Clinopyroxene–liquid thermometers and barometers specific to alkaline differentiated magmas

We present new thermometers and barometers based on clinopyroxene–liquid equilibria specific to alkaline differentiated magmas. The new models were calibrated through the regression analyses of experimental datasets obtained by merging phase equilibria experiments from the literature with new experiments performed by using trachytic and phonolitic starting compositions. The regression strategy was twofold: (1) we have tested previous thermometric and barometric equations and recalibrated these models using the new datasets; (2) we have calibrated a new thermometer and a new barometer including only regression parameters that closely describe the compositional variability of the datasets. The new models yield more precise estimates than previous thermometers and barometers when used to predict temperatures and pressures of alkaline differentiated magmas. We have tested the reliability of the new equations by using clinopyroxene–liquid pairs from trachytes and phonolites erupted during major explosive eruptions at the Phlegrean Fields and Mt. Vesuvius (central Italy). The test yielded crystallization conditions comparable to those determined by means of melt and fluid inclusion analyses and phase equilibria studies; this validates the use of the proposed models for precise estimates of crystallization temperatures and pressures in differentiated alkaline magmas. Because these magmas feed some of the most voluminous, explosive, and threatening volcanic eruptions in the world, a better understanding of the environmental conditions of their reservoirs is mandatory and this is now possible with the new models provided here.     

A thermodynamic model for the solubility of barite and celestite in electrolyte solutions and seawater to 200°C and to 1 kbar

This paper describes a model for barite and celestite solubilities in the Na–K–Ca–Mg–Ba–Sr–Cl–SO₄–H₂O system to 200°C and to 1 kbar. It is based on Pitzer's ion interaction model for the thermodynamic properties of the aqueous phase and on values of the solubility products of the solids revised in this work. It is shown how barite and celestite solubilities in electrolyte solutions can be accurately predicted as a function of temperature and pressure from previously determined Pitzer's parameters. The equilibrium constant for the BaSO₄(aq) ion pair dissociation reaction is calculated from recently reported barite solubility in Na₂SO₄ solutions from 0 to 80°C. Pressure corrections are evaluated through partial molal volume calculations and are partially validated by comparing model predictions to measured barite and celestite solubilities in pure water to 1 kbar and in NaCl solutions to 500 bars. The model is then used to investigate the tendency of ion pairing of Ca, Sr and Ba with sulfate in seawater. Finally, the activity coefficient of aqueous barium sulfate in seawater is calculated for temperature, pressure and salinity values found in the ocean and compared to published values.     

An experimental study of phase equilibria in the system H2O-CO2-NaCl at 800 °C and 9 kbar

Phase equilibria in the ternary system H₂O-CO₂-NaCl were studied at 800 °C and 9 kbar in internally heated gas pressure vessels using a modified synthetic fluid inclusion technique. The low rate of quartz overgrowth along the `b' and `a' axes of quartz crystals was used to avoid fluid inclusion formation during heating, prior to attainment of equilibrium run conditions. The density of CO₂ in the synthetic fluid inclusions was calibrated using inclusions in the binary H₂O-CO₂ system synthesised by the same method and measured on the same heating-freezing stage. In the two-phase field, two types of fluid inclusions with different densities of CO₂ were observed. Using mass balance calculations, these inclusions are used to constrain the miscibility gap and the orientation of two-phase tie-lines in the H₂O-CO₂-NaCl system at 800 °C and 9 kbar. The equation of state of Duan et al. (1995) approximately describes the P-T section of the ternary system up to about 40 wt% of NaCl. At higher NaCl concentrations the measured solubility of CO₂ in the brine is much smaller than predicted by the EOS. A “salting out” effect must be added to the equation of state to include coulomb interaction in the model of Anderko and Pitzer (1993) and Pitzer and Jiang (1996). The new experimental data together with published data up to 5 kbar (Shmulovich et al. 1995) encompass practically all subsolidus crustal P-T conditions. A feature of the new experimental results is the large compositional range in the H₂O-CO₂-NaCl system occupied by the stability fields of halite + CO₂-rich fluid ± H₂O-NaCl brine. The prediction of halite stability in equilibrium with CO₂-rich fluid in deep-crustal rocks is supported by recent petrological and fluid inclusion studies of granulites. Received: 29 June 1998 / Accepted: 17 March 1999     

A Compensated-Redlich-Kwong (CORK) equation for volumes and fugacities of CO2 and H2O in the range 1 bar to 50 kbar and 100–1600°C

We present a simple virial-type extension to the modified Redlich-Kwong (MRK) equation for calculation of the volumes and fugacities of H₂O and CO₂ over the pressure range 0.001–50 kbar and 100 to 1400°C (H₂O) and 100 to 1600°C (CO₂). This extension has been designed to: (a) compensate for the tendency of the MRK equation to overestimate volumes at high pressures, and (b) accommodate the volume behaviour of coexisting gas and liquid phases along the saturation curve. The equation developed for CO₂ may be used to derive volumes and fugacities of CO, H₂, CH₄, N₂, O₂ and other gases which conform to the corresponding states principle. For H₂O the measured volumes of Burnham et al. are significantly higher in the range 4–10 kbar than those presented by other workers. For CO₂ the volume behaviour at high pressures derived from published MRK equations are very different (larger volumes, steeper (P/T)_V, and hence larger fugacities) from the virial-type equations of Saxena and Fei. Our CORK equation for CO₂ yields fugacities which are in closer agreement with the available high pressure experimental decarbonation reactions.     

Calculation of the standard partial molal thermodynamic properties and dissociation constants of aqueous HCl0 and HBr0 at temperatures to 1000°C and pressures to 5 kbar

Dissociation constants of aqueous ion pairs HCl⁰ and HBr⁰ derived in the literature from vapor pressure and supercritical conductance measurements Quist and Marshall 1968b, Frantz and Marshall 1984 were used to calculate the standard partial molal thermodynamic properties of the species at 25°C and 1 bar. Regression of the data with the aid of revised Helgeson-Kirkham-Flowers equations of state Helgeson et al 1981, Tanger 1988, Shock et al 1989 resulted in a set of equations-of-state parameters that permits accurate calculation of the thermodynamic properties of the species at high temperatures and pressures. These properties and parameters reproduce generally within 0.1 log unit (with observed maximum deviation of 0.23 log unit) the log K values for HBr⁰ and HCl⁰ given by Quist and Marshall (1968b) and Frantz and Marshall (1984), respectively, at temperatures to 800°C and pressures to 5 kbar.     

Decoupling the mechanical role of pore liquids in soils to liquid viscous effect and solid–liquid adhesion effect

Acta Geotechnica - This paper presents a novel conceptual approach for evaluating the mechanical effect of pore liquids on the overall geotechnical behavior. The approach is based on empiric...     

“Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer”—reply to the comment of Poli and Schmidt

Conclusions Although only Al^iv appears in our thermometer expression, this in no way infers that we believe tschermakite (or katophorite, kaersutite and other) substitutions to be unimportant. A careful reading of our earlier papers makes it clear that the reverse is true, e.g. Holland and Richardson 1979; Will et al. 1990a, b; Guiraud et al. 1990. Indeed in B and H (p. 211) we state that natural and synthetic amphiboles are dominated by a combination of edenite, pargasite, hornblende and hastingsite substitutions. What we endeavoured to point out was that because of the nature of reaction (1) and the use of mixing-on-sites activity models the extent of Al substitutions on M2 or Na on M4 do not materially influence our expression for K₁ and consequently our thermometer. Certainly any sophisticated activity model for amphibole explicitly should account for all cross-site interactions between M-, Tl- and A-site cations, as alluded to by P and S in reference to Docka et al. (1987), as well as O3-site anions. However, such a day currently is well away and mixing-on-sites, with modifications as outlined above and to be detailed in T.J.B. Holland and J.D. Blundy (in preparation), seems rather promising for the purposes of amphibole thermometry. We do not share the rather negative and pessimistic outlook on activity models and thermobarometry implicit in P and S comments.     

Lead in K－Feldspar and Its Relations to Rb Metallogenesis

In intermediate-acid magmatic rocks,alkaline magmatic rocks,gneisses and migmatitic rocks K-feldspar is a rock-forming rock in which the contents of Pb are highest,just 2-10 times those of the whole rock,3-16 times those of mica minerals and 6-32 times those of quartz.The lowest contents of K-feldspar are recognized in Early Proterozoic and Achaean rocks,with Pb in the K-feldspar accounting for less than 10% of that in the whole rock;in post Middle Proterozoic alkaine magmatic rocks,K-feldspar-rich granites and metamorphic rocks the contents of K-feldspar tend to increase,with the proportion granites and metamorphic rocks the contents of K-feldspar tend to increase,with the proportion of Pb over that in the whole rock being obviously increased.In the alkaline rocks in which K-feldspar accounts for 50%-70% of the total in the whole rock,the contents of Pb in K-feldspar account approximately for 70%-95% of the total lead in the whole rock.Being accessible to hydrothermal alteration in the late periods,K-feldspar was conversed to sericite,calcite,quartz,etc.In the process of such conversion the lead would be leached out and then find its way into fluid phase.This kind of trans-formation can provide sufficient ore-forming material for later Pb metallogenesis.     

Storage conditions of Bezymianny Volcano parental magmas: results of phase equilibria experiments at 100 and 700 MPa

The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH₂O) to investigate the compositional evolution of residual liquids. The temperature (T) range of the experiments was 950–1,150 °C, aH₂O varied between 0.1 and 1, and the log of oxygen fugacity (fO₂) varied between quartz–fayalite–magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)–T–aH₂O–fO₂ conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2–2.5 wt% H₂O; they can be stored in upper crustal levels at a depth of ~15 km, and at this depth they start to crystallize at ~1,110 °C. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3–4 km because amphibole is present in natural magmas (>150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.     

Textures in deforming forsterite aggregates up to 8 GPa and 1673 K

We report results from axisymmetric deformation experiments carried out on forsterite aggregates in the deformation-DIA apparatus, at upper mantle pressures and temperatures (3.1–8.1 GPa, 1373–1673 K). We quantified the resulting lattice preferred orientations (LPO) and compare experimental observations with results from micromechanical modeling (viscoplastic second-order self-consistent model—SO). Up to 6 GPa (~185-km depth in the Earth), we observe a marked LPO consistent with a dominant slip in the (010) plane with one observation of a dominant [100] direction, suggesting that [100](010) slip system was strongly activated. At higher pressures (deeper depth), the LPO becomes less marked and more complex with no evidence of a dominant slip system, which we attribute to the activation of several concurrent slip systems. These results are consistent with the pressure-induced transition in the dominant slip system previously reported for olivine and forsterite. They are also consistent with the decrease in the seismic anisotropy amplitude observed in the Earth’s mantle at depth greater than ~200 km.     

Experimental study of uraninite solubility in aqueous HCl solutions at 500°C and 1 kbar

Uraninite solubility in 0.001–2.0 m HCl solutions was experimentally studied at 500°C, 1000 bar, and hydrogen fugacity corresponding to the Ni/NiO buffer. It was shown that the following U(IV) species dominate in the aqueous solution: U(OH)₄⁰, U(OH)₂Cl₂⁰, and UOH Cl₃⁰ Using the results of uraninite solubility measurement, the Gibbs free energies of U(IV) species at 500°C and 1000 bar were calculated (kJ/mol): −9865.55 for UO₂(aq), −1374.57 for U(OH)₂ Cl₂⁰, and −1265.49 for UOH Cl₃⁰, and the equilibrium constants of uraninite dissolution in water and aqueous HCl solutions were estimated: UO₂(cr) = UO₂(aq), pK ₀ = 6.64; UO₂(cr) + 2HCl⁰ = U(OH)₂ Cl₂⁰, pK ₂ = 3.56; and UO₂(cr) + 3HCl⁰ = UOHcl₃⁰ + H₂O, pK ₃ = 3.05. The value pK ₁ ≈ 5.0 was obtained as a first approximation for the equilibrium UO₂(cr) + H₂O + HCl⁰ = U(OH)₃Cl⁰. The constant of the reaction UO₂(cr) + 4HCl⁰ = UCl₄⁰ + 2H₂O (pK ₄ = 7.02) was calculated taking into account the ionization constants of U Cl₄⁰ and U(OH)₄⁰, obtained by extrapolation from 25 to 500°C at 1000 bar using the BR model. Intense dissolution and redeposition of gold (material of experimental capsules) was observed in our experiments. The analysis and modeling of this phenomenon suggested that the UO_{2 + x} /UO₂ redox pair oxidized Au(cr) to Au⁺(aq), which was then reduced under the influence of stronger reducers.     

A New Method Used to Calculate the Homogenization Pressure and Related Thermodynamic Parameters of CO2-H2O System at T ＜623.15K and P ＜100MPa

根据CO2-H2O体系均一法测温过程中出现的部分均一和完全均一现象,采用最新的热力学参数及相关模型,分别建立相应的热力学方程.根据同一体系的摩尔体积在均一法测温升温过程中几乎不变的特征可知,部分均一与完全均一状态下,体系的摩尔体积近似相等.据此对影响摩尔体积的充填度进行微调,通过迭代运算,直至两种条件下的摩尔体积近似相等,从而可以获得精确的摩尔体积和充填度,进而获得体系中的CO2含量、完全均—压力以及流体包裹体的总密度等热力学参数.本方法只需提供部分均一温度和完全均一温度以及部分均一方式便可求取相关热力学参数,符合地质研究方法和思路.该方法只适用于完全均—温度低于623.15K、完全均一压力小于100MPa以及最后均一至液相或临界点的CO2-H2O流体包裹体体系.对比研究表明,该方法也适用于盐度低于6％的NaCl-CO2-H2O流体体系,所获得的热力学参数相对误差在10％左右.     

Solid–liquid Phase Equilibria in the Aqueous Ternary System Containing Lithium, Potassium, and Sulfate ions at 288.15 K

正1 Introduction Salt lakes are widely distributed in the western of China,especially in the area of Qinghai-Xizang(Tibet)Plateau.A series of salt lakes in the Qaidam Basin,located in Qinghai Province,China,is famous for their abundance of lithium,potassium and boron resources(Zheng et al,1988;Deng et al,2012).It is well known that the     

Elasticity of TiO2 rutile to 1800 K

The ambient pressure elastic properties of single-crystal TiO₂ rutile are reported from room temperature (RT) to 1800 K, extending by more than 1200 oK the maximum temperature for which rutile elasticity data are available. The magnitudes of the temperature derivatives decrease with increasing temperature for five of the six adiabatic elastic moduli (C _ij ). At RT, we find (units, GPa): C ₁₁=268(1); C ₃₃=484(2); C ₄₄=123.8(2); C ₆₆=190.2(5); C ₂₃=147(1); and C ₁₂=175(1). The temperature derivatives (units, GPa K⁻¹) at RT are: (∂C ₁₁/∂T) _P =−0.042(5); (∂C ₃₃/∂T) _P =−0.087(6); (∂C ₄₄/∂T) _P =−0.0187(2); (∂C ₆₆/∂T) _P =−0.067(2); (∂C ₂₃/∂T) _P =−0.025; and (∂C ₁₂/∂T) _P −0.048(5). The values for K _S (adiabatic bulk modulus) and μ (isotropic shear modulus) and their temperature derivatives are K _S =212(1) GPa; μ=113(1) GPa; (∂K _S /∂T) _P =−0.040(4) GPa K⁻¹; and (∂μ/∂T) _P =−0.018(1) GPa K⁻¹. We calculate several dimensionless parameters over a large temperature range using our new data. The unusually high values for the Anderson-Gròneisen parameters at room temperature decrease with increasing temperature. At high T, however, these parameters are still well above those for most other oxides. We also find that for TiO₂, anharmonicity, as evidenced by a non-zero value of [∂ln (K _T )/∂lnV] _T , is insignificant at high T, implying that for the TiO₂ analogue of stishovite, thermal pressure is independent of volume (or pressure). Systematic relations indicate that ∂² K _S /∂T∂P is as high as 7×10⁻⁴ K⁻¹ for rutile, whereas ∂²μ/∂T∂P is an order of magnitude less. Received: 19 September 1997 / Revised, accepted: 27 February 1998     

Phase equilibria in the systems Fe2O3-MgO-TiO2 and FeO-MgO-TiO2 between 1173 and 1473 K, and Fe2+-Mg mixing properties of ilmenite, ferrous-pseudobrookite and ulvöspinel solid solutions

Detailed phase relations have been determined within the systems Fe₂O₃-MgO-TiO₂ and FeO-MgO-TiO₂. Experiments were performed over the temperature interval 1173–1473 K by equilibrating pelletized, fine-grained oxide mixtures in either inert calcia-stabilized zirconia pots (Fe₂O₃-MgO-TiO₂ system) or evacuated silica tubes (FeO-MgO-TiO₂ system). Equilibrium phase assemblages were determined by combined optical microscope, X-ray diffraction and EMP examination. Phase relations in the Fe₂O₃-MgO-TiO₂ ternary are dominated by the instability of the M₂O₃ solid solution relative to the phase assemblage M₃O₄ + M₃O₅. A miscibility gap along the M₂O₃ binary also gives rise to two, 3-phase fields (α-M₂O₃ + M₃O₅ + M₃O₄ and α′-M₂O₃ + M₃O₅ + M₃O₄) separated by the M₃O₄ + M₃O₅ phase field. Phase relations in the FeO-MgO-TiO₂ ternary were divided into two sub-systems. For the FeTiO₃-MgTiO₃-TiO₂ sub-ternary, there is complete solid solution along the M₂O₃ and M₃O₅ binary joins at high temperature. At low temperatures (T < 1373 K) the M₃O₅ pseudobrookite solid solution decomposes to M₂O₃ + TiO₂. Increasing the concentration of MgO in M₃O₅ phase results in a decrease in the temperature at which M₃O₅ becomes unstable and compositional tie lines linking M₂O₃ and TiO₂ fan out, before the appearance of a three-phase region where M₂O₃, M₃O₅, and TiO₂ coexist. Within the expanded FeO-MgO-TiO₂ system, at temperatures above ∼1273 K there is a continuous solid solution along the M₃O₄ binary. At low temperatures (T < 1273 K) the Mg₂TiO₄ end-member breaks down to MgO and MgTiO₃. The M₃O₄ phase shows significant non-stoichiometry, down to at least 1173 K. Fe²⁺-Mg partitioning data were obtained for coexisting M₂O₃-M₃O₅ and M₂O₃-M₃O₄ pairs in the FeO-MgO-TiO₂ ternary. Assuming a regular solution mixing model for all phases, the M₂O₃ and M₃O₄ solid solutions were both found to exhibit moderate positive deviations from ideality (∼2600 J/mol), whereas the data for the M₃O₅ binary suggest close to ideal behaviour. Received: 22 May 1998 / Accepted: 3 November 1998     

Experimental studies of Ta2O5 and columbite–tantalite solubility in fluoride solutions from 300 to 550°C and 50 to 100 MPa

It is well established that the fractionation of Li–F granitic magmas at depth leads to the accumulation of flux elements such as F and Li, and metal cations such as Ta and Nb in residual melts. However, it remains to be determined whether magmatic fractionation is sufficient to concentrate Nb and Ta into economically significant quantities, and what role hydrothermal–metasomatic processes play in the formation of such ore deposits. In the literature, reliable data about the solubility of Ta and Nb in hydrothermal solutions is missing or incomplete. This study provides a quantitative experimental estimation of the possible contribution from hydrothermal processes in Ta enrichment in cupolas of albitized and greisenized Li–F granite. Experimental studies of Ta₂O₅ and columbite–tantalite (Mn,Fe)(Nb,Ta)₂O₆ solubility were carried out in fluoride solutions consisting of HF, NaF, KF, and LiF. At low fluoride concentrations (0.01 and 0.1 m), Ta₂O₅ solubility at 550°C and 100 MPa under Co–CoO oxidizing conditions is low (near 10^?5–10^?4 m) in all fluoride solutions (HF, NaF, KF, LiF). At high fluoride concentrations (1 and 2 m) the highest Ta₂O₅ concentrations (10^?1 m) were detected in HF solutions. In KF, NaF, and LiF solutions, the Ta₂O₅ solubility is also high (10^?3–10^?2 m). The dependence of columbite–tantalite (Nb₂O₅-59 wt. %, Ta₂O₅-18 wt. %) solubility as a function of solution composition, T, and P has also been investigated. Tantalum and Nb concentrations have the highest values in HF solutions at reduced conditions (up to 10^?3 to 10^?2 m Ta in 1 m HF). In 1 m NaF solutions, the concentrations of Nb and Ta are, respectively, 2.5 and 3 orders of magnitude less than those in the 1 m HF solutions. Solubility of Ta and Nb in KF solutions has intermediate values. It is established that in NaF and KF solutions the dependence of solubility on pressure is distinctly negative. The Nb and Ta contents increase with increasing concentrations of HF and KF in solution, however, they do not change with increasing NaF concentration. In NaHCO₃, Na₂CO₃, and HCl solutions columbite–tantalite solubility is low. Even in 1 m chloride solutions the content is within the limits of 10^?5 m for Nb and 10^?6 to 10^?8 m for Ta. We conclude that hydrothermal transport of Ta and Nb is possible only in concentrated fluoride solutions.