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During accretion, nitrogen was distributed between metal melt, silicate melt, and the atmosphere and today's N deficit of bulk silicate Earth with respect to chondrites may be due to segregation into the core and/or atmospheric losses. To examine the former, we experimentally determined N solubilities in Fe‐dominated metal melts at 1200–1800 °C, 0.4–9.0 GPa. Results show that pressure has a strong positive influence on N solubility, increasing from 1.0 to 7.4 wt% at 1–9 GPa (1400 °C) while temperature has the inverse effect, N solubility decreasing from 1.3 to 0.6 wt% at 1200–1800 °C (1 GPa). The solubility data are parameterized as function of pressure and temperature. Our results suggest that core‐forming metal melts can dissolve large quantities of N, and the potential N contribution to the Earth's core density deficit could hence be much larger than previously assumed. Most importantly, N in the deep reduced mantle should be stored in the small metal fractions and not in silicates. On the early Earth nitrogen was redistributed between three prevailing reservoirs: the core forming metal, the silicate magma ocean, and the atmosphere. To shed light on the behavior of N during core segregation, we have experimentally determined N solubilities in Fe‐dominated metal melts at high temperatures and pressures (1200–1800 °C, 0.4–9.0 GPa) using high‐pressure devices. Based on our experimental results a model has been developed to describe N solubility into metal melts as a function of pressure and temperature. The model suggests that core‐forming metal melts can dissolve N quantities that are as high as the Earth's core density deficit. However, the N concentrations in the core‐forming metal are dependent on the accretionary scenario and its partitioning with silicate magma ocean; our solubilities provide an upper limit for possible N concentrations within the Earth's core. Nevertheless, this study shows that N in the modern mantle will largely dissolve in its small metal fraction and not in the dominating silicates. N solubility at high pressure and temperature provides an important upper bond for N concentration in planetary cores

Centrifuge experiments on olivine, chromite, and plagioclase aggregates saturated in basaltic liquid show evidence of viscous compaction by grain‐boundary diffusion‐controlled creep. The experiments confirm that the exponential dependence of shear viscosity on melt fraction, observed at low porosities in earlier shear deformation experiments, extends to sedimentary porosities. The compaction profiles are inconsistent with the porosity‐dependence commonly ascribed to viscosity in macroscopic compaction models, which underestimate the effect of matrix disaggregation and consequently overestimate the viscosities of crystal mushes by 1–2 orders of magnitude. The time to halve the porosity of natural olivine igneous sediments by compaction is estimated from the centrifuge experiments to be O(103)y. Half‐times for plagioclase and chromite layers are O(104–105)y, suggesting that such layers compact on magmatic time scales only if they are loaded by additional sedimentation. At conditions relevant to melt flow in asthenospheric settings and trans‐crustal magmatic systems, the bulk and shear viscosities inferred for olivine and plagioclase are O(1017)Pa s, 4 orders of magnitude less than inferred from earlier experimental studies of the diffusion creep rheology. The reduced viscosities imply time‐ and length‐scales for compaction processes that are substantially shorter than previously anticipated. Our analysis serendipitously reveals that the oft‐neglected solidity term of the Carman‐Kozeny porosity‐permeability relation is essential to prevent non‐physical behavior in models of cumulate compaction. The weight of the rocks overlying partially molten regions of the Earth squeezes melt toward the surface. This process is usually limited by rock viscosity and because rock viscosities are extremely high it is not easily observed. We review three sets of experiments on common crustal and mantle minerals in which melt expulsion was accelerated in a centrifuge. The results are consistent with recent theoretical models for rock viscosity and suggest that melt expulsion is substantially faster than previously anticipated. Experimental compaction profiles are consistent with a porosity‐weakening effect predicted for grain‐boundary controlled diffusion creepBulk viscosities for plagioclase and olivine aggregates are three orders of magnitude lower than reported from earlier experimentsExtrapolation to natural conditions indicates diffusion creep remains an efficient deformation mechanism in partially molten natural rocks Experimental compaction profiles are consistent with a porosity‐weakening effect predicted for grain‐boundary controlled diffusion creep Bulk viscosities for plagioclase and olivine aggregates are three orders of magnitude lower than reported from earlier experiments Extrapolation to natural conditions indicates diffusion creep remains an efficient deformation mechanism in partially molten natural rocks

Although alkali-alkali earth carbonates have not been reported from mantle-derived xenoliths, these carbonates may have a substantial role in mantle metasomatic processes through lowering melting temperatures. On the Na2Mg(CO3)2-K2Mg(CO3)2join only the Na-end-member eitelite (R3̅ space group), was reported in nature. The K-end-member (R3̅m) readily hydrates even at low temperatures, therefore, only baylissite, K2Mg(CO3)2·4H2O, has been observed. Because of the role of (K,Na)Mgdouble carbonates in mantle metasomatism, we performed high P-T experiments on K2Mg(CO3)2, (K1.1Na0.9)2Mg(CO3)2, and Na2Mg(CO3)2. Structure refinements were done upon compression of single crystals from 0 to 9 GPa at ambient temperature employing synchrotron radiation. Fitting the compression data to the second-order Birch-Murnaghan EoS resulted in V0= 396.2(4), 381.2(5), and 347.1(3) Å3and K0= 57.0(10), 54.9(13), and 68.6(13) GPa for K2Mg(CO3)2, (K1.1Na0.9)2Mg(CO3)2, and Na2Mg(CO3)2, respectively. These compressibilities are lower than those of magnesite and dolomite. The KMg-double carbonate transforms into a monoclinic polymorph at 8.05 GPa; the high-P phase is 1% denser than the low-P polymorph. The NaMg-double carbonate has a phase transition at ~14 GPa, but poor recrystallization has prevented structure refinement. The parameters for a V-T EoS were collected at 25-600 °C and ambient pressure and are ɑ0= 14.31(5) × 10-5K-1and 16.73(11) × 10-5K-1for K2Mg(CO3)2and Na2Mg(CO3)2, respectively. Moreover, fitting revealed an anisotropy of thermal expansion along the a- and c-axis: ɑ0(a) = 2.84(6) × 10-5and 4.78(5) × 10-5K-1and ɑ0(c) = 10.47(11) × 10-5and 8.72(5) × 10-5K-1for K2Mg(CO3)2and Na2Mg(CO3)2, respectively.

Eleven isobaric experimental series simulate the fractional crystallization of 1,150 km deep lunar magma ocean. Crystallization begins at 1,850°C with olivine (to 32 per cent solidified, pcs), followed at 1,600°C by olivine + opx ± Cr‐spinel (to 62 pcs), at 1,210°C cpx + plagioclase ± olivine ± Ti‐spinel (to 97 pcs) and at 1,060°C quartz + cpx + plagioclase + Ti‐spinel, leaving 1.8 wt% residual magma that crystallizes minor K‐feldspar and apatite in addition. Melt compositions remain near 45 wt% SiO2, while FeO increases from 11 to 26 wt%, TiO2peaks at 4 wt% at Ti‐spinel saturation. The available experimental liquid lines of descent yield an overall fractional crystallization sequence of olivine→opx→cpx + plagioclase→quartz→FeTi‐oxide. Plagioclase appears concomitantly with cpx, a result of the low magma ocean floor pressures (≤1 GPa) after 66%–76% of olivine + opx‐fractionation. A few wt% of FeTi‐oxides form mostly once the quartz + plagioclase + cpx‐cotectic is reached, cumulate densities remain ≤3,740 kg/m3. Scaled to a full magma ocean, plagioclase appears at 210–120 km depth, mainly as a function of bulk Al2O3. As buoyancy driven plagioclase‐cpx separation is likely limited, these depths may correspond to the primordial lunar crustal thickness. Allowing for complete plagioclase flotation to the quartz + plagioclase + cpx + FeTi‐oxide ± olivine cotectic yields 95–70 km primordial crust of anorthosite and quartz‐gabbro, far in excess of the 35–50 km observed. This supports an overturn of primordial layers, remelting of dense gabbroic cumulates in the harzburgitic cumulate mantle leading to further mixing and differentiation. We posit that such complex density induced convection led to a lunar marble cake mantle with primitive and fairly evolved reprocessed cumulates next to each other. Upon its accretion the Moon was likely completely molten, forming a global magma ocean. This study experimentally simulates the crystallization of this magma ocean and constrains the resulting mineral cumulate layers, the initial temperature distribution, and the nature of the original lunar crust. Overall this crust was 2–5 times thicker than observed nowadays, supporting that post‐magma ocean convection has removed the larger part of this in some layers quite dense crust. The down‐slumping crust remelts in the hot deeper lunar mantle, leading to a second generation of magmatism explaining part of the available lunar samples. Crystallization of a full Moon magma ocean defines the initial selenothermOur and previous results yield >95–70 km primordial crust, at least twice the modern value, requiring reprocessing through lunar overturnSlumping dense crust remelts in the cumulative harzburgitic mantle, adding further diversification to a lunar marble‐cake mantle Crystallization of a full Moon magma ocean defines the initial selenotherm Our and previous results yield >95–70 km primordial crust, at least twice the modern value, requiring reprocessing through lunar overturn Slumping dense crust remelts in the cumulative harzburgitic mantle, adding further diversification to a lunar marble‐cake mantle

Dolomite occurs in a wide range of rock compositions, from peridotites to mafic eclogites and metasediments, up to mantle depths of more than 200 km. At low-temperatures dolomite is ordered (R3̄), but transforms with increasing temperature into a disordered higher symmetry structure (R3̄c).

Remnant planetesimals might have played an important role in reducing the orbital eccentricities of the terrestrial planets after their formation via giant impacts. However, the population and the size distribution of remnant planetesimals during and after the giant impact stage are unknown, because simulations of planetary accretion in the runaway growth and giant impact stages have been conducted independently. Here we report results of direct N-body simulations of the formation of terrestrial planets beginning with a compact planetesimal disk. The initial planetesimal disk has a total mass and angular momentum as observed for the terrestrial planets, and we vary the width (0.3 and 0.5 AU) and the number of planetesimals (1000-5000). This initial configuration generally gives rise to three final planets of similar size, and sometimes a fourth small planet forms near the location of Mars. Since a sufficient number of planetesimals remains, even after the giant impact phase, the final orbital eccentricities are as small as those of the Earth and Venus.

Multi-anvil experiments have been performed in the system CaCO3-MgCO3at pressures of 5.0-7.0 GPa and temperatures of 800-1600 °C. The reaction dolomite = aragonite + magnesite has been reversed and located near 750 °C at 5.0 GPa, 900 °C at 6.0 GPa, and 1000 °C at 7.0 GPa. Between 5 and 6 GPa, the reaction boundary is strongly curved and its dP/dT slope increases from 2 to 12 MPa/°C, expanding the stability field of dolomite. This increase is attributed to increasing Ca-Mg disorder in the dolomite. In addition to the reaction boundary, an isobaric section of CaCO3-MgCO3has been determined at 6.0 GPa. There is a two-phase field of aragonite + dolomite on the Ca-rich side, which closes before minimum melting temperatures of 1350 °C are reached. The two-phase field on the Mg-rich side, where dolomite + magnesite coexist, intersects with the solidus. Inferred minimum melts are close to dolomite composition suggesting congruent melting of dolomite at 6 GPa. The melt compositions and temperatures in the pure carbonate system are surprisingly similar to solidus phase relations in the CMAS-CO2system, implying that minimum melting conditions in carbonated peridotite at high pressures are dominated and controlled by the carbonate component.

We have developed a novel analytical technique for diamond-trap experiments to directly analyze high-pressure, high-temperature fluid and melt compositions in equilibrium with mantle material. Experiments were conducted at a pressure of 6 GPa and temperatures between 900-1200 °C in a multi-anvil apparatus with a synthetic K-free eclogite doped with 860 ppm Cs, ~20 wt% H2O, and a layer of diamond aggregates serving as a fluid/melt trap. Experiments at identical conditions were analyzed with two different methods. In the new, “freezing,” approach, the capsule was frozen prior to opening and kept frozen during laser-ablation ICP-MS analysis, thus ablating the quenched fluid (precipitates together with water that unmixed upon quenching) in a solid state. Cesium, fractionating completely into the fluid or melt phase, was used as an internal standard for calculating the fluid compositions. Calculated uncertainties on H2O content in the fluid composition are 0.7-2.5%. In the conventional “evaporation” approach, water from the unmixed fluid was first evaporated from the capsule, then the remaining fluid precipitates were analyzed by LA-ICP-MS. The compositions of the residual eclogitic minerals were measured by electron microprobe, and the fluid composition was then determined by mass-balance. Uncertainties in mineral compositions lead to poor precision in fluid composition in this latter approach. Results of the two methods of fluid analysis were found to be in good agreement. Because the “freezing” approach analyzes the entire fluid directly and does not rely on mass balance for calculating fluid compositions, our new method provides a superior means for determining the composition of fluids. Secondly, it avoids loss of cations that remain soluble in water (e.g., Cs, K) after quenching the experiment.

We have developed a novel analytical technique for diamond-trap experiments to directly analyze high-pressure, high-temperature fluid and melt compositions in equilibrium with mantle material. Experiments were conducted at a pressure of 6 GPa and temperatures between 900-1200 °C in a multi-anvil apparatus with a synthetic K-free eclogite doped with 860 ppm Cs, ~20 wt% H2O, and a layer of diamond aggregates serving as a fluid/melt trap. Experiments at identical conditions were analyzed with two different methods. In the new, “freezing,” approach, the capsule was frozen prior to opening and kept frozen during laser-ablation ICP-MS analysis, thus ablating the quenched fluid (precipitates together with water that unmixed upon quenching) in a solid state. Cesium, fractionating completely into the fluid or melt phase, was used as an internal standard for calculating the fluid compositions. Calculated uncertainties on H2O content in the fluid composition are 0.7-2.5%. In the conventional “evaporation” approach, water from the unmixed fluid was first evaporated from the capsule, then the remaining fluid precipitates were analyzed by LA-ICP-MS. The compositions of the residual eclogitic minerals were measured by electron microprobe, and the fluid composition was then determined by mass-balance. Uncertainties in mineral compositions lead to poor precision in fluid composition in this latter approach. Results of the two methods of fluid analysis were found to be in good agreement. Because the “freezing” approach analyzes the entire fluid directly and does not rely on mass balance for calculating fluid compositions, our new method provides a superior means for determining the composition of fluids. Secondly, it avoids loss of cations that remain soluble in water (e.g., Cs, K) after quenching the experiment.

Potassic white micas were synthesized in the K2O-MgO-Al2O3-SiO2-H2O system along the pseudobinary join muscovite-aluminoceladonite (mu-Alcel). Composition of run products as measured by electron microprobe analysis are in the range mu89-Alcel11to mu01-Alcel99. Cell parameters were determined on powder samples by full-profile Rietveld refinement, using both a single-polytype and a multi-polytype model. The results of both analysis models are in full agreement, and show that the phengite cell parameters have a distinct dependence on the celadonite content: the c parameter shows a monotonic decrease over the full compositional range, whereas the a and b parameters both increase in the Alcel0-Alcel60range but decrease in the Alcel60-Alcel100range. The monoclinic b angle decreases slightly with increasing celadonite content. The overall behavior of the cell parameters indicates a decrease of the ditrigonal distortion of the tetrahedral 6-rings, and an increased trioctahedral character of the structure at high celadonite compositions. The molar volume along the solid solution join shows a maximum at about Alcel30. Molar volume vs. composition can be fitted by a symmetric function for the excess volume yielding a molar volume for end member aluminoceladonite of 13.957 ± 0.006 J/bar, for muscovite 14.076 ± 0.004 J/bar, and a symmetric positive deviation from ideal volumes of mixing with W = 0.198 ± 0.025 J/bar, and r2= 0.941. The use of an asymmetric excess volume function does not significantly improve the fit quality (r2= 0.945).

Abstract The structural behaviour of lawsonite CaAl2Si2O7(OH)2·H2O, has been studied under quasi-hydrostatic conditions in a diamond-anvil cell to 18 GPa at room temperature, using angle-dispersive X-ray powder diffraction and Raman spectroscopy. With increasing pressure, we observe a phase transition at P = 8.6(3) GPa, characterized by (1) the splitting of diffraction lines, (2) the emergence of new Raman bands, and (3) significant changes in the frequency shifts of the hydroxyl O-H stretching modes. The transition is displacive and fully reversible, without any detectable hysteresis. The high-pressure phase, referred to here as lawsonite III can be indexed into a monoclinic unitcell, with a = 5.6833(3), b = 8.5944(4), c = 12.8773(5) Å, ? = 91.42(4)° and V = 628.80(4) Å3 at P = 10.6 GPa. The space-group of lawsonite III is likely to be C1121/m, which is the unconventional representation of P21/m related to the low-pressure Cmcm symmetry. Assuming the change in space-group from Cmcm to C1121/m, the resulting components of the spontaneous strain tensor are analyzed in terms of the change in point group from mmm to 2/m. The pressure-dependence of the fourth power of the symmetry-breaking component e64 is linear, indicating a tricritical character for the transition. Both X-ray diffraction and Raman spectroscopy indicate that the overall aluminosilicate framework of lawsonite is retained through the transition. However, monoclinic lawsonite III is ~ 40% less compressible than the low-pressure orthorhombic polymorph. The Raman spectroscopic results, in good agreement with recent infrared ones reveal that this decrease in compressibility is likely to be related to the increase in the hydrogen bond strength involving the hydroxyl groups in the structure, whereas the hydrogen bond system around the water molecule does not appear to be modified at the transition.

The Al-in-hornblende barometer, which correlates Altot content of magmatic hornblende linearly with crystallization pressure of intrusion (Hammarstrom and Zen 1986), has been calibrated experimentally under water-saturated conditions at pressures of 2.5–13 kbar and temperatures of 700–655°C. Equilibration of the assemblage hornlende-biotite-plagioclase-orthoclasequartz-sphene-Fe-Ti-oxide-melt-vapor from a natural tonalite 15–20° above its wet solidus results in hornblende compositions which can be fit by the equation: P(±0.6 kbar) = -3.01 + 4.76 Alhbltotr2=0.99, where Altot is the total Al content of hornblende in atoms per formula unit (apfu). Altot increase with pressure can be ascribed mainly to a tschermak-exchange ( $$t\vec k,{\text{ Mg}}_{{\text{ - 1 }}} {\text{Al}}^{{\text{VI}}} {\text{Si}}_{{\text{ - 1}}} {\text{ Al}}^{{\text{IV}}}$$ ) accompanied by minor plagioclase-substitution ( $$\vec pl,{\text{ Ca}}_{{\text{ - 1 }}} {\text{Na}}^{{\text{M(4)}}} {\text{ Al}}_{{\text{ - 1}}}^{{\text{IV}}} {\text{ Si}}$$ ). This experimental calibration agrees well with empirical field calibrations, wherein pressures are estimated by contact-aureole barometry, confirming that contact-aureole pressures and pressures calculated by the Al-in-hornblende barometer are essentially identical. This calibration is also consistent with the previous experimental calibration by Johnson and Rutherford (1989b) which was accomplished at higher temperatures, stabilizing the required buffer assemblage by use of mixed H2O-CO2 fluids. The latter calibration yields higher Altot content in hornblendes at corresponding pressures, this can be ascribed to increased edenite-exchange ( $$\vec ed,{\text{ }}\square _{{\text{ }} - {\text{ }}1}^{ A} {\text{ Na}}^{\text{A}} {\text{Si }}_{ - {\text{ }}1} {\text{Al}}^{{\text{IV}}}$$ ) at elevated temperatures. The comparison of both experimental calibrations shows the important influence of the fluid composition, which affects the solidus temperature, on equilibration of hornblende in the buffering phase assemblage.

Experiments on tonalite and granodiorite were performed at conditions ranging from 2.1 to 18 kbar and 550 to 850 °C to establish the magmatic stability field of epidote as a function of P, T, and fO₂.

Phase egg, first described by Eggleton et al. (1978), was synthesized and its composition determined to be AlSiO3OH. The crystal structure of AlSiO3OH, including the position of the hydrogen, has been solved and refined from high-resolution X-ray powder diffraction. The resulting lattice constants are a = 7.14409(2) Å, b = 4.33462(1) Å, c = 6.95253(2) Å, and β = 98.396(1)°. The space group is P21\n; Z = 4, V0= 212.99(1) Å3, and the zero pressure density is 3.74 g/cm3. This phase, which has features in common with the sti-shovite structure, occurs above 11 GPa and 700 ℃. AlSiO3OH forms from topaz-OH with increasing pressure and persists to more than 17.7 GPa and 1300 ℃. From a Schreinemaker analysis, we predicted that phase egg decomposes with pressure to an unknown, possibly hydrous aluminosilicate. Potentially, phase egg could replace topaz-OH or kyanite in sub­ducted crustal bulk compositions and may transport some water into the deep Earth.

The lattice parameters of kyanite were measured at various pressures up to about 60 kbar by single-crystal X-ray diffraction in a diamond anvil cell. Unit-cell dimensions de­creased linearly with an almost uniform rate:

The pressure stability of kyanite was experimentally reversed with the use of a multi­anvil apparatus. Kyanite was found to decompose into its oxides stishovite and corundum between 14 ± 0.5 GPa (at 1000 °C) and 17.5 ±1.0 GPa (at 2000 °C).

The high-pressure phase relationships in a H2O-saturated synthetic CaO-Al2O3-SiO2- H2O (CASH) system were studied by multi-anvil experiments. The most extreme pressure condition under which pure lawsonite [CaAl2Si2O7(OH)2H2O] exists is 120 kbar at 960 °C. This maximum stability is located at the intersection of the lawsonite breakdown reaction with the topaz-OH + stishovite = phase “egg” reaction. At lower pressures and higher temperatures lawsonite decomposes to grossular + topaz-OH + stishovite + H2O, whereas at lower pressures and lower temperatures lawsonite first reacts to grossular + phase egg + topaz-OH + H2O and at still lower temperatures to grossular + phase egg + diaspore + H2O. The two latter reactions have positive dP/dT slopes, with lawsonite on the low-pressure side, and thus delimit the occurrence of lawsonite toward higher pres­sures. The occurrence of topaz-OH (10.7 wt% H2O) is limited through a reaction to phase egg (7.5 wt% H2O) + diaspore; the phase boundary extends from 110 kbar and 720 °C to 130 kbar and 920 °C. Phase egg is inferred to have a composition of AlSiO3(0H) and a monoclinic unit cell similar to that proposed by Eggleton et al. (1978).