Hydrogeological and geochemical assessments of the Gediz Graben geothermal areas, western Anatolia, Turkey

Gediz Graben is an important area for geothermal activity in Turkey. Menderes Massif rocks consisting of gneisses, schists, marbles and granodiorite, comprise the aquifers of the geothermal systems. Neogene terrestrial sediments made up mainly of sandy and clayey conglomerates cap the systems. Gediz Graben geothermal areas are physically divided into seven main groups: Turgutlu-Urganl, Sart-Çamur, Caferbeyli, Üfürük, Kurunlu, Kavakldere-Sazdere and Alaehir geothermal areas. The third highest aquifer in Turkey temperature (182 ^°C) after Kzldere (242 ^°C) and Germencik (232 ^°C) was discovered in the Kavakldere-Sazdere area. The thermomineral waters of the Gediz Graben geothermal areas have outlet temperatures of 25^–95 ^°C and an electrical conductivity of 874–6020 S/cm. Mineralization is mostly dominated by Na⁺ (188–2027 ppm) and HCO₃^– (544–2950 ppm). Kavakldere-Sazdere area shows the highest boron content among the entire geothermal aquifers of Turkey. Major geochemical processes for thermomineral waters are carbonate and silicate dissolution and mixing.     

Der Strukturtyp von Emmonsit, {Fe2[TeO3]3·H2O}·xH2O (x=0−1)

Zusammenfassung Emmonsit kristallisiert triklin, RaumgruppeP , Gitterkonstanten:a ₀=7,90 Å,b ₀=8,00 Å,c ₀=7,62 Å, =96^o44, =95^o 0, =84^o 28,Z=2. Der Strukturtyp wurde aus 3-dimensionalen photographischen Röntgendaten ermittelt. Die Eisenatome werden je von 6 Sauerstoffen verzerrt oktaedrisch koordiniert. Jedes Telluratom wird von 3 Sauerstoffen in einem Abstand <2,0 Å umgeben. Ein vierter Sauerstoff hat bezüglich dieser drei einen um etwa 25–35% größeren Abstand, so daß jedes Telluratom im weiteren Sinne eine (3+1)-Koordination aufweist.

---

The structure type of emmonsite, {Fe₂[TeO₃]₃·H₂O}·xxH₂O (x=0–1)

Summary Emmonsite is triclinic with space groupP , and lattice constantsa ₀=7.90 Å,b ₀=8.00 Å,c ₀=7.62 Å, =96^o 44, =95^o 0, =84⁰ 28,Z=2. The structure type is derived from 3-dimensional photographic X-ray data. The iron atoms are coordinated by six oxygens in the form of a distorted octahedron. Each tellurium atom is coordinated to 3 oxygens at a distance <2.0 Å. Compared with these 3 Te–O distance the distance of a fourth oxygen is only 25 to 35% greater; therefore each tellurium atom has a (3+1)-coordination of oxygens.

---

---

Mit 2 Abbildungen     

Oxygen isotope geochemistry of hydrothermally-altered synmetamorphic granitic rocks from South-Central Maine,USA

Hydrothermally-altered mesozonal synmetamorphic granitic rocks from Maine have whole-rock ¹⁸O (SMOW) values 10.7 to 13.8. Constituent quartz, feldspar, and muscovite have ¹⁸O in the range 12.4 to 15.2, 10.0 to 13.2, and 11.1 to 12.0, respectively. Mean values of _Q–F ( ¹⁸O_quartz– ¹⁸O_feldspar)=2.4 and _Q–M ( ¹⁸O_quartz– ¹⁸O_muscovite)=3.3 are remarkably uniform (standard deviations of both are 0.2). Measured _Q–F and _Q–M values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic ¹⁸O values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures. Analyzed muscovites have D (SMOW) values in the range –65 to –82.Feldspars in the granitic rocks are mineralogically altered to either (a) muscovite+calcite, (b) muscovite+calcite+epidote, (c) muscovite+epidote, or (d) muscovite only. A consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks, quartz, and feldspar. Rocks with assemblage (a) have whole-rock ¹⁸O>12.1 and contain quartz and feldspar with ¹⁸O>13.8 and >11.4, respectively. Rocks with assemblages (b), (c), and (d) have whole-rock ¹⁸O<11.4 and contain quartz and feldspar with ¹⁸O< 13.1 and <11.0, respectively. The correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration.Three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400°–150° C, 100°–150° C below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons. Calculations of mineral-fluid equilibria indicate that samples with assemblage (a) coexisted during the event with CO₂-H₂O fluids of and ¹⁸O=10.8 to 12.2 while samples with assemblages (b), (c), or (d) coexisted with fluids of and ¹⁸O=9.4 to 10.1. Compositional variations of the hydrothermal fluids were highly correlated: fluids enriched in CO₂ were also enriched in ¹⁸O. Because CO₂ was added to the granites during hydrothermal alteration and because fluids enriched in CO₂ were enriched in ¹⁸O, some or all of the variation in ¹⁸O of altered granites may have been caused by addition of ¹⁸O to the rocks during the hydrothermal event. The source of both the CO₂ and ¹⁸O could have been high-¹⁸O metasedimentary country rocks. The inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in ¹⁸O close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism.A close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from Maine is in marked contrast to hydrothermally-altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium. The difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics. Both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration. Deeper hydrothermal events occur at higher temperature and are longer-lived. Minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium. Shallower hydrothermal events occur at lower temperatures and are shorter-lived. Generally there is insufficient time for fluid to closely approach equilibrium with all minerals.     

Stable isotope geochemistry and phase equilibria of coesite-bearing whiteschists,Dora Maira Massif,western Alps

Peak metamorphic temperatures for the coesite-pyrope-bearing whiteschists from the Dora Maira Massif, western Alps were determined with oxygen isotope thermometry. The ¹⁸O(smow) values of the quartz (after coesite) (¹⁸O=8.1 to 8.6, n=6), phengite (6.2 to 6.4, n=3), kyanite (6.1, n=2), garnet (5.5 to 5.8, n=9), ellenbergerite (6.3, n=1) and rutile (3.3 to 3.6, n=3) reflect isotopic equilibrium. Temperature estimates based on quartz-garnet-rutile fractionation are 700–750 °C. Minimum pressures are 31–32 kb based on the pressure-sensitive reaction pyrope + coesite = kyanite + enstatite. In order to stabilize pyrope and coesite by the temperature-sensitive dehydration reaction talc+kyanite=pyrope+coesite+H₂O, the a(H₂O) must be reduced to 0.4–0.75 at 700–750 °C. The reduced a(H₂O) cannot be due to dilution by CO₂, as pyrope is not stable at X(CO₂)>0.02 (T=750 °C; P=30 kb). In the absence of a more exotic fluid diluent (e.g. CH₄ or N₂), a melt phase is required. Granite solidus temperatures are 680 °C/30 kb at a(H₂O)=1.0 and are calculated to be 70°C higher at a(H₂O)=0.7, consistent with this hypothesis. Kyanite-jadeite-quartz bands may represent a relict melt phase. Peak P-T-f(H₂O) estimates for the whiteschist are 34±2 kb, 700–750 °C and 0.4–0.75. The oxygen isotope fractionation between quartz (¹⁸O=11.6) and garnet (¹⁸O=8.7) in the surrounding orthognesiss is identical to that in the coesitebearing unit, suggesting that the two units shared a common, final metamorphic history. Hydrogen isotope measurements were made on primary talc and phengite (D(_SMOW)=-27 to-32), on secondary talc and chlorite rite after pyrope (D=-39 to -44) and on the surrounding biotite (D=-64) and phengite (D=-44) gneiss. All phases appear to be in nearequilibrium. The very high D values for the primary hydrous phases is consistent with an initial oceanicderived/connate fluid source. The fluid source for the retrograde talc+chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization. The similar D, but dissimilar ¹⁸O values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium, but not oxygen isotope equilibrium. The unusual hydrogen and oxygen isotope compositions of the coesite-bearing unit can be explained as the result of metasomatism from slab-derived fluids at depth.     

Cell parameters of thermally treated anorthite. Al,Si configurations in the average structures of the high temperature calcic plagioclases

Thermal treatments of anorthite carried out at up to 1,547° C show that the unit cell parameter changes as a function of the treatment temperature. The best fit curve found by non-linear least squares analysis is: =91.419-(0.327·10^-6)T ²+(0.199·10^-12)T ⁴-(0.391·10)T ⁶. The results obtained support significant Al,Si disorder (Al0.10, where Al=t ₁(0)-1/3 [t ₁(m)+t ₂(0)+t ₂(m)], Ribbe 1975), in anorthite equilibrated near the melting point and confirm a high temperature series differentiated from the low temperature series for calcic plagioclases in the An₈₅–An₁₀₀ range also. In the plot vs. An-content the high and low temperature curves intersect at An₈₅ composition and progressively diverge in the An₈₅–An₁₀₀ range. The trends of the high and low temperature curves in this range are interpretable on the basis of the degree of Al, Si order in the average structures of calcic plagioclases.     

Characteristics and chronology of fracture — fluid infiltration in the Archean,Eye Dashwa Lakes pluton,Superior Province: evidence from H,C, O-isotopes and fluid inclusions

The Archean Eye Dashwa Lakes pluton (2672±24 Ma) has domains of mineralogically fresh isotropic granite, domains that have undergone bulk hydrothermal alteration, and at least eleven sets of sequential fracture arrays, each with distinctive mineral assemblages. Fresh granite is characterized by whole rock ¹⁸O=8.1 to 8.6 and primary magmatic quartz-feldspar (+1.3), quartz-biotite (5.2 to 5.4) and quartz-magnetite (+9.8) fractionations. Magmatic fluids had a calculated isotopic composition of ¹⁸O=7.9±0.5, and D=–80±5. These isotropic volumes of the granite have not experienced significant incursion of external thermal waters. Pegmatites, quartz-molybdenite veins, and phlogopite-muscovite coated fractures are sporadically distributed in the granite, and were precipitated from high-temperature magmatic fluids where ¹⁸O=8.0 to 10.3 and D=–80±5.The most abundant variety of fracture filling assemblage is epidote-quartz-chlorite±muscovite: fractures are bounded by domains of mineralogically similar bulk hydrothermal alteration of the granite. These minerals formed at 160 to 280° C, in the presence of NaCl, and NaCl-MgCl₂ brines (up to 25 wt% NaCl equivalent) of probable evolved marine water origin ( ¹⁸O=+0.4 to +3.8, D=–10 to –35) undergoing transient boiling. Upper plateau ⁴⁰Ar/³⁹Ar ages for the muscovite are 2650±15 Ma. Sequentially in the chronology of fracture-infiltration events, calcite-fluorite veins were deposited from boiling fluids at 340 to 390° C, isotopically characterized by ¹⁸O=4.7 and ¹³C=–5; and rare prehnite-chlorite lined fractures formed at 250 to 290° C. A generation of adularia-bearing veins precipitated at 140 to 230° C, from CaCl₂-NaCl brines, where ¹⁸O=0 to –6.5 and D=–10 to –30. Incremental ⁴⁰Ar/³⁹Ar age spectra on the K-feldspar yield an upper plateau of 1100 Ma. Subsequently, hematite developed during reactivation of earlier fractures, at 140 to 210° C in the presence of fluids characterized by ¹⁸O=–0.4 to –5.4 and D=–15 to –25. Arrays of open fractures partially occupied by gypsum and goethite reflect a fluid infiltration event at temperatures <50° C. Many of the earlier generations of fracture minerals have transgranular fracture infillings which record the presence of low temperature (88–190° C), hypersaline CaCl₂-NaCl brines. Narrow fractures lined with clays±calcite are sites for seepage of modern ground-waters. The isotopic signature of clay ( ¹⁸O=12 to 20, D=–80±5) plots near the line for modern kaolinites, confirming its formation in the presence of recent surface waters. Calcites coexisting with the clay minerals, and in fractured pegmatite show a common isotopic signature ( ¹⁸O=23±0.5, ¹³C=–13.6), indicating precipitation from modern groundwaters, where reactivated fractures have acted as conduits for infiltration of surface waters to depths of 200 m. Intermittent fracture-infiltration has occurred over 2.7 Ga. The early sequences of fracture-related fluid flow are interpreted in terms of devolatilization of the granite, followed by thermal contraction fracturing, incursion of marine water and convective cooling in the Archean. Hematite and adularia fracture fillings correspond to a stage when meteoric water infiltrated the volcanicplutonic terrain during Proterozoic and later times. Episodic fracture-fluid expulsion events may have been driven by seismic pumping, in response to magmatically and tectonically induced stresses within the Shield, with surface waters penetrating to depths of 15 km in the crust.     

F-OH exchange equilibria between mica-amphibole mineral pairs

Fluoride-hydroxyl exchange equilibria between phlogopite-pargasite and phlogopite-tremolite mineral pairs were experimentally determined at 1,173K, 500 bars and 1,073–1,173 K, 500 bars respectively. The distribution of fluorine between phlogopite and pargasite was found to favor phlogopite slightly, G _ex ^. (1,173 K)=–1.71 kJ anion^–1, while in the case of phlogopite-tremolite, fluorine was preferentially incorporated in the mica, G _ex ^. (1,073)=– 5.67 kJ anion^–1 and G _ex ^. (1,173K)=–5.84 kJ anion^–1. These results have yielded new values of entropy and Gibbs energy of formation for fluortremolite, S _f =–2,293.4±16.0JK^–1 mol^–1 and G _f = –11,779.3±25.0 kJ mol^–1, respectively. In addition, F-OH mineral exchange equilibria support a recent molten oxide calorimetric value for the Gibbs energy of fluorphlogopite, G _f =–6,014.0±7.0 kJ mol^–1, which is approximately 40 kJ mol^–1 more exothermic than the tabulated value.This work performed in part at Sandia National Laboratories supported by the U.S. Department of Energy, DOE, under contract number DE-AC04-76DP00789     

Rooseveltit von San Francisco de los Andes und Cerro Negro de la Aguadita,San Juan,Argentinien

Zusammenfassung Rooseveltit findet sich in der Oxidationszone der Lagerstätten San Francisco de los Andes und Cerro Negro de la Aguadita, in der Provinz San Juan, Argentinien, auf 30°22 S und 69°33 W. Er bildet sehr feinkörnige, weiß-graue, nach Bismuthinit pseudomorphe Aggregate. Die Brechungsindizes liegen zwischenn=2,10 und 2,30. Die Vickershärte beträgt 513 (4–5 der Mohs'schen Härteskala). Mittels Elektronenmikrosonde wurde folgende chemische Zusammensetzung bestimmt: As=21,5±1%, Bi=60,9±2%. Rooseveltit ist monoklin mita ₀=6,878(1)Å, b₀=7,163(1) Å, c₀=6,735(1) Å, =104° 46±1, Z=4, _calc.=6,94 g·cm^–3, RaumgruppeP 2₁/n.Rooseveltit wurde nach drei verschiedenen Methoden synthetisiert. Die Pulverdiagramme der synthetischen Produkte stimmen mit dem des Minerals überein. Die Brechungsindizes wurden mitn =2,13(2) bzw. n=2,25(2) und die Dichte mit _obs.=7,01 g·cm^–3 bestimmt. Zellparameter: a₀-6,882(1) Å, b₀=7,164(1) Å, c₀=6,734(1) Å, =104° 50,5±0,7, _calc.=6,94 g·cm^–3. Das synthetische Material schmilzt um 950°C. Selbst nach mehrstündigem Erhitzen auf 920°C läßt sich keine Veränderung im Pulverdiagramm des Minerals festellen.Es wird versucht, die natürliche Bildung des Rooseveltits zu erklären.

---

Rooseveltite from San Francisco de los Andes and Cerro Negro de la Aguadita, San Juan, Argentina

Summary Rooseveltite occurs in the weathering zone of the San Francisco de los Andes and Cerro Negro de la Aguadita mines, located in the San Juan Province, Argentina, at 30° 22S and 69° 33W. It appears in grey, finegrained aggregates pseudomorph after bismuthinite. Refraction index ranges fromn=2.10 to 2.30. The Vickers microhardness is 513 (4–5 of Mohs' scale). Chemical composition from electron micro probe measurements is As 21.5±1% and Bi 60.9±2%. Rooseveltite is monoclinic, with a₀=6.878(1) Å, b₀=7.163(1) Å, c₀=6.735(1) Å, =104° 46±1, Z=4, _calc.=6,94 g·cm^–3, space groupP 2₁/n.The synthetic compound was prepared by three different methods. The powder pattern are the same as that of the mineral. Refraction index n=2.13(2) and n=2.25(2). The measured specific gravity is _pobs.=7,01 g·cm^–3. Cell parameters: a₀=6.882(1) Å, b₀=7.164(1) Å,c ₀=6.734(1) Å, =104° 50.5±0.7, _calc.=6,94 g·cm^–3. The synthetic material melts at about 950°C. After heating to 920°C no variations were observed in the powder diagram of the mineral.It is tried to explain the formation of rooseveltite in natural environment.

---

---

Mit 2 Abbildungen     

P - V - T equation of state of stishovite to the mantle transition zone conditions

In-situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on stishovite SiO₂ and pressure-volume-temperature data were collected at up to 22.5 GPa and 1,073 K, which corresponds to the pressure conditions of the base of the mantle transition zone. The analysis of room-temperature data yielded V₀=46.56(1) ų, K_{T 0}=296(5) GPa and K _T =4.2(4), and these properties were consistent with the subsequent thermal equation of state (EOS) analyses. A fit of the present data to high-temperature Birch-Murnaghan EOS yielded (K_T /T) _P =–0.046(5) GPa K^–1 and = a + bT with values of a =1.26(11)×10^–5 K^–1 and b =1.29(17)×10^–8 K^–2. A fit to the thermal pressure EOS gives ₀=1.62(9)×10^–5 K^–1, ( K _T / T) _V =–0.027(4) GPa K^–1 and (²P /T ²) _V =27(5)×10^–7 GPa K^–2. The lattice dynamical approach by Mie-Grüneisen-Debye EOS yielded ₀=1.33(6), q =6.1(8) and ₀=1160(120) K. The strong volume dependence of the thermal pressure of stishovite was revealed by the analysis of present data, which was not detectable by the previous high-temperature data at lower pressures, and this yields ( K _T / T) _V 0 and q 1. The analyses for the fictive volume for a and c axes show that relative stiffness of c axis to a axis is similar both on compression and thermal expansion. Present EOS enables the accurate estimate of density of SiO₂ in the deep mantle conditions.     

Equation of state,structural behaviour and phase diagram of synthetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as a function of pressure and temperature

The behaviour of synthetic Mg-ferrite (MgFe₂O₄) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K₀=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa^–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by _a0+_a1*(T–298)+_a2/(T–298)², where _a0=9.1(1) 10^–6 K^–1, _a1=4.9(2) 10^–9 K^–2 and _a2= 5.1(5) 10^–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol^–1 and =–17.6(± 1.2) kJ mol^–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe₂O₄, which shows that the high-pressure transition from spinel to orthorombic CaMn₂O₄-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe₂O₃.     

Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen,North China Craton: elemental and Sr–Nd–Pb isotopic constraints

A geochemical and isotopic study was carried out for three Mesozoic intrusive suites (the Xishu, Wuan and Hongshan suites) from the North China Craton (NCC) to understand their genesis and geodynamic implications. The Xishu and Wuan suites are gabbroic to monzonitic in composition. They share many common geochemical features like high Mg# and minor to positive Eu anomalies in REE patterns. Initial Nd–Sr isotopic compositions for Xishu suite are _Nd(135 Ma)=–12.3 to –16.9 and mostly I_Sr = 0.7056–0.7071; whereas those for Wuan suite are slightly different. Pb isotopic ratios for Xishu suite are (²⁰⁶Pb/²⁰⁴Pb)_i = 16.92–17.3, (²⁰⁷Pb/²⁰⁴Pb)_i=15.32–15.42, (²⁰⁸Pb/²⁰⁴Pb)_i=37.16–37.63, which are slightly higher than for Wuan suite. The Xishu–Wuan complexes are considered to originate from partial melting of an EM1-type mantle source, followed by significant contamination of lower crustal components. The Hongshan suite (mainly syenite and granite) shows distinctly higher _Nd(135 Ma) values (–8 to –11) and slightly higher Pb isotopic ratios than the Xishu–Wuan suites. It was formed via fractionation of a separate parental magma that also originated from the EM1-type mantle source, with incorporation of a small amount of lower crustal components. Partial melting of the mantle sources took place in a back-arc extensional regime that is related to the subduction of the paleo-Pacific slab beneath the NCC.     

Thermodynamic data from redox reactions at high temperatures. III. Activity-composition relations in Ni-Pd alloys from EMF measurements at 850–1250 K,and calibration of the NiO+Ni-Pd assemblage as a redox sensor

The assemblage NiO+Ni-Pd alloy has been calibrated as a precise oxygen fugacity sensor in the temperature range 850–1250 K at 1 bar, using an electrochemical technique with oxygen-specific CSZ electrolytes, and Ni+NiO and Cu+Cu₂O as the reference electrodes. Nine compositions were studied, ranging from 0.12 to 0.83 X _Ni ^alloy . Steady EMFs, implying equilibrium, were rapidly achieved in all cells, and were found to be reversible on increasing and decreasing temperature with a precision approaching 0.1 mV. The estimated accuracy of the measurements on each cell is ±0.2 mV (1, corresponding to ±0.003 log-bar units in fo₂ at 1273 K). Compositions of the Ni-Pd alloys were measured after each run by electron microprobe, and these compositions were then checked for internal consistency by measuring the lattice parameter by X-ray diffraction. Nickel-rich alloys show positive deviations from ideality and endothermic enthalpies of mixing, but palladium-rich compositions have exothermic enthalpies of mixing and strong negative deviations from ideality. The excess entropies of mixing are positive for all compositions, and correlate approximately with the excess volumes of mixing. The highly asymmetrical deviations from ideality are well described by a polynomial expression of the Redlich-Kister form, with three terms for the enthalpies, and two for the excess entropies and volumes of mixing. The experimental data from this study have been used to re-formulate the Ni-Pd oxygen fugacity sensor to give an expression; _O2 ^ss = _O2 ^NNO – 2RT ln X _Ni ^alloy – [2 · (1 – X _Ni ^alloy )² · [(–2165–7.958 · T) + (9409 – 0.888 · T) · (4 X _Ni ^alloy – 1) + 2089 · (6 X _Ni ^alloy – 1) · (2 X _Ni ^alloy – 1)]](850<T<1300) where _O2 ^ss is in J mol^-1, T is in kelvins, and the expression for _O2 ^NNO is that given by O'Neill and Pownceby (1993). Values in terms of log fo₂ may be obtained from the above by dividing by RT ln 10. The estimated standard error in _O2 ^ss is on the order of ±200 J mol^-1, which is approximately ±0.01 log-bar units in fo₂ at 1273 K.     

The crystal structures of CuSO4 · H2O and CuSeO4 · H2O,and their relationships to kieserite

Summary The crystal structures of hydrothermally grown CuSO₄ · H₂O and CuSeO₄ · H₂O were determined by single crystal X-ray methods [Space group ,a = 5.037 (1), 5.129 (1) Å,b = 5.170(1), 5.527(1)Å,c = 7.578(2), 7.469(2)Å, = 108.62(1), 103.98(1)°, = 108.39(1), 106.52(1)°, = 90.93(1), 97.19(1)°; Z = 2; R_w = 0.026, 0.030 for 2065, 2235 reflections with sin / 0.90 Å^–1]. The Cu atoms are [4 + 2]-coordinated to O atoms. These elongated octahedra are corner connected via the H₂O molecule to form chains. The formal units ¹ [Cu₂O₈(H₂O)2]^12- are interconnected by [XO₄]^2- groups (X=S,Se) and hydrogen bonds (bond lengths 2.72–2.83 Å). The crystal structures show pseudomonoclinic symmetry and are strongly related to the structure type of kieserite.[/p]

---

Die Kristallstrukturen von CuSO₄ · H₂O und CuSeO₄ · H₂O und ihre Beziehungen zum Kieserit

Zusammenfassung Die Kristallstrukturen von hydrothermal gezüchtetem CUSO₄ · H₂O und CuSeO₄. H₂O wurden an Einkristallen mittels Röntgenbeugung bestimmt [Raumgruppe ;a = 5.037(1), 5.129(1)Å,b = 5.170(1), 5.527(1)Å,c = 7.578(2), 7.469 (2) Å, = 108.62(1), 103.98(1)°, = 108.39(1), 106.52(1)°, = 90.93(1), 97.19(1)°; Z = 2; R_W = 0.026, 0.030 für 2065, 2235 Reflexe mit sin / 0.90)Å^–1]. Die Cu-Atome werden durch O-Atome [4+2]-koordiniert. Diese gestreckten /lOktaeder sind miteinander über Ecken durch die H₂O-Moleküle zu Ketten verknüpft. Die formalen Einheiten ¹ [CU₂O₈(H₂O)₂]^12– werden durch [XO₄]^2–-Gruppen (X = S, Se) und Wasserstoffbrücken (Bindungslängen 2.72–2.83Å) miteinander verbunden. Die Kristallstrukturen zeigen pseudomonokline Symmetrie und sind sehr nahe mit dem Strukturtyp des Kieserits verwandt.

---

---

With 1 Figure     

Solid solution of rare earth elements in synthetic titanite: a reconnaissance study

Summary Titanite varieties doped with rare earth elements (REE) have been prepared by ceramic synthesis and quenching in air. Their crystal structure was determined by Rietveld analysis of the powder X-ray diffraction patterns. Two different substitution schemes, Ca_1–xNa_x/2Sm_x/2TiSiO₅ and Ca_1–xDy_xTi_1–x SiO₅, are studied at x=0.2. Both synthetic varieties of titanite adopt space group A2/a. This implies that both single-site and complex multivalent substitutional schemes destroy the coherence of the off-centering of octahedral chains in the titanite structure resulting in a P2₁/aA2/a phase transition. Unit cell dimensions obtained for the REE-bearing titanite varieties are as follows: a=7.0541(1)Å; b=8.7247(1)Å; c=6.5664(1)Å; =113.732(1)° for Ca_0.8Na_0.1Sm_0.1TiSiO₅; and a=7.0021(1)Å; b=8.7256(1)Å; c=6.5427(1)Å; =113.294(1)° for . Both REE-doped titanite samples and a control sample of the pure titanite end member have similar unit cell parameters and consist of polyhedra distorted to a similar extent with the exception of more-distorted SiO₄ tetrahedron in CaSiTiO₅. The structural data suggest that the Ca_1–xNa_x/2Sm_x/2TiSiO₅ and Ca_1–xDy_xTi_1–xFe_xSiO₅ solid solutions adopting the titanite structure might extend to x sufficiently greater than 0.2 and involve both heavier and lighter trivalent rare earth elements.Permanent address: Geological Institute KSC RAS, 14 Fersmana St., Apatity, 184200 Russia     

Subseabed disposal of radioactive waste: effects of consolidational fluid flow

Subseabed disposal of radioactive waste applies a multiple-barrier concept with the sediment being the most important barrier for preventing a release of nuclides into the biosphere. While many investigations have been carried out to analyze the risk potential in this type of disposal, the effects of sediment consolidation and associated fluid flow have not fully been taken into consideration. Here, possible effects of consolidational fluid flow in the penetrator disposal option and possible consequences to the transport of nuclides in the sediment are analyzed. Results of numerical experiments demonstrate that consolidation contributes to the transport of radioactive nuclides released from containers buried in the sediment and to the release of nuclides at the sediment-water interface. Both depend on geological conditions and to a large extent on possible alterations of hydraulic conductivity i of the sediment in the vicinity of the entry path of a penetrator.Symbols c concentration ml m^–3 - c _a concentration of adsorbed solute mg kg^–1 (relative to dry weight of sorbing substance) - c _in solute concentration of source q mg m^–3 - c ₀ initial concentration mg m^–3 - ID dispersion tensorm ²s^–1 - ID ^* diffusion tensor m²s^–1 - D coefficient of dispersion m²s^–1 - d ₀ coefficient of molecular diffusion m²s^–1 - d coefficient of effective diffusion m²s^–1 - g gravity m²s^–1 - h piezometric pressure m - k hydraulic conductivity m²s^–1 - m mass kg - p pressure Pa - q source/sink m³s^–1 - S ₀ specific surface m²m^–3 - t time s - v velocity m s^–1 - x, z cartesian coordinates m - compressibiliy of sediment m²N^–1 - _L longitudinal dispersivity m - effective porosity (decimal fraction) - density kg m^–3 - _s density of sediment kg m^–3 - _w density of water kg m^–3 - decay constant per s - kinematic viscosity m²s^–1     

Contrasting serpentinization processes in the eastern Central Alps

Stable isotope compositions have been determined for serpentinites from between Davos (Arosa-Platta nappe, Switzerland) and the Valmalenco (Italy). D and ¹⁸O values (–120 to –60 and 6–10, respectively) in the Arosa-Platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water. One sample of chrysotile has a ¹⁸O value of 13 providing evidence of high W/R ratios and low formation temperature of lizardite-chrysotile in this area. In contrast, relatively high D values (–42 to –34) and low ¹⁸O values (4.4–7.4) for serpentine in the eastern part of the Valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water. The antigorite in the Valmalenco is the first reported example of continental antigorite with an ocean water signature. An amphibole sample from a metasomatically overprinted contact zone to metasediments (D=-36) indicates that the metasomatic event also took place in the presence of ocean water. Lower D values (–93 to –60) of serpentines in the western part of the Valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism. Low water/rock ratios during regional metamorphism (and metasomatism) have to be assumed for both regions.     

Anisotropic compression of edingtonite and thomsonite to 6 GPa at room temperature

Polycrystalline samples of natural edingtonite (New Brunswick, Canada) and thomsonite (Oregon, USA) were studied up to 6 GPa using monochromatic synchrotron X-ray powder diffraction and a diamond-anvil cell with a methanol:ethanol:water mixture as a penetrating pressure-transmitting fluid. Unlike natrolite, previously studied under the same conditions, edingtonite and thomsonite do not show any apparent pressure-induced hydration (PIH) or phase transitions. All these fibrous zeolites are characterized by their anisotropic compressibilities, with the linear compressibilities of the fibrous chains (c-axis) being as small as one third of those perpendicular to the chains (a-, b-axes); for edingtonite, ₀ ^a =0.0050(3) GPa^–1, ₀ ^b =0.0054(2) GPa^–1, ₀ ^c =0.0034(1) GPa^–1; for thomsonite, ₀ ^a = 0.0080(2) GPa^–1, ₀ ^b =0.0084(2) GPa^–1, ₀ ^c =0.0032(1) GPa^–1. The pressure–volume data were fitted to a second-order Birch–Murnaghan equation of state using a fixed pressure derivative of 4. As a result of the 0000-type connectivity of the chains, the bulk modulus of edingtonite is found to be about 40% larger than that of thomsonite; K^EDI ₀=73(3) GPa, K^THO ₀=52(1) GPa. Distance least-squares refinements were used to model the expected framework, following the observed linear compression behaviors. The chain-bridging T–O–T angle is proposed to be correlated with the different compressibilities across the chains in each framework type.     

Latest precambrian (Cadomian) zircon ages,Nd isotopic systematics and P-T evolution of granitoid orthogneisses of the Erzgebirge,Saxony and Czech Republic

Single zircons from two orthogneiss complexes, the Grey Gneiss and Red Gneiss, the lowermost tectonic units in the Erzgebirge, were dated. The grey Freiberg Gneiss is of igneous origin and has a ²⁰⁷Pb/²⁰⁶Pb emplacement age of 550±7 Ma. A quartz monzonite from Lauenstein contains idiomorphic zircons with a mean ²⁰⁷Pb/²⁰⁶Pb age of 555±7 Ma as well as xenocrysts ranging in age between 850 and 1910 Ma. Red gneisses from the central Erzgebirge contain complex zircon populations, including numerous xenocrysts up to 2464 Ma in age. The youngest, idiomorphic, zircons in all samples yielded uniform ²⁰⁷Pb/²⁰⁶Pb ages between 550±9 and 554±10 Ma. Nd isotopic data support the interpretation of crustal anatexis for the origin of both units. _Nd(t) values for the grey gneisses are –7.5 and –6.0 respectively, (mean crustal residence ages of 1.7–1.8 Ga). The red gneisses have a wider range in _Nd(t) values from –7.7 to –2.8 (T _DM ages of 1.4–1.8 Ga). The zircon ages document a distinct late Proterozoic phase of granitoid magmatism, similar in age to granitoids in the Lusatian block farther north-east. However, Palaeozoic deformation as well as medium pressure metamorphism ( 8 kbar/600–650° C) are identical in both gneiss units and distinguish these rocks from the Lusatian granitoids. The grey and red gneisses were overthrust by units with abundant high-pressure relicts and a contrasting P-T evolution. Zircon xenocryst and Nd model ages in the range 1000–1700 Ma are similar to those in granitoid rocks of Lusatia and the West-Sudetes, and document a pre-Cadomian basement in parts of east-central Europe that, chronologically, has similarities with the Sveconorwegian domain in the Baltic Shield.     

Sr-Nd isotopic constraints on the petrogenesis of the Central Bohemian Pluton,Czech Republic

The Sr-Nd isotopic data for selected granitoids of the Central Bohemian Pluton show a broad negative correlation with the total range of (⁸⁷Sr/⁸⁶Sr)₃₃₀ = 0.7051–0.7129 and _Nd ³³⁰ = +0.2 to –8.9. The older intrusions have more depleted Sr-Nd compositions and calc-alkaline geochemistry (Sázava suite), whereas the younger intrusions shift towards K-rich calc-alkaline (Blatná suite) and shoshonitic rocks (íany and ertovo bemeno suites) with more evolved isotopic signatures. The distribution of the data is interpreted as reflecting a diversity of sources and processes, rather than a single progressive crustal contamination trend. The Sázava suite could have originated by partial melting of metabasites, or of a mantle source with an isotopic composition close to bulk earth, or by hybridization of crustally-derived tonalitic and mantle-derived magmas. Variation within the Blatná suite is modelled by mixing between a moderately enriched [(⁸⁷Sr/⁸⁶Sr)₃₃₀ 0.708, _Nd ³³⁰ –3] mantle component with either an isotopically evolved metasedimentary component, or with more evolved magmas of the suite. The íany suite was most probably produced by partial melting of peraluminous lithologies, possibly of the adjacent Moldanubian unit. The ertovo bemeno suite evolved from strongly enriched mantle-derived magmas [(⁸⁷Sr/⁸⁶Sr)₃₃₀0.7128, _Nd ³³⁰ –7], either through closed-system fractional crystallization or interaction with magma corresponding to leucogranites of the Central Bohemian Pluton.     

Relationships among Gibbs free energies and enthalpies of formation of phosphates,oxides and aqueous ions

Two parameters _GO^2– and _HO^2– are defined as the differences between respectively the Gibbs free energies and the enthalpies of formation of an oxide and its corresponding aqueous cation. The Gibbs free energies and enthalpies of formation of phosphates from their consituent oxides are shown to be linear functions of respectively _GO^2– and _HO^2– of their constituent cations.