Pressure dependence of hydroxyl solubility in coesite

 The solubility of hydroxyl in coesite was investigated in multianvil experiments performed at 1200 °C over the nominal pressure range 5–10 GPa, at an f _O2 close to the Ni-NiO buffer. The starting material for each experiment was a cylinder of pure silica glass plus talc, which dehydrates at high P and T to provide a source of water and hydrogen (plus enstatite and excess SiO₂). Fourier-transform infrared (FTIR) spectra of the recovered coesite crystals show five sharp bands at 3606, 3573, 3523, 3459, and 3299 cm⁻¹, indicative of structurally bonded hydrogen (hydroxyl). The concentration of hydrogen increases with pressure from 285 H/10⁶ Si (at 5 GPa) to 1415 H/10⁶ Si (at 10 GPa). Assuming a model of incorporation by (4H)_Si defects, the data are fit well by the equation C _OH=Af ² _H2<\INF>Oexp(−PΔV/RT), with A=4.38 H/10⁶ Si/GPa, and ΔV=20.6 × 10⁻⁶ m³ mol⁻¹. An alternative model entailing association of hydrogen with cation substitution can also be used to fit the data. These results show that the solubility of hydroxyl in coesite is approximately an order of magnitude lower than in olivines and pyroxenes, but comparable to that in pyropic garnet. However, FTIR investigations on a variety of ultrahigh pressure metamorphic rocks have failed in all cases to detect the presence of water or hydrogen in coesite, indicating either that it grew in dry environments or lost its hydrogen during partial transformation to quartz. On the other hand, micro-FTIR investigations of quartz crystals replacing coesite show that they contain varying amounts of H₂O. These results support the hypothesis that preservation of coesite is not necessarily linked to fast exhumation rates but is crucially dependent on limited fluid infiltration during exhumation. Received: 23 August 1999 / Accepted: 10 April 2000     

Na2O solubility in CaO-MgO-SiO2 melts

The sodium solubility in silicate melts in the CaO-MgO-SiO₂ (CMS) system at 1400 °C has been measured by using a closed thermochemical reactor designed to control alkali metal activity. In this reactor, Na_(g) evaporation from a Na₂O-xSiO₂ melt imposes an alkali metal vapor pressure in equilibrium with the molten silicate samples. Because of equilibrium conditions in the reactor, the activity of sodium-metal oxide in the molten samples is the same as that of the source, i.e., aNa₂O_(sample) = aNa₂O_(source). This design also allows to determine the sodium oxide activity coefficient in the samples. Thirty-three different CMS compositions were studied. The results show that the amount of sodium entering from the gas phase (i.e., Na₂O solubility) is strongly sensitive to silica content of the melt and, to a lesser extent, the relative amounts of CaO and MgO. Despite the large range of tested melt compositions (0 < CaO and MgO < 40; 40 < SiO₂ < 100; in wt%), we found that Na₂O solubility is conveniently modeled as a linear function of the optical basicity (Λ) calculated on a Na-free basis melt composition. In our experiments, γNa₂O_(sample) ranges from 7 × 10⁻⁷ to 5 × 10⁻⁶, indicating a strongly non-ideal behavior of Na₂O solubility in the studied CMS melts (γNa₂O_(sample) ? 1). In addition to showing the effect of sodium on phase relationships in the CMS system, this Na₂O solubility study brings valuable new constraints on how melt structure controls the solubility of Na in the CMS silicate melts. Our results suggest that Na₂O addition causes depolymerization of the melt by preferential breaking of Si-O-Si bonds of the most polymerized tetrahedral sites, mainly Q⁴.     

CO2 solubility in dacitic melts equilibrated with H2O-CO2 fluids: Implications for modeling the solubility of CO2 in silicic melts

The solubility of CO₂ in dacitic melts equilibrated with H₂O-CO₂ fluids was experimentally investigated at 1250°C and 100 to 500 MPa. CO₂ is dissolved in dacitic glasses as molecular CO₂ and carbonate. The quantification of total CO₂ in the glasses by mid-infrared (MIR) spectroscopy is difficult because the weak carbonate bands at 1430 and 1530 cm⁻¹ can not be reliably separated from background features in the spectra. Furthermore, the ratio of CO_2,mol/carbonate in the quenched glasses strongly decreases with increasing water content. Due to the difficulties in quantifying CO₂ species concentrations from the MIR spectra we have measured total CO₂ contents of dacitic glasses by secondary ion mass spectrometry (SIMS).At all pressures, the dependence of CO₂ solubility in dacitic melts on x^fluid_CO2,total shows a strong positive deviation from linearity with almost constant CO₂ solubility at x_CO2fluid > 0.8 (maximum CO₂ solubility of 795 ± 41, 1376 ± 73 and 2949 ± 166 ppm at 100, 200 and 500 MPa, respectively), indicating that dissolved water strongly enhances the solubility of CO₂. A similar nonlinear variation of CO₂ solubility with x_CO2fluid has been observed for rhyolitic melts in which carbon dioxide is incorporated exclusively as molecular CO₂ (Tamic et al., 2001). We infer that water species in the melt do not only stabilize carbonate groups as has been suggested earlier but also CO₂ molecules.A thermodynamic model describing the dependence of the CO₂ solubility in hydrous rhyolitic and dacitic melts on T, P, f_CO2 and the mol fraction of water in the melt (x_water) has been developed. An exponential variation of the equilibrium constant K₁ with x_water is proposed to account for the nonlinear dependence of x_CO2,totalmelt on x_CO2fluid. The model reproduces the CO₂ solubility data for dacitic melts within ±14% relative and the data for rhyolitic melts within 10% relative in the pressure range 100-500 MPa (except for six outliers at low x_CO2fluid). Data obtained for rhyolitic melts at 75 MPa and 850°C show a stronger deviation from the model, suggesting a change in the solubility behavior of CO₂ at low pressures (a Henrian behavior of the CO₂ solubility is observed at low pressure and low H₂O concentrations in the melt). We recommend to use our model only in the pressure range 100-500 MPa and in the x_CO2fluid range 0.1-0.95. The thermodynamic modeling indicates that the partial molar volume of total CO₂ is much lower in rhyolitic melts (31.7 cm³/mol) than in dacitic melts (46.6 cm³/mol). The dissolution enthalpy for CO₂ in hydrous rhyolitic melts was found to be negligible. This result suggests that temperature is of minor importance for CO₂ solubility in silicic melts.     

Solubility of pyromorphite Pb5(PO4)3Cl-mimetite Pb5(AsO4)3Cl solid solution series

Pyromorphite Pb₅(PO₄)₃Cl and mimetite Pb₅(AsO₄)₃Cl are isostructural minerals with apatite. Due to their high environmental stability, they have gained considerable attention as metals sequestration agents in water treatment and contaminated soil remediation. Pyromorphite and mimetite can form a continuous solid solution series in near-Earth surface environments. Precipitation of the end members and intermediate members of the series is likely to occur in the areas where the cost-effective in situ immobilization reclamation method, based on phosphate amendments, is applied. In contrast to the widely studied thermodynamic parameters of pyromorphite and mimetite, knowledge of the thermodynamics of their solid solutions is sparse. To supplement the data, a number of compounds from the pyromorphite-mimetite series were synthesized at room temperature using a method to simulate the conditions in the near-Earth surface environments. Afterwards, batch dissolution and dissolution-recrystallization experiments of seven synthesized precipitates were conducted at 25 °C, pH = 2 and in a 0.05 M KNO₃ background electrolyte. The experiments were carried out for a period of 6 (dissolution) and 14 (dissolution-recrystallization) months. A plateau in the [Pb] evolution patterns was used to determine equilibrium. All seven dissolutions were congruent, and the ionic activity products (IAP) of the minerals from the pyromorphite-mimetite solid solution series were calculated based on the dissolution reaction: . The IAPs for pyromorphite and mimetite exhibit a significant difference in values over three orders of magnitude between approximately 10⁻⁷⁹ for pyromorphite and approximately 10⁻⁷⁶ for mimetite. The series appeared to be ideal, and Lippmann and Roozboom diagrams were used for better understanding of its thermodynamics. The results indicated a strong tendency of pyromorphite to partition into the solid phase in the series, which explains some of the naturally observed phenomena. The improvement of the lattice stability of the mimetite due to isostructural phosphate substitutions in anionic sites was observed. The thermodynamic data reported in this study supplement existing databases used in geochemical modeling.     

Phosphoinnelite, Ba4Na3Ti3Si4O14(PO4,SO4)2(O,F)3, a new mineral species from peralkaline pegmatite of the Kovdor pluton, Kola Peninsula

Phosphoinnelite, an analogue of innelite with P > S, has been found in a peralkaline pegmatite vein crosscutting calcite carbonatite at the phlogopite deposit, Kovdor pluton, Kola Peninsula. Cancrinite (partly replaced with thomsonite-Ca), orthoclase, aegirine-augite, pectolite, magnesioarfvedsonite, golyshevite, and fluorapatite are associated minerals. Phosphoinnelite occurs as lath-shaped crystals up to 0.2 × 1 × 6 mm in size, which are combined typically in bunch-, sheaf-, and rosettelike segregations. The color is yellow-brown, with vitreous luster on crystal faces and greasy luster on broken surfaces. The mineral is transparent. The streak is pale yellowish. Phosphoinnelite is brittle, with perfect cleavage parallel to the {010} and good cleavage parallel to the {100}; the fracture is stepped. The Mohs hardness is 4.5 to 5. Density is 3.82 g/cm³ (meas.) and 3.92 g/cm³ (calc.). Phosphoinnelite is biaxial (+), α = 1.730, β = 1.745, and γ = 1.764, 2V (meas.) is close to 90°. Optical orientation is Z^c ∼ 5°. Chemical composition determined by electron microprobe is as follows (wt %): 6.06 Na₂O, 0.04 K₂O, 0.15 CaO, 0.99 SrO, 41.60 BaO, 0.64 MgO, 1.07 MnO, 1.55 Fe₂O₃, 0.27 Al₂O₃, 17.83 SiO₂, 16.88 TiO₂, 0.74 Nb₂O₅, 5.93 P₂O₅, 5.29 SO₃, 0.14 F, −O=F₂ = −0.06, total is 99.12. The empirical formula calculated on the basis of (Si,Al)₄O₁₄ is (Ba_3.59Sr_0.13K_0.01)_Σ3.73(Na_2.59Mg_0.21Ca_0.04)_Σ3.04(Ti_2.80Fe _0.26 ³⁺ Nb_0.07)_Σ3.13[(Si_3.93Al_0.07)_Σ4O₁₄(P_1.11S_0.87)_Σ1.98O_7.96](O_2.975F_0.10)_Σ3.075. The simplified formula is Ba₄Na₃Ti₃Si₄O₁₄(PO₄,SO₄)₂(O,F)₃. The mineral is triclinic, space group P or P1. The unit cell dimensions are a = 5.38, b = 7.10, c = 14.76 ?; α = 99.00°, β = 94.94°, γ = 90.14°; and V = 555 ?³, Z = 1. The strongest lines of the X-ray powder pattern [d, ? in (I)(hkl)] are: 14.5(100)(001), 3.455(40)(103), 3.382(35)(0 2), 2.921(35)(005), 2.810(40)(1 4), 2.683(90)(200, 01), 2.133(80)( 2), 2.059(40)(204, 1 3, 221), 1.772(30)(0 1, 1 7, 2 2, 2 3). The infrared spectrum is demonstrated. An admixture of P substituting S has been detected in the innelite samples from the Inagli pluton (South Yakutia, Russia). An innelite-phosphoinnelite series with a variable S/P ratio has been discovered. The type material of phosphoinnelite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? I.V. Pekov, N.V. Chukanov, I.M. Kulikova, D.I. Belakovsky, 2006, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2006, No. 3, pp. 52–60. Considered and recommended by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, May 9, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 4, 2005 (proposal 2005-022).     

CO2 solubility in Martian basalts and Martian atmospheric evolution

To understand possible volcanogenic fluxes of CO₂ to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa and 1400-1625 °C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO₂ solubility. CO₂ contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe³⁺/Fe^T was measured by Mössbauer spectroscopy. The CO₂ contents of glasses show no dependence on Fe³⁺/Fe^T and range from 0.34 to 2.12 wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO₂ contents allowed calibration of an integrated molar absorptivity of 81,500 ± 1500 L mol⁻¹ cm⁻² for the integrated area under the carbonate doublet at 1430 and 1520 cm⁻¹. The experimentally determined CO₂ solubilities allow calibration of the thermodynamic parameters governing dissolution of CO₂ vapor as carbonate in silicate melt, K_II, (Stolper and Holloway, 1988) as follows: , ΔV⁰ = 20.85 ± 0.91 cm³ mol⁻¹, and ΔH⁰ = −17.96 ± 10.2 kJ mol⁻¹. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO₂ dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and f_O2. For the source region for Humphrey, constrained by phase equilibria to be near 1350 °C and 1.2 GPa, the resulting CO₂ contents are 51 ppm at the iron-wüstite buffer (IW), and 510 ppm at one order of magnitude above IW (IW + 1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540 °C and 1.2 GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240 ppm CO₂ at IW and 0.24 wt.% of CO₂ at IW + 1. For expected magmatic fluxes over the last 4.5 Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26 bars from sources at IW and IW + 1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2 bars at IW and IW + 1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO₂ to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW + 1.2), then significant contribution of volcanogenic CO₂ to an early Martian greenhouse is plausible.     

K-H3OFe3(SO4)2(OH)6铁矾的XRD研究

根据X射线衍射(XRD)分析发现: A Fe₃(SO₄)₂(OH)₆(A=K⁺、H₃O⁺)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K⁺含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K⁺含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K⁺、H₃O⁺离子位于较大空隙中,且沿着Z轴方向排列,当K⁺、H₃O⁺离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。     

Actinide crystal-liquid partitioning for clinopyroxene and Ca3(PO4)2

Using fission and alpha track radiography techniques, we have measured partition coefficients (D) for the actinide elements Th, U and Pu between diopsidic clinopyroxene, whitlockite [β-Ca₃ (PO₄)₂] and silicate liquid at 20kbar. Equilibrium partitioning at the crystal-liquid interface is assumed, and corrections for actinide zoning have been applied to the measured D values. Reproducibility for both actinide and minor element D values is carefully examined as a criterion for crystal-liquid interface equilibrium. The data are mostly compatible with interface equilibrium except for experiments at high cooling rates ( ? 30 deg/hr). Partition coefficients for Th/U/Pu of about 0.002/0.002/0.06 are measured for clinopyroxene and 1.2/0.5/3.4 for whitlockite. At an oxygen fugacity of 10^?8.5, Pu is much more readily incorporated into the crystalline phases than is U or Th because of the importance of trivalent Pu. The D_Pu(cpx) is similar to D(cpx) of the light rare earths supporting the concept of Pu/(rare earth) dating.     

CO2分压条件下煤中矿物质溶解度数值模拟

查明煤中矿物质在不同温度和CO₂分压条件下溶解度变化规律,能为注入CO₂过程中煤储层渗透率分析提供重要依据。借助水文地球化学模拟软件PHREEQC对在不同温度和CO₂分压条件下煤中各矿物的溶解度进行了水化学模拟,得出不同温度和CO₂分压条件下矿物质溶解度的变化规律。结果表明：在无CO₂分压时,随着温度的升高各矿物的溶解度增加;当溶液中CO₂分压增加到一定程度时,随着温度的升高各矿物的溶解度降低（石英除外）;在温度相同时,随着CO₂分压的增加,所有矿物（石英除外）溶解度均增加,方解石的溶解度随着CO₂分压的升高呈现出迅速增加的趋势,其他矿物随着CO₂分压的升高,溶解度增加的速率较为缓慢。     

N2-CH4（CO2）混合气体在线标样制备及其拉曼定量因子测定

利用混合气体的标准样品对激光拉曼探针进行标定,可以快速准确地对包裹体中的无机及有机气相组分进行定量分析。而常用的商用钢瓶装混合气体标样,存在费用高、气体组成单一固定等缺点。本文设计了一套在线标样制备装置,提出一种在线配置不同浓度和压力条件下混合气体标样的方法。利用高纯度(纯度99.999%)的N2、CH4以及CO2钢瓶气,经过在线混合增压,在5 MPa和10 MPa条件下制备了N2摩尔分数为30%、50%和70%的N2-CH4以及N2-CO2混合气体在线标样。该方法制备的标样与70%N2+30%CO2的商用钢瓶气标样对比表明,CO2与N2的拉曼相对峰高以及相对峰面积值的误差在4%以内,具有较高的准确度和重现性。通过不同压力和浓度条件下CH4以及CO2的拉曼相对定量因子测定表明,气体的相对定量因子在5~10 MPa压力条件下与压力及组成无关。地质样品应用结果表明,本方法可以方便、灵活、准确地按任意比例将两瓶及两瓶以上纯气体钢瓶样品进行混合及增压,为激光拉曼标定、气体组成原位测量等提供了一种新的技术思路。     

Rhondonite solubility and thermodynamic properties of aqueous MnCl2 in the system MnOSiO2HClH2O

The solubility of rhodonite, represented by the reaction MnSiO₃ (rhodonite) + 2HCl⁰ = MnCl₂⁰ + SiO₂ (quartz) + H₂O, was investigated experimentally in the temperature range 400°–700°C at 1 and 2 kbar by rapid-quench hydrothermal techniques and the Ag-AgCl buffer methods. Variations in the molalities of associated hydrogen chloride (m_HCl⁰) as a function of the molalities of total Mn indicate that Mn in the fluid in equilibrium with the assemblage rhodonite + quartz is predominantly associated as MnCl₂⁰. The Mn:Cl in the fluid ?2, indicating that Mn⁺² is the dominant oxidation state.The solubility data were used to calculate the equilibrium constant of the above reaction as a function of temperature, pressure, and the difference in Gibbs free energy of formation between MnCl₂⁰ and HCl⁰. The equilibrium constants of solubility for Mn minerals for which thermochemical data are available were also calculated. Calculated mineral solubilities were used in conjunction with the data of Frantz et al. (1981) to calculate the composition of supercritical fluids in equilibrium with Mn-bearing phases and assemblages. At 400°C and 1000 bars, supercritical fluids in equilibrium with olivines of compositions similar to those present in MORB tend to be enriched in Mn, despite the low mole fraction of tephroite in the olivine. Supercritical fluids in equilibrium with the assemblage quartz-hematite-rhodonite at 500° and 400°C and 1000 bars show high concentrations of Mn relative to Fe. Manganese concentrations in the fluids increase with decrease in the mole fraction of H, whereas Fe concentrations decrease. The data indicate that H fugacity plays a significant role in the separation of Mn from Fe in chloride-bearing hydrothermal fluids at supercritical temperatures.     

First-principles study of (MgH2SiO4)? n (Mg2SiO4) hydrous olivine structures. I. Crystal structure modelling of hydrous olivine Hy-2 a (MgH2SiO4) ? 3(Mg2SiO4)

 Recently, the Hy-2a hydrous olivine (MgH₂ SiO₄)·3(Mg₂SiO₄) occurring as nanometre-sized inclusions in mantle olivines has been found by TEM, and has been suggested to be a new DHMS phase (Khisina et al. 2001). A model of the crystal structure of Hy-2a has been proposed as a 2a-superstructure of olivine with one Me²⁺ -vacant octahedral layer in the (1 0 0) plane per Hy-2a unit cell (Khisina and Wirth 2002). In the present study the crystal structure of Hy-2a hydrous olivine is optimized by ab initio calculations. The aims of this study are: (1) verification of the suggested models of Hy-2a hydrous olivine structure; (2) calculation of the most stable configurations for Hy-2a structure with minimum static lattice energy, by assuming a possible formation of Me²⁺ vacancies in either M1 or M2 octahedral sites; (3) determination of the position of protons and hydrogen bonds in the Hy-2a structure. Several different possible configurations of the Hy-2a structure are optimized. The results support the idea of a stable olivine structure with ordered planar-segregated OH-bearing defects oriented parallel to (1 0 0). The data obtained indicate a preferred stability of the Hy-2a structure with the protons associated with M1 vacancies and bonded with O1 and O2 oxygen sites. The relative energy values of the optimized Hy-2a structure configurations correlate as a rule with the average shifts of atoms from their positions in pure forsterite structure. Received: 7 February 2002 / Accepted: 23 October 2002     

异构比φiC4 /φnC4 和φiC5 /φnC5 的石油地质意义

同分子量的正构烷烃和异构烷烃存在着物理化学性质差异,在运移过程中受围岩的物理化学性质及其它外部因素的影响必然产生分异效应,从而使二者在空间分布上具有一定的特征和规律,异构比指标可以在一定程度上反映出这种特征和规律性。用异构比φ_iC4 /φ_nC4 和φ_iC5 /φ_nC5 指标可以判断有机质的成熟度,研究轻烃运移的途径、方向、生成环境及轻烃的生物降解。     

Calorimetric measurements of fusion enthalpies for Ni2SiO4 and Co2SiO4 olivines and application to olivine-liquid partitioning

Calorimetric measurements of fusion enthalpies for Ni₂SiO₄ and Co₂SiO₄ olivines were carried out using a high-temperature calorimeter, and Ni and Co partitioning between olivine and silicate liquid was analyzed using the measured heats of fusion. The fusion enthalpy of Co₂SiO₄ olivine measured by transposed-temperature drop calorimetry was 103 ± 15 kJ/mol at melting point (1688 K). The fusion enthalpy of Ni₂SiO₄ olivine was calculated based on the enthalpies of liquids in the system An₅₀Di₅₀-Ni₂SiO₄ measured by transposed-temperature drop calorimetry at 1773 K, and was 221 ± 26 kJ/mol at its metastable melting point (1923 K). The fusion enthalpy of Ni₂SiO₄ is the largest among those of olivine group, this is caused by the large crystal field stabilization energy of six-coordinated Ni²⁺ in olivine. The larger fusion enthalpy of Ni₂SiO₄ can account for the large and variable partition coefficient of Ni between olivine and silicate liquid. Based on the comparison between partition coefficients calculated from thermodynamic data and those observed in partition experiments, it is considered that the magnitude of partition coefficients is primarily dependent on the heats of fusion of the components. Furthermore, the activity coefficients for Ni-, Co- and Mn-bearing components in magmatic liquid are nearly of the same magnitude.     

Carboxylic acid distribution patterns of temperate C3 and C4 crops

Agricultural grasses cover a major part of the land surface in temperate agro-ecosystems and contribute significantly to the formation of soil organic matter. Crop-derived lipids are assumed to be responsible for fast carbon turnover in soils. Differences in lipid distribution patterns between crops following C₃ and C₄ photosynthesis pathways have rarely been described, but could be useful for source apportionment of crop-derived input into soils or sediments. The distribution of long chain n-carboxylic acids (C₂₂, C₂₄, C₂₆) reveals significant differences between crop plants following either the C₃ or the C₄ photosynthetic carbon fixation pathway. The plant compartments leaves, stems and roots of C₄ plants contain relatively large proportions (> 40%) of n-C₂₄ carboxylic acid when compared to C₃ plants. These reveal larger relative proportions of n-C₂₂ and n-C₂₆ acids, whose relative abundance is subject to change between different plant compartments and during the growing season. The carboxylic acid ratio [CAR = n-C₂₄/(n-C₂₂ + n-C₂₆) carboxylic acids] provides distinct ratios for C₄ (> 0.67) and C₃ crops (< 0.67) and can thus be used as a molecular marker for the differentiation of crop plant biomass. In combination with the bulk stable carbon isotopic composition (δ¹³C) the CAR can be used as a tool for the estimation of the C₄ derived carbon proportion in soils or sediments.     

CO2 in haplo-phonolite melt: solubility, speciation and carbonate complexation

CO₂ solubility was measured in a synthetic iron-free phonolite (haplo-phonolite) by equilibrating melt with excess CO₂ fluid in a piston cylinder apparatus for a range of pressures (1.0- 2.5 GPa) and temperatures (1300 to 1550°C). The quenched glasses were then analysed using a bulk carbon analytical method (LECO). The measured solubilities are between 0.65 and 2.77 wt.% for the range of conditions studied and show a negative correlation with temperature as reported for most other silicate melt compositions.A range of carbonate species are present within the glass, as well as minor amounts of molecular CO₂. FTIR and NMR analyses suggest that carbonate is present as both ‘network’ and ‘depolymerised’ units as shown for relatively highly polymerised compositions in the model of Brooker et al. (2001b). The bulk CO₂ analyses were used to calibrate the IR extinction coefficient for the carbonate groups. However, the results show that the values obtained for the glasses vary with the melt equilibration conditions, presumably because the ratio of the different carbonate species changes as a complex function of run pressure, temperature and quench rate. Thus the use of IR may not be a reliable method for the quantification of dissolved CO₂ concentrations in natural glasses of ‘intermediate’ composition.     

橄榄岩-卤水反应实验生成富烷氢流体

<正>1研究目的(Objective)利用地球化学动力学实验室流动反应装置(国家发明专利)探索高温高压下水(卤水)与橄榄岩相互作用产出氢气和甲烷的生成机制。实验发现:400℃反应时释放很高浓度氢气和甲烷等可燃气,同时橄榄岩发生蛇纹石化。实验表明氢和甲烷可能来自地下深处,这是蛇绿岩与油气有关的实验依据。近年来发现:大西洋中脊的一些水热活动地区,热水与超镁铁岩石反应。喷口流体富含甲烷、氢和     

Carbon-13 exchange between CO2 and CH4 under geothermal conditions

On the basis of recently reported data on the kinetics of carbon-13 exchange between CO₂ and CH₄ at temperatures above 500°C, first order rate constants $\text{log k = 11.16?10,190/T}$ were derived allowing variations in Δ, the difference in the isotopic composition of coexisting CO₂ and CH₄, to be evaluated as a function of initial composition and cooling rate of the rising geothermal fluid. Observed Δ-values in geothermal discharges are likely to represent frozen in compositions attained after minimum residence times of 20 ka at 400°C or 10 Ma at 300°C. The carbon-13 contents of any biogenic gases are unlikely to have been affected by thermal re-equilibration at temperatures below 200°C. The chemical equilibrium involving CO₂ and CH₄ can be expected to proceed about a hundred times faster than isotopic equilibration.