Pressure–volume–temperature equation of state of andradite and grossular, by high-pressure and -temperature powder diffraction

 The thermoelastic parameters of natural andradite and grossular have been investigated by high-pressure and -temperature synchrotron X-ray powder diffraction, at ESRF, on the ID30 beamline. The P–V–T data have been fitted by Birch-Murnaghan-like EOSs, using both the approximated and the general form. We have obtained for andradite K ₀=158.0(±1.5) GPa, (dK/dT )₀=−0.020(3) GPa K⁻¹ and α₀=31.6(2) 10⁻⁶ K⁻¹, and for grossular K ₀=168.2(±1.7) GPa, (dK/dT)₀=−0.016(3) GPa K⁻¹ and α₀=27.8(2) 10⁻⁶ K⁻¹. Comparisons between the present issues and thermoelastic properties of garnets earlier determined are carried out. Received: 7 July 2000 / Accepted: 20 October 2000     

Suspended Matter,Chl-a,CDOM, Grain Sizes,and Optical Properties in the Arctic Fjord-Type Estuary,Kangerlussuaq, West Greenland During Summer

Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM), and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K _d(PAR)), upwelling PAR (K _u(PAR)), particle beam attenuation coefficient (c _p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K _d(PAR), particle beam attenuation coefficients (c _p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic suspended matter (SPMI) and diffuse attenuation coefficient K _d(PAR) (r ² = 0.92) and also for particle beam attenuation coefficient (c _p; r ² = 0.93). The obtained SPMI specific attenuation—K _d^*(PAR) = 0.13 m² g⁻¹ SPMI—and the SPMI specific particle beam attenuation—c _p^* = 0.72 m² g⁻¹—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r ² = 0.80) correlation with K _u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results are discussed and compared to similar studies from both temperate and tropical estuaries.     

Heat capacity of wadeite-type K2Si4O9 and the pressure-induced stable decomposition of K-feldspar

The heat capacity of synthetic, stoichiometric wadeite-type K₂Si₄O₉ has been measured by DSC in the 195≤T(K)≤598 range. Near the upper temperature limit of our data, the heat capacity observed by DSC agrees with that reported by Geisinger et al. (1987) based on a vibrational model of their infrared and Raman spectroscopic data. However, with decreasing temperature, the Cp observed by DSC is progressively higher than that predicted from the vibrational model, suggesting that the standard entropy of K₂Si₄O₉ is likely to be larger than 198.9 ± 4.0 J/K · mol computed from the spectroscopic data. A fit to the DSC data gave: Cp(T) = 499.13 (±1.87) − 4.35014 · 10³(±3.489 · 10¹) · T ^−0.5, with T in K and average absolute percent deviation of 0.37%. The room-temperature compressibilities of kalsilite and leucite, hitherto unknown, have been measured as well. The data, fitted to the Murnaghan equation of state, gave K _o = 58.6 GPa, K _o ^′ = 0.1 for kalsilite and K _o = 45 GPa, K _o ^′ = 5.7 for α-leucite. Apart from the above mentioned data on the properties of the individual phases, we have also obtained reaction-reversals on four equilibria in the system K₂O-Al₂O₃-SiO₂. The Bayesian method has been used simultaneously to process the properties of 13 phases and 15 reactions between them to derive an internally consistent thermodynamic dataset for the K₂O-Al₂O₃-SiO₂ ternary. The enthalpy of formation of K₂Si₄O₉ wadeite is in perfect agreement with its revised calorimetric value, the standard entropy is 232.1 ± 10.4 J/K · mol, ∼15% higher than that implied by vibrational modeling. The phase diagram, generated from our internally consistent thermodynamic dataset, shows that for all probable P-T trajectories in the subduction regime, the stable pressure-induced decomposition of K-feldspar will produce coesite + kalsilite rather than coesite + kyanite + K₂Si₄O₉ (cf. Urakawa et al. 1994). Received: 11 June 1997 / Accepted: 2 December 1997     

Thermoelastic properties of the high-pressure phase of SnO2 determined by in situ X-ray observations up to 30 GPa and 1400 K

 In situ synchrotron X-ray experiments in the system SnO₂ were made at pressures of 4–29 GPa and temperatures of 300–1400 K using sintered diamond anvils in a 6–8 type high-pressure apparatus. Orthorhombic phase (α-PbO₂ structure) underwent a transition to a cubic phase (Pa3ˉ structure) at 18 GPa. This transition was observed at significantly lower pressures in DAC experiments. We obtained the isothermal bulk modulus of cubic phase K ₀= 252(28) GPa and its pressure derivative K ^′=3.5(2.2). The thermal expansion coefficient of cubic phase at 25 GPa up to 1300 K was determined from interpolation of the P-V-T data obtained, and is 1.7(±0.7) × 10⁻⁵ K⁻¹ at 25 GPa. Received: 7 December 1999 / Accepted: 27 April 2000     

The partitioning of copper between silicate melts and two-phase aqueous fluids: An experimental investigation at 1 kbar, 800° C and 0.5 kbar, 850° C

 Experiments were performed in the three phase system high-silica rhyolite melt+low-salinity aqueous vapor+hydrosaline brine, to investigate the partitioning equilibria for copper in magmatic-hydrothermal systems at 800° C and 1 kbar, and 850° C and 0.5 kbar. D^aqm/mlt _Cu and apparent equilibrium constants, K^aqm/mlt _Cu,Na, between the aqueous mixture (aqm=quenched vapor+brine) and the silicate melt (mlt) are calculated. D^aqm/mlt _Cu increases with increasing aqueous chloride concentration and is a function of pressure. K^aqm/mlt _Cu,Na=215(±73) at 1 kbar and 800° C and K^aqm/mlt _Cu,Na=11(±6) at 0.5 kbar and 850°C. Decreasing pressure from 1 to 0.5 kbar lowers K^aqm/mlt _Cu,Na by a factor of approximately 20. Data revealed no difference in K^aqm/mlt _Cu,Na or D^aqm/mlt _Cu as a function of the melt aluminium saturation index. Within the 2-phase field the K^aqm/mlt _Cu,Na show no variation with total aqueous chloride, indicating that copper-sodium exchange between the vapor, brine and silicate melt is independent of the mass proportion of vapor and brine. Model copper-sodium apparent equilibrium constants for the hydrosaline brine and the silicate melt revealed a negative dependence on pressure. Model apparent equilibrium constants for copper-sodium exchange between the brine and vapor were close to unity at 1 kbar and 800° C. Received: 27 June 1994/Accepted: 30 March 1995     

Batiferrite, Ba[Ti2Fe10]O19, a new ferrimagnetic magnetoplumbite-type mineral from the Quaternary volcanic rocks of the western Eifel area, Germany

Summary Batiferrite, ideally Ba[Ti₂Fe₁₀]O₁₉, was found in the Quaternary volcanic rocks near üdersdorf, Graulai, and Altburg, western Eifel area, Germany. The new mineral typically occurs as euhedral platy grains in cavities of melilite- and leucite-nephelinite basalts. Associated minerals are hematite, magnetite, titanite, g?tzenite, clinopyroxene, nepheline, and biotite. It exhibits a hexagonal tabular habit flattened on {0001}, diameter 0.5–1 mm, thickness 20–125 μm, and {10&1macr;3}, {10&1macr;0} as observable forms. The mineral is opaque, of black color with submetallic lustre, and shows a ferrimagnetic behavior. VHN₅₀ is 793 with a range of 710–841 from ten indentations. The quantitative reflectance measurements of R_o/R_e on oriented grains in air and oil immersion, respectively, are [%]: for 470 nm 22.1/20.1 and 8.4/7.1, for 546 nm 21.0/19.4 and 7.8/6.6, for 589 nm 20.2/18.8 and 7.4/6.3, and for 650 nm 19.3/18.3 and 6.8/5.9. The bireflectance is distinct (air) to weak (oil), and parallel (0001) a moderate anisotropy with straight extinction can be observed. Typical microprobe analyses give [wt%] K₂O 0.28–0.33, Na₂O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al₂O₃ 0.31–0.33, TiO₂ 13.11–13.63, MnO 2.38–2.57, Fe₂O₃ 61.36–63.12, FeO 5.49–5.86 (Fe³⁺/Fe²⁺ calculated for charge compensation), which is equivalent to (Ba_0.84Na_0.06K_0.06Sr_0.05)_1.01(Fe_8.48 ³⁺Fe_0.86 ²⁺Ti_1.82Mg_0.37Mn_0.37Al_0.06)_11.96O₁₉ as the average composition based on 19 oxygen atoms. Batiferrite is a magnetoplumbite-type mineral with hexagonal symmetry, space group P6 ₃ /mmc (no. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?³, Z = 2, and a calculated density of 5.016 gcm⁻³. The structure was refined to R1 = 0.031 for 278 unique reflections with F_o ² > 4σ (F_o ²) and R1 = 0.079 for all 452 unique observations using single crystal X-ray data. The strongest reflections of the X-ray powder diffraction pattern are [d _obs, I/I_o, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). The new mineral is comparable to the other Ba containing magnetoplumbite-type minerals haggertyite and hawthorneite, the iron content, however, is much higher and in the range of magnetoplumbite. The large cation site (A) is dominated by Ba, and four of the five remaining crystallographic cation sites in the structure are dominated by Fe (M1, 2, 3, 5), the octahedrally coordinated M4-site is dominated by Ti. No oxygen vacancy on the O3-site like in plumboferrite can be observed. Batiferrite is named for its main chemical composition and the relationship to the M-type hexaferrites (polytype 5H).

---

Zusammenfassung Batiferrit, ein neues ferrimagnetisches Mineral des Magnetoplumbit-Typs aus den quart?ren Vulkaniten der West-Eifel, Deutschland Das neue Mineral Batiferrite, mit der Idealformel Ba[Ti₂Fe₁₀]O₁₉, wurde an drei Fundpunkten in den Quart?ren Vulkangesteinen der westlichen Eifel, Deutschland, in der N?he von üdersdorf, Graulai und Altburg gefunden. Das neue Mineral tritt typischerweise bl?ttchenf?rmig in kleinen Hohlr?umen von Melilith- und Leucit-Nephelininit Basalten auf. Vergesellschaftete Minerale sind H?matit, Magnetit, Titanit, G?tzenit, Klinopyroxen, Nephelin und Biotit. Der Habitus ist hexagonal tafelig nach {0001}, mit einem Durchmesser von 0.5–1 mm und einer Dicke von 20–125 μm, zus?tzlich k?nnen die Formen {10&1macr;3} und {10&1macr;0} beobachtet werden. Das Mineral ist opak, hat eine schwarze Farbe mit einem leicht metallischen Glanz, und ist ferromagnetisch. Die H?rte VHN₅₀ ist 793 mit einem Bereich von 710–841 aus 10 Eindruckbestimmungen. Die quantitativen Reflexionsmessungen von R_o/R_e an orientierten K?rnern in Luft beziehungsweise ?limmersion, ergaben [%]: für 470 nm 22.1/20.1 und 8.4/7.1, für 546 nm 21.0/19.4 und 7.8/6.6, für 589 nm 20.2/18.8 und 7.4/6.3, und für 650 nm 19.3/18.3 und 6.8/5.9. Die Bireflexion ist deutlich (Luft) bis schwach (?l) und parallel (0001) kann eine mittlere Anisotropie mit gerader Ausl?schung beobachtet werden. Eine typische Mikrosondenanalyse ergibt [wt%] K₂O 0.28–0.33, Na₂O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al₂O₃ 0.31–0.33, TiO₂ 13.11–13.63, MnO 2.38–2.57, Fe₂O₃ 61.36–63.12, FeO 5.49–5.86 (Fe³⁺/Fe²⁺ berechnet zum Ladungsausgleich), die mittlere chemische Formel auf der Basis von 19 Sauerstoffatomen lautet (Ba_0.84Na_0.06K_0.06Sr_0.05)_1.01 (Fe_8.48 ³⁺Fe_0.86 ²⁺Ti_1.82Mg_0.37Mn_0.37Al_0.06)_11.96O ₁₉. Batiferrit ist ein Mineral der Magnetoplumbitgruppe, hat hexagonale Symmetrie mit der Raumgruppe P6₃/mmc (Nr. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?³, Z = 2, und einer berechneten Dichte von 5.016 gcm⁻³. Die Struktur wurde aus Einkristall-R?ntgendaten bis zu einem R1-Wert von 0.031 für 278 F_o ² > 4σ(F_o ²), und einem R1-Wert von 0.079 für alle 452 F_o ² verfeinert. Die st?rksten Beugungsreflexe der Pulver-R?ntgendaten sind [d_obs, I/I_o, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). Das neue Mineral weist deutliche ?hnlichkeiten zu den anderen beiden Ba-reichen Mineralen Haggertyit und Hawthorneit der Magnetoplumbit-Gruppe auf, jedoch ist der Eisengehalt wesentlich h?her und im Bereich des Minerals Magnetoplumbit. Der gro?e Kationenplatz (A) ist von Barium dominiert, vier (M1, 2, 3, 5) der restlichen fünf kristallographischen Kationenpl?tze in der Struktur sind fast ausschlie?lich mit Fe, die oktaedrisch koordinierte M4-Position ist überwiegend mit Ti besetzt. An der O3-Position konnte kein Sauerstoffdefizit wie in Plumboferrit festgestellt werden. Batiferrit ist nach seiner chemischen Beschaffenheit und nach seiner Zugeh?hrigkeit zu den M-Typ Hexaferriten (Polytyp 5H) benannt.

---

---

Received December 14, 1999; accepted March 2, 2000     

A metallogenic survey of alkalic rocks of Mt. Somma-Vesuvius volcano

Summary Somma-Vesuvius is an alkaline volcano whose products (pumice, scoria and lava) have alkaline (Na₂O + K₂O) contents between 6 and 16 wt%, Mg number <50, SiO₂ 59–47 wt% and MgO 0–7.8 wt% (more than 50% of the samples have a content <2 wt%). Immobile-element ratios (Th/Yb, Ta/Yb, Ce/Yb) indicate a shoshonitic character, while the K₂O content (4–10 wt%) is characteristic of ultrapotassic rocks. The behavior of selected metals is discussed by grouping them on the basis of the stratigraphic sequence and differentiating the volcanic activity between plinian and interplinian (Rolandi et al., 1998; Ayuso et al., 1998). This allows observation of the variation within each formation from 25.000 y. BP to the last historic eruptive cycle (1631–1944 AD). The main processes to explain the wide distribution of the data presented are fractional crystallization of a mantle-derived magma, magma mixing, and contamination with heterogeneous lower and/or upper crust. Variation diagrams distinguish different behavior for groups of metals: Ag (0.01–0.2 ppm), Mo (1–8.8 ppm), W (1.3–13 ppm), Pb (16–250 ppm), Sb (0.2–2.6 ppm), Sc (0.2–61 ppm), Li (15–140 ppm) and Be (1–31 ppm) increase with increasing differentiation and tend to correlate with the incompatible trace elements (Th, Hf, etc). Cu (10–380 ppm), Au (2–143 ppb), Co (0.7–35.1 ppm) and Fe (1.3–6.2 wt%) decrease towards advanced stage of differentiation. Iron also identifies three magmatic groups. The ratio Fe³⁺/Fe²⁺ ranges between 0.2 and 1.8, and Fe₂O₃/(Fe₂O₃ + FeO) ranges between 0.2 and 0.8, giving rise to an oxidized environment; exceptions are in the samples belonging to the interplinian formations: I, II, medieval and 1631–1994 AD. Fluorine ranges between 0.1 and 0.4 wt% for the complete Mt. Somma-Vesuvius activity, except for the Ottaviano and Avellino plinian (0.8 wt%) events. Chlorine has a wider range, from 0.1 wt% to 1.6 wt%. Mt Somma-Vesuvius has some features similar to those of mineralized alkaline magmatic systems which coincide with the transition between subduction-related compression and extension-related to continental rifting. We infer that a prospective time for the formation of mineralization at Mt Somma-Vesuvius was during the 1631–1944 eruptive period. Received March 27, 2000; revised version accepted February 28, 2001     

Structure and compressibility of synthetic ZnAl2O4 (gahnite) under high-pressure conditions, from synchrotron X-ray powder diffraction

 The structural behavior of synthetic gahnite (ZnAl₂O₄) has been investigated by X-ray powder diffraction at high pressure (0–43 GPa) and room temperature, on the ID9 beamline at ESRF. The equation of state of gahnite has been derived using the models of Birch–Murnaghan, Vinet and Poirier–Tarantola, and the results have been mutually compared (the elastic bulk modulus and its derivatives versus P determined by the third-order Birch–Murnaghan equation of state are K ₀=201.7(±0.9) GPa, K ^′ ₀=7.62(±0.09) and K ^″ ₀=−0.1022 GPa⁻¹ (implied value). The compressibilities of the tetrahedral and octahedral bond lengths [0.00188(8) and 0.00142(5) GPa⁻¹ at P=0, respectively], and the␣polyhedral volume compressibilities of the four-␣and␣sixfold coordination sites [0.0057(2) and 0.0041(2) GPa⁻¹ at P=0, respectively] are discussed. Received: 15 January 2001 / Accepted: 23 April 2001     

Geochemical data as indicators of environmental change and human impact in sediments derived from downstream marshes of an ephemeral river,Northeast China

Recent sedimentary history of natural environmental change and anthropogenic influence in an ephemeral river catchment has been reconstructed using selected major and trace elements, element ratios, and their different geochemical phases (Tessier sequential extraction methods), pollen, and grain size combined with ²¹⁰Pb- and ¹³⁷Cs-dating method in marsh sedimentary cores. Attempts were made to use selected element ratios with different geochemical phases—residual phase of Ti, Al, V, Cr, Ni, Rb, K, Sr, and Ba; mobile Sr and Ba—combined with ²¹⁰Pb- and ¹³⁷Cs-chronology to interpret certain time information of environmental changes saved within the marsh sediments. Results indicate that there were two marked humid periods during 1850–1860 ad and 1890–1920 ad, and sand storm activities prevailed during 1920–1930 ad. After about 1900 ad, soil erosion has increased with the extensive agricultural activities in the Huolin River catchments, and further intensified after 1950s. After 1980, soil erosion has become even more intense, which is consistent with the reinforcement of human activities, the drastic loss of vegetation cover in the upstream lands, especially, the exploitation of the open cast coalmine in the upstream of Huolin River at that time. Influenced by the inundation of the Huolin River, the heavy metal pollution historical trends in Xianghai marsh wetland could be roughly divided into three periods by analysis of sediment enrichment factor (K_SEF) and the index of geoaccumulation (I _geo):1760–1880 ad, 1880–1980 ad, and 1980–now. Human activities accelerate the inputs of heavy metal, which leads to degradation of the marsh. This study also investigated on source of marsh sediments (by Ti/Al), redox condition [by V/Cr and V/(V + Ni)], and salinization indicators (by Sr/Ba and Rb/K). The results demonstrate that sources of sediments and redox conditions were partly similar for both riparian and depressional marshes. Besides, some differences in degree of salinization between two types of marsh were also identified, especially after 1880.     

An empirical model for the calculation of spinel-melt equilibria in mafic igneous systems at atmospheric pressure: 1. Chromian spinels

 In order to develop a model for simulating naturally occurring chromian spinel compositions, we have processed published experimental data on chromian spinel-melt equilibrium. Out of 259 co-existing spinel-melt experiments reported in the literature, we have selected 118 compositions on the basis of run time, melt composition and experimental technique. These data cover a range of temperatures 1150–1500° C, oxygen fugacities of −13<log f _O2< −0.7, and bulk compositions ranging from basalt and norite, to komatiite. Six major spinel components with Cr³⁺, Al³⁺, Ti⁴⁺, Mg²⁺, Fe³⁺ and Fe²⁺-bearing end-members were considered for the purpose of describing chromite saturation as a function of melt composition, temperature and oxygen fugacity at 1 atmosphere pressure (0.101 MPa). The empirically calibrated mineral-melt expression based on multiple linear regressions is: K ^Sp _i =A/T(K)+B log f _O2+C ln (Fe³⁺/Fe²⁺)_L+D ln R _L +E, where K ^Sp _i is an equilibrium constant and R _L is a melt structure-chemical parameter (MSCP). Twenty-eight forms of equilibrium constants were considered, including single distribution coefficients, exchange equilibrium constants, formation constants for AB₂O₄ components, as well as simple “spinel cation ratios”. For each form of the equilibrium constants, a set of 16 combinations of the MSCPs have been investigated. The MSCP is present in the form of composite ratios [e.g., Si/O, NBO/T,(Al+Si)/Si, or (Na+K)/Al] or as simple cation ratios (e.g., Mg/Fe²⁺). For the calculation of Fe³⁺ and Fe²⁺ species in silicate melts, we used existing equations, whereas the Fe³⁺/Fe²⁺ ratio of spinels was calculated from the spinel stoichiometry. The regression parameters that best repoduce the experimental data were for the following constants: (Fe³⁺/Fe²⁺) _Sp , (Mg/Fe²⁺) _Sp /(Mg/Fe²⁺) _L , (Cr/Al) _Sp / (Cr/Al) _L , K _FeCr2O4, and Ti _Sp /Ti _L . These expressions have been combined into a single program called SPINMELT, which calculates chromite crystallization temperature and composition at a given f _O2 with an average accuracy of ∼10° C and 1–2 mol%. An example of the use of SPINMELT is presented for a magma parental to the Bushveld Complex. Received: 30 May 1995/Accepted: 1 November 1995     

Thermodynamic data of the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite)

 Calorimetric and P–V–T data for the high-pressure phase Mg₅Al₅Si₆O₂₁(OH)₇ (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO·B₂O₃) at T=700 ^∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets; they range from −221.1 to −259.4 kJ mol⁻¹ (formation from the oxides) respectively −13892.2 to −13927.9 kJ mol⁻¹ (formation from the elements). The heat capacity of Mg₅Al₅Si₆O₂₁(OH)₇ has been measured from T=50 ^∘C to T=500 ^∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents the heat capacity over the entire temperature range to within the experimental uncertainty: C _P (Mg-sursassite) =(1571.104 −10560.89×T ^−0.5−26217890.0 ×T ⁻²+1798861000.0×T ⁻³) J K⁻¹ mol⁻¹ (T in K). The P V T behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8 GPa and 800 ^∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the bulk modulus was determined as 116.0±1.3 GPa, (K ^′=4), V _T,0 =446.49 ³ exp[∫(0.33±0.05) × 10⁻⁴ + (0.65±0.85)×10⁻⁸ T dT], (K _T/T) _P  = −0.011± 0.004 GPa K⁻¹. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg 1998); the best agreement was obtained with Δ_f H ⁰ ₂₉₈ (Mg-sursassite) = −13901.33 kJ mol⁻¹, and S ⁰ ₂₉₈ (Mg-sursassite) = 614.61 J K⁻¹ mol⁻¹. Received: 21 September 2000 / Accepted: 26 February 2001     

Experimental study of the K2ZrSi3O9 (wadeite)–K2TiSi3O9 and K2(Zr,Ti)Si3O9–phlogopite systems at 2–3 GPa

Experiments ranging from 2 to 3 GPa and 800 to 1300 °C and at 0.15 GPa and 770 °C were performed to investigate the stability and mutual solubility of the K₂ZrSi₃O₉ (wadeite) and K₂TiSi₃O₉ cyclosilicates under upper mantle conditions. The K₂ZrSi₃O₉–K₂TiSi₃O₉ join exhibits complete miscibility in the P–T interval investigated. With increasing degree of melting the solid solution becomes progressively enriched in Zr, indicating that K₂ZrSi₃O₉ is the more refractory end member. At 2 GPa, in the more complex K₂ZrSi₃O₉–K₂TiSi₃O₉–K₂Mg₆Al₂Si₆O₂₀(OH)₄ system, the presence of phlogopite clearly limits the extent of solid solution of the cyclosilicate to more Zr-rich compositions [Zr/(Zr + Ti) > 0.85], comparable to wadeite found in nature, with TiO₂ partitioning strongly into the coexisting mica and/or liquid. However, at 1200 °C, with increasing pressure from 2 to 3 GPa, the partitioning behaviour of TiO₂ changes in favour of the cyclosilicate, with Zr/(Zr + Ti) of the K₂(Zr,Ti)Si₃O₉ phase decreasing from ∼0.9 to ∼0.6. The variation in the Ti content of the coexisting phlogopite is related to its degree of melting to forsterite and liquid, following the major substitution ^VITi+^VI□=2^VIMg. Received: 26 January 1999 / Accepted: 10 January 2000     

Effect of pressure on the thermal expansion of MgO up to 8.2 GPa

Isobaric volume measurements for MgO were carried out at 2.6, 5.4, and 8.2 GPa in the temperature range 300–1073 K using a DIA-type, large-volume apparatus in conjunction with synchrotron X-ray powder diffraction. Linear fit of the thermal expansion data over the experimental pressure range yields the pressure derivative, (∂α/∂P) _T , of −1.04(8) × 10⁻⁶ GPa⁻¹ K⁻¹ and the mean zero-pressure thermal expansion α_{0, T}  = 4.09(6) × 10⁻⁵ K⁻¹. The α_{0, T} value is in good agreement with results of Suzuki (1975) and Utsumi et al. (1998) over the same temperature range, whereas (∂α/∂P) _T is determined for the first time on MgO by direct measurements. The cross-derivative (∂α²/∂P∂T) cannot be resolved because of large uncertainties associated with the temperature derivative of α at all pressures. The temperature derivative of the bulk modulus, (∂K _T/∂T) _P , of −0.025(3) GPa K⁻¹, obtained from the measured (∂α/∂P) _T value, is in accord with previous findings. Received: 2 April 1999 / Revised, accepted: 22 June 1999     

Fluid flow in marbles at Jervois, central Australia: oxygen isotope disequilibrium and zoning produced by decoupling of mineralogical and isotopic resetting

The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene, grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO₂ = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc) δ¹⁸O values of 9–18‰ and garnet (Gnt) δ¹⁸O values of 10–14‰. The δ¹⁸O(Gnt) values are only poorly correlated with δ¹⁸O(Cc), and the δ¹⁸O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the δ¹⁸O values of the rock were reset. The marbles contain  ≤15% garnet and, for water-rich fluids, garnet-forming reactions are predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively rapid. Texturally late epidote has δ¹⁸O values of 1.5–6.2‰ implying δ¹⁸O(H₂O) values of 2–7‰. Waters with such low-δ¹⁸O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water into a cooling hydrothermal system. Received: 29 April 1996 / Accepted: 12 March 1997     

The low-pressure stability of phase A,Mg7Si2O8(OH)6

 Phase A, Mg₇Si₂O₈(OH)₆, is a dense hydrous magnesium silicate whose importance as a host of H₂O in the Earth’s mantle is a subject of debate. We have investigated the low-pressure stability of phase A in experiments on the reaction phase A=brucite+forsterite. Experiments were conducted in piston-cylinder and multi-anvil apparatus, using mixtures of synthetic phase A, brucite and forsterite. The reaction was bracketed between 2.60 and 2.75 GPa at 500° C, between 3.25 and 3.48 GPa at 600° C and between 3.75 and 3.95 GPa at 650^° C. These pressures are much lower than observed in the synthesis experiments of Yamamoto and Akimoto (1977). At 750^° C the stability field of brucite + chondrodite was entered. The enthalpy of formation and entropy of phase A at 1 bar (10⁵ Pa), 298 K, were derived from the experimental brackets on the reaction phase A=brucite+forsterite using a modified version of the thermodynamic dataset THERMOCALC of Holland and Powell (1990), which includes a new equation of state of H₂O derived from the molecular dynamics simulations of Brodholt and Wood (1993). The data for phase A are: ΔH ^o _f =−7126±8 kJ mol^-1, S ^o=351 J K^-1 mol^-1. Incorporating these data into THERMOCALC allows the positions of other reactions involving phase A to be calculated, for example the reaction phase A + enstatite=forsterite+vapour, which limits the stability of phase A in equilibrium with enstatite. The calculated position of this reaction (753° C at 7 GPa to 937° C at 10 GPa) is in excellent agreement with the experimental brackets of Luth (1995) between 7 and 10 GPa, supporting the choice of equation of state of H₂O used in THERMOCALC. Comparison of our results with calculated P-T paths of subducting slabs (Peacock et al. 1994) suggests that, in the system MgO–SiO₂–H₂O, phase A could crystallise in compositions with Mg/Si>2 at pressures as low as 3 GPa. In less Mg rich compositions phase A could crystallise at pressures above approximately 6 GPa. Received: 3 July 1995/Accepted: 14 December 1995     

Biogeochemistry of Major Redox Elements and Mercury in a Tropical Reservoir Lake (Petit Saut,French Guiana)

The hydroelectric reservoir of Petit Saut, French Guiana, was created in 1994–1995 by flooding 350 km² of tropical forest. When sampled in 1999, the lake exhibited a permanent stratification separating the 3–5 m thick, oxygenated epilimnion from the anoxic hypolimnion. The rate of anaerobic organic carbon mineralization below the oxycline was on the order of 1 μmol C m⁻² s⁻¹ and did not show a pronounced difference between wet and dry seasons. Methanogenesis accounted for 76–83% of anaerobic carbon mineralization, with lesser contributions of sulfate reduction and dissimilatory iron reduction. Upward mixing of reduced inorganic solutes explained 90% of the water column O ₂ demand during the dry season, while most O ₂ consumption during the wet season was coupled to aerobic respiration of organic matter synthesized in the surface waters. Inorganic mercury species represented 10–40% of total dissolved mercury in the epilimnion, but were of relatively minor importance (≤10%) in the anoxic portion of the water column. Net production of soluble organic mercury compounds in the flooded soils and anoxic water column did not vary significantly between wet and dry seasons. Methylmercury accounted for about 15% of total dissolved mercury below the oxycline. Its estimated net production rate, 0.04 mg m⁻² yr⁻¹, is of the same order of magnitude as values reported for contaminated lakes and flooded terrestrial ecosystems.     

The groundwater resources and sustainable yield of Cheju volcanic island, Korea

 Hydrogeologic data of 455 water wells comprising geologic logs, water qualities, and aquifer test results are analyzed to determine hydrogeological characteristics, water quality, and sustainable yield of the groundwater resources of Cheju volcanic island. The groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed basaltic and andesitic rocks as high-level, basal, and parabasal groundwater under unconfined conditions. The total storage of groundwater is estimated at about 44 billion m³. The average transmissivity and specific yield of the aquifer are at about 0.34 m² s^–1(29300 m² day^–1) and 0.12, respectively. The average annual precipitation is about 3.39 billion m³, of which 1.49 billion m³– equivalent to 44.0% of the total annual precipitation – is recharged into aquifers, with 0.638 billion m³ year^–1 of runoff and 1.26 billion m³ year^–1 of evapotranspiration. Based on a groundwater budget analysis, the sustainable yield is estimated at about 0.62 billion m³ year^–1, equivalent to 41.6% of annual recharge. A low-permeability marine sedimentary formation (Sehwari formation), composed of loosely cemented sandy silt, was recently found to be situated at 120±68 m below mean sea level. If the said marine sediment is distributed as a basal formation of the freshwater zone of the island, most of its groundwater will be of parabasal type. So the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area. Received: 16 January 1997 / Accepted: 16 June 1997     

An experimental study of the Fe-Mn exchange between garnet and ilmenite

The exchange equilibrium

Kinetics of selenomethionine disappearance from reclaimed coal mine soils of Wyoming, U.S.A.

 Selenomethionine (SeM) is an organic toxicant that is present in seleniferous environments. No kinetic data is yet available regarding SeM reactions in coal mine environments, where selenium (Se) toxicity is a potential concern. A kinetic study was conducted on two reclaimed coal mine soils (Typic Torriorthents) from Wyoming having sandy and clayey textures. Four levels of SeM treatments (0, 50, 100 μM, and plant amendment from the mine vegetation) were reacted with the soils for 4, 7, 14, 28, 42, 56, and 84 days to characterize the kinetic behavior of overall SeM disappearance from soil solutions. Detection of SeM in soil solutions at the control level (0 μM SeM) indicated occurrence of indigenous SeM in the soils. In the plant-amended soil solutions, much greater concentrations of SeM were observed as compared with the soil-only systems. This indicated the plant material was a more potential source of SeM than the mine soils. A time-dependent loss in solution SeM concentrations was observed for both soils under 0, 50, 100 μM SeM treatments. For the soil-plant mixtures, the solution SeM concentration increased initially, reached a maximum after 14 days, and then decreased thereafter. In the plant-amended soil solutions, SeM concentrations at all time intervals were higher for the sandy as compared to the clayey soil. At 50 and 100 μM SeM treatments, the solution pH was linearly related to the percentages of SeM disappeared from the solutions; greater percentage of SeM was removed from solutions at comparatively lower pH levels, which was ≥90% at pH 7.7 for both soils. Solution SeM concentrations decreased exponentially with time following first-order kinetic reactions. Under all applications (except for the control), C ₀ (SeM concentration at t=0) values for the sandy soil were greater than those determined for the clayey soil, indicating higher solution SeM availability for the former and more SeM retention by the latter at t=0. Comparison of C ₀ in controls (0 μM SeM addition) suggested greater indigenous SeM in the clayey soil. For both soils, C ₀ values under different treatments followed the order, (soil+100 μM)>(soil+50 μM)>(soil+0 μM). The specific reaction rate constants (K _r) of SeM for both soils were similar (0.031 and 0.029 day^–1 for sandy and clayey soils, respectively); low K _r values indicated that SeM loss from our reclaimed coal mine soil solutions would follow rather slow kinetics. The half-life (t _0.5) of SeM varied from 15 to 55 days depending on treatment level. The knowledge obtained from this study should contribute in developing time-based Se reclamation strategies in coal mine environments. Received: 18 September 1995 · Accepted: 28 December 1995     

Origin of the Maoduan Pb–Zn–Mo deposit, eastern Cathaysia Block, China: geological, geochronological, geochemical, and Sr–Nd–Pb–S isotopic constraints

The Maoduan Pb–Zn–Mo deposit is in hydrothermal veins with a pyrrhotite stage followed by a molybdenite and base metal stage. The Re–Os model ages of five molybdenite samples range from 138.6 ± 2.0 to 140.0 ± 1.9 Ma. Their isochron age is 137.7 ± 2.7 Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the nearby exposed Linggen granite porphyry gave a ²⁰⁶Pb/²³⁸U age of 152.2 ± 2.2 Ma and the hidden Maoduan monzogranite yielded a mean of 140.0 ± 1.6 Ma. These results suggest that the intrusion of the Maoduan monzogranite and Pb–Zn–Mo mineralization are contemporaneous. δ ³⁴S values of sulfide minerals range from 3.4‰ to 4.8‰, similar to magmatic sulfur. Four sulfide samples have ²⁰⁶Pb/²⁰⁴Pb = 18.252–18.432, ²⁰⁷Pb/²⁰⁴Pb = 15.609–15.779, and ²⁰⁸Pb/²⁰⁴Pb = 38.640–39.431, similar to the age-corrected data of the Maoduan monzogranite. These isotope data support a genetic relationship between the Pb–Zn–Mo mineralization and the Maoduan monzogranite and probably indicate a common deep source. The Maoduan monzogranite has geochemical features similar to highly fractionated I-type granites, such as high SiO₂ (73.7–75.2 wt.%) and alkalis (K₂O + Na₂O = 7.8–8.9 wt.%) and low FeO_t (0.8–1.3 wt.%), MgO (~0.3 wt.%), P₂O₅ (~0.03 wt.%), and TiO₂ (~0.2 wt.%). The granitic rocks are enriched in Rb, Th, and U but depleted in Ba, Sr, Nb, Ta, P, and Ti. REE patterns are characterized by marked negative Eu anomalies (Eu/Eu^* = 0.2–0.4). The Maoduan monzogranite, having (⁸⁷Sr/⁸⁶Sr) _t  = 0.7169 to 0.7170 and ε_Nd(t) = −13.8 to −13.7, was probably derived from mixing of partial melts from enriched mantle and the Paleoproterozoic Badu group in an extensional tectonic setting.