MR11A-0884 0800h
Generation of Methane Via High Pressure Carbonate Reduction
We have designed and conducted experiments to make in situ observations of hydrocarbon formation at conditions relevant to Earth's upper mantle. Specifically, we have used both laser and resistively heated diamond anvil cells to examine an assemblage initially consisting of FeO, CaCO$_{3}$ and H$_{2}$O. We have spanned pressures from 2 to 11 GPa and temperatures from 200 to 1500$^o$C. Synchrotron x-ray diffraction was used to identify solid phases and Raman spectroscopy was used to detect hydrocarbon species. At high pressures and temperatures FeO oxidizes to form Fe$_{3}$O$_{4}$-magnetite. We have found the conditions most productive for methane formation are at pressures less than 5 GPa and temperatures near 500$^o$C, but that methane forms at all conditions of this study. Furthermore, the results are shown to be consistent with multi-phase thermodynamic calculations based on the statistical mechanics of soft particle mixtures. The assemblage FeO-CaCO$_{3}$-H$_{2}$O was studied by previous workers at 5 GPa and 1,500 $^o$C using an apparatus by which run products were analyzed after pressure and temperature quench. Contrary to the previous work, our in situ observations do not indicate the presence of heavier hydrocarbons. However, the observation of methane formation at mantle conditions is significant because it demonstrates the existence of abiogenic pathways for the formation of hydrocarbons in the Earth's interior and suggests that the hydrocarbon budget of the bulk Earth may be larger than conventionally assumed. It is conceivable that heavier hydrocarbons may yet be produced by high pressure carbonate reduction.
MR11A-0885 0800h
Crystal structure of norbergite under high-pressures up to 8.2 GPa
High-pressure single crystal X-ray diffraction study of norbergite, Mg$_{3}$SiO$_{4}$(OH,F)$_{2}$, was performed up to 8.2 GPa with a diamond anvil cell using synchrotron radiation. The sample of single crystal was from the Sterling Hill Mine, New Jersey, U.S.A.. The chemical formula of this sample was Mg$_{2.984(10)}$Fe$_{0.014(2)}$Ti$_{0.011(1)}$Si$_{0.988(5)}(OH$_{0.31(5)}$F$_{1.69(5)}$) from the average of 11 data points measured by EPMA (JEOL, JXA-8800M). The hydrogen contents were calculated based on OH+F=2. The X-ray diffraction intensity data were measured using synchrotron radiation by an automated four-circle X-ray diffractometer installed at the BL-10A beam line, Photon Factory, High-Energy Accelerator Research Organization, Tsukuba, Japan. The wavelength of synchrotron radiation was calibrated by the unit cell constant of a ruby standard crystal. The lattice parameters of this sample were measured at ambient, 0.5, 3.1, 4.2, 4.7, 5.4, 6.3, 7.6 and 8.2 GPa. No discontinuity of the lattice parameters was observed in this pressure range. From the data of these lattice parameters, the axial liner compressibilities of this sample was calculated as {\it $\beta$$_{a}$}=2.18(4)${\times}$10$^{-3}$, {\it $\beta$$_{b}$}=2.93(7)${\times}$10$^{-3}$ and {\it $\beta$$_{c}$}=2.77(6)${\times}$10$^{-3}$ (GPa$^{-1}$). The unit cell was based on {\it Pbnm} setting. The isothermal bulk modulus of the norbergite, calculated from the Birch-Murnaghun equation of state, was {\it K$_{T}$}=113(2) GPa assuming {\it K'}=4. The structural parameters were refined at ambient, 4.7, 6.3 and 8.2 GPa conditions. {\it R} and {\it R$_{w}$} values of these refinements were 2.2${%}$ and 4.8${%}$ for 0.0001 GPa, 4.6${%}$ and 6.7${%}$ for 4.7 GPa, 5.3${%}$ and 7.0${%}$ for 6.3 GPa, 5.3${%}$ and 7.1${%}$ for 8.2 GPa, respectively. In the norbergite structure, there are three types of (OH,F)-(OH,F) distances, which related hydrogen bonding. Unshared (OH,F)-(OH,F) distances were decreased 2.9${%}$ and 1.8${%}$ up to 8.2 GPa, respectively. Shared (OH,F)-(OH,F) distance was decreased 0.8${%}$ in the pressure range investigated. The volume of polyhedral site at 8.2 GPa were 94.0${%}$ for M1 site, 93.5${%}$ for M2 site and 97.4${%}$ for T site, compared to those at ambient conditions.
MR11A-0886 0800h
Investigation on cell assemblies for mantle rheology
Several types of cell assemblies are being tested on large volume press apparatus at Sam85, NSLS to determine their suitability for high pressure rheology experiments, with present focus on the influence of different cells on water fugacity and the thermal efficiency. SanCarlos olivine, both lab dry and super dry, is being used as the testing material. Three types of pressure media including mullite, MgO and boron:epoxy (BE) are used for both DIA and T-cup apparatus in the test. For lab dry sample assemblies, 2ͦ3 hours heating at 130C in the vacuum environment is applied before experiment in order to drive off the absorptive water. Different pressure media in each apparatus are carried out at the same P-T path. After experiments the recovered samples are examined on the synchrotron infrared (IR) spectrometer at U2A beamline of NSLS to evaluate the water concentration. IR results suggest that mullite cell offers an acceptable dry environment for the rheology study. Among the tested cell assemblies, mullite cell has a comparable thermal efficiency as BE cell does. Both of them show much higher heating efficiency than MgO cell does. This preliminary study suggests that mullite has great potential as the pressure medium for the high pressure and high temperature experiment.
MR11A-0887 0800h
High-pressure, high-temperature Raman spectroscopic study of ilmenite-type MgSiO$_{3}$, MgGeO$_{3}$ and MgTiO$_{3}$
Ilmenite-type MgSiO$_{3}$ is a high-pressure polymorph of enstatite, and characterized by a relatively narrow stability field in the 20-24 GPa and 1370-2270 K range. Since MgSiO$_{3}$-ilmenite is stable at thermodynamically low temperature, it is considered to be a candidate component in 600-700 km of subducting slabs. It is important for earth science to understand its crystal structure on the basis of lattice vibrations at high pressure and temperature. High-pressure and high-temperature Raman spectra of ilmenite-type MgSiO$_{3}$ have already been collected up to 7 GPa and 1030 K, respectively (Reynard and Rubie, 1996). In this study, we conducted a high-pressure, high-temperature Raman spectroscopic study of ilmenite-type MgSiO$_{3}$, MgGeO$_{3}$ and MgTiO$_{3}$. From the viewpoint of elasticity and bonding energy, we investigate the behavior of ilmenite at high-pressure and high-temperature and compare structures of ilmenites that have different compositions. Raman spectroscopy was a NRS2100 triple microspectrometer equipped with Ar ion laser (operating at 514.5 nm and 70-80 mW). High-temperature experiments were performed using a Pt-electric resistant heater. Temperature was monitored with chromel-almel thermocouples. For the high-pressure experiments, a diamond-anvil cell (DAC) was used. H$_{2}$O was preferred to an alcohol mixture as the pressure media because it has no strong Raman bands in the measured region. Pressures were determined from the shift of the ruby fluorescence R$_{1}$ line, excited by the Ar ion laser. Raman spectra of each sample were collected up to 770 K at ambient pressure and 30 GPa at room temperature, respectively. For ilmenite, 10 bands were expected from symmetry analysis (five A$_{g}$ and five E$_{g}$). At ambient conditions, we could observe seven (for MgSiO$_{3}$), eight (for MgGeO$_{3}$) and nine (for MgTiO$_{3}$) Raman bands, respectively. With increasing temperature, each band shifted to lower wavenumber. The temperature dependence of the force constant, k, was the order of MgGeO$_{3}$, MgSiO$_{3}$ and MgTiO$_{3}$. The tendency induces the relative expansion rate for each XO$_{6}$ (X=Si,Ge,Ti) octahedron. This is consistent with the fact that MgTiO$_{3}$ ilmenite is the only stable phase up to 770 K at ambient pressure in this study. With increasing pressure at room temperature, each Raman band shifted to higher wavenumber. We also discuss the pressure dependence of the force constant, k.
MR11A-0888 0800h
A New Laser Heating and Temperature Measurement System
The laser-heated diamond anvil cell enables measurements of material properties in situ at high pressures and temperatures. An ideal measurement consists of a sample subjected to uniform pressure throughout the sample chamber. However, due to the small size of the samples and the high thermal conductivity of the diamond anvils temperature gradients are always present. Therefore, the gradient must be measured to be able to interpret results from the laser heated diamond cell, and to evaluate methods employed to reduce temperature gradients. In order to characterize these gradients, we have designed and installed a new laser heating and temperature measurement system at UCLA. This system specializes in a precise, quantitative measurement of the radial temperature gradient. Our design is anchored by a 20 Watt diode-pumped Nd:YLF laser for heating and measures temperature by collecting spectral intensity information from the hotspot. The temperature and the associated gradient are measured simultaneously using two cameras: 1) a high speed CCD camera coupled with a 150 mm imaging spectroradiometer that measures temperature, 2) a high dynamic range CCD camera that measures two-dimensional intensity distribution, at a variety of chosen spectral ranges. Information from both cameras is combined to provide the two-dimensional temperature distribution of the hotspot. The spectral intensity of a Gaussian-shaped hotspot has a maximum in the center part of the hotspot, and the sample temperature and therefore spectral intensity decreases radially from the center as proscribed by the thermal properties of the experiment and Planck's law. The intensity is a much more sensitive indication of temperature change. For example, in the case of a hotspot with a 2000K peak temperature, a 15% decrease in intensity at a given wavelength (e.g. 500 nm) corresponds to a temperature drop of 20 K, a 1% decrease, well below most estimates of precision in temperature measurement of laser heated spots. Therefore, relative spectral intensity provides a more reliable estimate of two-dimensional temperature gradients in high P, T experiments. In addition, this method bypasses most additional errors induced by chromatic aberration (a wavelength dependent focusing effect) of the objective lens. As a test of the ability of this system to measure temperature gradients, we have measured the thermal diffusivity anisotropy of highly oriented graphite. A graphite sample oriented perpendicular to the basal plane will create an elliptical hotspot from a radially symmetric laser power input due to faster heat transport along the basal plane (D~1.10x10-3 m2/sec) compared with the c direction (D~ 4.6x10-6 m2/sec). Therefore, the ellipticity of the hotspot is a direct measure of the systems ability to measure thermal diffusivity. Side by side comparison of the high dynamic range camera and the imaging spectroradiometer shows that the high dynamic range attains better measurements of the temperature gradients of a graphite hotspot. For example, at 75% of the peak temperature, the high dynamic range camera measured an ellipticity of 2.8, while the imaging spectroradiometer was smeared out to 2.2. We will present preliminary results from the laser-heating system including calibration information new data on the high P,T behavior of a metals, silicates, oxides, and ices.
MR11A-0889 0800h
Laser Heated Diamond Anvil Cell at the Advanced Light Source
We have designed and installed a laser heating system for the diamond anvil cell at endstation 2 of beamline 12.2.2 of the Advanced Light Source in Berkeley, CA. The system incorporates an 80 watt Nd:YLF (cw) laser operated in TEM01 mode. The laser beam is split into 2 paths that are directed through the opposing diamond anvils and heat the sample from both sides. Graphite mirrors steer the laser beams coaxial with the x-ray beam from the superbend magnet (energy range 12-30 KeV) with very little x-ray absorption, and direct the emitted light from the heated sample into two separate spectrometers for temperature measurement by spectroradiometry. A feedback system using a photoreciever and variable waveplate attenuator with a response time of about 10 ms is used to control the amount of laser light entering the sample chamber in order to precisely control heating. Technical details of the experimental setup will be presented along with initial results.
MR11A-0890 0800h
Crystal Chemistry of Transition Metal Arsenides and the High Pressure Behavior of CoAs
Transition metal arsenide compounds provide a number of intriguing structural and bonding problems, and provide challenges in the description of their crystal chemistry that are quite different from those of traditional oxide and silicate minerals. The most striking of these is perhaps the the range of crystal structures adopted by monoarsenides of composition MAs as the metal is varied across the first transition series. NiAs and CoAs/FeAs, for example, exhibit different crystal structures despite the fact that the ionic radii of the metals are essentially identical, but differ by one and two electrons at the metal for Co and Fe, respectively. These compounds may be profitably understood as alloy compounds with a nominal oxidation state of 2+ at the metal, in contrast to the traditionally assigned 3+, with a Jahn-Teller distortion driving the distortion in CoAs/FeAs from the ideal NiAs arrangement. At approximately 6-8 GPa, single crystals of CoAs (modderite) undergo a transformation to a lower-symmetry phase which at this point is not determined as a result of the twinning that takes place at the onset of the transition. Using a combination of first-principles computational methods and semi-empirical molecular orbital techniques in concert with high pressure diffraction data, we describe the evolution of the electronic structure of CoAs with pressure and discuss possible structural alternatives for the high pressure phase and the phase transformation mechanism. This study illustrates the surprising power of electronic effects in controlling crystal structure preference and shows the utility of employing a range of computational methods as a useful complement to diffraction experiments and a valuable aid in understanding the structural and bonding properties of high pressure mineral phases.
MR11A-0891 0800h
Volume of {\it C}2/{\it c} Pyroxenes at Mantle P, T, and {\it x}
The variations in unit cell volumes of mantle minerals as functions of P and T are important parameters in the description of the interior of the Earth and the behavior of materials. Recently, Thompson and Downs (2004) presented a model for the crystal structures of pyroxenes parameterized in terms of the O3-O3-O3 angle and the oxygen radius. This model has proven useful in the analysis of compression and expansion mechanisms in pyroxenes, providing an understanding of the O3-O3-O3 angle and the oxygen radius as functions of P and T. However, it did not provide a basis for analyzing changes in some properties that are highly dependent on composition. In this paper, we show that ambient cell volumes of the {\it C}2/{\it c} pyroxenes are strongly correlated with M1 cation radius. This relationship can be exploited to estimate ambient condition cell volumes. From this starting point, pyroxene cell volume variation with P and T can be modeled as a function of O3-O3-O3 angle (itself a function of P and T), and the oxygen radius, r(P,T). This relationship is investigated for diopside, hedenbergite, acmite, jadeite, and kosmochlor. The model reproduces observed cell volumes of these phases recorded at P to within 0.09% and at T to within 0.10%, at simultaneous P and T for jadeite to within 0.57%, and at simultaneous P and T for diopside to within 1.20%. K$_{o}$ and K' from third order Birch-Murnaghan fits to the observed volume versus pressure relationships and the volume versus pressure relationships calculated from the Thompson-Downs model are the same within error. The fit of the Thompson-Downs EOS to the observed data is compared to the fit of the third order Birch-Murnaghan. The model is used to estimate volume as a function of P and T for diopside, hedenbergite, acmite, jadeite, and kosmochlor. Thompson, R.M., and Downs, R.T. (2004) Model pyroxenes II: Structural variation as a function of tetrahedral rotation. American Mineralogist 89, 614-628.
MR11A-0892 0800h
The Compression of Perovskites
While silicate perovskite is the dominant phase in the Earth's mantle, very little is known about its detailed structural state and most inferences are based upon the assumption that the silicate octahedra are incompressible. Recent advances in laboratory based single-crystal techniques for measuring the intensities of diffraction from crystals held at high pressures in the diamond-anvil cell have been used to determine the role of polyhedral compression in the response of the ABO3 perovskite structure to high pressures. All perovskites studied exhibit compression of the BO6 octahedra. We have been able to show that when the BO6 octahedra are less compressible than the AO12 sites the octahedra become more tilted with increasing pressure [1]. When the BO6 octahedra are more compressible than the AO12 sites the structure becomes less tilted and evolves towards a higher-symmetry configuration [2]. We have developed a new model, based on the bond valence concept, that successfully predicts the relative compressibilities of the cation sites in most oxide perovskites [3] and hence their response to pressure. The possibilities for extending these measurements to higher pressures will be reviewed. [1] Zhao, J., Ross, N. L. & Angel, R. J. (2004). Phys Chem Miner. 31, 299-305. [2] Ross, N. L., Zhao, J. & Angel, R. J. (2004). J. Solid State Chemistry 177,1276-1284. [3] Zhao, J., Ross, N. L. & Angel, R. J. (2004). Acta Cryst. B60, 263-271.
MR11A-0893 0800h
Unified analytic model of the Gr\"{u}neisen parameter, melting temperature, and shear modulus
A unified analytic model of the Gr\"{u}neisen parameter, melting temperature, and shear modulus is presented. It is based on three essential components. First is a relation between the melting temperature and the shear modulus at melt obtained from the dislocation-mediated melting model, second is a relation between the Gr\"{u}neisen gamma and the density derivative of the zero-temperature shear modulus, and third is a linear approximation for the temperature dependence of the shear modulus at a given density. We model the density dependence of the Gr\"{u}neisen parameter as $\gamma(\rho)=1/2+\gamma_1/\rho^{1/3}+\gamma_2/\rho^{q}$, where $\gamma_1$, $\gamma_2$, and $q>1$ are constants. This form accurately represents the experimentally determined low-pressure behavior of gamma, and its high-compression limit follows from a generalization of the Slater, Dugdale-MacDonald, and Vashchenko-Zubarev forms. We calculate melting curves for a number of substances of geophysical and general interest and compare them to available experimental melt data.
MR11A-0894 0800h
The Threshold Dependencies of Thermal Conductivity and Implications on Mantle Dynamics
New experimental measurements of thermal diffusivity using a laser-flash apparatus show that the lattice component of thermal conductivity for minerals becomes independent of temperature within experimental uncertainty above roughly 1200 to 1900 K. This behavior is seen in MgO, Al$_{2}$O$_{3}$, several olivines, diopside, albite, microcline, SrTiO$_{3}$ perovskite, rutile, garnet, quartz, various ceramics, rhyolite, and basalt. Recent revision of the formulation for an effective thermal conductivity due to radiative transfer shows that a different type of threshold dependence on the grain-size with greater complexity in the temperature dependence for large grains, and a dependence on Fe content. Similar behavior is seen for krad calculated from visible spectra of olivine and of (MgFe)SiO$_{3}$ perovskite, which shows that the particulars of the absorption spectra are unimportant. The combination of these threshold effects in thermal conductivity have ramifications on the style of mantle convection, since radiative transfer acts to stabilize the flow, whereas the lattice contribution tends to destabilize the boundary layer. However, radiative transfer can make convection chaotic and time-dependent as the sign of dk$_{rad}$/dT is sometimes negative, e.g., for large, Fe-rich grains. The specific domains in thermal conductivity suggest sluggish lower mantle flow, but a strongly time-dependent pattern for the upper mantle-transition zone. That radiative transfer decreases as Fe/(Fe+Mg) increases beyond 0.1 suggests that thermo-chemical plumes can form at the base of the lower mantle through a positive feedback involving chemical enrichment, thermal conductivity, and viscosity. This mechanism would be particularly effective in stagnant points of the upwelling. The above cross-scaling connection of microscopic processes in solids with macroscopic transport mechanisms in the mantle plays an important role in differentiation of the Earth.
MR11A-0895 0800h
The Relationship Between Thermal Diffusivity and Symmetry of Carbonates
Carbonates are among the most abundant rock forming minerals of the Earth's crust. Nevertheless, only little is understood about the thermal transport processes of carbonates. We'll present a comprehensive study on new thermal transport property data of carbonates, both, as a function of temperature (up to 600 $ \deg C$) and orientation. These data are a prerequisite to model the temperature distribution of the crust, in regions where carbonates are present. On the other hand, carbonates are an ideal group of minerals to study the influence of crystal symmetry, sound velocity, and atomic mass of cations on thermal transport properties, as isotyp carbonates exist with different -- light and heavy -- cations and various sound velocities (Maj, 1974). Furthermore, two carbonate polymorphs -- trigonal and orthorhombic -- are available to study the influence of symmetry on thermal transport properties. The higher symmetry of trigonal calcite like structures lead to a higher thermal diffusivity. It will be shown that increasing mass of cations decreases thermal diffusivity {--} from light Mg$^2$\textsuperscript{+} Magnesite [100] (6.22 mm$^2$/s at 25 $ \deg C$) to the heavy Pb$^2$\textsuperscript{+} Cerussite [100] (0.85 mm$^2$/s at 25 $ \deg C$). As expected from Debye's theory, thermal diffusivity decreases with increasing temperature. The anisotropy of thermal diffusivity reaches more than 80 % (Magnesite with 86 %) and decreases with increasing temperature. The results show that for carbonates mean free path length of phonons depends on sound velocity (H\"{o}fer & Schilling, 2002). Maj, S., 1974. A note on the relationship among phonon conductivity, density, and mean atomic weight for carbonate minerals. Acta Geophysica Polonica, 22 (3): 247- 250. H\"{o}fer, M. & Schilling, F. R., 2002. Heat transfer in quartz, orthoclase, and sanidine at elevated temperature. Phys. Chem. Min., 29: 571- 584.
MR11A-0896 0800h
Density Measurement of Iron-Bearing Sodium Disilicate by High-Pressure X-ray Absorption Method
Density is one of the important physical properties of silicate melts to understand the magmatic process in the Earth inteiror. Recently, we have applied x-ray absorption technique to measure density of silicate glasses and melts at high-pressure, using highly brilliant synchrotron x-ray and a multi-anvil apparatus. Very low absorption of silciates for x-ray reduces absorption contrast between silicate samples and surrounding materials to make density measurement difficult. We have overcome this difficulty by use of a single crystal diamond ring as a sample container, which is transparent for x-ray and less reactive with silicate melt. High-pressure and temperature x-ray absorption experiments were conducted using the cubic-type press SMAP-1 at BL22XU of SPring-8, Japan. Starting sample is the Fe-bearing Na disilicate glass with the composition of Na$_{2}$FeSi$_{2}$O$_{6}$. Energy of monochromatic x-ray is tune to be 25 keV and intensities of incident and transmitted x-rays are measured by ion chambers. Density is evaluated from x-ray absorption profile along a radial direction of a cylindrical sample using equation of I = I$_{0}$exp(-\mu\rho t). We reported the results of the density measurements of Na$_{2}$FeSi$_{2}$O$_{6}$ glass up to 5 GPa and 600 K at AGU Fall meeting in 2003. Now we succeed the density measurement of that melt up to 3 GPa and 1400 K. Althogh these pressure and temperature conditions are out of the stability field of diamond, diamond ring survives after several hours heating. Measured density of Na$_{2}$FeSi$_{2}$O$_{6}$ changes discontinuously with phase transitions from glass to crystal and from crystal to melt. Apparent density increase of Na$_{2}$FeSi$_{2}$O$_{6}$ melt with increasing pressure is also observed, indicating that this method has a potential to determine equation of state of silicate melts.
MR11A-0897 0800h
From Technological Materials to Mantle Minerals: Perovskites at High Pressures and Temperatures
Strongly correlated electron states, intermediate between the freely mobile electrons of simple metals and the fully pinned (localized) electrons of insulators, are poorly understood yet define key properties of many oxides, from crystal structure and cation valence to magnetic ordering and electrical conductivity. Pressure can be especially effective in characterizing strongly-correlated systems by tuning the interplay between crystal structure (interatomic distances and coordinations) and electronic degrees of freedom (density of state, mobility, magnetic superexchange). In particular, we show that pressure - counter-intuitively - suppresses the coupling of electronic states to lattice vibrations and structural distortions (Jahn-Teller effect) in an important class of oxides. We have studied orthorhombic perovskite-structured ({\it Pbnm}) LaMnO$_{3}$ at high pressures and temperatures, using a laser-heated diamond anvil cell with synchrotron x-ray diffraction at the Advanced Photon Source HP-CAT beamline. This material is a structural analog of mantle perovskites, and is closely related to compounds exhibiting colossal magnetoresistance (CMR). Alternating long and short Mn-O distances in the ab plane of the LaMnO$_{3}$ crystal structure are due to a cooperative Jahn-Teller (JT) distortion removing the degeneracy of the eg orbitals in the {\it t$^{3}$$_{2g}$e$^{1}$$_{g}$} electron configuration of the Mn$^{3+}$ ions, and stabilizing the {\it 3d(3z$^{2}$-r$^{2}$)} type with respect to the {\it 3d(x$^{2}$-y$^{2}$)} type orbitals. The insulating character of LaMnO$_{3}$ has been attributed to either i) the strong Jahn-Teller electron-phonon coupling localizing the {\it e$_{g}$} electrons as polarons, or ii) electron-electron interactions resulting in a Mott-insulator. The latter is exemplified by Fe$_{2}$O$_{3}$ hematite, which was previously thought to take on the perovskite structure but now is instead known to undergo a Mott transition at high pressure. Compression to 11 GPa at room temperature decreases the degree of crystal-structural distortion of LaMnO$_{3}$, implying a suppression of the Jahn-Teller effect in accord with previous observations [Loa, et al., 2001]. Laser-heating to $\sim$2000 K at 11 GPa causes the appearance of two new diffraction peaks that are not due to the Pbnm structure, and further suppresses Jahn-Teller distortion. Both temperature and pressure thus appear to suppress the electronically-induced crystal-structural distortion (Jahn-Teller effect), and LaMnO$_{3}$ appears to be a Mott insulator like Fe$_{2}$O$_{3}$ at low pressure.
MR11A-0898 0800h
$\it In$ $\it situ$ X-ray diffraction study of post-spinel transformation in peridotite mantle: Implication to 660 km discontinuity
The 660-km seismic discontinuity in the Earth's mantle is identified with the transformation of ringwoodite (spinel (Mg,Fe)$_2$SiO$_4$-phase) to (Mg,Fe)SiO$_3$-perovskite and (Mg,Fe)O-ferropericlase. It was suggested using quench experiments that the transformation boundary has significant negative Clapeyron slope (-3 MPa/K, Ito and Takahashi, 1989) responsible for depressions and elevations of the 660-km discontinuity in subduction zones and hot spots of mantle plumes. Recent $\it in$ $\it situ$ x-ray diffraction studies in Mg$_2$SiO$_4$ system indicate that negative slope of the boundary is much gentler (-1.3 MPa/K) (Fei et al., 2004). Therefore there must be another factors resulting in significant depth variations of the 660-km discontinuity. In this study, we present the phase relations in anhydrous pyrolite by $\it in$ $\it situ$ X-ray diffraction measurements to examine the influence of additional components and Mg/Si-ratio on post-spinel phase transformation. Experiments were carried out using Speed-1500 multianvil apparatus installed at BL04B1 at synchrotron radiation facility `Spring-8' (Hyogo, Japan). Starting materials were synthetic glass representing SiO$_2$-Al$_2$O$_3$-FeO-MgO-CaO-pyrolite. Graphite capsule were used as a sample container. Co-doped MgO was used as the pressure medium and a cylindrical LaCrO$_3$ heater was used as the heating element. Temperature was measured with a WRe thermocouple. Different equation of states for Au and MgO was used for pressure calibration. The phase relations were determined at 20-25 GPa and temperature up to 2300 K. We observed easy nucleation of Mg-perovskite and ferropericlase from ringwoodite-bearing assembly in the temperature range of 1600-2200 K. The obtained post-spinel phase boundary can be expressed as P (GPa) = - 0.0004 T (K) + 22.26 using pressures calibrated by Au scale (Anderson et al., 1989). The choice of pressure scale does not have significant influence on the slope of phase transformation. Our experiments demonstrated that variations of chemical composition of pyrolite relative to Mg$_2$SiO$_4$ do not affect on post-spinel phase transformation. Therefore, we should carefully account some other factors, like effect of water on phase transformation or experimental problems like effect of pressure on emf of thermocouples.
MR11A-0899 0800h
Simultaneous Measurements of Sound Velocities and Density: Brillouin Scattering and Synchrotron X-Ray Measurements at GSECARS, Advanced Photon Source
Simultaneous measurements of density (by x-ray diffraction) and sound velocities (by Brillouin scattering) would allow the determination of an absolute pressure scale. The equation of state and velocities as a function of pressure could be determined without resort to a secondary pressure standard. The accurate determination of pressure is one of the outstanding technical challenges in experimental mineral physics today. As a mean of performing such measurements, a Brillouin spectrometer is being installed at the GSECARS Sector 13 of the Advanced Photon Source (APS). Brillouin scattering would allow velocity measurements to be made on transparent samples at high pressures and/or high temperatures while xray diffraction on the samples will yield the density. We describe here the design of the system and progress toward a commissioning of this unique facility. Important design characteristics for the system are: 1) that it be user-friendly. It should be possible for the general user to operate the system without being an expert. 2) Doing a Brillouin experiment on the beam line should require a minimum of set-up time. In order to achieve these characteristics, we have adopted a novel optical design that allows the Brillouin optics into place easily and should not require frequent alignment of the sensitive spectrometer optics. In addition, all adjustments of the optics that are normally performed during a Brillouin experiment can be performed from outside the hutch. We describe in this presentation the detailed design characteristics of this facility.
MR11A-0900 0800h
Path Integral Simulations of Hydrogen Melting at High Pressures
The melting line of hydrogen at high pressure and low temperature is studied using computer simulations. Using path integral Monte Carlo, we focus on the regime where the protons form a Wigner crystal. The Lindemann ratios, structure factors, and pair correlation functions are used to characterize melting due to increases in both pressure and temperature. The effects of electron screening on the stability of the crystal are investigated by comparing results from Coulomb and Yukawa simulations.
MR11A-0901 0800h
Elastic Properties of Zinc Ferrite and Aluminate Spinels
Spinels are important ternary oxides of Earth's crust and upper mantle, and silicate spinel (ringwoodite) is the stable high-pressure phase of Mg$_{2}$SiO$_{4}$ in Earth's lower transition zone. The zinc ferrite spinel, franklinite (ZnFe$_{2}$O$_{4}$ ) exhibits ferrimagnetism at room pressure. Here we report the effects of iron-aluminium substitution on the single-crystal elastic properties of the zinc ferrite spinel (franklinite) and zinc aluminate spinel, gahnite (ZnAL$_{2}$O$_{4}$)using gigahertz ultrasonic interferometry. We studied natural franklinite from New Jersey and gahnite from North Carolina with measured cell parameters of 8.4456(6) and 8.0985(2), respectively. The adiabatic bulk modulus K$_{S0}$ (Voigt-Reuss-Hill average) of these two spinels is 179(6) GPa for franklinite and 209(5) GPa for gahnite. The shear modulus of the zinc spinels increases dramatically upon substitution of Al for Fe, with G = 65(3) GPa for franklinite and G = 102(3) GPa gahnite. The elastic moduli of franklinite are comparable to those of the magnetite, which we measured to be K$_{S0}$ = 186(3) GPa and G = 60(3) GPa. In an earlier study, we reported the negative pressure dependence of C$_{44}$ and G for magnetite. High-pressure shear-wave measurements are currently underway with franklinite and gahnite in order to determine whether or not pressure-induced shear-mode softening is common also to the zinc spinels.
MR11A-0902 0800h
Hyper-Raman spectroscopy of Earth related materials
Raman and infrared spectroscopy proved extremely successful in obtaining structural information and thermodynamic data on samples under high pressure conditions in a diamond anvil cell [1,2]. With substantial advances in CCD detector technology and the possibility to focus visible laser light down to several microns, Raman spectroscopy can nowadays be regarded one of the standard techniques for diamond anvil cell investigations. Nevertheless, Raman scattering suffers from often strong fluorescence and the strong Raman signal of the diamonds. Infrared spectroscopy is limited by the sample size and the diffraction limit of mid- or far-infrared radiation. With increasing pressure, diamonds also show strong infrared activity, which can interfere with the signal from the sample. Detectors in the mid- and far-infrared are inherently noisy, often leading to low signal-to-noise ratios for infrared measurements. With new techniques and instrumentation available, such as low noise CCD cameras and stable diode-pumped solid state laser systems, more demanding techniques become feasible as well. Especially hyper-Raman scattering, a nonlinear optical variant of infrared spectroscopy, can be used on a more routine basis for the first time. Pioneering work in the 70s and 80s have explored some of the capabilities of Hyper-Raman spectroscopy [3]. Unlike infrared spectroscopy, Hyper-Raman is not limited by the diffraction limit of mid- or far-infrared radiation, typically restricting the lower frequency limit to several hundred wave numbers. The major advantages of hyper-Raman are essentially background free spectra and the use of wavelengths in the near-infrared and visible, making possible micro focusing and taking advantage of high efficiencies, low noise, and smooth wavelength dependencies of CCD detectors. Hyper-Raman does not suffer from saturation caused by strong absorption in the infrared and is therefore less sensitive to surface effects. For centrosymmetric materials conventional Raman and hyper-Raman are complimentary. In many cases the combined information of both techniques can reveal all the vibrational information of a material. This information can be used to calculate thermodynamic properties, to identify mineral phases ('finger-printing'), or to investigate the dynamics related to phase transitions ('soft-modes'). First results on planetary materials will be presented, including MgO and stichovite. Corundum as another possible high pressure transmitting material is characterized as well. Further measurements are underway, including MgSiO$_3$ and CaSiO$_3$ perovskite. [1] A. M. Hofmeister, in: Infrared Spectroscopy in Geochemistry, Exploration Geochemistry, and Remote Sensing, Vol. 33 (ed. P. K. King, M. S. Ramsey, and G. A. Swayze), Mineralogical Society of Canada (2004) [2] P. F. McMillan, R. J. Hemley, and P. Gillet, in : Mineral Spectroscopy: A Tribute to Roger G. Burns, Vol. 5 (ed. D. Dyar, C. McCammon, and M. W. Schaefer), The Geochemical Society Special Publication (1996). [3] H. Vogt, in: Topics in Applied Physics, Vol. 50, Light scattering in solids II (ed. M. Cardonna and G. Guentherodt), Springer-Verlag, Heidelberg, New York (1982).
MR11A-0903 0800h
Single Crystal Elastic Constants From Surface-Wave Measurements on Petrologic Thin-sections
Although single-crystal elastic constants for many common rock-forming minerals have been measured, significant gaps remain in mineral databases. Several authors have noted a continuing need to estimate mineral properties in order to compare seismic profiles with petrologically constrained elastic models for the crust and mantle. In part, the problem is associated with the difficulty of obtaining samples of sufficient size and quality to undertake laboratory studies. The solution suggested here makes use of samples within standard petrologic thin-sections. Individual single crystals within the section are oriented using electron backscattered diffraction (EBSD). Compositions are determined from standard microprobe analytic techniques. The Impulsive Stimulated Light Scattering method allows measurement of surface-wave velocities as a function of direction in the plane of the thin section. Velocities from several crystals of the same composition but with differing orientations relative to the thin section are inverted to determine the single crystal elastic constants tensor. An advantage of this method is the ability to work with many small and homogeneous crystals (as small as 50 microns) that can be prepared simultaneously using standard petrological techniques. The surface finish necessary for the EBSD analysis is sufficient for the acoustic measurements. Working with light back scattered from the surface removes the difficulty with previous light-transmission methods (Brillouin and ISLS) that required nearly imperfection-free crystals. Although surface waves have a strong dependence on shear elastic constants, the elliptical particle motion couples velocities to all elastic constants. Plagioclase-group minerals constitute 30% or more of the oceanic crust and a larger fraction of the continental crust. Only pseudo-single-crystal (monoclinic) properties have been reported for these triclinic minerals. We report results obtained on individual single crystals that allow investigation of the full elastic tensor. Extension of the work to high pressure is possible.
MR11A-0904 0800h
Linear and Nonlinear Time Reverse Acoustics in Geomaterials
Linear and Nonlinear Time Reverse Acoustics in Geomaterials P. A. Johnson, A.Sutin and J. TenCate Time Reversal Acoustics (TRA) is one of the most interesting topics to have emerged in modern acoustics in the last 40 years. Much of the seminal research in this area has been carried out by the group at the Laboratoire Ondes et Acoustique at the University of Paris 7, who have demonstrated the ability and robustness of TRA (using Time Reversal Mirrors) to provide spatial control and focusing of an ultrasonic beam (e.g. Fink, 1999). The ability to obtain highly focused signals with TRA has numerous applications, including lithotripsy, ultrasonic brain surgery, nondestructive evaluation and underwater acoustic communication. Notably, the study of time reversal in solids and in the earth is still relatively new. The problem is fundamentally different from the purely acoustic one due to the excitation and propagation of both compressional (bulk) and shear waves as well as the scattering and potentially high dissipation of the medium. We conducted series of TRA experiments in different solids using direct-coupled transducers on solids in tandem with a large bandwidth laser vibrometer detector. A typical time reversal experiment was carried out using the following steps (Sutin et al. 2004a). Laboratory experiments were conducted in different geomaterials of different shapes and sizes, including Carrera marble, granite and Berea sandstone. We observed that, in spite of potentially huge numbers of wave conversions (e.g., compressional to shear, shear to compressional, compressional/shear to surface waves, etc.) for each reflection at each free surface, time reversal still provides significant spatial and temporal focusing in these different geophysical materials. The typical size of the focal area is approximately equivalent to the shear wavelength and the focal area, but becomes larger with increasing wave attenuation (Sutin et al. 2004a; Delsanto et al., 2003)). The TR-induced focusing of wave energy at a point in space and time is ideal from the perspective of enhancing elastic wave, nonlinear response (for example, higher harmonic generation or wave modulation effects). We call this technique Nonlinear Time Reverse Acoustics (NLTRA) (Sutin et a. 2004b). We investigated the harmonic generation in TRA signals focused above a small crack (2mm) in a glass cube. Large second harmonic amplitudes were observed above the crack. Scanning of the surface by applying the laser vibrometer simultaneous with TRA focusing of the signal to an array of corresponding scanning points provided nonlinear imaging of the surface, showing all cracks in the scanned region. References: Delsanto, P. P., P. A. Johnson, M. Scalerandi, J. A. TenCate, LISA simulations of time-reversed acoustic and elastic wave experiments, J. of Physics D: Applied Physics 35, 3145-3152, (2003). M. Fink, Time Reversed Acoustics, Scientific American, 91-97 (1999). Sutin, A., J. TenCate and P. A. Johnson, Single-channel time reversal in elastic solids, J. Acoust. Soc. Am., in press (2004a). Sutin, A., P. Johnson, and J. TenCate, Development of nonlinear time reverse acoustics (NLTRA) method for crack detection in solids, Proceedings of the World Congress on Acoustics (Paris) [http://www.sfa.asso.fr/wcu2003/] 121-124 (2003b).
MR11A-0905 0800h
Measuring Porosity and Tortuosity of Rocks by Means of Air Ultrasound
An ultrasonic burst reflection method for estimating porosity and tortuosity of rocks is being developed. This method is based on measuring ultrasound reflection from the first interface of a solid material as a function of incidence angle [1]. The reflected 600 kHz waveform is compared to the wave reflected from a polished steel mirror to obtain estimates for the porosity and the tortuosity of the sample. As a milestone on our way to prove the suitability of this method to determine the structural properties of rock materials we report on our first results measured on micro sphere - silicon samples of 5-50% porosity. The proposed method is intended for applications in rock physics where porosity is an important parameter that provides information about the origin and evolution of the rock sample. The method should also find application in meteorite characterization since meteorite porosity carries information about the evolution and structure of meteorite parent bodies. This method is fast, inexpensive and non-destructive in comparison to other current laboratory methods that determine the porosity. The samples are relatively easy to prepare for the measurement, as well. After some improvements this ultrasonic measurement system could be used as an automated portable field measurement device without moving parts. The only requirement is the presence of a flat and polished surface on the rock sample. The necessary surface preparation can also be performed with portable device [2]. References: [1] Z.E.A. Fellah, et.al., "Measuring the porosity and the tortuosity of porous materials via reflected waves at oblique incidence" J. Acoust. Soc. Am 113 (5) p.2424-2433 (2003) [2] http://mars.jpl.nasa.gov/mer/mission/spacecraft\_instru\_rat.html
MR11A-0906 0800h
Marked Decrease in Vp of Anorthosite above 400 $\deg$C
We measured ultrasonic compressional wave velocity (Vp) of anorthosite (An content=49-53) with pulse reflection method. We carried out Vp measurement with piston-cylinder apparatus at 1 GPa up to 700 $\deg$C. The anorthosite exhibits reversible and nonlinear change in Vp during heating and cooling. $\delta$Vp/$\delta$T of the anorthosite changes from -1.9 to -4.8 x10$^{-4}$ km s$^{-1}$ $\deg$C$^{-1}$ at around 400 $\deg$C. In previous study, we observed abrupt change in $\delta$Vp/$\delta$T from -2.4 and -2.1 to -4.7 and -4.5 x10$^{-4}$ km s$^{-1}$ $\deg$C$^{-1}$ at around 400 $\deg$C in the gabbronorite and pyroxene granulite, which are mainly composed of clinopyroxene, orthopyroxene and plagioclase (An content=47-55), and it is difficult to explain by the previously proposed mechanisms, such as thermal cracking, dehydration reaction, and/or partial melting (Kono et al., 2003). Similarly to the gabbronorite and pyroxene granulite, some papers have reported marked decrease in Vp of plagioclase-rich rocks at high temperatures (e.g. Matsushima, 1981). Abrupt change in $\delta$Vp/$\delta$T of the anorthosite observed in this study explains these marked Vp decrease at high temperatures. Contrary to nonlinear change in Vp of plagioclase-rich rocks, we observed linear decrease in Vp of peridotite (wehrlite) up to 900 $\deg$C at 1 GPa. We therefore consider that marked decrease in Vp above 400 $\deg$C is a unique property of plagioclase-rich rock. We expect that this marked decrease in Vp of plagioclase above 400 $\deg$C cause seismic low velocity zones in plagioclase-rich crusts.
MR11A-0907 0800h
Impact of Inconsistencies in Experimental Thermodynamic Data on Thermophysical Properties of Planetary Mantles
A new thermodynamic analysis has been performed on experimental thermophysical and phase diagram data of $(Mg,Fe)_2SiO_4$ olivine, wadsleyite and ringwoodite solid solutions. The analysis demonstrates that large inconsistencies exist in the V- P- T data of wadsleyite and ringwoodite. It has been suggested in recent literature that a hydration effect is able to explain the large differences in volume measured by several independent groups of investigators [1,2]. However, this hydration effect does not explain the combination of a large measured volume associated with a large measured bulk modulus for a number of experimental V- P- T data sets [3-7]. We show the effects of the inconsistencies on the calculated phase diagram, bulk sound velocities and other thermodynamic properties. We have applied our thermodynamic analysis to iron rich compositions at pressure/temperature/iron content conditions representative for the mantles of Earth and Mars. For these conditions a strong compositional effect on thermodynamic properties in two- phase regions is observed from our thermodynamic model. This compositional effect is associated with the slopes of two- phase boundaries in pressure- composition and temperature- composition phase diagrams leading to a change up to 100% or more for specific thermodynamic properties thermal expansivity $\alpha$, specific heat $c_P$ and bulk modulus $k_S$. The amplitude of the anomalies increases with iron content larger than 10%. These anomalous two-phase zones, where olivine transforms to ringwoodite via wadsleyite, cover a pressure range of about 5 GPa. In the Earth's mantle transition zone these two-phase zones therefore occupy a depth range of some 150 km and the impact of these strong variations in $\alpha$ and $c_P$ on mantle dynamics may be limited. Planet Mars with its weaker gravity field and reduced pressure gradient is an environment more susceptible to the impact of these two-phase compositional effects, even more so since the iron content of the Martian mantle is likely about twice as high as for Earth's mantle. We will show preliminary results of convection modeling including these effects for both Earth and Mars like conditions. Putting the variations in thermophysical properties in perspective we can say that at conditions prevailing in the Martian mantle, the V- P- T inconsistencies affect thermodynamic properties in two- phase regions by about 7%. This is substantially less than the mentioned variations up to 100%, due to the composition effect. On the other hand differences between properties computed with several modern thermodynamic databases amount to about 30%. [1] Smyth JR, Holl CM, Frost DJ, Jacobsen SD, Langenhorst F, McCammon CA (2003), Am. Miner. 88, 1402-1407. [2] Inoue T, Tanimoto Y, Irifune T, Suzuki T, Fukui H and Ohtaka O (2004), Physics Earth Planet. Int., in press. [3] Hazen RM Zhang J and Ko J (1990), Phys. Chem. Miner., 17, 416-419. [4] Hazen RM, Downs RT, Finger LW and Ko J (1993), Am. Miner. 78, 1320-1323. [5] Fei Y, Mao HK, Shu J, Parthasarathy, Bassett WA and Ko J (1992), J. Geophys. Res. 97, 4489-4495. [6] Meng Y et al., J. Geophys. Res. 98, 22199-22207. [7] Meng Y, Fei Y, Weidner DJ, Gwanmesia GD and Hu J (1994), Phys. Chem. Minerals 21, 407-412.
MR11A-0908 0800h
The new Developed System for Elastic-Wave Velocity Measurement Under High P-T Condition of Seismogenic Zone
We have developed a new experimental system that can measure elastic-wave velocities under high-temperature, confining pressure (Pc) and pore pressure (Pp) conditions with in the argon-gas pressure vessel. The elastic-wave velocities of fault rocks are important clues to reveal the rock composition of seismogenic zone. The detailed rock composition model in the deep part of seismogenic fault zones is very important to understand the structure of fault zones and the earthquake process. We measured elastic-wave velocities of cylindrical Westerly granite and Berea sandstone (20mm diameter and 20mm length) under high-pressure and high-temperature in the wet and dry conditions. The experiments were carried out with the gas-medium high-pressure and high temperature deformation apparatus at AIST, Japan. Temperature varied from room temperature to $200\deg$ C. In the dry conditions, experiments were conducted under the confining pressure up to 200MPa. In the wet conditions, pore water pressure was applied up to 200MPa. The rock sample was put between upper and lower WC and pistons. The lithium-niobate transducers (LiNbO$_{3}$, 1.0mm thick) set at the end surface of the lower piston were used to emit and receive the ultrasonic signals. We used the lower WC piston as a buffer rod to isolate the transducers from the high-temperature environment. The elastic waves reflected at the WC piston-Sample boundary and sample - WC plate boundary are recorded. We measured the difference of arrival times of these two reflected waves. The elastic-wave velocities are calculated from these measured travel times and the sample core length. Our preliminary results of Vp measurement show that, Vp of Westerly granite increased rapidly from 4.92 km/s at 20 MPa to 5.78 km/s at 80 MPa in the dry condition. Over 100 MPa up to 160 MPa, the Vp increased slightly up to 160 MPa from 5.80 km/s to 5.83 km/s. This Vp -Pressure curve is similar to those of many previous studies. The Vp of Berea sandstone increased form 3.71 km/s at 5 MPa (Pp=5MPa) to 4.13 km/s at 25MPa (Pp=20MPa).
MR11A-0909 0800h
High Pressure - Temperature Effects on Cation Ordering in Magnesioferrite, MgFe$_{2}$O$_{4}$, Using in situ Synchrotron X-ray Powder Diffraction up to 1430 K and 6 GPa
The structural behaviour of magnesioferrite, MgFe$_{2}$O$_{4}$, was determined from in situ synchrotron X-ray powder-diffraction data at room pressure and temperatures up to 1255 K on heating and cooling ($\lambda$ = 0.92225(4) $\AA$), and also at 6, 5, and 3 GPa and temperatures up to 1430 K ($\lambda$ = 0.3738(4) $\AA$). Cation order was analyzed in terms of the inversion parameter, {\it x}, {$^{iv}$ [Mg$_{1-x}$Fe$_{x}$]$^{vi}$ [Mg$_{x/2}$Fe$_{1-x/2}$]$_{2}$O$_{4}$}. At room pressure, {\it x} shows no change on heating until the temperature is high enough to cause exchange of Mg$^{2+}$ and Fe$^{3+}$ cations between the octahedral (vi) and tetrahedral (iv) sites. At 854 K, the sample achieves the maximum ordered state on heating ({\it x}$_{max.}$ = 0.867(4)) and begins to move towards equilibrium. Above 854 K, the cations continuously disorder along the equilibrium pathway to the maximum temperature studied ({\it T}$_{max.}$ = 1255 K, {\it x} = 0.769(3)) and reverse along the equilibrium pathway on cooling. At the blocking temperature, {\it T}$_{B}$, the maximum equilibrium order is frozen in, and maintained to room temperature, where {\it x}$_{max.}$ = 0.895(4). With increasing pressure at a constant temperature, magnesioferrite becomes more inverse. Therefore, pressure induces cation ordering in magnesioferrite. Higher pressures require higher temperatures for cations to disorder and reach equilibrium (e.g., \sim 1010 K at 6 GPa, \sim 995 K at 5 GPa, \sim 970 K at 3 GPa, \sim 854 K at room pressure). O'Neill and Navrotsky (1983) and Landau models were used to describe the equilibrium non-convergent ordering process in MgFe$_{2}$O$_{4}$, and they both fit the data well within the measured experimental range.
MR11A-0910 0800h
The variation of the crystal structure of magnesium silicate perovskite with chemical composition
Being the major constituent of the lower mantle, magnesium silicate perovskite MgSiO$_{3}$ has been subject to numerous past studies. More recently a lot of emphasis has been put on the physical properties and substitution mechanism of Al and Fe into the structure.While the structure of pure-MgSiO$_{3}$ and (Mg,Fe)SiO$_{3}$ have been determined, no data has been reported on the crystal structure of (Mg, Fe, Al)SiO$_{3}$ and how it varies with Al and Fe substitution. The knowledge of cell parameters, atomic positions and site occupancy of (Mg, Fe, Al)SiO$_{3}$ and how it changes with composition is of critical importance for a complete understanding of its physical properties. We have therefore carried out single-crystal X-ray structure determination at ambient pressure of two Al-Fe rich perovskites with different amounts of Al and Fe. One sample contains approximately 5 wt % of Al$_{2}$O$_{3}$ and 6 wt % of FeO and the other one has 13 wt % Al$_{2}$O$_{3}$ and 26 wt % FeO. Preliminary results show that (i) the Fe atoms tend to occupy the A-site only and (ii) that the B-site expands with total Al content of the perovskite,which indicates that the Al atoms tend to occupy the octahedral site. The implications of these first results for the evolution of the structure of (Mg, Fe, Al)SiO$_{3}$ perovskite at high pressures will be discussed.
MR11A-0911 0800h
Pressure dependence of (Mg,Fe)SiO3 ilmenite and perovskite determined by a multi-anvil apparatus with sintered diamond anvils
Geophysical observations such as the MT method suggest that the electrical conductivity increases from 1 to 10 S/m from the top to the bottom of the lower mantle (Olsen1999). Measurement of electrical conductivity of silicate perovskite under lower mantle conditions is indispensable to explain such geophysical observations, because the lower mantle is believed to be mainly composed of silicate perovskite. Many workers have conducted electrical conductivity measurements at high pressures and temperatures. Xu et al. (1998) measured electrical conductivity of silicate perovskite at 25 GPa and $1400-1600 \deg$C by using a multi-anvil apparatus. However, their pressure condition is limited to 25 GPa because of use of WC anvils, and therefore, they were not able to determine pressure dependence of electrical conductivity of silicate perovskite. In this study, we try to determine pressure dependence of electrical conductivity of mantle minerals, by using a multi-anvil apparatus with sintered diamond anvils, which allows us to measure electrical conductivity of minerals in a wide pressure range. We first measured electrical conductivity of (Mg$_{0.93}$Fe$_{0.07}$) SiO$_{3}$ ilmenite at pressures of 25, 30 and 35 GPa and temperatures of 300 to 1200 K. We obtained the activation energy and volume of 0.69(4) eV and -0.9(1) cm$^{3}$/mol, respectively. Thus electrical conductivity of ilmenite has large pressure dependence. For example, the ilmenite conductivity increases by 20 times at 500 K with increasing pressure from 25 to 35 GPa. Next, we conducted measurement for (Mg$_{0.93}$Fe$_{0.07}$) SiO$_{3}$ perovskite at pressures of 30 and 35 GPa and temperatures of 300 to 1400 K, showing the activation energy and volume of 0.39(4) eV, and -0.06(4) cm$^{3}$/mol, respectively. In contrast to ilmenite, electrical conductivity of perovskite has very small pressure dependence. We have calculated the electrical conductivity of the model lower mantle using the present experimental results, suggesting that it increases from 2.7 to 4.75 S/m from the top to the bottom of the model lower mantle. Thus it is difficult to explain the large increase in the electrical conductivity of the lower mantle shown by Olsen (1999) from the present experimental data.
MR11A-0912 0800h
The Equation of State of Fe3P-iron phosphide to 54 GPa
We have measured the volume and lattice parameters of end-member Fe3P-schreibersite in the diamond anvil cell to pressures of 54 GPa at 300 K. Samples of Fe3P were also laser heated to temperatures of ~2100 K at 50 GPa, and examined following thermal quench. No pressure-induced or quenchable temperature-induced phase transitions are observed over the conditions of this study. Our pressure-volume data were fit to a 2nd-order Birch Murnaghan equation of state, yielding a best-fit isothermal bulk modulus, K0T, of 190 ± 5 with an assumed of 4; fit to a 3rd-order EOS yielded a K0T of 252 (± 15) GPa with a dK/dP of 1.0 (± 0.6). The wide stability range of the tetragonal Fe3P-structure and its ubiquity in iron-rich meteorites make schreibersite the most likely phase by which P was originally incorporated in deep planetary interiors. The moderately enhanced bulk modulus of this P-bearing alloy relative to pure iron could partially compensate for a bulk modulus depression induced by other possible lighter alloying components of planetary cores, such as sulfur.
MR11A-0913 0800h
X-ray Fluorescent Phosphors as {\it in Situ} Markers of X-ray Position for High-Pressure X-ray Techniques: Equation of State and X-ray Fluorescence Spectra to 40 GPa
Their small size and heterogeneity make high-pressure samples in the diamond-anvil cell difficult to place perfectly in an x-ray beam to perform any of several analytical techniques (diffraction, scattering, etc.). X-ray fluorescent materials may help to solve this problem by providing a visual marker of the precise location of the x-ray beam or probe. In order to assess the utility of x-ray fluorescent markers for x-ray beam location at high-pressure conditions, we have characterized the high-pressure behavior of common x-ray fluorescent materials, particularly paying attention to structural stability at 300 K and high temperature, adequate fluorescence brightness, and potential use as an {\it in situ} pressure calibrant. We present x-ray diffraction and x-ray fluorescence (excited by x-rays, fluorescent in the visible range) data for two common x-ray phosphors: "red phosphor," Y$_{2}$O$_{3}$ doped with Eu, and "green phosphor," Gd$_{2}$O$_{2}$S doped with Tb. Red phosphor yttrium oxide undergoes two phase transitions from its initial cubic structure at 8 $\pm$ 2 GPa and 18 $\pm$ 2 GPa, and a third phase transformation occurs at high temperature during laser heating. In contrast Gd$_{2}$O$_{2}$S:Tb retains its hexagonal crystal structure with only slight modification to 40 GPa and during laser heating, and its volume and fluorescence peaks may be followed with increasing pressure making it a good material for {\it in situ} calibration of pressure as well as x-ray position. High pressure and temperature crystal structures, fluorescence spectra, and equation of state information will be presented for these two materials.
MR11A-0914 0800h
Rock Physical study on an Upper-Palaeozoic Chert and Carbonate Interval in Wells from the Eastern Norwegian Barents Sea.
Due to their general interest as hydrocarbon reservoir, the Upper Palaeozoic chert and carbonate interval in the Norwegian Barents Sea has been investigated from seismic data and well logs. We established a framework for geophysical well log analysis and reservoir characterization for the Finnmark Platform, an area situated in the South-Eastern part of the Norwegian Barents Sea. The interval is composed by approximately 600 m carbonate facies covered by a 60 m interval of spiculitic chert facies. The carbonate facies is characterized by lateral and vertical lithological variations including limestones, dolomites, evaporites and clastic material. The spiculitic interval exists in spiculitic chert and clay alternated with limestones. Data extends over an area with different palaeo environments from inner platform settings to continental slope and even basinal settings. Log curve data from four wells were processed through geophysical well log analysis using Powerlog and Matlab. Multi-well trend analysis was performed for a diagnostic modeling of the rock physical parameters. The examination of the variation of petrophysical properties, and how that variation transfers into the elastic domain is a key to the correlation of rock properties and the seismic attribute information. The final goal is to improve porosity and mineralogy predictions in pseudo-wells from 3D seismic data. The analyses of cross plots allow distinguishing several intervals which in certain cases correspond to individual stratigraphic units. The spiculite interval shows for example different rock types based on rock physics and these parameters can be linked with seismic. For the synthetic seismogram an s-wave velocity log has been modeled. We observed that for several lithological intervals such as the mixed limestone-dolomites and spiculites the Greenberg-Castagna model fitted the best, but for pure dolomite intervals the Krief model is more accurate. Furthermore, for the purest limestone the best fit was obtained for the differential effective medium equations. These intervals should be treated differently for obtaining the best fitting velocity-porosity relations.
MR11A-0915 0800h
Relation between Transport Properties and Heterogeneities from Grain and Sample Scale in Fontainebleau Sandstone
We carried out an experimental study of Fontainebleau sandstone for correlation between pore structure and transport properties. Eight blocks of the sandstone were available from different locations. Several cored samples, 30 mm in diameter and 60 mm in length, were prepared from each block. The available blocks yield a range in porosity from about 3 to 11% with no difference between connected and total porosity. Scanning Electronic Microscope analysis revealed a clayless-pure ($>$99$%$ quartz), well sorted sandstone with different porosity and pore geometry for different blocks. The pore texture varies from risolated pores to risolated grains in two-dimensional images. To further constrain the effect of heterogeneities in sample scale on bulk fluid transport properties we tested samples with up to six sawcuts parallel or perpendicular to the flow direction. The planar faces of the saw cuts were machined to a smooth finish. We also stacked pieces alternating between two sandstone varieties of 6 and 9$%$ porosity to model inhomogeneity for one-dimensional fluid transport varying in scale. On intact sample, we measured ultrasonic velocity, electrical conductivity, hydraulic permeability and specific storage. Ultrasonic velocity and electrical conductivity were measured on as-is, oven-dry, and water-saturated samples at room temperature and atmospheric pressure. Permeability and specific storage were determined from steady state, linear injection and oscillatory tests at different effective pressures ranging up to 200 MPa at room temperature. The variation of the ultrasonic velocity covers the full range between the lower and the upper Hashin-Shtrickman bound. The velocity ranges relate to the pore geometry rather than porosity; e.g. high velocity in samples with risolated pores and low velocity in samples with risolated grains. The electric impedance and hydraulic permeability of the sandstone correlates strongly with the connected porosity. The permeability depends negatively on effective stress only for lower porosity samples ($<$5$%$. Elastic moduli and transport properties of our porous sandstone samples are not only sensitive to the volume fraction of pore but also to the grain-scale heterogeneity of the pore space, i.e., the presence of pore-like and crack-like conduits. Cuts perpendicular to the main flow direction constitute a barrier in high porosity samples because the fluid channels are not perfectly matched between the two polished surfaces. Cuts parallel to the main flow direction perturb the flow field yielding increased scatter in permeability. The apparent specific storage and permeability of inhomogeneous samples composed of six discs alternating between the two sandstone varieties show a positive linear relationship with pore pressure but little variation with oscillation period. In contrast, the hydraulic parameters of samples assembled of two pieces, one of low and the other of high porosity, depend on oscillation period in a similar way as the homogeneous low-porosity sample, i.e., both hydraulic parameters increase with a decreasing rate with increasing period, and asymptotically approach a maximum value. The variations in specific storage and permeability result in a decrease of hydraulic diffusivity with increasing oscillation period suggesting that pore pressure diffusion becomes less efficient owing to increasing storage in rdead-end parts of the pore network. The low porosity sample is closer to the percolation threshold and the percentage of the network constituting dead storage is relatively larger than in the more porous sample.
MR11A-0916 0800h
Calibration of Mobile NMR Instruments in Respect to Porosity and Pore Size Distribution of Drill Cores
The focus of our research is set on the calibration of two different and new developed light weight mobile NMR scanning systems: (1) the NMR-MOUSE and (2) the HALBACH device for measuring porosity and pore size distribution of different drill cores recovered from the International Ocean Drilling Program (IODP). Further goals are to adapt current NMR processing techniques, the development of new measurement routines, and to evaluate precision and accuracy of this method. Transverse relaxation on water-saturated drill cores were measured using a CPMG sequence. A regularized Laplace transform analysis based on the UPEN program yields the distribution of transverse relaxation times. The signal amplitudes and the integrals of distribution correlate directly to the core porosity. The main advantage of our mobile NMR scanning systems compared to conventional methods is their small size and weight, which is particularly attractive for the shipboard use and on any drilling platform envisioned for IODP. Both tools, the NMR-MOUSE and the HALBACH scanner are suitable for routine measurements of porosity and pore-size distribution of drill core sections. In contrast to the NMR-MOUSE, the HALBACH tool has a sufficiently homogeneous magnetic field and is more sensitive. It can determine porosities as low as 3 %. While the NMR-MOUSE can be applied on core sections of any geometry, the Halbach tool is especially designed for the size of standard drill cores recovered from the deep sea ocean floor by the IODP. Combined with a mobile NMR spectrometer and special software for porosity and pore size distribution measurements, both light and mobile devices are particularly attractive for the use on research vessels and logging platforms and thus alow to determine prosity and permeability on very fresh material.
MR11A-0917 0800h
The formation of dislocations in single crystal Durango apatite
Low temperature thermochronometric tools such as apatite fission track (FT) analysis and apatite U-Th/He dating are commonly used to evaluate rates of surficial processes. The closure temperatures for these systems, as in other thermochronometric systems are a function of diffusion rates. However, little is known about the effects of microstructures on diffusion rates in thermochronometers, specifically apatite. Given that many thermochronometric studies involve rocks that have undergone the orogenic cycle, the minerals analyzed inevitably were deformed and generally contain deformation-produced defects. It is therefore critical to evaluate the effects of crystal defects on diffusion rates. The first step towards understanding these effects in apatite is characterization of crystal defect formation. The paucity of literature regarding conditions under which dislocations form necessitates a series of deformation experiments in apatite. New results from preliminary deformation experiments on single crystal Durango apatite are presented. Three experiments were conducted in a Paterson gas-medium press with a confining pressure of 300 MPa at a temperature of 1273 K and differential stresses from 125 MPa to 150 MPa. Single crystals were prepared using optically clear Durango apatite oriented such that the basal and prism planes were at approximately 45$\deg$ to the maximum principal stress, $\sigma$1, thereby maximizing shear stress acting on those crystallographic planes. Deformed surfaces parallel to $\sigma$1 were polished and etched in 5N HNO3 for 10 seconds to reveal any defects created. In all experiments, bands of high dislocation density are observed at 45$\deg$ to $\sigma$ 1, suggesting crystallographic control on band formation. The high-density bands are separated by virtually defect free zones. High dislocation density bands are cross cut by highly etched regions. Our preliminary interpretation of these regions is they represent zones of extremely high dislocation density. TEM analyses will aide in more accurate characterization of these zones and how they relate to defect free regions of the crystals. These results will serve as a foundation for diffusion experiments in the presence of these defects.
MR11A-0918 0800h
Na- and Zn- bearing (Mg,Fe)Al2O4 spinel exsolution from ilmenite and magnetite of eclogite in the CCSD Main Hole
In the eclogite of the main hole, CCSD, there were found ilmenite\- titanomagnetite and ilmenite\-magnetite oxide series, each of which is formed intergrowth textures. Titanomagnetite takes near 40%, ilmenite 30% and magnetite 30% in volume proportion. In those two series, many micro-exsoluted lamellas are found in ilmenite and magnetite and are never in titanomagnetite. By synchrotron light source analyses, those minerals are spinel with space group of Fd3m and unit cell parameter of a=8.3781$\AA$. The spinel exsolutions are mostly aligned and parallel to the long axis of lensoidal ilmenite, about several $\mu$m to 30$\mu$m long and several $\mu$m wide, the largest found to be about 30$\mu$m$\times$60$\mu$m. The exsoluted spinel lamellas in magnetite are 5$\sim$100$\mu$m long and several $\mu$m wide, oriented in three $<$111$>$ crystallographic planes of magnetite. Microprobe analyses show that spinel exsoluted in ilmenite is composed of Na$_{2}$O 0.091$\sim$0.241, MgO 18.617$\sim$22.337, ZnO 1.649$\sim$6.386, Al$_{2}$O$_{3}$ 64.514$\sim$66.492, FeO 9.105$\sim$10.639, TiO$_{2}$ 0.035$\sim$0.127, with total of 99.696$\sim$100.472wt%. Its chemical formula is (Na$_{0.008}$Mg$_{0.8}$Fe$_{0.14}$Zn$_{0.06}$)(Al$_{1.94}$Fe$_{0.06}$)$_{2}$O$_{4}$. The ilmenite is composed of MgO 3.604$\sim$4.826, TiO$_{2}$ 50.376$\sim$51.820, FeO 41.862$\sim$44.727, Cr$_{2}$O$_{3}$ 0.050$\sim$0.263, Al$_{2}$O$_{3}$ 0.025, with total of 98.641$\sim$99.047wt%. The titanomagnetite is MgO 0.923, Al$_{2}$O$_{3}$ 0.124, TiO$_{2}$ 12.430, FeO 79.306, Cr$_{2}$O$_{3}$ 0.035, with total of 92.819wt%. Magnetite contains MgO 0.377, Al$_{2}$O$_{3}$ 0.157, TiO$_{2}$ 0.015, FeO 92.049, Cr$_{2}$O$_{3}$ 0.053, with total of 92.688wt%. According to the intergrowth and exsolution textures, there widely exists a miscibility gap in (Mg,Fe)TiO$_{3}$-Fe(Ti,Fe)$_{2}$O$_{4}$\-(Na,Mg,Fe,Zn)(Al,Fe)$_{2}$O$_{4}$-Fe$_{3}$O$_{4}$ series and (Mg,Fe)(Al,Fe)$_{2}$O$_{4}$-Fe$_{3}$O$_{4}$ series. In light of the FeO-Fe$_{2}$O$_{3}$-MgO-TiO$_{2}$ join experiment (Pinckney and Lindsley, 1976), the coexisting temperatures for titanomagnetite occurrence is around 750$\sim$800$\deg$C, when magnetite takes 30% mole ratio in Ni-NiO buffer. All of those spinel exsolutions as well as their host ilmenite-titanomagnetite and magnetite are associated with garnet and omphacite. According to main and trace element compositions of the eclogite in the main hole, Na$_{2}$O and Zn (Zhang et al., 2004) are relatively abundant. Na and Zn occurrence in the spinel is closely related with the formation of the eclogite. The peak metamorphic temperature of the eclogite is 700$\sim$850$\deg$C (You et al., 2004), which is close to the miscibility temperature of the magnetite and imenite.
MR11A-0919 0800h
Kinetic analysis of room temperature structural transformations in zinc sulfide nanoparticles using simultaneously collected SAXS/WAXS
Natural inorganic nanoparticles are always subject to ligand or solvent surface interactions and are frequently aggregated. In previous work, we have shown that such surface effects can drive significant changes in interior nanoparticle structure. For example, water addition to nanoparticle surfaces drives a solid-state transformation in zinc sulfide (ZnS) nanoparticles and reversible aggregation-driven transformations can be observed at room temperature. In general, changes in surface interaction may be accompanied by changes in aggregation state, so we have developed an approach for the simultaneous collection of in-situ small-angle and wide-angle x-ray scattering (SAXS and WAXS, respectively). We used this method to distinguish the kinetics of the structural transformation and aggregation of ZnS nanoparticles in methanol when water is added. The rate of structural transformation exhibits a marked temperature dependence over the range of 20 - 60 °C. However, the rate of nanoparticle aggregation increases only slightly over the same temperature range. Longer-range aggregate structure, as quantified by the fractal dimension derived from the SAXS data, is weakly changed following water addition. Thus, we conclude that water adsorption and not aggregation is driving the structural transformation and that either water adsorption or interior nucleation is the rate-limiting step for the transformation. These experiments were conducted at the APS on the DND-CAT beamline 5 ID-D.
MR11A-0920 0800h
Radiogenic Heat Production in the Cretaceous Sediments of Yola Arm of Nigeria Benue Trough: Implications for Thermal History and Hydrocarbon Generation
Yola Arm is an east-west extension of the upper Benue Trough of Nigeria with Cretaceous sediments of Albian to Coniacian ages. Thirteen samples which are mainly sandstone, shale, mudstone, clay, siltstone, limestone and coal were collected from six different geological units namely: Bima Sandstone (BS), Yolde Formation (YF), Dukul Formation (DF), Sukuliye Formation (SF), Numanhan Formation (NF) and Lamja Sandstone (LS). This is to determine their radioactive heat production and implications for thermal history and hydrocarbon generation. The result shows that concentration and rate of heat production of $^{40}$K, $^{232}$Th, and $^{238}$U in the samples varies widely with lithologies and stratigraphic intervals. Three groups of total heat production (HP) were identified and designated as low (LHP), moderate (MHP), and high (HHP). The LHP includes sandstones of BS, limestone of DF and coal of LS with total heat production of $<$750 pW/Kg. Clay of BS, siltstone of YF, limestone of SF and NF, and sandstone of LS belong to MHP with total heat production of between 750 and 1500 pW/Kg. Shale of YF, SF and NF with total heat production of $>$1500 pW/Kg belong to HHP. The HHP group corresponds to shale units at different ages in the study area, and may have produced enough heat for hydrocarbon generation. The total heat production studies have suggested that the Cretaceous sediments experienced complex temperature history with at least two sudden thermal pulses. They could have been related to Cretaceous synsedimentary volcanism or to the emplacement of the basaltic pluton.
http://www.agu.org
MR11A-0921 0800h
Neutron Diffraction and Local Atomic Structure of Fontainebleau Sandstone: Evidence for an Amorphous Phase?
Total neutron scattering measurements of solid Fontainebleau sandstone were carried out. Standard Rietveld analysis, yielding only average structural information, reveals that the long range average structure of this sandstone is pure quartz. Atomic pair distribution function (PDF) analysis, however, shows significant local structural deviations from the quartz structure. These deviations manifest themselves as an excess of 5-10% of nearest neighbor (NN) Si-O and O-O bonds. No evidence of deviations from the average quartz structure can be found for atom-atom separations larger that the NN O-O bond. This could be understood as an additional glassy SiO$_2$ phase being present in the sandstone. [Work supported by Los Alamos Institutional Support (LDRD) and the DOE Office of Basic Energy Sciences. The Manuel Lujan Jr. Neutron Scattering Center is a national user facility funded in part by the U.S. DOE.]
MR11A-0922 0800h
Free SiO2 from Mantle of Ophiolite in Tibet, China
Free SiO$_{2}$ and their host minerals were discovered from podiform chromitites of the Luobusa ophiolite, Tibet. The ophiolitic body is about 200 km east-southeast of Lhasa in the Indus-Yarlung Zangbo suture zone. It is a fault-bounded slab, 1-2 km thick, with about 70 km$^{2}$ in area. Luobusa ophiolitic body consists of harzburgite, cumulative and melange phases. Numerous ultra-high pressure minerals including diamond have been recovered in the podiform chromitites. Since upper mantle peridotites are silica-unsaturated, free SiO$_{2}$ and olivine never coexist in peridotite. Therefore, in mantle peridotite and ultramafic rocks, primary free SiO$_{2}$ has not been found yet. But recently, free SiO$_{2}$ (quartz and coesite) was discovered from the podiform chromitites in mantle peridotites of Luobusa ophiolite. The free silica presented as inclusions in OsRuIr alloys and PtFe alloys, or as intergrowth with TiO$_{2}$ and FeO. These occurrences of free silica show their mantle origin and excluding the possibilities of secondary genesis or contamination. Early high pressure and temperature experiments proved that under the conditions of the lower mantle, olivine from the upper mantle is decomposed to mixtures of periclase and stishovite. Therefore, the free SiO$_{2}$ from the podiform chromitites in mantle peridotite in Tibetan ophiolite is most likely derived from the lower mantle. Besides the free SiO$_{2}$, other simple oxides, such as FeO, MgO, CaO, Al$_{2}$O$_{3}$, Cr$_{2}$O$_{3}$, Fe$_{2}$O$_{3}$ and Fe$_{3}$O$_{4}$, are also found in the same sample from Luobusa chromitites. How is the free SiO$_{2}$ in Tibetan ophiolite protected and transported from the lower mantle to the upper mantle? A reasonable explanation is that silica must be contained within residual mineral and the latter was brought up to oceanic mantle depth by an upwelling plume from the core-mantle boundary.
MR11A-0923 0800h
Physical properties of rocks from the Trans-Hudson orogen, Canada
A physical properties database of rock types from the Trans Hudson orogen is presented. Measurements have been made on 320 samples representing metamorphosed Archaean and juvenile Proterozoic orogenic rocks. Water saturated densities were generally between 2600 and 3100 kg m-3. In most cases the porosity was less than 1 percent. Except for a few samples, magnetic susceptibility ranged from 20 to 4000 x 10 exp-6 SI units. P-wave velocities and S-wave velocities were made under maximum uniaxial stress and triaxial stresses equivalent to depths of ca 4 km. P-wave and S-wave velocities measured were in the range 5-7 km s-1 and 3-4 km s-1 respectively. The velocity data show a wide variation in impedance between neighbouring domains and within domains: seismic reflection coefficients greater than 0.1 would appear to be routinely possible. Thermal conductivity measurements made using a `divided-bar' apparatus, yielded values between 1 and 5 W m-1 K-1. Electrical resistivity measurements were made at room temperature from 5 Hz to 10 kHz after samples were oven dried and after saturation in solutions with salinity up to 1.0 M. The porosity - resistivity data is in reasonable overall agreement with Archie's Law for all rock types. A minimum value for the resistivity of those samples not containing significant sulphide minerals or graphite, was 50 ohm-m. For sulphide and graphite-bearing samples, resistivity was as low as 1 ohm-m. The resistivity data are consistent with the hypothesis that North American Central Plains(NACP) conductivity anomaly is due to the presence in the crust of graphite- and/or sulphide-rich bodies or saline pore fluids.
MR11A-0924 0800h
Direct measurements of the dissolution of silica-mica interfaces and its implication for pressure solution mechanisms
Pressure solution is a rock deformation process defined by many authors as the dissolution of materials under high stress at grain to grain contacts, and precipitation at interfaces under low stress. Despite the fact that this dissolution-transport-precipitation mechanism has been under scrutiny for many years, the controls and kinetics of this process are still poorly discerned, in part because of the large time-scales involved. Using the Surface Forces Apparatus (SFA) technique for measuring the forces (or pressures) between two solid surfaces pressed together in liquid, and an optical interference technique for in situ visualization of the nano-scale deformations and dissolution of the surfaces at the junction, we report on our studies of mica-mica, amorphous silica-silica and quartz-mica interactions in various aqueous electrolyte solutions. Dissolution rates as slow as 1 nm per day could be recorded in real time, corresponding to geological rates as slow as 1 m per 3 million years. In the `symmetric case' of two mica surfaces, our results show that two muscovite mica surfaces in high NaCl salt solutions and normal pH experience a repulsive electrostatic and `structural hydration' force at short-range (<2-4 nm) that prevents the surfaces from coming into contact, but that does not appear to prevent water and ions from diffusing into or out of the junction (the nanometer thin water film between the two mica surfaces). In addition, no dissolution of the mica surfaces (the basal plane) was observed under any conditions. However, in the presence of calcium ions (CaCl2) calcite crystals were seen to grow on the mica surfaces as well as in the gap between two surfaces, which is similar to the observed occurrence of carbonate minerals preferentially growing between mica cleavages. In the `symmetric case' of two amorphous silica surfaces, the short-range forces were similar to those measured between mica surfaces, and again no dissolution of the (amorphous) silica surfaces was observed. In the `asymmetric' case of a quartz crystal surface against mica, dissolution of the quartz surfaces was observed that depended on the solution conditions, the externally applied `lithostatic' pressure, and on which crystal face was exposed to the mica surface. Quantitatively, our experiments show that there is an initial stage after fresh solution or acidic calcium solution is added in which the spacing between the surfaces increases. However, the thickness decreased continually after approximately four hours of exposure. For a particular set of conditions the process eventually slows down and reaches equilibrium after some time, but increasing the pressure at this point increases the rate of dissolution again. Addition of fresh solution later in the experiment has a similar effect. We discuss how our results may provide a better understanding of the molecular processes associated with pressure solution, and also relate these processes to other, apparently related, phenomena in materials science such as corrosion and Chemical Mechanical Polishing (CMP). These results are consistent with the observation that pressure solution of quartz is greatly enhanced when in contact with mica.
MR11A-0925 0800h
Shock Veins as Recorders of Shock Pressures in Chondrites: Pressure Histories from Thin vs. Thick Veins
High-pressure minerals are generally found within or adjacent to shock-induced melt veins and melt pockets in highly shocked chondrites. The minerals that crystallize in the melt veins and pockets and the distribution of these minerals provide a record of crystallization and quench histories that can be used to constrain shock pressure and pulse duration. Most previous investigations have focused on relatively thick veins ($>$100 $\mu$m in width) because they tend to contain high-pressure minerals that are observable using petrography or scanning electron microscopy. However, the mineralogy of thin shock veins can provide additional constraints on the pressure history of shocked meteorites. Because shock veins cool predominantly by conduction to the surrounding matrix, rather than by adiabatic decompression, the timing of shock-vein crystallization depends strongly on vein thickness and position within the veins. Therefore, the thinnest melt veins, which solidify within tens of nanoseconds after melting, provide a brief crystallization history at the time of formation whereas thicker veins provide a longer history that may reflect crystallization during decompression. If thin veins form during compression or early in the shock pulse, they will likely record the equilibrium shock pressure or the peak pressure. The goal of this study is to characterize the mineralogy of thin melt veins and to compare the results to those of thicker veins in the same samples. We have investigated three L chondrites that contain a wide range of melt vein sizes. These include Tenham (several $\mu$m to 600 $\mu$m in width), Roy (10 $\mu$m to 150 $\mu$m in width) and Umbarger (35 $\mu$m to 300 $\mu$m in width). Thick veins in these samples have been previously investigated using FESEM and TEM, resulting in crystallization pressures of approximately 25, 20 and 18 GPa for Tenham, Roy and Umbarger, respectively. Thin veins from these samples were investigated using TEM. Three thin veins in Tenham show three different assemblages including glass, high-pressure minerals and low-pressure minerals. The thin vein from Roy contains uniform majorite throughout, whereas a thin vein from Umbarger contains fine ringwoodite grains and Ca-clinopyroxene. The fact both low- and high-pressure assemblages occur in the thin veins from Tenham indicates that melt-vein formation occurs during pressure release as well as during compression. Further details of the shock-pressure history of these samples will be presented.
MR11A-0926 0800h
Reaction-Induced Permeability Change in Thermally Cracked and Deformed Aplite: Importance of Reactive Surface Area and Mineralogy
This experimental study investigates hydrothermal reactions in a granitic system and attempts to quantify how such reactions affect hydrologic properties, namely specimen permeability. Of specific interest is the evolution of permeability under variable differential stress conditions, from the compactional and dilatancy regimes to that of shear failure. Under these different stress conditions, reactive surface area will vary, possibly affecting the rate and absolute magnitude of permeability change. Experiments were conducted using a Paterson gas apparatus capable of independently controlling confining pressure (Pc), pore pressure (Pp) and axial load. Most experiments were conducted at Pc=100 MPa and Pp=50 MPa with temperatures of 200-600$\deg$C. Under isostatic conditions, permeability was observed to increase with temperature due to increased thermal cracking at grain boundaries. As differential stress was increased in each experiment, permeability was first observed to decrease, presumably due to crack closure. Upon continued loading to higher stresses, dilatancy resulted in significant permeability enhancement. In later experiments, permeability was allowed to evolve at each stress level and was observed to decay by an exponential function of the form k $\alpha$ 1-$\mu$(1-exp$^{(-rt)}$)$^{2}$, suggesting a precipitation type mechanism for the observed permeability change. The rate constant progressively increased up to 500$\deg$C, but was much smaller in the 600$\deg$C experiment, indicating a possible change in the precipitating mineral assemblage as suggested by experimental studies in the KNASH system. Overall, reaction rates were enhanced during dilatancy and after rupture, an observation suggesting a negative feedback effect, in which enhanced mineral precipitation moderates permeability generation during episodes of deformation. The nature of fluid flow in such systems is crucial to the formation of porphyry metal deposits and also plays a major role for the development of some geothermal energy projects. These experimental results will also have important implications for precipitation-induced sealing in granitic fault zones, where hydrologic changes might alter various physical properties of the fault.
MR11A-0927 0800h
Natural Radioactivity of Quarry raw Material in Israel
During the past decade Natural Occurring Radioactive Material (NORM) has been receiving growing attention by radiation protection agencies, including chronic exposure to radon and radiation from building materials. A new Israeli standard (5098) which limit the radionuclide concentration in building material entered into force in 2003. Building materials are often made of natural raw materials which contain natural radionuclides from the $^{238}$U-$^{226}$Ra, $^{232}$Th decay series and $^{40}$K that occur naturally in the Earth's crust. The radionuclide concentration in the building material depends on the source of the raw material, manufacturing process and the addition of technically enhanced NORM (Te NORM) like fly ash, phospho-gypsum, etc. The aim of this study was to investigate the spatial variation of the natural radioactivity in quarries in Israel, the dependency on the type of quarried substance and to asses the raw materials by radiation protection criteria. The study covered a total of 25 quarries all over Israel that manufacture different types of quarried substances (Limestone, Dolomite, Basalt, Gypsum etc.). Each of the quarries was sampled for three different aggregate sizes. The quarries were selected according to geological-geographical criteria such that all types of quarried materials throughout Israel will be investigated. The radionuclide measurement was performed by Gamma spectrometry according to standard procedures. A simulation was carried out on different concrete mixtures to asses the individual effective dose from the building materials. Results indicate large variations in the radionuclide concentration of raw materials in Israel. An optimization based on radiation protection criteria is proposed to minimize radiation exposure from building material.
MR11A-0928 0800h
Electrical Conductivity Beneath Slave Craton (Canada) From Laboratory Experiments
The electrical conductivity beneath Slave craton in North Canada has been characterized on the base of the laboratory measurements of peridotite sample resistance, which have been studied mineralogically in previous works (Kopylova & Russel, 2000; Kopylova & Garo, 2004). The chemical composition of peridotites representing differing depths beneath the Slave craton has been chosen as follows, for the depth from 36 to 100 km spinel peridotite (40-16), from 100 to 140 km low-T spinel-garnet perodotite (41-4), from 140 to 160 km low-T garnet peridotite (8-7), from 160- to 260 km high-T garnet peridotite (40-9). The conductivity of samples were determined in piston-cylinder apparatus at 1 and 2 GPa and in the temperature interval from 600 to 1150$\deg$C. The electrical measurements were conducted in the frequency range from 100 kHz to 10 mHz in a measuring cell having a coaxial capacitor geometry with a geometric factor c. 5-6 cm. The temperature dependence of electrical conductivity follows the Arrhenius dependence with the activation energy varying from 1.94 (sample 40-9) to 1.77 eV (sample 8-7). The pressure increase from 1 GPa to 2 GPa results ina a small increase of the activation energy for $\sim$0.1 eV. Using the temperature profile beneath Slave craton based on thermobarometry of mantle xenolithes from Jericho pipe (Kopylova et al. 1999) the depth profile of the electrical conductivity has been constructed. The magneto-telluric response of these model has been compared with the field MT observations (Jones et al., 2003) with a satisfactory agreement for phase and apparent resistivity in the frequency range $10^{-2}$ to $10^2$ Hz.
MR11A-0929 0800h
3D Simulation of Borehole Breakouts in High-Porosity Sandstone Using the Discrete Element Method
Dependent upon the microstructure of a rock, different mechanical behavior and failure mechanisms have been noted in stress-induced borehole breakouts. Relatively recently, Haimson [1] has identified a somewhat counter-intuitive material response for high-porosity rocks such as Berea Sandstone. Long, slot-like fractures emanating from the borehole, perpendicular to the maximum principal stress, were observed in laboratory samples that had been subject to far-field stresses while undergoing drilling. It has been proposed that the failure mechanism for this phenomenon is compaction band formation in front of the crack-tip and is dependent upon the grain bonding characteristics [2]. This paper discusses the numerical simulation of borehole breakouts in high porosity sandstones using the 3-D discrete element method (DEM) code, OpenDEM. DEM models use discrete particles that interact only with neighboring particles. Therefore, there is great advantage to using a DEM code for this type of analysis where there is dis-aggregation of material in the region of interest. This advantage stems from the formulation of assumptions inherent to DEM that are more closely aligned to the micro-structural behavior of the rock. The numerical model uses a bonded particle model where the rock is represented as a collection of randomly sized spherical particles that are densely packed and bonded together at the particle contact points. The drilling action is modeled by incrementally removing particles in the region of the borehole. Drilling fluid is not modeled. Therefore, in order to account for the flushing action of the drill fluid that carry the de-bonded sand particles from the fracture, as the DEM particles break free from the simulation matrix, they are removed from the simulation. Simulation results will be presented showing qualitative representation of the borehole breakouts. References [1] B.C. Haimson, Phys. Chem. Earth (A), 26(1-2), 15 (2001) [2] B. Haimson, H. Lee, Intl. J. Rock Mech. And Mining Sci., 41, 287 (2004)
MR11A-0930 0800h
"Fossil" bright layer recorded in the low-P/T metamorphic rocks
The "fossil" (geological time) bright layer was recognized in the Cretaceous low-P/T Ryoke metamorphic rocks in the Iwakuni-Yanai area, southwest Japan. Silicified pelitic schists distribute as layers or lenticular bodies several to fifteen meters in thickness, and they are restricted in the greenschist facies conditions within structurally vertical thickness about one kilometer. Silicified pelitic schist is mainly composed of fine-grained quartz and minor muscovite and biotite, and some of colored minerals are decolored by alteration more or less. The boundary between silicified layer and underlying pelitic schist is fairly distinct but that between the overlying pelitic schist is rather gradual. Quartz veins crossing high angles with schistosity were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent ductile flow, were observed in the pelitic schist. En echelon quartz vein and fishnet-like quartz veins are characteristic of silicified rocks. The mode of occurrences of quartz veins indicates that silicified rocks are competent relative to underlying pelitic schist. Fluid inclusion studies were conducted from two kinds of quartz-filled veins: crosscutting foliation in silicified pelitic schist and foliation-parallel in pelitic schist. Fluid inclusions in quartz from a vein crosscutting foliation in silicidied pelitic schist occur as isolated individual inclusions or clusters with preferred spatial arrangement. The isolated inclusions display negative crystal geometries, and are generally range in size from 5 to 10 $\mu$m, with some inclusions up to 20 $\mu$m across. Fluid inclusions in quartz from a foliation-parallel vein are rounded and usually small about a few $\mu$m. Homogenization of the vapour and liquid phases to a single liquid phase occurred at temperatures (Th) between 275 and 330 $\deg$C except in rare instances. The value is considered to be close to the condition of vein formation. Importantly, the homogenization-temperature distributions for vein quartz in silicifeid rocks and pelitic schists are similar. The Raman spectra for the vapour phase within water-rich inclusions indicate that these inclusions contain CO$_{2}$ alone or CO$_{2}$ and CH$_{4}$, in varying molar proportions. The volatile phase is dominated by CO$_{2}$ with small amount of N$_{2}$. All these observations suggest that the silicification of the Ryoke pelitic rocks was a result of silica precipitation from fluids and occurred at the fore-arc region before or coincident with the low-P/T metamorphism. The subducting slab releases fluids into wedge mantle. Deeper fluids may be channelized updip. Silicification occurred in the middle crust and caused sealing process to form impermeable-competent layers. Fluids may likely concentrate just below the bright layer.
MR11A-0931 0800h
Modelling the physical properties of cracked rocks using fracture mechanics and statistical physics
Cracks play a major role in most rocks submitted to crustal conditions. Mechanically, cracks make the rock much more compliant. They also make it much easier for fluid to flow through any rock body. Relying on Fracture Mechanics and Statistical Physics, we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks. The main different schemes which can be used to derive the elastic effective moduli of a rock are presented. It is shown from experimental results that an excellent approximation is the so called non-interactive scheme (Kachanov [1994]). The main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow. Experimental data and model fit on very different rock types (basalt, granite and marbles) show both of these behaviors. We perform a simple least square fit inversion of our data in order to recover the common evolution of the crack density and aspect ratio with stress. The agreement between data and predicted velocities is in general very good, with average error between model and data points lower than 0.1km/sec, demonstrating that the inversion was very stable as a direct consequence of the well constrained laboratory data. At a larger scale, macroscopic fluid flow takes place through the crack network above the percolation threshold. Two macroscopic fluid flow regimes can be distinguished: the percolative regime close to the percolation threshold and the connected regime well above it. Using Statistical Physics and permeability models based on Gu\'eguen and Dienes [1989], we also show how to successfully predict the evolution of permeability, again for comparison to well constrained laboratory results. These results clearly demonstrate the importance of understanding the details of specific rock physical properties, and how they change in response to pressure and temperature in interpreting data from field-scale.
http://www.lassondeinstitute.utoronto.ca/young/people/alex2.htm
MR11A-0932 0800h
The rate-controlling processes during pressure solution: insights from a simple contact model
Intergranular pressure solution in porous grain aggregates may be an important mechanism in deformation of the upper crust and in diagenesis of sedimentary rocks. Three processes may affect the rate of compaction: enhanced dissolution along the highly-stressed grain contacts, diffusion of solute from the contacts into the pore fluid, and low-stress precipitation of the solute within pores. These related processes operate at near the same rate, which is determined by the slowest or rate-controlling process. All three processes are affected by characteristics of the grains and pore fluid (e.g., grain size, reaction rate constants, diffusivity), and by the contact stresses, which change with increasing deformation. We develop a simple mathematical model of a contact between two grains, surrounded by pore fluid. The model is scaled to highlight the important collections of parameters that determine which process is rate-controlling. For simplicity, our model focuses on the early stages of dissolution on a single contact between two grains in a hydrostatic packing of identical grains. Except for fluid expelled during porosity loss, we assume that there is no fluid flow. We model the evolution of the solute concentration in the fluid along the contact and within the pore fluid. The concentration varies between the equilibrium concentration in the pore fluid, and a higher equilibrium concentration on the grain contact (a function of stress on the contact). The degree to which a system is rate-controlled by a particular process depends on the concentrations, relative to these two equilibrium values. The solutions are determined by two dimensionless parameters that are ratios of characteristic times scales for diffusion, contact dissolution and pore precipitation. We calculate how a system evolves through this parameter space with increasing strain. For a cubic packing of spherical grains, we show that dissolution on the contact is always the rate-controlling process at very small strains, with diffusion becoming the rate-controlling process at a strain determined by the system parameters. For example, in coarse (1 mm) quartz sand, assuming a diffusivity of 10$^{-7}$ cm$^{2}$/s, diffusion becomes rate-controlling at volume strains $<$ 1%, while for fine sand (0.1 mm), dissolution remains rate-controlling up to 30% strain. For the quartz aggregates examined, precipitation in the pores is never the rate-controlling mechanism at strains $<$ 30%.
MR11A-0933 0800h
Physical Properties of Rocks and Geophysical Data as Tools for Targeting Fe-Oxide Cu-Au Mineralisations in Northern Sweden
It is well documented that ore mineralisations are frequently associated with various types of rock alterations. These rock alterations may affect in different extents the physical properties of rocks. The present work focuses on the petrophysical and geophysical properties of Fe-oxide Cu-Au mineralisations (IOCG) in the western Kiruna mining district, northern Sweden, with special attention to the Tjarrojakka IOCG mineralisations. Exploration models developed in different areas worldwide (e.g. Australia, Canada) show that IOCG mineralisations are preferentially located in proximity of faults associated with deformation zones of regional relevance, and that IOCG mineralisations are hosted in areas affected by potassic to sodic alteration. This study indicates that at semi-regional scale IOCG mineralisations are located within areas of high gravity anomalies, high values of calculated K content and high K/Th ratios (from airborne radiometric data), which is expression of potassic alteration. In addition to this, extremely high magnetic anomalies situate Fe-oxide (magnetite) occurrences, while low linear magnetic anomalies mark fault/shear zones, in proximity of which the majority of the IOCG-mineralisations are found. At local scale, the IOCG mineralisations of Tjarrojakka are associated with high magnetic and gravity anomalies and high values of the K/Th ratio. Combined petrophysical and geochemical analysis indicate that ferromagnetic minerals (Ti-magnetite) are widely present in the area, together with an alteration phase that is interpreted as Ti-haematite. Cu-sulphides occurrences seem to be related to potassic altered zones, as suggested by Ba enrichment.