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Olivine, the most abundant mineral in the upper mantle, plays a key role in controlling the thermodynamic properties in the Earth's and planetary interiors, like the temperature distribution along the adiabatic geotherm. In this study, we conducted simultaneous high-pressure (P) and high-temperature (T) Raman measurements on a San Carlos olivine sample in an externally heated diamond-anvil cell (DAC). The intrinsic anharmonic parameters, ai, are calculated as functions of both pressure and temperature, and the isochoric (CV) and isobaric (CP) heat capacities are computed at various P-T conditions with the anharmonic correction. The harmonic heat capacities are CV = 807.7 J/kg/K and CP = 815.4 J/kg/K at ambient conditions, with anharmonic contribution of ΔC = 7.9 J/kg/K. Relative to the previous vibrational measurements conducted at high-P or high-T conditions, this simultaneous high-P-T experiment indicates that the anharmonic contribution to heat capacities is overestimated if the anharmonic parameters (ai) are treated as constants, as done previously. The pressure effect is marginal on the intrinsic anharmonic contribution to thermodynamic properties, whereas it has a much more significant effect on the external anharmonicity (thermal expansivity). The pressure dependence of CP (dCP/dP, in J/kg/K/GPa) increases from –3.14 at 300 K to –1.94 at 700 K, and then decreases smoothly to –5.03 at 1800 K. Combining the derived high-P-T capacity with a reliable P-V-T equation of state (EoS) for olivine, we further modeled the thermodynamic Grüneisen parameter, γ(P-T). The Grüneisen parameter is important for the connection between isothermal and adiabatic compressions of minerals, which can be decreased by approximately 5% with the anharmonic correction at high temperatures. The modeled adiabatic bulk modulus and bulk sound velocity can be expressed as: KS(T,P) (GPa) = 127.5(1) + 4.32(5)·P – 0.018(1)·(T – 300) and VΦ(T-P) (km/s) = 6.22(2) + 0.069(3)·P – [3.74(15)–0.075(13)·P]·10–4·(T – 300). The adiabatic temperature gradient, dTS/dP, which is almost independent of pressure, equals 13.40(16) and 12.35(16) K/GPa in the harmonic and anharmonic models, respectively. This study provides a useful example for modeling the radial temperature distribution in adiabatic planetary mantles. [ABSTRACT FROM AUTHOR]

Jeffbenite (Mg3Al2Si3O12) is a tetragonal phase found in so far only in superdeep diamonds, and its thermoelastic parameters are a prerequisite for determining entrapment pressures as it is regarded as a potential indicator for superdeep diamonds. In this study, the thermoelastic properties of synthetic Fe3+‐jeffbenite were measured up to 33.7 GPa and 750 K. High‐temperature static compression data were fitted, giving (∂KT0/∂T)P = −0.0107 (4) GPa/K and αT = 3.50 (3) × 10−5 K−1. The thermoelastic properties and phase stability are applied to modeling isomekes, or P‐T paths intersecting possible conditions of entrapment in diamond. We calculate that under ideal exhumation, jeffbenite entrapped at mantle transition zone conditions will exhibit a high remnant pressure at 300 K (Pinc) of ∼5.0 GPa. Elastic geobarometry on future finds of jeffbenite inclusions can use the new equation of state to estimate entrapment pressures for this phase with still highly uncertain stability field in the mantle. Plain Language Summary: Ongoing superdeep diamonds research is providing new insights into the Earth's deep mantle. Natural superdeep diamonds and its inclusions can show compelling evidence for retrograde conversion from the lower mantle or transition zone precursors; along with carbonate melt‐peridotite reactions. Jeffbenite with a composition of Mg3Al2Si3O12, found in so far only in superdeep diamonds can be regarded as a potential indicator mineral for superdeep diamonds. Recent synthesis of Fe3+‐rich jeffbenite provides an opportunity for in‐situ measurements to study the thermodynamic properties of jeffbenite at deep‐mantle conditions. Thus, in this study, we explored the high pressure and temperature stability and thermoelastic properties of Fe‐bearing jeffbenite up to 33.7 GPa and 750 K. The thermoelastic data and phase stability were measured and the results are applied to modeling the isomekes, or P‐T paths intersecting possible conditions of entrapment and along which the pressure on the inclusion is equal to the external pressure on the diamond host. Our finding can be applied to determining entrapment pressures in such diamond inclusions in future finds and its primary or retrograde history is essential in understanding mantle dynamics and the hidden consequences of plate tectonics. Key Points: We measure the phase stability and thermoelastic properties on synthetic Fe‐bearing jeffbeniteThe thermoelastic data are applied to modeling isomekes and the remnant pressure (Pinc) is determinedThe smaller thermal expansivity of jeffbenite gives rise to a broader pressure and temperature stability field in the upper lower mantle [ABSTRACT FROM AUTHOR]

The transition zone of the Earth's upper mantle is characterized by three discontinuities in seismic wave velocity profiles. One of these at about a depth of 520 km is assigned to the transformation of wadsleyite (β-) to ringwoodite [γ-(Mg, Fe).sub.2SiO.sub.4] (e.g., Shearer in J Geophys Res 101:3053-3066, 1996 (See CR32)). The exact location, width, and other properties of that discontinuity are affected by a multitude of parameters. The present study specifically focuses on the effect of water, iron content, and redox environment on the depth of the phase transition. We performed high-pressure experiments in a multi-anvil apparatus at 1200 °C with variation in Mg-Fe compositions (0.10 < x.sub.Fe < 0.24), water contents (0 < [Formula omitted] < 2 wt%), and the redox environment [using different buffers: Fe/FeO (reducing), Re/ReO.sub.2 (oxidizing)]. Run products were investigated using electron microprobe and Fourier transform infrared spectroscopy to obtain the composition including the hydroxyl concentration of coexisting phases. Mossbauer (MB) spectroscopy and electron energy loss spectroscopy as well as single-crystal X-ray diffraction were applied to gain insight into the Fe.sup.3+ content and incorporation mechanisms. Under hydrous and reducing conditions, the wadsleyite-ringwoodite boundary shifts by 0.5 GPa to higher pressures accompanied by a broadening of the region of coexisting wadsleyite and ringwoodite. In contrast, under hydrous and oxidizing conditions, the two-phase field gets narrower and the shift of the two-phase field to higher pressure is amplified. Thus, the stability field of wadsleyite is extended to higher pressure, most likely due to the higher water and Fe.sup.3+ content in the wadsleyite structure compared to ringwoodite. Based on results from MB spectroscopy and single-crystal X-ray diffraction, we infer that Fe.sup.3+ in wadsleyite is incorporated as a spinelloid component and stabilizes wadsleyite to higher pressures. Electronic supplementary material The online version of this article (doi:10.1007/s00410-015-1163-2) contains supplementary material, which is available to authorized users., Author(s): Maria Mrosko[sup.1] , Monika Koch-Müller[sup.1] , Catherine McCammon[sup.2] , Dieter Rhede[sup.3] , Joseph R. Smyth[sup.4] , Richard Wirth[sup.1] Author Affiliations: (1) Sektion 3.3, Chemie und Physik der Geomaterialien, Deutsches [...]

MgSi[O.sub.3] akimotoite is stable relative to majoritegarnet under low-temperature geotherms within steeply or rapidly subducting slabs. Two compositions of Mg-akimotoite were synthesized under similar conditions: Z674 (containing about 550 ppm wt [H.sub.2]O) was synthesized at 22 GPa and 1,500°C and SH1101 (nominally anhydrous) was synthesized at 22 GPa and 1,250°C. Crystal structures of both samples differ significantly from previous studies to give slightly smaller Si sites and larger Mg sites. The bulk thermal expansion coefficients of Z674 are (153-839 K) of [a.sub.1] = 20(3) x [10.sup.-9] [K.sup.-2] and [a.sub.0] = 17(2) x [10.sup.-6] [K.sup.-1], with an average of [α.sub.0] = 27.1(6) x [10.sup.-6] [K.sup.-1]. Compressibility at ambient temperature of Z674 was measured up to 34.6 GPa at Sector 13 (GSECARS) at Advanced Photon Source Argonne National Laboratory. The second-order Birch-Murnaghan equation of state (BM2 EoS) fitting yields: [V.sub.0] = 263.7(2) [Å.sup.3], [K.sub.T0] = 217(3) GPa (K fixed at 4). The anisotropies of axial thermal expansivities and compressibilities are similar: [α.sub.a] = 8.2(3) and [α.sub.c] = 10.68(9) ([10.sup.-6][K.sup.-1]); [β.sub.a] = 11.4(3) and [β.sub.c] = 15.9(3) ([10.sup.-4] GPa). Hydration increases both the bulk thermal expansivity and compressibility, but decreases the anisotropy of structural expansion and compression. Complementary Raman and Fourier transform infrared (FTIR) spectroscopy shows multiple structural hydration sites. Low-temperature and high-pressure FTIR spectroscopy (15-300 K and 0-28 GPa) confirms that the multiple sites are structurally unique, with zero-pressure intrinsic anharmonic mode parameters between -1.02 x [10.sup.-5] and +1.7 x [10.sup.-5] [K.sup.-1], indicating both weak hydrogen bonds (O-H ... O) and strong OH bonding due to long O ... O distances. Keywords Akimotoite * Crystal structure * Thermal expansion * Compressibility * Anisotropy * FTIR, Introduction Akimotoite (ilmenite-type MgSi[O.sub.3]) is stable at pressures of 18- 25 GPa and up to about 2,000 K in the MgSi[O.sub.3] system, with wadsleyite plus stishovite stable at lower pressures, [...]

Two samples of hydroxyl-clinohumite, sample SZ0407B with approximate composition Mg8674(14) [Fe0.374.sub.(4)][([Si.sub.0.99(1)][O.sub.4]).sub.4][(OH).sub.2] and sample SZ0411B with composition [Mg.sub.9][(Si[O.sub.4]).sub.4][(OH).sub.2], were synthesized at 12 GPa and 1,250°C coexisting with olivine. Unit-cell parameters determined by single-crystal X-ray diffraction are given as follows: a = 4.7525(4) Å, b = 10.2935(12) Å, c = 13.7077(10) Å, α = 100.645(9)°, V = 659.04(9) [Å.sup.3] for SZ0407B, and a = 4.7518(6) Å, b = 10.2861(12) Å, c = 13.7008(9) Å, α = 100.638(9)°, V = 658.15(9) [Å.sup.3] for SZ0411B. Single-crystal X-ray intensity data were collected for crystal structure refinements of both samples. Relative to the pure-Mg sample, Fe decreases M3-OH bond lengths by ~0.010(3) Å, consistentwithsome ferriciron ordering into M3. Raman spectroscopy shows two strong bands in the lattice-mode region at 650 and 690 [cm.sup.-1] in the Fe-bearing sample, which are not observed in the pure-Mg sample. Spectra in the [H.sub.2]O region show at least five bands, which are deconvolved into seven distinct O-H-stretching modes. Thermal expansion measurements were carried out for both samples from 153 to 787 K by single-crystal X-ray diffraction. The average a-, b-, c-axial and volumetric thermal expansion coefficients ([10.sup.-6] [K.sup.-1]) are 10.5(1), 12.3(2), 12.5(2) and 34.9(5) for SZ0407B, respectively, and 11.1(1), 12.6(3), 13.7(3), 36.8(6) for SZ0411B, respectively. After heating, the unit-cell parameters were refined again for each sample at ambient condition, and no significant changes were observed, indicating no significant oxidation or dehydration during the experiment. For the DHMS phases along the brucite-forsterite join, linear regression gives a systematic linear decrease in expansivity with increasing density. Further, substitution of ferrous iron into these structures decreases thermal expansivity, making the Fe-bearing varieties slightly stiffer. Keywords Clinohumite * Crystal structure * Thermal expansion * Iron effect, Introduction The dense hydrous magnesium silicate (DHMS) minerals along the brucite (Br)-forsterite (Fo) join have been widely studied and proposed as potential carriers of water into the Earth's mantle(McGetchinetal., 1970;Wunder [...]

Hydrous wadsleyite ([beta]-[Mg.sub.2]Si[O.sub.4]) with 2.8 wt% water content has been synthesized at 15 GPa and 1250[degrees]C in a multi-anvil press. The unit-cell parameters are: a = 5.6686(8), b = 11.569(1), c = 8.2449(9) [Angstrom], [beta] = 90.14(1)[degrees], and V = 540.7(1) [[Angstrom].sup.3], and the space group is I2/m. The structure was refined in space groups Imma and I2/m. The room-pressure structure differs from that of anhydrous wadsleyite principally in the increased cation distances around O1, the non-silicate oxygen. The compression of a single crystal of this wadsleyite was measured up to 61.3(7) GPa at room temperature in a diamond anvil cell with neon as pressure medium by X-ray diffraction at Sector 13 at the Advanced Photon Source, Argonne National Laboratory. The experimental pressure range was far beyond the wadsleyite-ringwoodite phase-transition pressure at 525 km depth (17.5 GPa), while a third-order Birch-Murnaghan equation of state (EoS) [[V.sub.0] = 542.7(8) [[Angstrom].sup.3], [K.sub.TO] = 137(5) GPa, K' = 4.6(3)] still fits the data well. In comparison, the second-order fit gives [V.sub.0] = 542.7(8) [[Angstrom].sup.3], [K.sub.T] = 147(2) GPa. The relation between isothermal bulk modulus of hydrous wadsleyite [K.sub.TO] and water content [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is: KTO = 171 ( 1)-12(1 ) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (up to 2.8 wt% water). The axial-compressibility [[beta].sub.c] is larger than both [[beta].sub.a] and [[beta].sub.b], consistent with previous studies and analogous to the largest coefficient of thermal expansion along the c-axis. Keywords: Compressibility, hydrous wadsleyite, neon, orthorhombic DOI: 10.2138/am.2010.3533

We present a detailed [sup.29]Si NMR spectroscopic study of isotopically enriched samples of forsterite and of anhydrous and hydrous wadsleyite and ringwoodite ([alpha], [beta], and [gamma] phases of [Mg.sub.2]Si[O.sub.4]), which complement previous extensive studies of these minerals by XRD and vibrational spectroscopy, [sup.VI]Si is not detected in any of the phases at levels of about 0.1 to 0.5%. When coupled with recent theoretical calculations on ringwoodite, this suggests the possibility of re-ordering of high-temperature octahedral-tetrahedral disorder during cooling. Cross-polarization ([sup.29]Si{[sup.1]H } CPMAS) NMR supports the protonation of O1 oxygen atoms in hydrous wadsleyite without formation of significant amounts of Si-OH groups, in contrast, new NMR peaks appear in hydrous ringwoodite that cross-polarize very rapidly, indicating very short Si-H distances and the presence of Si-OH, as expected from models in which much of the [H.sup.+] substitutes into [Mg.sup.2+] vacancies. Static NMR spectra provide new constraints on chemical shift anisotropies in wadsleyite and are fully consistent with the cubic structure of ringwoodite. Spin-lattice relaxation in all phases is much better fitted by a stretched exponential function than with a more conventional '[T.sub.1]' exponential, as expected when relaxation is dominated by paramagnetic impurities. However, the effects of paramagnetic impurity on ion contents on relaxation, and on the formation of newly observed minor peaks that may result from 'pseudo-contact shifts,' appear to depend on mineral structure, and will require considerable future study to understand in detail. Keywords: NMR spectroscopy, forsterite, wadsleyite, ringwoodite, water in mantle

Single-crystal X-ray diffraction has been used to measure the thermal expansion coefficients of forsterite, wadsleyite, ringwoodite, and their hydrous forms at ambient pressure, from temperatures as low as 133 K to as high as 919 K. Second-order polynomial fitting to ln(V/[V.sub.0]) vs. T was applied to derive the expansion coefficients in the form of [alpha] = [a.sub.l] x T + [a.sub.0]. The single crystal of anhydrous wadsleyite persisted up to 859 K. Hydrous forsterite was observed to dehydrate at 919 K, whereas hydrous wadsleyite started to dehydrate at 655 K. The crystal of ringwoodite with 0.20 wt% broke down at 911 K, and the two ringwoodite samples with 0.74 and 2.4 wt% [H.sub.2]O, were observed to break down with an irreversible unit-cell expansion at 808 and 606 K, respectively. From room temperature to high temperatures in this study, the mean thermal volume expansion coefficients are 36.4(5) and 38.1 (9) x [10.sup.-6] [K.sup.-1], respectively, for anhydrous and hydrous forsterite; 28.5(5) and 35.8(8) x [10.sup.-6] [K .sup.-1], respectively, for the anhydrous and hydrous wadsleyite; 30.6(9), 35.2(15), and 34.9(7) x [10.sup.-6] [K.sup.-1] for the samples ofringwoodite with 0.2, 0.74, and 2.4 wt% [H.sub.2]O, respectively. Thus, forsterite, wadsleyite, and ringwoodite all have larger thermal expansion coefficients in their hydrous forms than in their anhydrous forms. Keywords: Thermal expansion, forsterite, wadsleyite, ringwoodite, single crystal

The crystal structure of hydrous pure magnesium forsterite ([Mg.sub.2]Si[O.sub.4]) containing 8900 ppmw [H.sub.2]O, synthesized at 12 GPa and 1250[degrees]C, has been refined. The major hydration mechanism appears to be M1 cation vacancy with protonation of the O1-O2 octahedral edge of M1. Raman spectra up to 41 GPa show strong coupling between the two [A.sub.g] modes (824.4and 856.2 [cm.sup.-1]). Mode Gruneisen parameters [[gamma].sub.i], related to Mg(2)[O.sub.6] translation mode decrease relative to anhydrous forsterite. This is attributed to the fact that the M2 site shows full occupancy compared to the M1 site, and the vacancy predominantly occurs at the M1 site. Pressure dependencies of four OH vibrations in the region 3548-3615 [cm.sup.-1] suggest that positional ordering of hydrogen ion (proton) takes place with increasing pressure. The OH mode at 3615 [cm.sup.-1] shows complex response as a function of pressure: the ([partial derivative]v/[partial derivative]P) slope changes from -0.43 below l0 GPa to 1.97 between 10 and 20 GPa, and does not show clear pressure dependence above 20 GPa. Single-crystal X-ray data were used to assign the OH band to the structural sites, O1 and O2. The proton is closer to O2 than O1. The distance between the proton and O2 is 0.96 [Angstrom]. In view of the empirical relation between OH-stretching frequencies and O ... O distances (Libowitzky 1999), the pressure dependence of the OH mode (3615 [cm.sup.-1]) is well correlated with the O1-O2 distance and the degree of hydrogen bonding. Keywords: Forsterite, X-ray diffraction, Raman spectroscopy, hydration mechanism, high pressure

We present here high-resolution [sup.29]Si MAS NMR data for synthetic samples of forsterite ([alpha]- [Mg.sub.2]Si[O.sub.4]), wadsleyite ([beta]), and ringwoodite ([gamma]). Enrichment to >99% [sup.29]Si provides greatly enhanced signal-to-noise ratios and thus great sensitivity to small features in the spectra. At a detection limit of 0.1 to 0.5%, no six-coordinated Si ([sup.vi]si) is observed in any of the polymorphs, although these results could be consistent with theoretical predications of 1 to 2% Mg-Si site disorder in ringwoodite if re-ordering occurs rapidly during cooling. Several small [sup.iv]Si peaks in ringwoodite samples may be related to residual defects from this process. In forsterite and wadsleyite, several very small 'extra' peaks are observed, many of which are at positions far outside the known range of chemical shifts for [sup.29]Si in silicates. These may be caused by 'pseudo-contact' shifts from dipolar interactions with unpaired electron spins on trace impurities of paramagnetic transition metal cations. Keywords: NMR spectroscopy, forsterite, ringwoodite, wadsleyite, high-pressure studies

While it is widely agreed that automated and autonomous vehicles may provide safety benefits over vehicles with lower level or no automation, due to other road users there will still likely be situations where a collision is unavoidable. What should a vehicle that is operating autonomously do when it has no choice but to have a collision? And who should decide which vehicle manoeuvre is the most acceptable? These situations create moral dilemmas requiring consideration of the most acceptable and moral action of the vehicle. In this paper we explore current research in this domain and work towards enabling ethical solutions. We identify current experimental work (practical studies rather than theoretical studies) on this problem often contains fundamental flaws due to the lack of real-world validity within the studied scenarios. We argue that morality is highly context dependent and that participants need to be more engaged in the choices they are claiming to make. Suggestions for future work include virtual reality or simulation methodologies which promote immersivity to ensure procedural validity whilst retaining safety. We also identify current guidelines contradict public viewpoint and argue public attitude needs to be better understood to give autonomous and automated vehicle manufacturers confidence in their design. [ABSTRACT FROM AUTHOR]

A suite of pure magnesian wadsleyite ([beta]-[Mg.sub.2]Si[O.sub.4]) samples containing 0.005, 0.38, 1.18, and 1.66 wt% [H.sub.2]O was studied by single-crystal X-ray diffraction to determine the effects of hydration on cation ordering and crystal symmetry. Separate compressibility experiments were carried out to 9.6 GPa to determine the effects of hydration on isothermal equations of state. Crystal-structure refinements at ambient conditions show cation vacancies order onto the M3 site. The most hydrous sample (1.6 wt% [H.sub.2]O) displayed monoclinic symmetry with [beta] = 90.090(7)[degrees], whereas the samples with lower content were statistically orthorhombic. The density of wadsleyite decreases with increasing water content at STP according to the empirical relation, [rho] = 3.470(2) -0.046(2) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] g/[cm.sup.3] (with [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] in wt% [H.sub.2]O). Bulk moduli and pressure derivatives of wadsleyite are [K.sub.T0] = 173(5) GPa, [K.sub.0]' = 4.1(15) for 0.005 wt% [H.sub.2]O; [K.sub.T0] = 161(4) GPa, [K.sub.0]' = 5.4(11) for 0.38 wt% [H.sub.2]O; [K.sub.T0] = 158(4) GPa, [K.sub.0]' = 4.2(9) for 1.18 wt% [H.sub.2]O; and [K.sub.T0] = 154(4) GPa, [K.sub.0]' = 4.9(11) for 1.66 wt% [H.sub.2]O. Variation of the bulk modulus of wadsleyite with water content is non-linear, which may be attributable to softening of the structure by ordering of vacancies onto two non-equivalent M3 sites (M3a and M3b) and an accompanying dilution of orthorhombic symmetry. Keywords: Wadsleyite, bulk modulus, equation of state, nominally anhydrous minerals, mantle Transition Zone