Redox-controlled iron isotope fractionation during magmatic differentiation: an example from the Red Hill intrusion, S. Tasmania

This study presents accurate and precise iron isotopic data for 16 co-magmatic rocks and 6 pyroxene–magnetite pairs from the classic, tholeiitic Red Hill sill in southern Tasmania. The intrusion exhibits a vertical continuum of compositions created by in situ fractional crystallisation of a single injection of magma in a closed igneous system and, as such, constitutes a natural laboratory amenable to determining the causes of Fe isotope fractionation in magmatic rocks. Early fractionation of pyroxenes and plagioclase, under conditions closed to oxygen exchange, gives rise to an iron enrichment trend and an increase in $ f_{{{\text{O}}_{2} }} $ of the melt relative to the Fayalite–Magnetite–Quartz (FMQ) buffer. Enrichment in Fe³⁺/ΣFe_melt is mirrored by δ⁵⁷Fe, where ^VIFe²⁺-bearing pyroxenes partition ⁵⁷Fe-depleted iron, defining an equilibrium pyroxene-melt fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{px}} - {\text{melt}}}} \le - 0.25\,\permille \times 10^{6} /T^{2} $ . Upon magnetite saturation, the $ f_{{{\text{O}}_{2} }} $ and δ⁵⁷Fe of the melt fall, commensurate with the sequestration of the oxidised, ⁵⁷Fe-enriched iron into magnetite, quantified as $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{melt}}}} = + 0.20\,\permille \times 10^{6} /T^{2} $ . Pyroxene–magnetite pairs reveal an equilibrium fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{px}}}} \approx + 0.30\,\permille $ at 900–1,000?°C. Iron isotopes in differentiated magmas suggest that they may act as an indicator of their oxidation state and tectonic setting.     

A multi-isotope approach for understanding sources of water,carbon and sulfur in natural springs of the Central Appalachian region

Natural springs have been reliable sources of domestic water and have allowed for the development of recreational facilities and resorts in the Central Appalachians. The structural history of this area is complex and it is unknown whether these natural springs receive significant recharge from modern precipitation or whether they discharge old water recharged over geological times scales. The main objective of this study was to use stable isotopes of water ( $\delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}}$ and $\delta^{2} {\text{H}}_{{{\text{H}}_{2} {\text{O}}}}$ ), dissolved inorganic carbon ( $\delta^{13} {\text{C}}_{\text{DIC}}$ ) and dissolved sulfate ( $\delta^{34} {\text{S}}_{{{\text{SO}}_{4} }}$ and $\delta^{18} {\text{O}}_{{{\text{SO}}_{4} }}$ ) to delineate sources of water, carbon and sulfur in several natural springs of the region. Our preliminary isotope data indicate that all springs are being recharged by modern precipitation. The oxygen isotope composition indicates that waters in thermal springs did not encounter the high temperatures required for O isotope exchange between the water and silicate/carbonate minerals, and/or the residence time of water in the aquifers was short due to high flow rates. The carbon isotopic composition of dissolved inorganic carbon and sulfur/oxygen isotopic composition of dissolved sulfate provide evidence of low-temperature water–rock interactions and various biogeochemical transformations these waters have undergone along their flow path.     

Petrological cannibalism: the chemical and textural consequences of incremental magma body growth

The textures of minerals in volcanic and plutonic rocks testify to a complexity of processes in their formation that is at odds with simple geochemical models of igneous differentiation. Zoning in plagioclase feldspar is a case in point. Very slow diffusion of the major components in plagioclase means that textural evidence for complex magmatic evolution is preserved, almost without modification. Consequently, plagioclase affords considerable insight into the processes by which magmas accumulate in the crust prior to their eventual eruption or solidification. Here, we use the example of the 1980–1986 eruptions of Mount St. Helens to explore the causes of textural complexity in plagioclase and associated trapped melt inclusions. Textures of individual crystals are consistent with multiple heating and cooling events; changes in total pressure (P) or volatile pressure ( $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O ) are less easy to assess from textures alone. We show that by allying textural and chemical analyses of plagioclase and melt inclusions, including volatiles (H₂O, CO₂) and slow-diffusing trace elements (Sr, Ba), to published experimental studies of Mount St. Helens magmas, it is possible to disambiguate the roles of pressure and temperature to reconstruct magmatic evolutionary pathways through temperature–pressure–melt fraction (T– $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O –F) space. Our modeled crystals indicate that (1) crystallization starts at $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O  > 300 MPa, consistent with prior estimates from melt inclusion volatile contents, (2) crystal cores grow at $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O  = 200–280 MPa at F = 0.65–0.7, (3) crystals are transferred to $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O  = 100–130 MPa (often accompanied by 10–20 °C of heating), where they grow albitic rims of varying thicknesses, and (4) the last stage of crystallization occurs after minor heating at $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O  ~ 100 MPa to produce characteristic rim compositions of An₅₀. We hypothesize that modeled $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O decreases in excess of ~50 MPa most likely represent upward transport through the magmatic system. Small variations in modeled $P_{{{\text{H}}_{ 2} {\text{O}}}}$ P H 2 O , in contrast, can be effected by fluxing the reservoir with CO₂-rich vapors that are either released from deeper in the system or transported with the recharge magma. Temperature fluctuations of 20–40 °C, on the other hand, are an inevitable consequence of incremental, or pulsed, assembly of crustal magma bodies wherein each pulse interacts with ancestral, stored magmas. We venture that this “petrological cannibalism” accounts for much of the plagioclase zoning and textural complexity seen not only at Mount St. Helens but also at arc magmas generally. More broadly we suggest that the magma reservoir below Mount St. Helens is dominated by crystal mush and fed by frequent inputs of hotter, but compositionally similar, magma, coupled with episodes of magma ascent from one storage region to another. This view both accords with other independent constraints on the subvolcanic system at Mount St. Helens and supports an emerging view of many active magmatic systems as dominantly super-solidus, rather than subliquidus, bodies.     

The dilatant behaviour of sand–pile interface subjected to loading and stress relief

Property and behaviour of sand–pile interface are crucial to shaft resistance of piles. Dilation or contraction of the interface soil induces change in normal stress, which in turn influences the shear stress mobilised at the interface. Although previous studies have demonstrated this mechanism by laboratory tests and numerical simulations, the interface responses are not analysed systematically in terms of soil state (i.e. density and stress level). The objective of this study is to understand and quantify any increase in normal stress of different pile–soil interfaces when they are subjected to loading and stress relief. Distinct element modelling was carried out. Input parameters and modelling procedure were verified by experimental data from laboratory element tests. Parametric simulations of shearbox tests were conducted under the constant normal stiffness, constant normal load and constant volume boundary conditions. Key parameters including initial normal stress ( $ \sigma_{{{\text{n}}0}}^{\prime } $ ), initial void ratio (e ₀), normal stiffness constraining the interface and loading–unloading stress history were investigated. It is shown that mobilised stress ratio ( $ \tau /\sigma_{\text{n}}^{\prime } $ ) and normal stress increment ( $ \Updelta \sigma_{\text{n}}^{\prime } $ ) on a given interface are governed by $ \sigma_{{{\text{n}}0}}^{\prime } $ and e ₀. An increase in $ \sigma_{{{\text{n}}0}}^{\prime } $ from 100 to 400 kPa leads to a 30 % reduction in $ \Updelta \sigma_{\text{n}}^{\prime } $ . An increase in e ₀ from 0.18 to 0.30 reduces $ \Updelta \sigma_{\text{n}}^{\prime } $ by more than 90 %, and therefore, shaft resistance is much lower for piles in loose sands. A unique relationship between $ \Updelta \sigma_{\text{n}}^{\prime } $ and normal stiffness is established for different soil states. It can be applied to assess the shaft resistance of piles in soils with different densities and subjected to loading and stress relief. Fairly good agreement is obtained between the calculated shaft resistance based on the proposed relationship and the measured results in centrifuge model tests.     

H2O–CO2 solubility in mafic alkaline magma: applications to volatile sources and degassing behavior at Erebus volcano, Antarctica

We present new equilibrium mixed-volatile (H₂O–CO₂) solubility data for a phonotephrite from Erebus volcano, Antarctica. H₂O–CO₂-saturated experiments were conducted at 400–700 MPa, 1,190 °C, and ~NNO + 1 in non-end-loaded piston cylinders. Equilibrium H₂O–CO₂ fluid compositions were determined using low-temperature vacuum manometry, and the volatile and major element compositions of the glassy run products were determined by Fourier transform infrared spectroscopy and electron microprobe. Results show that the phonotephrite used in this study will dissolve ~0.8 wt% CO₂ at 700 MPa and a fluid composition of $ X_{{{\text{H}}_{ 2} {\text{O}}}} $ ~0.4, in agreement with previous experimental studies on mafic alkaline rocks. Furthermore, the dissolution of CO₂ at moderate to high $ X_{{{\text{H}}_{ 2} {\text{O}}}}^{\text{fluid}} $ in our experiments exceeds that predicted using lower-pressure experiments on similar melts from the literature, suggesting a departure from Henrian behavior of volatiles in the melt at pressures above 400 MPa. With these data, we place new constraints on the modeling of Erebus melt inclusion and gas emission data and thus the interpretation of its magma plumbing system and the contributions of primitive magmas to passive and explosive degassing from the Erebus phonolite lava lake.     

Crystallographic preferred orientation in wüstite (FeO) through the cubic-to-rhombohedral phase transition

Magnesiowüstite, (Mg_0.08Fe_0.88)O, and wüstite, Fe_0.94O, were compressed to ~36?GPa at ambient temperature in the diamond anvil cell (DAC) at the Advanced Light Source. X-ray diffraction patterns were taken in situ in radial geometry in order to study the evolution of crystallographic preferred orientation through the cubic-to-rhombohedral phase transition. Under uniaxial stress in the DAC, {100}_c planes aligned perpendicular to the compression direction. The {100}_c in cubic became { $\left\{ {10\bar 14} \right\}$ }_r in rhombohedral and remained aligned perpendicular to the compression direction. However, the {101}_c and {111}_c planes in the cubic phase split into { ${10{\bar{1}}4}$ }_r and { ${11{\bar{2}}0}$ }_r, and (0001)_r and { ${10{\bar{1}}1}$ }_r, respectively, in the rhombohedral phase. The { ${11{\bar{2}}0}$ }_r planes preferentially aligned perpendicular to the compression direction while { ${10{\bar{1}}4}$ }_r oriented at a low angle to the compression direction. Similarly, { ${10{\bar{1}}1}$ }_r showed a slight preference to align more closely perpendicular to the compression direction than (0001)_r. This variant selection may occur because the 〈 ${10{\bar{1}}4}$ 〉_r and [0001]_r directions are the softer of the two sets of directions. The rhombohedral texture distortion may also be due to subsequent deformation. Indeed, polycrystal plasticity simulations indicate that for preferred { ${10{\bar{1}}4}$ }〈 ${1{\bar{2}}10}$ 〉_r and { ${11{\bar{2}}0}$ }〈 ${{\bar{1}}101}$ 〉_r slip and slightly less active { ${10{\bar{1}}1}$ }〈 ${{\bar{1}}2{\bar{1}}0}$ 〉_r slip, the observed texture pattern can be obtained.     

The crystal structure of waylandite from Wheal Remfry, Cornwall, United Kingdom

Sr- and Ca-rich waylandite, $ {\left( {{\hbox{B}}{{\hbox{i}}_{0.{54}}}{\hbox{S}}{{\hbox{r}}_{0.{31}}}{\hbox{C}}{{\hbox{a}}_{0.{25}}}{{\hbox{K}}_{0.0{1}}}{\hbox{B}}{{\hbox{a}}_{0.0{1}}}} \right)_{\Sigma 1.12}}{{\hbox{H}}_{0.{18}}}{\left( {{\hbox{A}}{{\hbox{l}}_{{2}.{96}}}{\hbox{C}}{{\hbox{u}}_{0.0{2}}}} \right)_{\Sigma 2.98}}{\left[ {{{\left( {{{\hbox{P}}_{0.{97}}}{{\hbox{S}}_{0.0{3}}}{\hbox{S}}{{\hbox{i}}_{0.0{1}}}} \right)}_{\Sigma 1.00}}{{\hbox{O}}_4}} \right]_2}{\left( {\hbox{OH}} \right)_6} $ , from Wheal Remfry, Cornwall, United Kingdom has been investigated by single-crystal X-ray diffraction and electron microprobe analyses. Waylandite crystallises in space group R $ \overline 3 $ ? m, with the cell parameters: a?=?7.0059(7) Å, c?=?16.3431(12) Å and V?=?694.69(11) ų. The crystal structure has been refined to R ₁?=?3.76%. Waylandite has an alunite-type structure comprised of a rhombohedral stacking of (001) composite layers of corner-shared AlO₆ octahedra and PO₄ tetrahedra, with (Bi,Sr,Ca) atoms occupying icosahedrally coordinated sites between the layers.     

An experimental study of Ti and Zr partitioning among zircon, rutile, and granitic melt

In order to evaluate the effect of trace and minor elements (e.g., P, Y, and the REEs) on the high-temperature solubility of Ti in zircon (zrc), we conducted 31 experiments on a series of synthetic and natural granitic compositions [enriched in TiO₂ and ZrO₂; Al/(Na + K) molar ~1.2] at a pressure of 10 kbar and temperatures of ~1,400 to 1,200 °C. Thirty of the experiments produced zircon-saturated glasses, of which 22 are also saturated in rutile (rt). In seven experiments, quenched glasses coexist with quartz (qtz). SiO₂ contents of the quenched liquids range from 68.5 to 82.3 wt% (volatile free), and water concentrations are 0.4–7.0 wt%. TiO₂ contents of the rutile-saturated quenched melts are positively correlated with run temperature. Glass ZrO₂ concentrations (0.2–1.2 wt%; volatile free) also show a broad positive correlation with run temperature and, at a given T, are strongly correlated with the parameter (Na + K + 2Ca)/(Si·Al) (all in cation fractions). Mole fraction of ZrO₂ in rutile $ \left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) $ in the quartz-saturated runs coupled with other 10-kbar qtz-saturated experimental data from the literature (total temperature range of ~1,400 to 675 °C) yields the following temperature-dependent expression: $ {\text{ln}}\left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) + {\text{ln}}\left( {a_{{{\text{SiO}}_{2} }} } \right) = 2.638(149) - 9969(190)/T({\text{K}}) $ , where silica activity $ a_{{{\text{SiO}}_{2} }} $ in either the coexisting silica polymorph or a silica-undersaturated melt is referenced to α-quartz at the P and T of each experiment and the best-fit coefficients and their uncertainties (values in parentheses) reflect uncertainties in T and $ \mathop X\nolimits_{{{\text{ZrO}}_{2} }}^{\text{rt}} $ . NanoSIMS measurements of Ti in zircon overgrowths in the experiments yield values of ~100 to 800 ppm; Ti concentrations in zircon are positively correlated with temperature. Coupled with values for $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ for each experiment, zircon Ti concentrations (ppm) can be related to temperature over the range of ~1,400 to 1,200 °C by the expression: $ \ln \left( {\text{Ti ppm}} \right)^{\text{zrc}} + \ln \left( {a_{{{\text{SiO}}_{2} }} } \right) - \ln \left( {a_{{{\text{TiO}}_{2} }} } \right) = 13.84\left( {71} \right) - 12590\left( {1124} \right)/T\left( {\text{K}} \right) $ . After accounting for differences in $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ , Ti contents of zircon from experiments run with bulk compositions based on the natural granite overlap with the concentrations measured on zircon from experiments using the synthetic bulk compositions. Coupled with data from the literature, this suggests that at T ≥ 1,100 °C, natural levels of minor and trace elements in “granitic” melts do not appear to influence the solubility of Ti in zircon. Whether this is true at magmatic temperatures of crustal hydrous silica-rich liquids (e.g., 800–700 °C) remains to be demonstrated. Finally, measured $ D_{\text{Ti}}^{{{\text{zrc}}/{\text{melt}}}} $ values (calculated on a weight basis) from the experiments presented here are 0.007–0.01, relatively independent of temperature, and broadly consistent with values determined from natural zircon and silica-rich glass pairs.     

Biradical states of oxygen-vacancy defects in ��-quartz: centers E_{2}^{\prime \prime } and E_{4}^{\prime \prime }

Several new radiation defects with total electron spin S?=?1 occurring in electron-irradiated, synthetic ??-quartz have been observed by using electron paramagnetic resonance spectroscopy. These defects are considered to be biradicals, i.e., pairs of S?=?1/2 species. The concentration of these centers depends on the condition of the fast-electron irradiation. They have different decay behaviors that allow measurements of any individual species especially when it predominates over the others. The primary spin Hamiltonian parameter matrices g ₁, g ₂, D have now been determined for two similar defects, which herein are labeled $ E_{2}^{\prime \prime } $ and $ E_{4}^{\prime \prime } $ . Inter-electron distances estimated by using the magnetic dipole model, suggest that the structures of centers $ E_{2}^{\prime \prime } $ and $ E_{4}^{\prime \prime } $ both involve the unpaired electrons each located in orbitals of two silicon atoms next to a common oxygen vacancy but which have slightly different Si?CSi distances at 0.90 and 0.79?nm, respectively. This model is consistent with previous DFT calculations of the triplet configurations with local energetic minima. Observed decay behaviors suggest a transformation of centers $ E_{2,4}^{\prime \prime } $ to the analogous $ E_{1}^{\prime \prime } $ center. These triplet centers in quartz provide new insights into the structures of analogous defects in amorphous silica.     

Contribution of {\text{P}}_{{{\text{CO}}_{ 2} {\text{eq}}}} and 13CTDIC Evaluation to the Identification of CO2 Sources in Volcanic Groundwater Systems: Influence of Hydrometeorological Conditions and Lava Flow Morphologies—Application to the Argnat Basin (Chaîne des Puys, Massif Central, France)

Mineralization of groundwater in volcanic aquifers is partly acquired through silicates weathering. This alteration depends on the dissolution of atmospheric, biogenic, or mantellic gaseous CO₂ whose contributions may depend on substratum geology, surface features, and lava flow hydrological functionings. Investigations of $ {\text{P}}_{{{\text{CO}}_{ 2} {\text{eq}}}} $ and δ¹³C_TDIC (total dissolved inorganic carbon) on various spatiotemporal scales in the unsaturated and saturated zones of volcanic flows of the Argnat basin (French Massif Central) have been carried out to identify the carbon sources in the system. Mantellic sources are related to faults promoting CO₂ uplift from the mantle to the saturated zone. The contribution of this source is counterbalanced by infiltration of water through the unsaturated zone, accompanied by dissolution of soil CO₂ or even atmospheric CO₂ during cold periods. Monitoring and modeling of δ¹³C_TDIC in the unsaturated zone shows that both $ {\text{P}}_{{{\text{CO}}_{ 2} {\text{eq}}}} $ and δ¹³C_TDIC are controlled by air temperature which influences soil respiration and soil-atmosphere CO₂ exchanges. The internal geometry of volcanic lava flows controls water patterns from the unsaturated zone to saturated zone and thus may explain δ¹³C heterogeneity in the saturated zone at the basin scale.     

The Activity of H2O,Fugacity of O2 and Variation of Their Chemical Potential During Metamorphic Peak of the Granulite Complex Near Taipingzhai—Louzishan Region,East Hebei Province

The thermodynamic calculation of dehydration reacton suggests very low activity of H2O during metamorphic peak of the Archaean granulite complex in the region studied.The αH2O values for Al-rich gneiss and hypersthene biotite gneiss-granulite in the Taipingzhai region are usually between 0.10 and 0.20,and those in the Louzishan region are 0.15-0.25.The fugacity of O2 in terms of lgf O2 in whole region ranges form-8to-14.The average coefficients of (δμH2O/δHMg^Bt)and(δμO2/δXMg^Bt)in the Taipingzhai region are-0.293 and-1.60 respectively,and those in the Louzishan region are-0.364and-1.420.The activity of H2O is very low in the whole region,but its values and other data mentioned above are considerably constant from place to place within a given region,even in rocks of dirrerent lithological characters.However,they show a certain gradient between different regions.Such characteristics are compatible with the genetic mechanism known as“carbonic metamorphism” put forward by Newton et al.,i.e.,the α H2O during the peak stage is controlled by permeation of pervasive CO2 influx of the mantle source,and shows features of external buffering.     

Natural Cr(VI) contamination of groundwater in the Cecina coastal area and its inner sectors (Tuscany,Italy)

A detailed hydrogeochemical study of groundwater in the Cecina coastal plain (Livorno province, Italy) and its inner sectors was undertaken in 2008, as chemical analyses carried out on groundwater since 2006 have revealed Cr(VI) concentrations of up to 49 μg/L (well above the permissible limit of 5 μg/L). Ophiolite outcrops are present throughout the study area, and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton. Waters delivered by the serpentinite outcrops have a typically Mg–HCO₃ composition, whereas those of the coastal plain are prevailingly of the Ca/Mg–HCO₃ type with significant Mg contents. Significant NO₃ contamination characterises the studied coastal plain, and an interesting negative correlation exists between Cr(VI) and both NO₃ and SO₄ deriving from the widespread use of (NH₄)₂SO₄ as a farm fertilizer. Chromium speciation calculations carried out using the EQ3NR code reveal that the prevailing Cr(VI) species in solution is CrO₄ ^2?; however, CaCrO₄° and MgCrO₄° neutral complexes represent significant percentages (up to 42 %). These findings suggest that the mobility and consequently the bioavailability of Cr(VI) can be significantly enhanced by these neutral complexes, which are not considered to be affected by adsorption/desorption processes. The Cr(VI) source, investigated by means of the Mg/SiO₂ molar ratio, seems to be represented mainly by Mg-bearing minerals of the chlorite group. Petrographic observations confirm the occurrence of this mineral group. The interaction between rainwater and the local serpentinite rock was simulated at different $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ conditions by reaction path modelling using the EQ3/6 software package. $P_{{{\text{O}}_{ 2} }}$ was varied in accordance with the assumption that redox conditions are determined in part by NO₃. Results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater, which plot in a rather wide $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ field. Although the dissolved Cr content is mostly of natural origin, fertilization may affect its fate.     

Anharmonic effect on the equation of state (EoS) for NaCl

We find clear intrinsic anharmonicity in the NaCl-B1 phase by examining the equation of state (EoS) based on previous ultrasonic velocity data for pressures up to 0.8 GPa and temperatures up to 800 K. The experimental EoS for this phase shows that its specific heat at constant volume (C _V ) is significantly smaller than that based on a harmonic model. Also, the sign of $\left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial P}}} \right. \kern-0pt} {\partial P}}} \right)_{T} ,$ which is normally negative in the quasi-harmonic approximation, is unexpectedly positive. The thermodynamic Grüneisen parameter (γ), which has frequently been assumed to be a single-variable function of molar volume, shows not only volume dependence but also negative temperature dependence. To understand these features of C _V and γ, we introduce a thermodynamic model including positive quartic anharmonicity. To make an anharmonic model advancing the ordinarily quasi-harmonic approximation model, we introduce two parameters: anharmonic characteristic temperature (θ _a ) and its volume derivative. In the anharmonic model, the value of C _V is calculated along an isochore using classical statistical mechanics and a harmonic quantum correction. At high temperatures, the decrease in C _V from the Dulong-Petit limit is related to the value of T/θ _a . For infinitely large θ _a , the system is approximately quasi-harmonic. The temperature dependence of γ is related to C _V by the thermodynamic identity $\left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial \ln V}}} \right. \kern-0pt} {\partial \ln V}}} \right)_{T} = C_{V} \left( {{{\partial \gamma } \mathord{\left/ {\vphantom {{\partial \gamma } {\partial \ln T}}} \right. \kern-0pt} {\partial \ln T}}} \right)_{V} + \gamma \left( {{{\partial C_{V} } \mathord{\left/ {\vphantom {{\partial C_{V} } {\partial \ln T}}} \right. \kern-0pt} {\partial \ln T}}} \right)_{V}.$ Even though our modification of the quasi-harmonic approximation is simple, our anharmonic model succeeds in reproducing the experimental γ and C _V simultaneously for the NaCl-B1 phase.     

Elasticity of calcite: thermal evolution

The elastic properties of calcite have been determined by Brillouin spectroscopy for temperatures up to 600 °C. The results reveal that the variations of the aggregate bulk (K _VRH) and shear (G _VRH) moduli of calcite with respect to temperature can be approximately expressed as follows: $$\begin{aligned} K_{{{\text{VRH}}}} ({\text{GPa}}) & = 79.57-0.0230\;T\, (T\;{\text{in}}\;^{^\circ } {\text{C}}) \\G_{{{\text{VRH}}}} ({\text{GPa}}) & = 32.23 - 0.0097\;T. \\\end{aligned}$$ This indicates a nearly constant Poisson’s ratio (0.322) for calcite from 22 to 600 °C. A further analysis shows that the compressibility along the c axis (β _||) and that perpendicular to the c axis have comparable contributions to the volume compressibility of calcite, although the contribution of β _|| decreases with an increase in the temperature.     

Multiple-pumped-well aquifer test to determine the anisotropic properties of a karst limestone aquifer in Pasco County, Florida, USA

Groundwater-level data from an aquifer test utilizing four pumped wells conducted in the South Pasco wellfield in Pasco County, Florida, USA, were analyzed to determine the anisotropic transmissivity tensor, storativity, and leakance in the vicinity of the wellfield. A weighted least-squares procedure was used to analyze drawdowns measured at eight observation wells, and it was determined that the major axis of transmissivity extends approximately from north to south and the minor axis extends approximately from west to east with an angle of anisotropy equal to N4.54°W. The transmissivity along the major axis ${\left( {T_{{\xi \xi }} } \right)}$ is 14,019 m² day^–1, and the transmissivity along the minor axis ${\left( {T_{{\eta \eta }} } \right)}$ is 4,303 m² day^–1. The equivalent transmissivity $T_{e} = {\left( {T_{{\xi \xi }} T_{{\eta \eta }} } \right)}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} = 7,767{{\text{m}}^{2} } \mathord{\left/ {\vphantom {{{\text{m}}^{2} } {{\text{day}}^{{ - {\text{1}}}} }}} \right. \kern-0em} {{\text{day}}^{{ - {\text{1}}}} }$ , and the ratio of anisotropy is 3.26. The storativity of the aquifer is 7.52?×?10^?4, and the leakance of the overlying confining unit is 1.37?×?10^?4 day^?1. The anisotropic properties determined for the South Pasco wellfield in this investigation confirm the results of previous aquifer tests conducted in the wellfield and help to quantify the NW–SE to NE–SW trends for regional fracture patterns and inferred solution-enhanced flow zones in west-central Florida.     

Heat capacity of hydrous trachybasalt from Mt Etna: comparison with CaAl<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript> (An)–CaMgSi<Subscript>2</Subscript>O<Subscript>6</Subscript> (Di) as basaltic proxy compositions

The specific heat capacity (C _p) of six variably hydrated (~3.5 wt% H₂O) iron-bearing Etna trachybasaltic glasses and liquids has been measured using differential scanning calorimetry from room temperature across the glass transition region. These data are compared to heat capacity measurements on thirteen melt compositions in the iron-free anorthite (An)–diopside (Di) system over a similar range of H₂O contents. These data extend considerably the published C _p measurements for hydrous melts and glasses. The results for the Etna trachybasalts show nonlinear variations in, both, the heat capacity of the glass at the onset of the glass transition (i.e., C _p ^g ) and the fully relaxed liquid (i.e., C _p ^l ) with increasing H₂O content. Similarly, the “configurational heat capacity” (i.e., C _p ^c  = C _p ^l  ? C _p ^g ) varies nonlinearly with H₂O content. The An–Di hydrous compositions investigated show similar trends, with C _p values varying as a function of melt composition and H₂O content. The results show that values in hydrous C _p ^g , C _p ^l and C _p ^c in the depolymerized glasses and liquids are substantially different from those observed for more polymerized hydrous albitic, leucogranitic, trachytic and phonolitic multicomponent compositions previously investigated. Polymerized melts have lower C _p ^l and C _p ^c and higher C _p ^g with respect to more depolymerized compositions. The covariation between C _p values and the degree of polymerization in glasses and melts is well described in terms of SM_hydrous and NBO/T _hydrous. Values of C _p ^c increase sharply with increasing depolymerization up to SM_hydrous ~ 30–35 mol% (NBO/T _hydrous ~ 0.5) and then stabilize to an almost constant value. The partial molar heat capacity of H₂O for both glasses (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{g}} \)) and liquids (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \)) appears to be independent of composition and, assuming ideal mixing, we obtain a value for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) of 79 J mol^?1 K^?1. However, we note that a range of values for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) (i.e., ~78–87 J mol^?1 K^?1) proposed by previous workers will reproduce the extended data to within experimental uncertainty. Our analysis suggests that more data are required in order to ascribe a compositional dependence (i.e., nonideal mixing) to \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \).     

The effect of drained pre-shearing on the undrained behaviour of loose sand with a small amount of fines

Stress history is recognised to play a major role in determining stress–strain behaviour of soil in undrained shearing. Most experimental studies on the effects of stress history on undrained behaviour are mainly limited to clean sand. In this paper, an experimental study carried out to investigate the effect of stress history on the undrained behaviour of loose sand with a small amount of fines is presented. Four series of triaxial compression tests, with different types of drained stress histories to near-failure prior to commencement of undrained shearing, were conducted. The experimental results indicate that drained pre-shearing to near-failure affects significantly the undrained behaviour of loose sand. In general, the drained pre-shearing improves the subsequent undrained behaviour of loose sand to the extent that liquefaction may not occur. It is shown that the effect of drained pre-shearing cannot be explained by the reduction in void ratio induced by drained pre-shearing. However, for specimens subjected to drained pre-shearing, $ p_{{{\text{d}}0}}^{\prime } $ / $ p_{{{\text{u}}0}}^{\prime } $ can be used as a parameter for analysing the effects of preloading history. It is also shown that for different preloading histories that brought the same change in void ratio or state parameter, drained pre-shearing to near-failure is the most effective, whereas pre-compression alone is the least effective in improving subsequent undrained behaviour of loose sand.     

Crystal structures and phase transitions in Sr2InTaO6 perovskite

The preparation and crystal structure of the double perovskite oxide Sr₂InTaO₆ are reported. This oxide has a monoclinic structure in space group P2₁/n at room temperature, where In and Ta display a rock-salt type ordering with a = 5.73356(10), b = 5.74052(10), c = 8.10905(14) Å and β = 90.022(6)°. Variable temperature neutron diffraction measurements demonstrate this displays the sequence of phase transitions $ P2_{1} /n\mathop{\longrightarrow}\limits^{{605\,^\circ {\text{C}}}}I2/m\mathop{\longrightarrow}\limits^{{705\,^\circ {\text{C}}}}I4/m\mathop{\longrightarrow}\limits^{{930\,^\circ {\text{C}}}}Fm\bar{3}m $ as a consequence of the sequential loss of tilting of the corner shared octahedra upon heating. The evolution of Sr₂InTaO₆ crystal structure upon heating is analysed and described in terms of symmetry-adapted distortion modes. The GM4+ and X3+, that are responsible for anti-phase and in-phase tilting, respectively, are highly temperature dependent, with the GM4+ mode having the largest amplitude at room temperature.     

Oxygen fugacity control in piston-cylinder experiments: a re-evaluation

Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni–NiO or Co–CoO) and H₂O, with an inner gold–palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010). H₂O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9–10):985–994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333–1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni–NiO and Co–CoO buffers, which is incorrect since the melts are all undersaturated in H₂O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log $a_{{{\text{H}}_{ 2} {\text{O}}}}$ .     

Interpretation of lithogeochemical and geophysical data to identify the buried mineralized area in Cu-Au porphyry of Dalli-Northern Hill

Geochemical and statistical analyses of 165 soil samples led to Cu-Au anomaly separation in Dalli-Northern Hill by using fractal geometry and U-spatial statistic. There was a good correlation between the anomaly areas and outcrops of quartz diorite porphyry (QDP) in the study area. Based on the interpretation of soil data and anomaly areas determination, one trench was suggested in NE-SW direction for follow-up exploration. Based on the rock sample analyses from the trenches in QDP rocks, the ratio of $ \frac{{{\mathrm{Ba}} \times {\mathrm{K}}}}{{{\mathrm{Ca}} \times {\mathrm{Zn}}}} $ clearly separated the mineralization area and considered as an index ratio for follow-up exploration stage. Dalli-Northern Hill anomaly includes pyrite/chalcopyrite/bornite, which is dominantly abundant in the ore body. Three IP profiles (IP04, IP05, and IP06) confirmed the conductivity of the sulfide zone. The background chargeability in the study area was about 5.4 mV/V and the average of maximum apparent chargeability in the study area was 44.4 mV/V, which could be related to the higher intensity of Cu-Fe sulfide minerals. The contact of andesite and quartz diorite has shown the strongest chargeability (71 mV/V) and high magnetic anomalies in the study area. DDH03 and DDH04 boreholes mostly confirmed that the IP/magnetic/geochemical anomalies were related to the contact of intrusive rocks and the wall rock of andesite. The combination of geochemical information from soil and rock together with geophysical data (induced polarization/resistivity) led to the subsurface geological cross sections and location of the mineralized zone enriched of sulfide. The mineralized zone in Dalli-Northern Hill distinct could be identified by potassic to weak sericitic and trace chloritic alteration, high values of the $ \frac{{{\mathrm{Ba}} \times {\mathrm{K}}}}{{{\mathrm{Ca}} \times {\mathrm{Zn}}}} $ ratio accompanied with high gold and copper values and enrichment from magnetite minerals. The high magnetic susceptibility, low resistivity, and high chargeability are considered as geophysical properties of the mineralized zones.