O dissolved. These reactions lead to a linear dependence of the thermodynamic activity of H₂O (a^m_w) on the square of its mole fraction (X^m_w) for values of X^m_w, up to 0.5 and an exponential dependence on X^m_w at higher H₂O contents. Thus, for values of $\text{X}{}^{\mathrm{m}}{}_{\mathrm{w}}\text{? 0.5, a}{}^{\mathrm{m}}{}_{\mathrm{w}}\text{= k(X}{}^{\mathrm{m}}{}_{\mathrm{w}}\text{)}{}^2$, where k is a Henry's law constant for the dissociated solute.Extension of the thermodynamic model for NaAlSi₃O₈-H₂O to predict H₂O solubilities and other behavior of compositionally more complex aluminosilicate melts (magmas) requires placing these melts on an equimolal basis with NaAlSi₃O₈. This is readily accomplished using chemical analyses of quenched glasses by normalizing to the stoichiometric requirements of NaAlSi₃O₈, first in terms of equal numbers of exchangeable cations for mole fractions of H₂O up to 0.5 and secondly in terms of 8 moles of oxygen for higher H₂O contents. Chemical analyses of three igneous-rock glasses, ranging in composition from tholeiitic basalt to lithium-rich pegmatite, were thus recast and the experimental H₂O solubilities were computed on this equimolal basis. The resulting equimolal solubilities are all the same, within experimental error, as the solubility of H₂O in NaAlSi₃O₈ melt calculated from the thermodynamic relations.The equivalence of equimolal solubilities implies that the Henry's law constant (k), which is a function of temperature and pressure, is independent of aluminosilicate composition over a wide range. Moreover, as a consequence of the Gibbs-Duhem relation and the properties of exact differentials, it is clear that the silicate components of the melt, properly defined, mix ideally. Thus, a relatively simple mixing model for H₂O in silicate melts has led to a quantitative thermodynamic model for magmas that has far-reaching consequences in igneous petrogenesis.     

Hydrous pyrolysis of New Albany and Phosphoria Shales: production kinetics of carboxylic acids and light hydrocarbons and interactions between the inorganic and organic chemical systems

Hydrous pyrolysis in flexible gold-bag autoclaves was used to study the production of carboxylic acids and light hydrocarbons from two marine type IIb source rocks (New Albany and Phosphoria Shales). Kerogen pyrolysis produced significant amounts of the monocarboxylic acids (acetic > propionic > butyric). The gases were dominated by CO₂ and methane, in that order, and progressively smaller amounts of the alkanes (ethane > propane > butane > pentane). Kinetic analyses of production rates for the New Albany Shale suggest mean activation energies (E) of 51-54 kcal/mol for both the light hydrocarbons and acids. Pressure had little effect on measured production rates for either shale over the pressure range investigated. Chemical thermodynamic speciation modeling suggests that in these experiments metal-organic acid anion complexation had little impact on aluminum speciation/solubility, but was important with respect to the alkaline earths.     

Factors explaining the dispersal of Hendra virus disease in South-East Queensland

Hendra virus (HeV) was first described in 1994 following the outbreak of a new disease fatally affecting horses and humans in South-east Queensland. The disease kills 70% of the infected horses and under some circumstances the virus is spread to humans who have had close contact with the infected horses. Fruit bats (Pteropus spp.) commonly known as flying foxes have been identified as the natural host of the virus. A preliminary analysis of the incidents and the flying fox roosting sites revealed a strong relationship between the temporary and seasonal roosting sites in the South-east Queensland. The aim of this paper is to determine the potential factors that can explain the dispersal of HeV incidents in the study area. Based on the preliminary results, a further analysis was done on the roosting sites by considering factors such as the species of flying foxes, foraging range and pregnancy period. Spatial autocorrelation (Global Moran’s I) revealed significant clustering of P. alecto and P. scapulatus species. Kernel density estimation analysis helped in identifying a strong relationship between P. alecto & P. scapulatus species density and the outbreak events in the study area. Buffer analysis established an initial relationship between P. alecto & P. poliocephalus species birth periods and the incidents. Ordinary least-squares regression identified P. poliocephalus species as statistically significant at a global context across the study area. Geographically weighted regression analysis was performed to study the local spatial variations of the explanatory variables. P. alecto & P. poliocephalus species exhibited a significant positive relationship in most of the regions where as pregnancy period variable exhibited a significant negative relationship to the HeV incidents in the study area.     

Trouble with Sense of Place in Working Landscapes

The sense of place (SOP) conceptual framework offers theoretical and empirical evidence that links peoples’ multifaceted connections to place(s) to their engagement in pro-environmental and conservation behaviors. The bulk of this research has focused on peoples’ connection to high-amenity places and landscapes. Recent research applies SOP in working landscapes—however, these studies encounter “troubles” that include measurement challenges and mixed results in predicting statistical relationships with conservation outcome variables. As authors of some of these studies, we propose three opportunities and corresponding survey items for developing meaningful SOP measures in future working landscapes research: (1) modify existing SOP dimensions and items to better capture the working landscape dynamics; (2) address how scale may affect behavior and SOP dimensions; and (3) incorporate a conservation ethic dimension into the SOP framework in working lands.     

Synthetic fluid inclusions in natural quartz. III. Determination of phase equilibrium properties in the system H2O-NaCl to 1000°C and 1500 bars

Phase equilibria in the system H₂O-NaCl have been determined to 1000°C and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion-free Brazilian quartz in the presence of the two coexisting, immiscible H₂O-NaCl fluids at various temperatures and pressures. Petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present, or mixtures of the two. Salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single, homogeneous fluid phase.Results of the present study are consistent with previously published data on the H₂O-NaCl system at lower temperatures and pressures, and indicate that the two-phase field extends well into the P-T range of most shallow magmatic-hydrothermal activity. As a consequence, chloride brines exsolved from many epizonal plutons during the process of “second-boiling” should immediately separate into a high-salinity liquid phase and a lower salinity vapor phase and produce coexisting halite-bearing and vapor-rich fluid inclusions. This observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions, particularly the porphyry copper deposits, in which halite-bearing and coexisting vapor-rich inclusions are commonly associated with the earliest stages of magmatic-hydrothermal activity.     

Corrigendum

Corrigendum

Corrigendum     

Biological markers from Green River kerogen decomposition

Isoprenoid and other carbon skeletons that are formed in living organisms and preserved essentially intact in ancient sediments are often called biological markers. The purpose of this paper is to develop improved methods of using isoprenoid hydrocarbons to relate petroleum or shale oil to its source rock. It is demonstrated that most, but not all, of the isoprenoid hydrocarbon structures are chemically bonded in kerogen (or to minerals) in Green River oil shale. The rate constant for thermally producing isoprenoid, cyclic, and aromatic hydrocarbons is substantially greater than for the bulk of shale oil. This may be related to the substantial quantity of CO₂ which is evolved coincident with the isoprenoid hydrocarbons but prior to substantial oil evolution. Although formation of isoprenoid alkenes is enhanced by rapid heating and high pyrolysis temperatures, the ratio of isoprenoid alkenes plus alkanes to normal alkenes plus alkanes is independent of heating rate. High-temperature laboratory pyrolysis experiments can thus be used to predict the distribution of aliphatic hydrocarbons in low temperature processes such as in situ shale oil production and perhaps petroleum formation. Finally, we demonstrate that significant variation in biological marker ratios occurs as a function of stratigraphy in the Green River formation. This information, combined with methods for measuring process yield from oil composition, enables one to relate time-dependent processing conditions to the corresponding time-dependent oil yield in a vertical modified-in situ retort even if there is a substantial and previously undetermined delay in drainage of shale oil from the retort.