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All available volume and elasticity data for the garnet end-members grossular, pyrope, almandine and spessartine have been re-evaluated for both internal consistency and for consistency with experimentally measured heat capacities. The consistent data were then used to determine the parameters of third-order Birch–Murnaghan EoS to describe the isothermal compression at 298 K and a Mie–Grüneisen–Debye thermal-pressure EoS to describe the PVT behaviour. In a full Mie–Grüneisen–Debye EoS, the variation of the thermal Grüneisen parameter with volume is defined as γ = γ 0 V V 0 q . For grossular and pyrope garnets, there is sufficient data to refine q which has a value of q  = 0.8(2) for both garnets. For other garnets, the data do not constrain the value of q and we therefore refined a q- compromise version of the Mie–Grüneisen–Debye EoS in which both γ / V and the Debye temperature θ D are held constant at all P and T , leading to ∂ C V ∂ P T = 0 , parallel isochors and constant isothermal bulk modulus along an isochor. Final refined parameters for the q- compromise Mie–Grüneisen–Debye EoS are: Pyrope Almandine Spessartine Grossular V 0 (cm 3 /mol) a 113.13 115.25 117.92 125.35 K 0T (GPa) 169.3 (3) 174.6 (4) 177.57 (6) 167.0 (2) K 0 T ′ 4.55 (5) 5.41 (13) 4.6 (3) 5.07 (8) θ D0 771 (28) 862 (22) 860 (35) 750 (13) γ 0 1.185 (12) 1.16 (fixed) 1.18 (3) 1.156 (6) for pyrope and grossular, the two versions of the Mie–Grüneisen–Debye EoS predict indistinguishable properties over the metamorphic pressure and temperature range, and the same properties as the EoS based on experimental heat capacities. The biggest change from previously published EoS is for almandine for which the new EoS predicts geologically reasonable entrapment conditions for zircon inclusions in almandine-rich garnets.

Elastic geothermobarometry is a method of determining metamorphic conditions from the excess pressures exhibited by mineral inclusions trapped inside host minerals. An exact solution to the problem of combining non-linear Equations of State (EoS) with the elastic relaxation problem for elastically isotropic spherical host-inclusion systems without any approximations of linear elasticity is presented. The solution is encoded into a Windows GUI program EosFit-Pinc. The program performs host-inclusion calculations for spherical inclusions in elastically isotropic systems with full P-V-T EoS for both phases, with a wide variety of EoS types. The EoS values of any minerals can be loaded into the program for calculations. EosFit-Pinc calculates the isomeke of possible entrapment conditions from the pressure of an inclusion measured when the host is at any external pressure and temperature (including room conditions), and it can calculate final inclusion pressures from known entrapment conditions. It also calculates isomekes and isochors of the two phases.

The pressure dependence of the polarized Raman scattering of quartz was studied under hydrostatic conditions up to 9 GPa. We extended the available pressure calibrations, usually limited to the two most intense peaks, to a larger number of modes, providing polynomial functions that describe the relationship between pressure P and wavenumber shift Δ ω for the 128-, 206-, 265-, 464-, 696-, 809-, 1080- and 1161- cm - 1 modes. For the first time, the pressure behavior of the LO-TO splitting is characterized up to 9 GPa under hydrostatic conditions. The pressure-induced wavenumber changes and derived phonon compressibilities show that longitudinal and transverse modes can be used interchangeably for the calculation of strains through the Grüneisen tensor to derive the strains in crystals, such as mineral inclusions, under non-hydrostatic conditions. A careful examination of the linewidths as a function of pressure shows that they are sensitive to the metastability of the quartz structure with respect to the high-pressure silica polymorphs. It is proposed that strong multiphonon interactions contribute to the stability of the structure of quartz at ambient conditions.

The ultrahigh-pressure (UHP) whiteschists of the Brossasco-Isasca unit (Dora-Maira Massif, Western Alps) provide a natural laboratory in which to compare results from classical pressure (P)–temperature (T) determinations through thermodynamic modelling with the emerging field of elastic thermobarometry. Phase equilibria and chemical composition of three garnet megablasts coupled with Zr-in-rutile thermometry of inclusions constrain garnet growth within a narrow P–T range at 3–3.5 GPa and 675–720 °C. On the other hand, the zircon-in-garnet host-inclusion system combined with Zr-in-rutile thermometry would suggest inclusion entrapment conditions below 1.5 GPa and 650 °C that are inconsistent with the thermodynamic modelling and the occurrence of coesite as inclusion in the garnet rims. The observed distribution of inclusion pressures cannot be explained by either zircon metamictization, or by the presence of fluids in the inclusions. Comparison of the measured inclusion strains with numerical simulations shows that post-entrapment plastic relaxation of garnet from metamorphic peak conditions down to 0.5 GPa and 600–650 °C, on the retrograde path, best explains the measured inclusion pressures and their disagreement with the results of phase equilibria modelling. This study suggests that the zircon-garnet couple is more reliable at relatively low temperatures (< 600 °C), where entrapment conditions are well preserved but chemical equilibration might be sluggish. On the other hand, thermodynamic modelling appears to be better suited for higher temperatures where rock-scale equilibrium can be achieved more easily but the local plasticity of the host-inclusion system might prevent the preservation of the signal of peak metamorphic conditions in the stress state of inclusions. Currently, we cannot define a precise threshold temperature for resetting of inclusion pressures. However, the application of both chemical and elastic thermobarometry allows a more detailed interpretation of metamorphic P–T paths.

Elasticity is a key property of materials, not only for predicting volumes and densities of minerals at the pressures and temperatures in the interior of the Earth, but also because it is a major factor in the energetics of structural phase transitions, surface energies, and defects within minerals. Over the 40 years of publication of Physics and Chemistry of Minerals , great progress has been made in the accuracy and precision of the measurements of both volumes and elastic tensors of minerals and in the pressures and temperatures at which the measurements are made. As an illustration of the state of the art, all available single-crystal data that constrain the elastic properties and pressure–volume–temperature equation of state (EoS) of mantle-composition olivine are reviewed. Single-crystal elasticity measurements clearly distinguish the Reuss and Voigt bulk moduli of olivine at all conditions. The consistency of volume and bulk modulus data is tested by fitting them simultaneously. Data collected at ambient pressure and data collected at ambient temperature up to 15 GPa are consistent with a Mie–Grünesien–Debye thermal-pressure EoS in combination with a third-order Birch–Murnaghan (BM) compressional EoS, the parameter V 0  = 43.89 cm 3  mol −1 , isothermal Reuss bulk modulus K TR,0 = 126.3 ( 2 ) GPa , K TR,0 ′ = 4.54 ( 6 ) , a Debye temperature θ D = 644 ( 9 ) K , and a Grüneisen parameter γ 0  = 1.044(4), whose volume dependence is described by q  = 1.9(2). High-pressure softening of the bulk modulus at room temperature, relative to this EoS, can be fit with a fourth-order BM EoS. However, recent high- P , T Brillouin measurements are incompatible with these EoS and the intrinsic physics implied by it, especially that ∂ K TR ′ ∂ T P > 0 . We introduce a new parameterisation for isothermal-type EoS that scales both the Reuss isothermal bulk modulus and its pressure derivative at temperature by the volume, K TR ( T , P = 0 ) = K TR,0 V 0 V ( T ) δ T and K TR ′ ( T , P = 0 ) = K TR,0 ′ V ( T ) V 0 δ ′ , to ensure thermodynamic correctness at low temperatures. This allows the elastic softening implied by the high- P , T Brillouin data for mantle olivine to be fit simultaneously and consistently with the same bulk moduli and pressure derivatives (at room temperature) as the MGD EoS, and with the additional parameters of α V0  = 2.666(9) × 10 −5  K −1 , θ E = 484 ( 6 ) , δ T  = 5.77(8), and δ ′  = −3.5(1.1). The effects of the differences between the two EoS on the calculated density, volume, and elastic properties of olivine at mantle conditions and on the calculation of entrapment conditions of olivine inclusions in diamonds are discussed, and approaches to resolve the current uncertainties are proposed.

The internal structure and dynamics of Earth have been shaped by the 660 km boundary between the mantle transition zone and lower mantle. However, due to the paucity of natural samples from this depth, the nature of this boundary—its composition and volatile fluxes across it—remain debated. Here we analyse the mineral inclusions in a rare type IaB gem diamond from the Karowe mine (Botswana). We discovered recovered lower-mantle minerals ringwoodite + ferropericlase + low-Ni enstatite (MgSiO 3 ) in a polyphase inclusion, together with other principal lower-mantle minerals and hydrous phases, place its origin at ~23.5 GPa and ~1,650 °C, corresponding to the depth at the 660 km discontinuity. The petrological character of the inclusions indicates that ringwoodite (∼Mg 1.84 Fe 0.15 SiO 4 ) breaks down into bridgmanite (∼Mg 0.93 Fe 0.07 SiO 3 ) and ferropericlase (∼Mg 0.84 Fe 0.16 O) in a water-saturated environment at the 660 km discontinuity and reveals that the peridotitic composition and hydrous conditions extend at least across the transition zone and into the lower mantle. Hydrous conditions extend across the 660 km discontinuity between Earth’s mantle transition zone and lower mantle, according to analysis of a polyphase mineral inclusion in a gem diamond from the Karowe mine, Botswana

The origin of diamonds in ureilite meteorites is a timely topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within Earth’s mantle. We investigated fragments of three diamond-bearing ureilites (two from the Almahata Sitta polymict ureilite and one from the NWA 7983 main group ureilite). In NWA 7983 we found an intimate association of large monocrystalline diamonds (up to at least 100 μm), nanodiamonds, nanographite, and nanometric grains of metallic iron, cohenite, troilite, and likely schreibersite. The diamonds show a striking texture pseudomorphing inferred original graphite laths. The silicates in NWA 7983 record a high degree of shock metamorphism. The coexistence of large monocrystalline diamonds and nanodiamonds in a highly shocked ureilite can be explained by catalyzed transformation from graphite during an impact shock event characterized by peak pressures possibly as low as 15 GPa for relatively long duration (on the order of 4 to 5 s). The formation of “large” (as opposed to nano) diamond crystals could have been enhanced by the catalytic effect of metallic Fe-Ni-C liquid coexisting with graphite during this shock event. We found no evidence that formation of micrometer(s)-sized diamonds or associated Fe-S-P phases in ureilites require high static pressures and long growth times, which makes it unlikely that any of the diamonds in ureilites formed in bodies as large as Mars or Mercury.

The structural and chemical properties of zircon inclusions in garnet megablasts from the Dora Maira Massif (Western Alps, Italy) were characterized in detail using charge contrast imaging, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The aim of this work is to determine to what extent the degree of metamictization, metamorphic recrystallization, inherent structural heterogeneity, chemical composition, and zoning, along with the elastic stress imposed by the host mineral, can influence the Raman peak position of the zircon inclusion and hence, the residual pressure estimated via Raman geo-thermobarometry. We show and confirm that metamictization and inherent structural heterogeneity have a major influence in the Raman spectra of zircon in terms of peak position and peak width. We suggest that, for spectral resolution of 2 cm , the peak width of the B mode near 1008 cm of reliable grains must be smaller than 5 cm . The method can be applied to both inherited igneous and newly formed Alpine metamorphic crystals. By coupling structural and chemical information, we demonstrate that there are no significant diferences between the Raman spectra of zircon with oscillatory-zoned texture, formed during magmatic crystallization, and those formed by fluid-induced Alpine (re)crystallization. The discrimination between magmatic and metamorphic zircon based only on micro-textural constraints is not robust. Finally, our results allow establishing a protocol devoted to the selection of reliable buried zircon inclusions, relying only on Raman spectroscopic measurements, to use for elastic thermobarometry applications.

Spinel is potentially one of the best minerals for elastic geobarometry, but the large uncertainties in the published equation of state (EoS) of spinel prevent the application of elastic geobarometry using spinel. We have determined the EoS of MgAl 2 O 4 from literature data on the volume, elasticity, and isobaric heat capacity by paying particular attention to the consistency of the thermoelastic data within the dataset and the influence of the inversion degree ( i ; (Mg 1- i Al i )[Mg i Al 2- i ]O 4 ) on the physical properties. After appropriate data selection, normalization, and correction, the resulting dataset was fitted with various EoS. Thermal pressure EoS that combined the third-order Birch–Murnaghan EoS and the Mie–Grüneisen–Debye EoS explain the data most successfully. The analysis yielded the following six EoS parameters: V 0  = 39.78 cm 3 /mol (fixed), K T 0  = 196.43(12) GPa, K ′ T 0  = 4.37(4), θ D0  = 898(10) K, γ 0  = 1.136(11), and q  = 1.94(9). The EoS has the properties at room conditions of α V  = 1.6765(10) × 10 –5  K –1 and K S 0  = 197.55(12) GPa. Combining our EoS with the published EoS, it was found that MgAl 2 O 4 inclusions trapped in olivine and orthopyroxene derived from the spinel-lherzolite stability field should always have positive residual pressures ( P inc ) at room conditions. This implies that elastic geobarometry using these host-inclusion systems can be expected to be new methods for estimating the depth provenance of spinel-bearing peridotites. In contrast olivine, orthopyroxene, and clinopyroxene inclusions in MgAl 2 O 4 are expected to have P inc  > 0 only when trapped (or re-equilibrated) in geological environments with geotherms corresponding to surface heat flows below about 50, 60 and 70 mW/m 2 , respectively.

Extraterrestrial carbon gives insights into the origin of life and processes that took place billions of years ago in our solar system. Here, the authors provide an overview of what is known and of unanswered questions with a meteoritical focus.