The pressure dependence of the zirconium-in-rutile thermometer

The solubility of ZrO₂ in rutile is strongly temperature-dependent and has been identified as a potentially powerful thermometer when the rutile coexists with an appropriate buffer assemblage, e.g. zircon + quartz. In combination with experimental data at 10 kbar, previous consideration of data on natural rutile has not identified a pressure dependence for the thermometer. However, the expected volume change as a result of substitution of the larger Zr⁴⁺ cation for Ti⁴⁺ suggests that the Zr content of rutile should decrease with increasing pressure. To investigate the pressure dependence of the thermometer, piston cylinder (at 10, 20 & 30 kbar) and 1 atm furnace experiments were performed in the system ZrO₂-TiO₂-SiO₂. The solubility of ZrO₂ in rutile, in the presence of zircon and quartz was reversed at each pressure value. From these experiments, the thermodynamics of the end-member reaction ZrSiO₄ = SiO₂ + ZrO₂ (in rutile) have been determined. There is a secondary pressure effect accompanying the primary temperature dependence of the Zr content of rutile. New thermometer equations are, in the α -quartz field: in the β -quartz field and in the coesite field in which φ is ppm Zr, P is in kbar and R is the gas constant, 0.0083144 kJ K⁻¹. Thermometric results using these equations are shown for a range of geological settings.     

Trace element systematics in granulite facies rutile: implications for Zr geothermometry and provenance studies

Metamorphic rutile from granulite facies metapelitic rocks of the Archean Pikwitonei Granulite Domain (PGD; Manitoba, Canada) provides constraints on the systematics of trace elements in rutile during high‐temperature conditions and subsequent slow cooling. Compositional profiles and maps of the Zr concentrations in rutile grains (120–600 μm) from three metapelitic gneisses were acquired by electron probe micro‐analysis, using a spatial resolution of down to 2 μm. Simultaneously, profiles were analysed for Nb, Cr and V, which have significantly different diffusion characteristics in rutile. The profiles of all elements show relatively homogeneous concentrations within most grains, but significant inter‐grain differences even within a single thin section. Some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements. The lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information. The Nb and Cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases. High retentiveness for Zr implies that the Zr‐in‐rutile geothermometer is highly robust to diffusive re‐equilibration, even during very slow cooling (<2 °C Ma^?1) from granulite facies conditions. Most grains have high Zr contents (3000–4600 ppm). Differences between high Zr contents suggest that during growth under vapour‐absent conditions there may not be saturation of Zr in rutile, even if zircon is present. Therefore, several rutile grains need to be analysed in a sample to obtain a useful minimum peak temperature. The highest Zr concentrations correspond to ～900 °C. This is significantly higher than previous peak temperature estimates of 820 °C based on two‐feldspar thermometry. On a regional scale this implies that part of the PGD was affected by ultra‐high temperature (UHT) metamorphism. It also implies that rutile is able to preserve primary compositions even to UHT conditions. This study shows that, if combined with textural information, Zr‐in‐rutile has the potential to be a very useful tool for estimating rutile crystallization temperatures and peak metamorphic conditions. For granulite facies rocks, Zr‐in‐rutile yields more reliable peak metamorphic temperatures than most other exchange geothermometers, which tend to partially re‐equilibrate by diffusion during cooling.     

Reversed experimental calibration of the garnet-clinopyroxene Fe — Mg exchange thermometer

The temperature-sensitive Fe,Mg exchange equilibrium,

Temperature dependence of large-scale water-retention curves: a case study

A local-scale model for temperature-dependence of water-retention curves may be applicable to large scales. Consideration of this temperature dependence is important for modeling unsaturated flow and transport in the subsurface in numerous cases. Although significant progress has been made in understanding and modeling this temperature effect, almost all the previous studies have been limited to small scales (on the order of several centimeters). Numerical experiments were used to investigate the possibility of extending a local-scale model for the temperature-dependence of water retention curves to large scales (on the order of meters). Temperature effects on large-scale hydraulic properties are of interest in many practical applications. Numerical experiment results indicate that the local-scale model can indeed be applicable to large-scale problems for special porous media with high air entry values. A typical porous medium of this kind is the porous tuff matrix in the unsaturated zone of Yucca Mountain, Nevada, the proposed geologic disposal site for national high-level nuclear wastes. Whether this finding can approximately hold for general cases needs to be investigated in future studies.     

Temperature dependence of photoluminescence emission characteristics in a natural fluorite

Summary The temperature dependence of photoluminescence emission of a natural fluorite has been studied in the wavelength region of 380–500 nm and in the temperature range of 17.5–300 K. The emission spectra of the sample show a broad emission band between 380 and 500 nm for temperatures above 100 K. At 100 K and below, vibronic lines appear on the emission band at approximately 413.3, 418.1, 419.3, 420.2, 423.9 and 427.1 nm. This broad emission band and the vibronic lines in fluorite are usually associated with phonon-coupled electronic transitions from 4f⁶5d to 4f⁷ in the Eu²⁺ ion. Temperature dependences of the peak energy, intensity and full-width at half-maximum of the broad emission band are discussed, and the behaviour explained in terms of a configurational coordinate model. The excited state vibrational energy was obtained to be 0.023 ± 0.001 eV and this is lower than the LO phonon energy of 0.062 eV in pure fluorite. The activation energy of thermal quenching of the photoluminescence intensity was found to be 0.022 ± 0.002 eV.     

Temperature dependence of Pt and Rh solubilities in a haplobasaltic melt

The temperature dependence of the solubilities of Pt and Rh in a haplobasaltic (anorthite-diopside 1-bar eutectic composition) melt has been investigated at 1 bar and 1300 to 1550°C using the mechanically assisted equilibration technique (Dingwell et al., 1994). The experiments were performed at almost constant oxygen fugacity (log fO₂ = −2.5 ± 0.3) over the entire temperature range. Major element concentrations in the quenched glass samples were determined using an electron microprobe. Pt and Rh concentrations were obtained by laser ablation inductive coupled plasma mass spectrometry. From our data, we obtain the following expressions for the solubilities of pure Pt and pure Rh in anorthite-diopside eutectic melt at 1 bar and log fO₂ = −2.5:

     

Calibration and testing of an empirical chloritoid-chlorite Mg-Fe exchange thermometer and thermodynamic data for daphnite

A compilation of literature data on the Fe-Mg composition of coexisting chlorite and chloritoid from metapelites metamorphosed at various P - T  conditions shows that the logarithm of the Fe-Mg partitioning (ln K _D) varies linearly with the inverse of temperature, from about 2.4 at 300  °C to about 1.3 at 600  °C. In contrast, no trend was observed with pressure, and the molar volumes of Mg- and Fe-chlorite end-members suggest that the pressure dependence of ln K _D is not significant. Therefore, the chloritoid-chlorite Mg-Fe exchange reaction is a potential thermometer and has been empirically calibrated using the analyses of 112 chloritoid-chlorite pairs from 28 different localities. Temperatures estimated using the Chl-Cld thermometer were checked against independent estimates for 20 samples not involved in the calibration (Beni Mzala window, Morocco), and the results are in fair agreement with independent temperature estimates. However, the analytical uncertainties and errors are too large to obtain reliable temperature estimates for extremely Mg-rich or Fe-rich compositions. The Chl-Cld thermometer is unreliable at XMg-_CLD<0.2 and XMg-_CLD>0.8 at 700  °C, and XMg-_CLD<0.1 and XMg-_CLD>0.9 at 300  °C. Using the results of the empirical calibration, we calculated new thermodynamic data for daphnite. Implementing these data, it becomes possible to estimate T  and P conditions of metamorphism for the invariant chlorite-chloritoid-quartz-aluminosilicate assemblage that is widespread in low-grade metapelites. These estimates appear to be relevant only in the stability field of kyanite, whereas the uncertainties on the calculated pressure conditions are very large in the stability field of kaolinite and pyrophyllite.     

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.     

Temperature dependence of Mn(II) oxidation in lakewaters: a test of biological involvement

The oxidation rates of Mn(II) in water samples from two English lakes, Esthwaite Water and Rostherne Mere, display clear temperature optima, varying from 15°C to 30°C, in the pH range 7–8. This is strong evidence of biological mediation of the oxidation. The types and concentrations of Mn-oxidising organisms appear to vary with depth and time in both lakes.     

南召泌阳金红石矿带金红石赋存规律

为了开发利用南召—泌阳金红石矿带的金红石,综合分析了以往资料,并在实地踏勘、样品测试和重点地段综合研究基础上,查明了各矿段金红石矿基本地质特征、金红石赋存状态、嵌布特征、粒度变化特征、金红石富矿体的主要赋存位置。区内粗粒易选富矿体位于矿带中段的左老庄组一段上部（北部）。采用以微生物提纯金红石粗精矿为标志的新工艺,取得了良好的选矿试验效果。刘岗矿区的1号和2号富矿体可作为进一步研究和开发利用的重点。     

Temperature dependence of the OH-stretching frequencies in topaz-OH

Hydrogen bonding in topaz-OH, Al₂SiO₄(OH)₂, was investigated by IR spectroscopic analysis of the temperature dependence of the OH-stretching frequencies. Low-temperature spectra ranging from −196 to −160°C prove the existence of four non-equivalent H-positions in the crystal structure from the occurrence of four different OH-bands. With increasing temperature, these bands merge first, above −160°C, into two OH-bands and then above 400°C into one asymmetric broad band. Shifting of the OH-bands is caused by thermally induced hydrogen order–disorder. Low temperature fixes the protons in their positions; increasing temperature induces proton movement and allows switching between the different positions. Autocorrelation analysis of the IR spectra reveals two phase transitions, one at about −155°C from P1 to Pbn2 ₁ characterized as static–dynamic change and the second at about 380°C from Pbn2 ₁ to Pbnm caused by disordering of the protons. The increasing symmetry with temperature is due to advanced proton movement and dynamical averages over the proton distribution densities.     

Intersector element partitioning in tourmaline: a potentially powerful single crystal thermometer

Hourglass sector zoning, and related polar overgrowths, are common features of metamorphic tourmaline, developing as a result of variations in element preference on the different growth surfaces. For sector-zoned crystals, three domains are present for each growth zone (c ⁺, c ⁻ and a), with compositional differences most distinct for Ca and Ti, and among c ⁺ and c ⁻ sectors. Intersector differences vary, commonly showing decreasing fractionation from core to rim attributed to increasing metamorphic grade. Here we show that intersector element partitioning is temperature dependent and derive empirical geothermometers based on c ⁺ –c ⁻ and c ⁺ –a partitioning of Ca and Ti. These thermometers are applicable over a range of temperatures and bulk-rock compositions. Intersector partitioning is not affected by re-equilibration and records and preserves complete T-histories of individual tourmaline grains from prograde to peak and on to retrograde growth. Information on element mobility is preserved by tourmaline composition, because intersector partitioning is independent of element concentration. These factors make intersector partitioning an ideal tool to elucidate the thermal history of tourmaline grains and thus their host environment and tourmaline’s refractory nature preserves these signatures even into the sedimentary record. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Ferric-ferrous ratio and oxygen fugacity calculations for primitive mantle-derived melts: calibration of an empirical technique

Summary Several experimentally-based, empirical calibrations of the fO₂ of natural silicate melts at atmospheric pressure as a function of melt composition, melt Fe²⁺/Fe³⁺, and crystallization temperature have been developed (e.g.Sack et al., 1980;Kilinc et al., 1983;Kress andCarmichael, 1988;Borisov andShapkin, 1990). Cr-Al spinel is a liquidus phase of primitive mantle-derived melts, and is commonly found as inclusions in near-liquidus phenocrysts (mainly olivine). The established atmospheric pressure correlation between Fe²⁺/Fe³⁺ values in spinel and coexisting melts over a broad range of basaltic compositions (Maurel andMaurel, 1982) can be used to calculate the Fe²⁺/Fe³⁺ value of a melt if the composition of the equilibrium spinel is known. Compositions and crystallization temperatures of primitive melts can be determined by experimental studies of melt inclusions trapped by early-formed refractory phenocrysts. Thus, the association of spinel and melt inclusions in early liquidus phenocrysts can be used to estimate fO₂ conditions at the time of their crystallization.In this paper, we present a calibration of this method and discuss its applications. We conclude that combination of the equations ofMaurel andMaurel (1982) andBorisov andShapkin (1990) can be used to calculate fO₂ with an accuracy of ±0.71og units, when liquidus spinels have TiO₂ <2.5 wt% and Cr₂O₃ > 13 wt.%, and melt compositions are in the range from basaltic to picritic with H₂O contents <6 wt.%.Using this technique we find NNO fO₂ values of –0.8 to –1.4 for MORB dredged at the VEMA Fracture Zone in the Atlantic, and 0 to + 1 for Tongan high-Ca boninites.

---

Die Berechnung von Fe²⁺/Fe³⁺ und der Sauerstoff-Fugazitäten für primitive Mantelschmelzen: Kalibration einer empirischen Methode

Zusammenfassung Empirische, auf Experimenten basierende, Kalibrationen zur Berechnung von fO₂ natürlicher Silikatschmelzen bei atmosphärischem Druck in Abhängigkeit von der Schmelzzusammensetzung, des Fe²⁺/Fe³⁺ Verhältnisses und der Kristallisationstemperatur wurden z.B. vonSack et al. (1980),Kilinc et al. (1983),Kress undCarmichael (1988) undBorisov undShapkin (1980) entwickelt. Cr-Al-Spinell ist eine Liquidusphase primitiver Mantelschmelzen und kommt üblicherweise als Einschluß in near-liquidus Phänokristallen (hauptsächlich in Olivin) vor. Die Korrelation des Atmosphärendruckes zwischen Fe²⁺/Fe³⁺ in Spinell und koexistierender Schmelze kann dazu verwendet werden, das Verhältnis von Fe²⁺/Fe³⁺ der Schmelze für einen weiten Bereich basaltischer Zusammensetzungen zu berechnen, wenn die Zusammensetzung des im Gleichgewicht gebildeten Spinells bekannt ist (Maurel undMaurel, 1982). Die Zusammensetzungen und Kristallisationstemperaturen primitiver Schmelzen können durch experimentelle Studien von Schmelzeinschlüssen, die in früh gebildeten refraktären Phänokristallen eingeschlossen wurden, ermittelt werden. Daher lassen sich Spinelle und assoziierte Schmelzeinschlüsse in frühen Liquidus-Phänokristallen dazu benützen, die fO₂-Bedingungen während der Kristallisation abzuschätzen.In dieser Arbeit präsentieren wir eine neue Kalibration dieser Methode und diskutieren ihre Anwendungen. Wir schlußfolgern, daß unter Kombination der verwendeten Gleichungen vonMaurel undMaurel (1982) sowie vonBorisov undShapkin (1990) fO₂ mit einer Genauigkeit von ±0.7 log Einheiten berechnet werden kann, soferne die Liquidus-Spinelle < 2.5 Gew.% TiO₂ und > 13 Gew.% Cr₂O₃ haben und die Schmelzzusammensetzungen von basaltisch bis pikritisch, mit maximal 6 Gew.% H₂O, reichen.Unter Verwendung dieser Technik wurden die NNO fO₂ Werte für die von der VEMA Fracture Zone im Atlantik stammenden MORB Proben mit 0.8 bis - 1.4, die der der High-Ca Boninite von Tonga mit 0 bis + 1 bestimmt.

---

---

With 7 Figures     

温度对颗粒膨润土热传导特性的影响EI北大核心CSCD

颗粒膨润土作为优良的接缝和间隙回填材料,在高放废物深地质处置库中具有较大的应用前景。以颗粒高庙子膨润土为研究对象,采用热探针法测试颗粒膨润土在不同条件下的热传导性能,探讨了温度、干密度和含水率等因素的影响。试验结果表明:相同含水率和干密度下,粉末膨润土压制样的热传导系数大于颗粒膨润土压制样;相同含水率下,随着干密度的增大,粉末压制样和颗粒压制样之间的热传导系数差异渐小。温度越高,含水率越大,干密度越小,颗粒压制样热传导系数的温度效应越显著。相同干密度下,粉末压制样内集聚体间大孔隙的孔径较颗粒压制样的孔径要小,更有利于热量在土中的传递,其热传导系数也就更大;随着干密度的增大,颗粒压制样内集聚体间孔隙减少,削弱了水汽潜热传输的影响,温度效应有所减弱。     

Temperature dependence of the reactivity of cemented paste backfill

The environmental performance of cemented paste backfill (CPB; a mixture of tailings, water and binder), which contains sulphide mineral-bearing tailings, is strongly influenced by its reactivity. However, our understanding of the reactivity of CPB under various thermal loading conditions as well as its evolution with time is limited. Hence, a laboratory investigation is conducted to study the effects of curing and ambient (atmospheric) temperatures on the reactivity of CPB. Oxygen consumption (OC) tests are conducted on CPB specimens cured at different temperatures to study their reactivity. Furthermore, microstructural analyses (e.g., x-ray diffraction (XRD), mercury intrusion porosimetry, and thermogravimetry/derivative thermogravimetry) are performed to assess the microstructural characteristics of the tested CPBs. The results show that the reactivity of CPB is temperature-dependent. As the curing temperature increases, the reactivity generally decreases. The reactivity is also affected by the ambient temperature. The reactivity increases as the atmospheric temperature increases. However, the extent of the effect of the temperature depends on the curing time and is generally more pronounced at the early ages. Furthermore, the presence of sulphate in the pore water of CPB can significantly affect the reactivity of CPB cured at high temperatures (50 °C). The findings of this study will therefore help to better assess and predict the environmental behavior of CPB under various field thermal conditions.     

Temperature dependence of sulfide and sulfate solubility in olivine-saturated basaltic magmas

The sulfur concentration at pyrrhotite- and anhydrite-saturation in primitive hydrous basaltic melt of the 2001-2002 eruption of Mt. Etna was determined at 200 MPa, T = 1050-1250 °C and at log fO₂ from FMQ to FMQ+2.2 (FMQ is Fayalite-Magnetite-Quartz oxygen buffer). At 1050 °C Au sample containers were used. A double-capsule technique, using a single crystal olivine sample container closed with an olivine piston, embedded in a sealed Au₈₀Pd₂₀ capsule, was developed to perform experiments in S-bearing hydrous basaltic systems at T > 1050 °C. Pyrrhotite is found to be a stable phase coexisting with melt at FMQ-FMQ+0.3, whereas anhydrite is stable at FMQ+1.4-FMQ+2.2. The S concentration in the melt increases almost linearly from 0.12 ± 0.01 to 0.39 ± 0.02 wt.% S at FeS-saturation and from 0.74 ± 0.01 to 1.08 ± 0.04 wt.% S at anhydrite-saturation with T ranging from 1050-1250 °C. The relationships between S concentration at pyrrhotite and/or anhydrite saturation, MgO content of the olivine-saturated melt, T, and log fO₂ observed in this study and from previous data are used to develop an empirical model for estimating the magmatic T and fO₂ from the S and MgO concentrations of H₂O-bearing olivine-saturated basaltic melts. The model can also be used to determine maximum S concentrations, if fO₂ and MgO content of the melt are known. The application of the model to compositions of melt inclusions in olivines from Mt. Etna indicates that the most primitive magmas trapped in inclusions might have been stored at log fO₂ slightly higher than FMQ+1 and at T = 1100-1150 °C, whereas more evolved melts could have been trapped at T ? 1100 °C. These values are in a good agreement with the estimates obtained by other independent methods reported in the literature.     

Temperature dependence of goethite dissolution promoted by trihydroxamate siderophores

This article reports an investigation of the temperature dependence of goethite dissolution kinetics in the presence of desferrioxamine B (DFO-B), a trihydroxamate siderophore, and its acetyl derivative, desferrioxamine D1 (DFO-D1). At 25 and 40°C, DFO-D1 dissolved goethite at twice the rate of DFO-B, whereas at 55°C, the behavior of the two ligands was almost the same. Increasing the temperature from 25 to 55°C caused little or no significant change in DFO-B or DFO-D1 adsorption by goethite. A pseudo-first-order rate coefficient for dissolution, calculated as the ratio of the mass-normalized dissolution rate coefficient to the surface excess of siderophore, was approximately the same at 25 and 40°C for both siderophores. At 55°C, however, this rate coefficient for DFO-D1 was about half that for DFO-B. Analysis of the temperature dependence of the mass-normalized dissolution rate coefficient via the Arrhenius equation led to an apparent activation energy that was larger for DFO-B than for DFO-D1, but much smaller than that reported for the proton-promoted dissolution of goethite. A compensation law was found to relate the pre-exponential factor to the apparent activation energy in the Arrhenius equation, in agreement with what has been noted for the proton-promoted dissolution of oxide minerals and for the complexation of Fe³⁺ by DFO-B and simple hydroxamate ligands in aqueous solution. Analysis of these results suggested that the siderophores adsorb on goethite with a only single hydroxamate group in bidentate ligation with an Fe(III) center.     

Oxygen isotope fractionation between oxygen of different sites in illite minerals: a potential single-mineral thermometer

The experimental results of Hamza and Epstein mark internal oxygen isotope fractionations of hydrosilicates as potential single-mineral thermometers. In this study methodical investigations were made to determine the oxygen isotope ratios of hydroxyl groups in silicate minerals. As a reference material a commercial kaolinite was examined by vacuum extraction and by use of a modified partial fluorination technique first deseribed by Hamza and Epstein. The concordance of the results argue against oxygen isotope fractionation during dehydroxylation. Consequently, vacuum extraction can be used to determine the internal fractionation of minerals, which contain no ferrous iron. For calibration of the internal oxygen isotope fractionation, hydrothermally formed illites from the Lone Gull uranium deposit in Canada and from the Leuggern exploration drill site in Switzerland were investigated. Formation temperatures of the hydrothermal mineralization were estimated by mineral paragenesis, illite crystallinity and by oxygen isotope fractionations on coexisting mineral phases. the oxygen isotope fractionation between oxygen of different sites in several selected illites from both regions has been analysed. The results indicate a linear correlation between the illite-OH oxygen isotope fractionation and temperature. The fractionation can be expressed by the following equation: