The elasticity of the upper mantle orthosilicates olivine and garnet to 3 GPa

The elastic moduli of single crystals of pyrope-rich garnet and San Carlos olivine have been measured over a 3 GPa pressure range at room temperature. The combination of improved ultrasonic techniques and this large pressure range provide for more reliable characterization of the pressure dependence of acoustic wave velocities than has previously been possible. First and second pressure derivatives of the velocities have been determined within 1 percent and 10 percent respectively. The Hashin-Shtrikman bounds for the pressure dependences of the bulk and shear moduli of the garnet used in this study are; K = 173.6 GPa, K = 4.93, K = –0.28 GPa^–1, G= 94.9 GPa, G = 1.56, G = –0.08 GPa^–1 and the Hashin-Shtrikman least-upper bounds and greatestlower bounds for the pressure dependences of the bulk and shear moduli of the San Carlos olivine are K=129.8 GPa, K = 4.66, K= –0.15 GPa^–1, G = 77.8 GPa, G = 1.93, G = –0.11 GPa^–1 and K = 129.2 GPa, K = 4.63, K= –0.15 GPa^–1 G = 77.3 GPa, G=1.96, G = –0.11 GPa^–1 respectively. The determination of the room-pressure elastic moduli of this pyrope-almandine garnet removes the previously observed anomaly in the predictions of systematic treatments of variations of the elastic moduli of garnets with composition. The determination of the second pressure derivatives of the moduli of garnet and olivine illustrates the importance of these terms in extrapolations to higher pressures — with K/P for these crystals being reduced by 17 percent and 9 percent respectively over the 3 GPa pressure range.     

Diamagnetic anisotropies of oxide minerals

The diamagnetic anisotropy of oxide minerals is analyzed in terms of a new model, in which the anisotropy is assigned to the individual chemical bond in the [MO₆] octahedral unit of the crystal. The diamagnetic principal axis of the individual M-O bond is assumed to be parallel to the direction of the bond. The calculated anisotropy based on this model shows a good correlation with the measured diamagnetic anisotropy, , for various minerals such as talc, sericite, kaolinite of the sheetsilicate group, forsterite of the orthosilicate group, and corundum of the hematite group. The values of many diamagnetic minerals are still unknown since the measurement is difficult to perform by means of conventional methods. The magnetic grain orientation recently observed in the mineral suspensions is effective for estimating the value, when the single crystal of the mineral cannot be obtained. The observation of fieldinduced crystal oscillation in the high magnetic fields can be applied for measuring the minerals with small values of less than 5 × 10^–10 emu/cc. The chemical bond model on the diamagnetic anisotropy can be confirmed, when the compiling of data on various mineral is made by means of the above two methods.     

Cation distribution in pentlandites (Fe,Ni)9S8: Dependence on pressure and temperature and kinetics of the cation exchange reaction

This paper describes the distribution of Fe and Ni between the octahedral and tetrahedral sites in pentlandite (Fe,Ni)₉S₈. The dependence of the distribution on pressure and temperature and the activation energy of the cation exchange reaction were determined through annealing experiments. Synthetic crystals were annealed at 433–723 K and pressures up to 4 GPa, and natural crystals were annealed at 423, 448 and 473 K in evacuated silica capillary tubes for various durations. The cation distributions in the synthetic crystals were determined with an X-ray powder method employing the anomalous dispersion effect of CuK. and FeK radiations, while those of natural crystals were calculated from the cell dimensions. The values of U, S and V for the Fe/Ni exchange reaction are –6818 J mol^–1, 20.52 J K^–1 mol^–1, and 6.99 × 10^–6 m³ mol^–1, respectively. The dependence of the Fe/Ni distribution on pressure (Pa) and temperature (Kelvin) was determined as lnK = 2.47+8.20 × 10² T ^–1+8.41 x 10^–7 T ^–1 P, where K = (Fe/Ni)_octahedral /(Fe/Ni)_tetrahedral. The activation energy of the cation exchange reaction was 185 kJ mol^–1.     

Field-induced oscillation and rotation of diamagnetic oxide crystals

The harmonic oscillations of large diamagnetic mineral samples induced by a magnetic field is reported, for single crystals of quartz, corundum, and calcite. It was seen for the first time that the period of oscillation, , was proportional to the reciprocal of the magnetic field, H, where the restoring force of the string suspending the crystal became negligible in the high magnetic field. Accordingly, the value of diamagnetic anisotropy, , could be measured from the — H curve with a sensitivity of 5 × 10^–10 emu/cc. The values were 5.50 × 10^–9 emu/cc for quartz, 4.20 × 10^–9 emu/cc for corundum, 9.9 × 10^–8 emu/cc for calcite, and 8.8 × 10^–8 emu/cc for polycrystalline talc piled with the (001) planes aligned parallel. Significant field-induced rotations were observed for the suspended crystals. When the field was applied along the direction of the diamagnetic hard axis of the stationary crystal, the crystal gradually rotated with increasing field, so that the direction of the hard-axis was perpendicular to the applied field. The field-induced energy has a the maximum value when the field is applied along the diamagnetic hard axis. This reorientation of the crystal occurs because the torque due to the field-induced anisotropic energy exceeds that of the restoring force in high magnetic fields.     

Pressure-volume-temperature behavior of fayalite based on static compression measurements at 400° C

Twenty-one energy-dispersive X-ray diffraction spectra for fayalite at 400° C constitute the basis for an elevated-temperature static compression isotherm for this important silicate mineral. A Murnaghan regression of the resulting molar volumes yields 103.8 GPa and 7.1 for the 400° C, room-pressure values of the isothermal bulk modulus (K ₀) and its first pressure derivative (K₀), respectively. When compared to the room-temperature static compression isotherm of Yagi et al. (1975), our 400° C value for K ₀ yields 5.4 ×10^–2 GPa/deg for (K/T)₀₀. When combined with literature volume data, our measurements indicate that the fayalite isochores are strongly concave toward the pressure axis [( ² T/P ² ) _v <>This is publication number 1125 of the School of Earth Sciences, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA     

Mg tracer diffusion in synthetic forsterite and San Carlos olivine as a function of P,T and fO2

We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo₁₀₀) and San Carlos olivine (Fo₉₂) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ/mol (96 kcal/mol) and 275 (±25) kJ/mol (65 kcal/ mol) in forsterite and San Carlos olivine, respectively, along [001] at a fO₂ of 10^–12 bars. There is no change in activation energy of Mg tracer diffusion within this temperature range. Mg tracer diffusion in a nominally pure forsterite is found to be anisotropic (D_c > D_a > D _b) and a function of fO₂. This fO₂ dependence is different from that in olivine containing Fe as a major element, which suggests that the diffusion mechanism of Mg in forsterite is different from that in Fe-bearing olivine at least over some range of fO₂. The diffusion mechanism in nominally pure forsterites may involve impurities present below the limits of detection or alternately, Si or Fe³⁺ interstitial defects, Fe being present as impurity (ppm level) in forsterite. Pressure dependence of Mg tracer diffusivity in forsterite measured to 10 GPa in a multianvil apparatus yields an activation volume of approximately 1–3.5 cm³/ mol. It is found that presence of small amounts of hydrogen bearing species in the atmosphere during diffusion anneal (f_H2 0.2 bars, f_H20 0.24 bars) do not affect Mg tracer diffusion in forsterite within the resolution of our measurement at a total pressure of 1 bar. The observed diffusion process is shown to be extrinsic; hence extrapolation of the diffusion data to lower temperatures should not be plagued by uncertainties related to change of diffusion mechanism from intrinsic to extrinsic.     

Electron paramagnetic resonance of Sc3+-stabilized CO 3 3− molecule-ion in natural calcite

Electron paramagnetic resonance (EPR) spectra of CO ₃ ^3– molecule-ions stabilized by Sc³⁺ in natural calcite were identified and studied at X-band frequencies and room temperature. The principal values of the g-tensor (g _xx= 1.9997, g _yy = 2.0030, g _zz = 1.9972) and the direction cosines of the g and A tensors for CO ₃ ^3– -Sc³⁺ center were found to be close to that for the well-known CO ₃ ^3– -Y³⁺ center. A quantitative comparison of different impurity contents in calcite samples and analysis of the intensities of forbidden transitions were used to identify Sc³⁺. An estimation of the unpaired electron spin density on the nuclei of paramagnetic centers confirms that both centers, CO ₃ ^3– -Sc³⁺ and CO ₃ ^3– -Y³⁺, have the same nature.     

Thermodynamic properties of strontianite-witherite solid solution (Sr,Ba)CO3

Structural parameters and thermodynamic properties of strontianite — witherite solid solutions have been studied by X-ray powder diffraction, heat flux Calvet calorimetry and cation-exchange equilibria technique. X-ray study of the synthetic samples have shown linear and quadratic (for c-parameter) composition dependencies of the lattice constants in the carbonate solid solution. The thermodynamic energy parameters demonstrate the non-ideal character of strontianite — witherite solid solutions. Enthalpies of solution of the samples have been measured in 2PbO*B₂O₃ at 973 K. The new data on the enthalpy of formation H _f,298.15 ⁰ of SrCO₃ and BaCO₃ were obtained: -1231.4±3.2 and -1209.9±5.8 kJ*mol^-1 respectively. The enthalpy of mixing of the solid solution was found to be positive and asymmetric with maximum at X_Ba (carbonate)=0.35. The composition dependence of the enthalpy of mixing may be described by two — parametric Margules model equation: H _mix=X _BaX _Sr[(4.40±3.91)X _Ba+(28.13±3.91)X _Sr] kJmol^–1 Cation-exchange reactions between carbonates and aqueous SrCl₂-BaCl₂ supercritical solutions (fluids) were carried out at 973 and 1073 K and 2 kbar. Calculated Margules model parameters of the excess free energy are: for orthorhombic carbonate solid solutions W _Sr=W _Ba=11.51±0.40 kJmol^–1 (973 K) and W _Sr=W _Ba=12.09±0.95 kJmol^– (1073 K) for trigonal carbonate solid solutions W _Sr=W _Ba=13.55±0.40 kJmol^– (1073 K).     

Spontaneous strain at the structural phase transition in NaNO3

The temperature dependence of the hexagonal c unit cell parameter of high-purity NaNO₃ shows an anomaly at 553 K corresponding to the orientational ordering transition. The a unit cell parameter is barely influenced by the transition. The single component spontaneous strain for this zone boundary instability is large (55×10^–3 at 295 K), and couples quadratically with the order parameter. The critical exponent is found to have the value 0.22 ± 0.01, which differs from that expected in the classical case. Below ca 450 K, crossover to tricritical behaviour is observed (=1/4). The temperature evolution of the macroscopic order parameter as revealed by the temperature dependence of the spontaneous strain follows a tricritical behaviour between 70 K and 450 K. At temperatures below 70 K order parameter saturation is observed. Combined with recent data from specific heat measurements, the critical exponents suggest that the three-dimensional, three-states Potts model may describe the transition.Precursor spontaneous strain above T _c is consistent with local ordering and may result from fluctuations associated with an antiordered NO₃ group pair configuration.     

Rb−Sr- und K−Ar-Isotopen-Alter an Pegmatiten aus Kor- und Saualpe,SE-Ostalpen, Österreich

Zusammenfassung An sieben Pegmatiten aus der Kor- und Saualpe wurden insgesamt 12 Rb–Sr-Gesamtgesteins-Analysen durchgeführt, an Muskoviten aus den Pegmatiten sind 16 Rb–Sr-Analysen und 15 K–Ar-Bestimmungen gemacht worden.Alle Pegmatite haben zwei Hellglimmergenerationen, die deutlich unterscheidbar sind.Mit der Rb–Sr-Methode ergeben die großen Muskovite (bis 20 cm ) in acht Fällen praealpidische Alterswerte: 240 bis 265 M, J. Mit der gleichen Methode wird an den Muskoviten der zweiten Generation (bis 3 cm ) alpidisches Alter bestimmt: 72 bis 122 M. J.Die Rb–Sr-Gesamtgesteins-Analysen deuten auf ein geöffnetes System für Rb–Sr in alpidischer Zeit, vergleichbar mit den Paragneisen (Morauf, 1980b).Die K–Ar-Bestimmungen an den Muskoviten beider Generationen ergeben alpidische Alterswerte; 71–116 M. J. Es ist ein Einfluß der Korngröße auf den Alterswert feststellbar sowie Unterschiede zwischen Kern und Rand bei den Muskoviten der ersten Generation.Prae-alpidische Mineral-Alter sind im Bereiche der Kor-und Saualpe nur noch in großen Pegmatit-Muskoviten nachweisbar, da durch eine altalpidische druckbetonte Metamorphose (vor 80 M. J.) nicht nur kleine Glimmer verjüngt/gebildet wurden, sondern auch die Gesamtgesteine zum teilweise offenen System für Rb und Sr wurden. Die prägende Deformation muß nach den vorliegenden Daten ebenfalls altalpidisch sein.

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Rb–Sr and K–Ar isotopic ages of pegmatites from Koralpe and Saualpe, South-Eastern Alps, Austria

Summary 12 Rb–Sr-whole rock analyses on seven pegmatites of the Kor- and Saualpe were performed, as well as 16 Rb–Sr-determinations and 15 K–Ar measurements on the white micas of these pegmatites. All the pegmatites show clearly two generations of mica growth.The white mica from the first generation with books up to 20 cm yielded eight pre-Alpidic Rb–Sr-ages between 240 and 265 my. The second generation of white micas ( up to 3 cm) give Alpidic ages of 72–122 my.The K–Ar-determinations on white micas of both generations yielded only Alpidic ages within the range of 71–116 my. Both grainsize as well as position in the large grains (core-rim) influence the age value: Smaller grains and rims of first generation muscovite giving younger ages, than the larger grains as well as cores of the first generation.The Rb–Sr-whole-rock-analyses point to an open system for Rb and Sr during the early Alpidic metamorphism, similar to the paragneisses (Morauf, 1980b). Considering all the data of Kor- and Saualpe (Morauf, 1980 a, b and this paper) it can be shown that 1) pre-Alpidic mineral ages only survived in large pegmatitic muscovites; 2) During the influence of the intensive old-Alpidic metamorphism small pre-Alpidic white micas where not only rejuvenated, but new micas grew and kyanite recrystallized, while the whole rock was partially open for the Rb–Sr-system.According to the data presented in this paper the main deformation of the area has to be of Alpidic age.

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Mit 3 Abbildungen     

Thermal expansion,heat capacity,and entropy of MgO at mantle pressures

The pressure dependence of the Raman spectrum of forsterite was measured over its entire frequency range to over 200 kbar. The shifts of the Raman modes were used to calculate the pressure dependence of the heat capacity, C _v, and entropy, S, by using statistical thermodynamics of the lattice vibrations. Using the pressure dependence of C _v and other previously measured thermodynamic parameters, the thermal expansion coefficient, , at room temperature was calculated from = K _S (T/P) _S C _V/TVK _T, which yields a constant value of ( ln / ln V)_T= 6.1(5) for forsterite to 10% compression. This value is in agreement with ( ln / ln V)_T for a large variety of materials.At 91 kbar, the compression mechanism of the forsterite lattice abruptly changes causing a strong decrease of the pressure derivative of 6 Raman modes accompanied by large reductions in the intensities of all of the modes. This observation is in agreement with single crystal x-ray diffraction studies to 150 kbar and is interpreted as a second order phase transition.     

Thermodynamic data from redox reactions at high temperatures. V. Thermodynamic properties of NiO−MnO solid solutions from emf measurements

Divariant oxide plus metal assemblages potentially make useful redox sensors for use in hydrothermal and other high pressure experiments. Here we report the calibration of the (Ni, Mn)O/Ni redox sensor in which the Ni/NiO (NNO) oxygen buffer is displaced to lower oxygen chemical potentials (O₂), by the solid solution of MnO in the oxide phase. This assemblage was chosen because: (1) it covers a useful range of O₂; (2) the system can be calibrated very accurately. Values of O₂ defined by the (Ni, Mn)O/Ni assemblage were determined electrochemically, from 900 to 1300 K, using calcia-stabilized zirconia solid electrolytes. The oxide compositions (8 in total, ranging from 0.1X _NiO0.8) were analysed afterwards by electron microprobe, and were checked for internal consistency by measuring the lattice parameters (a₀), using powder XRD. The accuracies of the measurements, both assessed theoretically and established empirically, are (1): ±80J/mol in O₂, ±0.0002 Å in a₀ and ±0.002 to 0.005 in X _NiO. Activity-composition relations were fitted to the Redlich-Kister formalism. There is a slight asymmetry (corresponding to a subregular model) across the solution with A ₀ ^G =9577(±45) J/mol, and A ₁ ^G =–477(±80) J/mol. The experimental data were also used to derive the parameters V^ex, H^ex and S^ex. There is no obvious relationship between excess volumes and enthalpies of mixing, nor between excess volumes and excess entropies. The experimental data from this study have been used to formulate the (Ni, Mn)O/Ni redox sensor expression: O₂ = ₂(NNO) + 2RTlnX _NiO + 2(1 – X _NiO)²[11483 – 1.697T] – 477(4X _NiO – 1)(900 < T(K) < 1300) where O₂(NNO)=–478967+248.514T–9.7961 T In T, from O'Neill and Pownceby(1993a).     

The Urumieh Plutonic Complex (NW Iran): Record of the geodynamic evolution of the Sanandaj–Sirjan zone during Cretaceous times – Part II: Magnetic fabrics and plate tectonic reconstruction

The Urumieh complex, to the north of the Sanandaj–Sirjan zone (NW Iran), belongs to a plutonic arc that took place above the northeastward dipping subduction of Arabia under Iran during Late Cretaceous times. Seven granitoid bodies occupying an area of 300 km² can be sorted into three suites. According to the isotope chronology study of Ghalamghash et al. [Ghalamghash, J., Nédélec, A., Bellon, H., Vousoughi-Abedini, M., Bouchez, J.L., in press. The Urumieh Plutonic Complex: a magmatic record of the geodynamic evolution of the Sanandaj–Sirjan zone (NW Iran) during Cretaceous times – Part II: petrogenesis and 40K/40Ar dating. Journal of Asian Earth Sciences], the two first suites were emplaced during the same event at 100 Ma, and the third one was emplaced 20 Ma later: (1) the diorites form the largest bodies and comprise the Ghamishlu and Dourbeh stocks; (2) the biotite-granites are composed by the Sehkani, Nari and Doustak bodies, and (3) the younger bodies are represented by the Bardkish syenite and the Dourbeh granite. These bodies were subjected to systematic microstructural observations, and magnetic fabric measurements that yield information about their emplacement kinematics. The magnetic lineations of the diorites and biotite-granites (the early suites) call for a dominant NW-trending stretching during their intrusion, attributed to the transpressive deformation of the overriding Sanandaj–Sirjan microplate during the north-to northeastward motion of the subducting western branch of the Neo-Tethys. Oblique plate motion with 20% of strain partitioning along a NNW-trending plate boundary accounts for the observed magmatic structures. Intrusion of the younger bodies took place after consumption of this western oceanic domain at about 80 Ma. The NW-trending lineations of the syenite suggest that the transpressive regime was continuing, while the steep lineations and the peculiar microstructures of the Dourbeh granite call for a forceful intrusion. Our study suggests that the motion of Arabia with respect to Central Iran was more northerly directed than estimated before, for the 100–80 Ma time interval during which plate tectonic markers are not available.     

Mössbauer study of a California desert celadonite and its pedogenically-related smectite

Celadonite from the northwestern Mojave Desert area of California was examined by detailed Mössbauer spectroscopy at temperatures from 10 K to 400 K. In addition to the predominant Fe³⁺ doublet with isomer shift 0.4 mm s^–1 and quadrupole splitting 0.4 mm s^–1, another Fe³⁺ doublet with 0.4, 1.2 mm/s and two Fe²⁺ doublets with 1.1, 1.7, 2.7 mm s^–1 at 300 K were distinguished. The minor Fe³⁺ component is ascribed to dehydroxylated surface sites. Most of the remaining Fe(90%) is M2 cis-OH octahedral in an ordered M⁺–M²⁺ array. However, about 10% is M1 trans-OH Fe²⁺. Isomer shift vs. T gives Debye temperatures of 570 K for Fe³⁺ in M2 and 380 K for both Fe²⁺ sites, indicating greater vibrational freedom for Fe²⁺. Quadrupole splitting vs. T for Fe²⁺ gives a valence electronic energy splitting of 760 cm^–1 between the ground and first excited state for M2. The M1 sites have a more drastic variation in vs. T which indicates not only a lower first excited state but a rhombic distortion at these sites. A proposed explanation is a neighboring M2 site vacancy. The soil clay formed from this celadonite, which is mostly Fe-rich smectite, was also studied by Mössbauer spectroscopy. About half the Fe²⁺ has been oxidized in the clay, but the isomer shifts and quadrupole splittings are essentially the same as in the original celadonite. A texture orientation in the clay absorber was detected by measuring the absorber at 55° to the source radiation. This texture effect produces asymmetric doublets in the usual 90° measurement.     

Reversible Markov grain sequences in granite

A key feature of an ideal granite is the occurrence of grain sequences which are reversible Markov chains. This property was tested using a ² test on a 2 × 6 contingency table consisting of reversible grain pairs for microcline, plagioclase, quartz, and biotite, and on a 2 × 12 contingency table consisting of reversible grain triads. All 28 samples examined from the Pacolet Mills pluton, South Carolina, passed the ² test for grain pairs, and all but three of these passed the ² test for grain triads. The coefficients of the reversibility matrix were examined for statistical significance after normalization, using a logarithmic transformation. For all three phases of the Pacolet Mills pluton, the average coefficients were in the range 1.08–0.89. Elevated and depressed values of these coefficients suggested possible differences among the three phases of the granite in their crystallization paths.     

β(Mg0.9, Fe0.1)2SiO4: Single crystal structure,cation distribution,and properties of coordination polyhedra

The synthesis boundaries of the phase transformation; ++ in (Mg_0.9, Fe_0.1)SiO₄, have been clarified at temperatures to 2000° C and pressures up to 20 GPa in order to synthesize single crystals of high quality. A single crystal of (Mg_0.9, Fe_0.1)₂SiO₄ was grown successfully to a size of 500 m. The crystal structure has been refined from single-crystal X-ray intensities. The ferrous ions prefer M1 and M3 sites to over the larger M2 site. The volume change of all the occupied polyhedra does not contribute to the decrease of total volume in the transformation; rather it tends to increase the bulk volume through the expansion of occupied tetrahedra. The volume reduction in the phase transformations is accounted for by unoccupied polyhedra, with the octahedra contributory 60% and the tetrahedra 40% to the V of the transition. The volume change in the transformation is caused also partly by the volume decrease of MO ₆ (25%), partly the unoccupied tetrahedra (45%) and octahedra (30%).     

Shock-induced transformations in the system NaAlSiO4—SiO2: a new interpretation

New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, Jadeite, and nepheline in the system NaAlSiO₄-SiO₂, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60–80 GPa. The third order Birch-Murnaghan equation of state parameters are: K_os=275±38 GPa and K_os=1.6±1.5 for the calcium ferrite type NaAlSiO₄, K_os=186±33 GPA and K_os=2.6±1.7 for the albite-rich hollandite, K_os=236±45 GPa and K_os=2.3±2.0 for the orthoclase-rich hollandite, and K_os=190 to 210 GPa and K_os2.2 for the anorthite-rich hollandite.     

An obliquity-controlled Early Pleistocene river terrace record from Western Turkey?

Investigation of the Pleistocene sequence of the Gediz River, Western Turkey, has revealed a record of Early Pleistocene river terraces. Eleven terraces spanning the interval from 1.67 to 1.245 million years ago (MIS 59–37) are preserved beneath basaltic lava flows. The high number of terraces over this short time period reflects high-frequency sedimentation/incision cycles preserved due to the fortuitous combination of relatively high uplift rates (0.16 mm yr⁻¹) and progressive southwards valley migration. Comparison of this record with ODP967 from the Eastern Mediterranean Basin suggests a link between the production of terraces and obliquity-driven 41,000 year climate cycles in the Early Pleistocene.     

Partition of Ni between olivine and sulfide: equilibria with sulfide-oxide liquids

The partition of Ni between olivine and monosulfide-oxide liquid has been investigated at 1300–1395° C, =10^–8-9–10^–6.8, and =10^–2.0–10^–0.9, over the composition range 20–79 mol. % NiS. The product olivine compositions varied from Fo98 to Fo59 and from 0.06 to 3.11 wt% NiO. The metal/sulfur ratio of the sulfide-oxide liquid increases with increase in , decrease in , and increase in NiS content. The Ni/Fe exchange reaction has been perfectly reversed using natural olivine and pure forsterite as starting materials. The FeO and NiO contents of olivine from runs equilibrated at the same and form isobaric distributions with NiS content, which, to a first approximation, are dependent at constant temperature and total pressure on a variable term, –0.5 log ( / ). The Ni/Fe distribution coefficient (K _D3) exhibits only a weak decrease from 35 to 29 with increase in from the IW buffer to close to the FMQ buffer. At values higher than FMQ, the sulfide-oxide liquid has the approximate composition (Ni,Fe)₃±_xS₂K _D358. The present K _D3 vs O/(S+O) data define a trend which extrapolates to K _D320 at 10 wt% oxygen in the sulfide-oxide liquid. The compositions of olivine and Ni-Cu sulfides associated with early-magmatic basic rocks and komatiites are consistent, at 1400° C, with a value of -log ( / ) of about 7.7, which is equivalent to 0.0 wt% oxygen in the hypothesized immiscible sulfide-oxide liquid. Therefore, K _D3 would not be reduced significantly from the 30 to 35 range for sulfide-oxide liquids with low oxygen contents.