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Peridotites of Ulten Zone (Eastern Alps, N Italy) show a transition from coarse protogranular spinel lherzolites to fine‐grained amphibole + garnet peridotites, recorded by the crystallization of garnet coronas around spinel. Pyroxenite veins, transposed along the peridotite foliation, show a similar metamorphic evolution from coarse‐grained (garnet‐free) websterites to fine‐grained garnet websterites. In both peridotites and websterites, garnet previously exsolved from porphyroclastic high‐temperature pyroxenes and later crystallized along the foliation. This evolution has been interpreted to reflect cooling and pressure increase of websterites and host peridotites from spinel‐ to garnet‐facies conditions. Microstructures and crystallographic orientation data indicate that the re‐equilibration of garnet websterites in the garnet stability field occurred during deformation. Porphyroclastic pyroxenes have been interpreted to deform by dislocation glide and creep. In particular, TEM observations indicate the activation of the (100)[010] slip system in orthopyroxene. Core‐and‐mantle microstructures also suggest that dislocation creep was aided by subgrain rotation recrystallization, leading to the formation of neoblastic pyroxenes. These recrystallized grains deformed by diffusion‐accommodated grain boundary sliding, as indicated by the occurrence of quadruple junctions and straight, aligned grain boundaries. The transition from dislocation creep to diffusion creep in websterites was accompanied by the crystallization of garnet along foliation, which triggered the pinning of the recrystallized matrix and stabilized the fine‐grained microtexture for diffusion creep, promoting rheological weakening. Garnet websterites of Ulten Zone thus offer a unique opportunity to investigate the effects of reaction softening during the corner flow in the supra‐subduction lithospheric mantle induced by the descending slab. Plain Language Summary: When tectonic plates converge, one plate slides beneath the other plate descending into the Earth's mantle. During this process (the so‐called subduction), rocks forming the Earth's mantle, such as peridotites and pyroxenites, can be dragged to great depths and later transported back to the surface by a combination of two processes known as corner flow and exhumation. Rocks that experienced this journey are now exposed at the surface only in few mountain belts in the world (such as the European Alps) and represent natural laboratories to study the processes that occur at great depths in the Earth's mantle. In this study, we reconstruct the metamorphic and deformation evolution of pyroxenites of the Ulten Zone (Eastern Alps, N Italy). Minerals in pyroxenites deformed through different deformation processes, including dislocation creep and diffusion creep mechanisms. Our data indicate that minerals within pyroxenites record a transition in the deformation mechanism from dislocation to diffusion creep. This switch of the deformation mechanism was responsible for a significant rheological weakening of pyroxenites, suggesting that pyroxenites can play a major role in the processes that control the deformational behavior of the Earth's mantle. Key Points: In websterites of Ulten zone, pyroxenes switch from dislocation to diffusion‐creep‐dominated deformationThe transition in deformation mechanism took place during the prograde re‐equilibration of websterites in the garnet stability fieldThis results in the rheological weakening of websterites during the corner flow of the lithospheric mantle induced by the slab subduction [ABSTRACT FROM AUTHOR]

The article analyzes Geoscience Digital Data Resource and Repository Service (GeoDaRRS) workshop being held during August 7-9, 2018, at the National Center of Atmospheric Reasearch (NCAR). It is noted that more than 60 geoscience researchers, technology experts, scientific publishers, funders and data repository personnel attended the workshop to analyzes data management planning support resources and repository services for geoscience researchers.

The northerly Etesian winds blow persistently over the Aegean Sea and eastern Mediterranean (EM) during summer months (June, July and August). This study investigates the July–August (JA) characteristics of the Etesians for a present time period (1981–2000) from both ECMWF ERA‐Interim Reanalysis data set (observations) and 11 EURO‐CORDEX regional climate model (RCM) simulations and assesses future changes using the associated RCP8.5 simulations. An EOF analysis applied to observations near surface meridional wind component (v10) over eastern Mediterranean demonstrates its strength as the leading mode, which explains 43.6% of the total variance, as the principal component (PC) time series of EOF1 has a very high correlation (r = 0.98) with an index showing the intensity of the Etesians. A composite analysis involving the opposite phases in the PC time series reveals that the strong Etesians develop when high pressure takes place towards Balkans and the Black Sea, which increases the meridional pressure gradient over the Aegean Sea. Some of the RCMs reproduce quite realistically pressure system and its associated Etesian winds. However, the intensity of the Etesians in these simulations is usually not as high as that in observations despite their higher horizontal resolutions. In general, the Etesians are projected to be stronger in the future periods as a result of the increasing pressure gradient over the Aegean Sea. This result suggests that the wind energy potential of the region that already attracts investment from the energy sector will increase in the future. Study area with topography (in meters) over the EUR‐11 CORDEX domain. [ABSTRACT FROM AUTHOR]

Omphacite is a major mineral phase of eclogite, which provides the main driving force for the slab subduction into the Earth's interior. We have measured the single‐crystal elastic moduli of omphacite at high pressures for the first time up to 18 GPa at ambient temperature using Brillouin spectroscopy. A least squares fit of the velocity‐pressure data to the third‐order finite strain equation of state yields KS0′ = 4.5 (3), G0′ = 1.6 (1) with ρ0 = 3.34 (1) g/cm3, KS0 = 123 (3) GPa, and G0 = 74 (2) GPa. In addition, the synchrotron single‐crystal X‐ray diffraction data have been collected up to 18 GPa and 700 K. The fitting to Holland‐Powell thermal‐pressure equation of state yields KT0′ = 4.6 (5) and α0 = 2.7 (8) × 10−5 K−1. Based on the obtained thermoelastic parameters of omphacite, the anisotropic seismic velocities of eclogite are modeled and compared with pyrolite between 200 and 500 km. The largest contrast between the eclogite and pyrolite in terms of seismic properties is observed between ~310 and 410 km. Key Points: Thermal equation of state and single‐crystal elasticity measurements is performed on omphacite crystalsWith the newly obtained thermoelastic parameters of omphacite, anisotropic seismic properties of eclogite are modeledThe maximum Vp, Vs, and anisotropy contrast between pyrolite and eclogite is between 310 and 410 km [ABSTRACT FROM AUTHOR]

Superdeep diamonds contain unique information from the sublithospheric regions of Earth's interior. Recent studies suggest that reaction between subducted carbonate and iron metal in the mantle plays an important role in the production of superdeep diamonds. It is unknown if this reaction is kinetically feasible in cold slabs subducted into the deep mantle. Here we present experimental data on real‐time tracking of the magnesite‐iron reaction at high pressures and high temperatures to demonstrate the production of diamond at the surface conditions of cold slabs in the transition zone and lower mantle. Our data reveal that the diamond production rate has a positive temperature dependence and a negative pressure dependence, and along a slab geotherm it decreases by a factor of three at pressures from 14.4 to 18.4 GPa. This rate reduction provides an explanation for the rarity of superdeep diamonds from the interior of the mantle transition zone. Plain Language Summary: Superdeep diamonds originate from great depths inside Earth, carrying samples from inaccessible mantle to the surface. The reaction between carbonate and iron may be an important mechanism to form diamond through interactions between subducting slabs and surrounding mantle. Interestingly, most superdeep diamonds formed in two narrow zones, at 250–450 and 600–800 km depths within the ~2,700‐km‐deep mantle. No satisfactory hypothesis explains these preferred depths of diamond formation. We measured the rate of a diamond forming reaction between magnesite and iron. Our data show that high temperature promotes the reaction, while high pressure does the opposite. Particularly, the reaction slows down drastically at about 475(±55) km depth, which may explain the rarity of diamond formation below 450 km depth. The only exception is the second zone at 600–800 km, where carbonate accumulates and warms up due to the stagnation of subducting slabs at the top of lower mantle, providing more reactants and higher temperature for diamond formation. Our study demonstrates that the depth distribution of superdeep diamonds may be controlled by reaction rates. Key Points: Real‐time tracking of diamond production from iron‐magnesite reaction at high pressures and high temperaturesThreefold reduction in the rate of iron‐magnesite reaction from 14.4 to 18.4 GPaDepth distribution of superdeep diamonds may be explained by reaction kinetics [ABSTRACT FROM AUTHOR]

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Located in the northeast of the Iberian Peninsula, Cerdanya experiences intense cold-air pool (CAP) episodes in which a decoupling between the valley atmosphere and the regional circulation develops, especially in winter. A network of 40 temperature sensors was deployed from 2012 to 2015 along seven elevational transects to collect hourly data of temperature and humidity, enabling the measurement of CAP characteristics and behaviour. Empirical orthogonal functions (EOFs) of minimum temperature anomalies were examined to study the spatial distribution of CAP. Days were classified as CAP or no-CAP using EOF analysis. The temporal variation of EOF analysis scores for the first component (PC1) indicates days prone to CAP. A synoptic analysis using principal component analysis (factorization), cluster analysis (classification) and a discriminant analysis (reclassification) was performed successively. Results showed CAP days to be associated with high pressure and light winds, while no-CAP days were associated with surface northerly or north-easterly flow behind frontal passages. [ABSTRACT FROM AUTHOR]

Soil water distribution induced by freezing has a significant influence on the mechanical response of the artificial frozen wall. To understand the effects of the high pressure on soil moisture redistribution is vital important for soil buried in deep underground since the soil to be frozen was often suffered from high ground pressure during its formation. This paper investigates the freezing-induced moisture redistribution in a fine-grained soil under the condition of applied high pressure. By using the specific freezing-thawing experimental equipment, the thermal state and the freezing front propagation of tested soil column are determined during its freezing, and the moisture content profile within the soil column is measured at the end of the freezing process, to determine the position of the stable freezing front and the characteristic of water redistribution. It is found that for all the soil columns under applied high pressure, the freezing front reaches a stable state when a certain temperature gradient has been applied to the soil column for about 14.5 h, whereas the stable position moving towards the warm side with the increment of temperature gradient. The moisture content of frozen zone is generally high compared with that of the unfrozen zone. The minimum moisture content in frozen fringe close to the freezing front relates to the applied pressure rather than the temperature gradient. On the contrary, the increment of the temperature gradient will cause an increase in the maximum moisture content in the ice lens area. This further confirms that for the soil column under applied high pressure condition, the water in unfrozen zone will go through the frozen fringe to ice lens zone continuously and do not accumulate within frozen fringe when it is froze under a closed system by one-dimension freezing way. [ABSTRACT FROM AUTHOR]

High-pressure (HP) mafic granulites in the Daqingshan–Wulashan Complex from the central segment of the Khondalite Belt of the North China Craton occur as irregular lenses or deformed dike swarms within dioritic–granitic gneisses and meta-sedimentary rocks. The HP mafic granulites contain three distinct mineral assemblages: a peak HP granulite-facies assemblage (M 1 ) that consists of garnet + clinopyroxene + plagioclase + amphibole ± quartz ± Fe–Ti oxides; a post-peak decompression assemblage (M 2 ) that is characterized by symplectites of orthopyroxene + clinopyroxene + plagioclase ± amphibole ± Fe–Ti oxides; a late cooling assemblage (M 3 ) represented by symplectites of amphibole + plagioclase + Fe–Ti oxides. Pseudosection modeling using THERMOCALC in the NCFMASHTO system and conventional thermobarometers constrain the P–T conditions of the M 1 , M 2 , and M 3 assemblages to P = 1.25–1.40 GPa and T = 760–815 °C, P = 0.72–0.80 GPa and T = 825–860 °C, and P = 0.69–0.81 GPa and T = 645–730 °C, respectively. In-situ U–Pb dating of zircons show that the protolith ages of the HP mafic granulites are 2100–2000 Ma and the timing of peak HP granulite-facies metamorphism is 1960–1940 Ma. The medium- to low-pressure amphibolite- to granulite-facies retrogression occurred mainly from 1920 to 1820 Ma. Petrographic investigations, mineral compositions, metamorphic reaction histories, P–T calculations, and geochronological data define a clockwise P–T–t path involving near-isothermal decompression and near-isobaric cooling, which suggests that the Daqingshan–Wulashan Complex underwent initial crustal thickening from 1960 to 1940 Ma, followed by relatively rapid exhumation, cooling, and retrogression from 1920 to 1820 Ma. This P–T–t path was likely the result of the Paleoproterozoic continental–continental (or arc) collision during the amalgamation of the North China Craton. [ABSTRACT FROM AUTHOR]

The availability of a deep well that penetrates deep into the Ultra High Pressure (UHP) metamorphic rocks is unusual and consequently offers a unique chance to study the metamorphic rocks. One such borehole is located in the southern part of Donghai County in the Sulu UHP metamorphic belt of Eastern China, from the Chinese Continental Scientific Drilling Main hole. This study reports the results obtained from the analysis of oxide log data. A geochemical logging tool provides in situ, gamma ray spectroscopy measurements of major and trace elements in the borehole. Dry weight percent oxide concentration logs obtained for this study were SiO 2 , K 2 O, TiO 2 , H 2 O, CO 2 , Na 2 O, Fe 2 O 3 , FeO, CaO, MnO, MgO, P 2 O 5 and Al 2 O 3 . Cross plot and Principal Component Analysis methods were applied for lithology characterization and mineralogy description respectively. Cross plot analysis allows lithological variations to be characterized. Principal Component Analysis shows that the oxide logs can be summarized by two components related to the feldspar and hydrous minerals. This study has shown that geochemical logging tool data is accurate and adequate to be tremendously useful in UHP metamorphic rocks analysis. [ABSTRACT FROM AUTHOR]

LiNbO3-type Mg2.98(2)Al1.99(2)Si3.02(2)O12 (py-LN) was synthesized by recovering a run product from 2000 K and 45 GPa to ambient conditions using a large volume press. Rietveld structural refinements were carried out using the one-dimensional synchrotron XRD pattern collected at ambient conditions. The unit-cell lattice parameters were determined to be a = 4.8194(3) Å, c = 12.6885(8) Å, V = 255.23(3) ų, with Z = 6 (hexagonal, R3c). The average A-O and B-O distances of the AO6 and BO6 octahedra have values similar to those that can be obtained from the sum of the ionic radii of the averaged A- and B-site cations and oxygen (2.073 and 1.833 Å, respectively). The present compound has the B-site cations at the octahedral site largely shifted along the c axis compared with other LiNbO3-type phases formed by back-transition from perovskite (Pv)-structure, and as a result, the coordination number of this site is better described as 3+3. It appears therefore that the B-site cation in the octahedral position cannot be completely preserved during the back-transition because of the small size of Si and Al, which occupy usually a tetrahedral site at ambient conditions. The formation of py-LN can be explained by the tilting of BO6 octahedra of the perovskite structure having the pyrope composition and formed at high P-T conditions. The tilting is driven by the decrease in ionic radius ratio between the A-site cation and oxygen during decompression. This also explains why there is no back-transition from the Pvstructure to the ilmenite-structure during decompression, since this is a reconstructive phase transition whose activation energy cannot be overcome at room temperature. Py-LN may be formed in shocked meteorites by the back-transformation after the garnet-bridgmanite transition, and will indicate shock conditions around 45 GPa and 2000 K. [ABSTRACT FROM AUTHOR]

Microbes not only show sensitive responses to environmental changes but also play important roles in geochemical and geophysical systems. It is well known that microbes have caused major changes in surface environments and biogeochemical cycles through Earth history. Microbial processes can also induce the synthesis of certain minerals under Earth-surface conditions that previously were believed to form only under high temperatures and pressures in the deep Earth. For example, microbes can promote the conversion of smectite to illite, synthesis of authigenic plagioclase, precipitation of dolomite, and biotransformation of geolipids. These effects of microbes are due to their large surface/volume ratios, enzyme production, and abundant functional groups. Microbial catalyzation of chemical reactions proceeds through reaction-specific enzymes, a decrease in Gibbs's free energy, and/or break through the dynamics reaction thresholds via their metabolisms and physiology. Microbes can lower the surface free energy of mineral nuclei via biophysical adsorption due to their large surface/volume ratios and abundant functional groups. The mineral precipitation and transformation processes induced by microbes are functionally equivalent to geological processes operating at high temperatures and pressures in the deep Earth, suggesting that microbial processes can serve as analogs to deep abiotic processes that are difficult to observe. [ABSTRACT FROM AUTHOR]

The inter-salt shale-oil reservoir in Liutun Sag of the Dongpu Depression in the Bohai Bay Basin, China, has a strong overpressure and produces abundant heavy oil with little water. The previous researches claimed that the overpressure was mainly a result of disequilibrium compaction, which seemingly contradicts with the little water production. More systematic work is required to understand the origin of the overpressure and the oil/water production. Formation testing, mud weight and wireline-log data were used to recognize overpressure and equivalent depth method and sonic transit time-density crossplot were used to identify the overpressure mechanisms. In addition, the tectonic evolution was included in the analysis, aiming at understanding the oil/water production features. Disequilibrium compaction is considered as the main overpressure mechanism, due to the sealing of salt rocks. Hydrocarbon generation, which mainly generated low maturity heavy oil, contributes to the overpressure feature with the help of tectonic uplift. The overpressure evolution, which corresponds to the tectonic evolution, consists of three phases: early disequilibrium compaction, middle fluid substitution and late disequilibrium compaction. The tectonic uplift in the middle phase, it is proposed, contributes most to the little water production. With the tectonic uplift, a lot of fractures formed, which would promote oil and water drain. However, due to the low mobility of heavy oil, more water tended to be drained away from the region of strong overpressure, and thus the intuitive fluid substitution occurred. The findings above indicate that the exploration of inter-salt shale-oil reservoirs in Liutun Sag or even the other areas of Dongpu Depression may additionally consider some special strategies, including the occurrence of salt rocks and the hybrid overpressure feature of disequilibrium compaction and fluid expansion besides tectonic uplift. [ABSTRACT FROM AUTHOR]

Seafloor massive sulfides (SMSs) are formed as precipitation products from hot hydrothermal fluids as a result of mixing with cold seawater and are mostly found at depths between 1500 and 3600 m. These deposits are formed in tectonically active zones of oceans (midocean ridges and “back-arc” spreading systems) and are the result of the global heat transfer from the mantle in the oceanic crust. As these fluids mix with the cold surrounding seawater, metal sulfides in the water are precipitated on or in the nearby seabed. The appearance of the solid mineral occurs as cylindrical chimney structures: the so-called black and white smoker (caused mainly by the presence of iron, copper, zinc, and sulphur). Larger sulfide occurrences are mostly originated in several generations of hydrothermal cycles, and they form deposits that can range from several thousands to about million tons. SMS contains pyrite (iron), galena (lead), sphalerite (zinc), and chalcopyrite (copper). Deep-sea mining is concentrating now to exploit such deposits. So far, the only known commercial project is the one developed by Nautilus Minerals, which is based on a horizontal system. This paper describes a preliminary design of a novel cutting tool developed for a vertical mining approach. The vertical mining method is preferred when rough terrain is expected and the device is easy to relocate. Using an atmospheric and hyperbaric cutting model, the cutting energy for two selected SMS deposits has been estimated and validated with real onshore excavation sites performed with a cutting tool normally used for diaphragm wall installation (i.e., the trench cutter technology). Preliminary results suggest that the estimated cutting energy \bf E\bf SP is 2.9 times higher with respect to the measured one in atmospheric conditions. This could be because the model considers the worst case scenario, i.e., higher energy due to the maximum cutting forces assumed. This factor has been used to design a cutting tool which is able to work up 2000-m water depth to mine SMS deposits. [ABSTRACT FROM PUBLISHER]

Thermodynamic datasets are essential for phase equilibrium computations, from which metamorphic pressure and temperature conditions of rocks can be estimated. In addition, they are used to model rock properties such as volume or density. The theoretical framework for thermodynamic volume modeling is imposed by the equation of state (EOS), which can be represented using many possible formulations. Until the 1990’s, the Bridgman Power Series was a popular approach to model mineral volumes. Many experiments were fitted to this equation and input parameters for almost every mineral exist. Unfortunately, the equation has a drawback and does not allow the extrapolation of mineral volumes to pressures above 1 GPa. In this paper, an inverted EOS is introduced which uses the same input parameters as the Bridgman Power Series. Converting the fit parameters of the Bridgman Power Series to commonly used physical input parameters at reference conditions (k00, K'00, and α00, α'00) allows extrapolation of mineral volumes to very high pressure (20 GPa). The results from this study show in detail how the extended EOS improves the volumes of solid mineral phases such as coesite, jadeite and forsterite above 1 GPa, while retaining consistent volumes at low pressure temperature conditions. In this manner, the extended EOS also improves the phase equilibrium computations of the thermodynamic datasets built on the Bridgman Power Series. The proposed inverted EOS could be easily implemented by thermodynamic software packages with no modification of the dataset because the same input parameters are used. [ABSTRACT FROM AUTHOR]

The oscillation of loads in high-pressure zones ( hpz s) formed in ice compressive failure is shown, under the right conditions, to constitute a regular self-sustained oscillation. This occurs in a system comprising the moving ice field, which supplies an internal source of energy, and a compliant structure with which the ice interacts. The supplied energy is dissipated within a layer of microstructurally modified ice by means of viscoelastic deformation enhanced by damage processes, as well as by spalling fracture. An important question arises with regard to vibrations found in large structures such as the Molikpaq. Given that high-pressure zones in field situations are on the order of 1 m in size, how do large structures respond and participate in ice-induced vibrations? The concept of ‘entrainment’ or synchronization of hpz s via elastic and inertial structural feedback is introduced. In this, failure of one high-pressure zone leads to failure of another through structurally-coupled feedback, whereby the first failure increases the load on another as a result of elastic rebound of the structure. This constitutes in-phase coupling and synchronization, but anti-phase coupling whereby failure of one high-pressure zone leads to a decrease in load on another, is also considered. These hypotheses were confirmed in an experimental programme, in which a series of tests with a compliant beam applying load to ice specimens through a pair of indentors was carried out. The test results confirm the hypotheses, with both in- and anti-phase synchronization being observed. Relevance to real structural systems is discussed in the context of the Molikpaq structure and the JZ-20-2-1 jacket platform. [ABSTRACT FROM AUTHOR]

The paper commences with a review of ice-induced vibrations in full-scale structures in the field, in medium-scale tests, and particularly, in small-scale indentation tests. The mechanics of compressive ice failure is reviewed, with emphasis on the processes leading to the formation of a layer of microstructurally modified material under the indenter, as well as fracture. Previous tests in the present series using small-scale indentors are reviewed, and a recently conducted series of tests is introduced. This series involved confined ice specimens of cylindrical shape 154 mm in diameter moving at various constant displacement rates against a 20-mm diameter indentor attached to an elastic-compliant structure. The displacement rates (ice speeds) were chosen so as to induce “sawtooth” vibrations. Two beam structures, one stiff and the other flexible, were used. In general, the desired sawtooth pattern was achieved, particularly with the more flexible system, but also with the stiffer one at higher ice speeds. Some results involving “lock-in” were obtained with the stiffer setup. Measurements were made of the distribution of pressure at the ice–indentor interface using pressure-sensitive film, and thin sections were taken from the indented samples. The thin sections in all cases showed the presence of a microstructurally modified layer of ice adjacent to the indentor. Pressure distributions showed that regular vibrations were associated mainly with activity in the layer, whereas the larger spall fractures generally caused irregular load patterns with significant loss of contact area under the indentor. The regular failure can be analysed as a self-sustained oscillation, which is common among dissipative systems. The system in this case comprises the moving ice field and the compliant structure with which the ice interacts, resulting in autonomous vibrations of the sawtooth variety. Regularity was interrupted by the larger spalling fractures. [ABSTRACT FROM AUTHOR]

Synchrotron X‑ray diffraction data were obtained to simultaneously measure unit-cell volumes of W and WO2 at pressures and temperatures up to 70 GPa and 2300 K. Both W and WO2 unit-cell volume data were fit to Mie-Grüneisen equations of state; parameters for W are KT = 307 (±0.4) GPa, K′T = 4.05 (±0.04), g0 = 1.61 (±0.03), and q = 1.54 (±0.13). Three phases were observed in WO2 with structures in the P21/c, Pnma, and C2/c space groups. The transition pressures are 4 and 32 GPa for the P21/c-Pnma and Pnma-C2/c phase changes, respectively. The P21/c and Pnma phases have previously been described, whereas the C2/c phase is newly described here. Equations of state were fitted for these phases over their respective pressure ranges yielding the parameters KT = 238 (±7), 230 (±5), 304 (±3) GPa, K′T = 4 (fixed), 4 (fixed), 4 (fixed) GPa, g0 = 1.45 (±0.18), 1.22 (±0.07), 1.21 (±0.12), and q = 1 (fixed), 2.90 (±1.5), 1 (fixed) for the P21/c, Pnma, and C2/c phases, respectively. The W-WO2 buffer (WWO) was extended to high pressure using these W and WO2 equations of state. The T-f,O2 slope of the WWO buffer along isobars is positive from 1000 to 2500 K with increasing pressure up to at least 60 GPa. The WWO buffer is at a higher fO2 than the iron-wüstite (IW) buffer at pressures lower than 40 GPa, and the magnitude of this difference decreases at higher pressures. This implies an increasingly lithophile character for W at higher pressures. The WWO buffer was quantitatively applied to W metal-silicate partitioning by using the WWO-IW buffer difference in combination with literature data on W metal-silicate partitioning to model the exchange coefficient (KD) for the Fe-W exchange reaction. This approach captures the non-linear pressure dependence of W metal-silicate partitioning using the WWO-IW buffer difference. Calculation of KD along a peridotite liquidus predicts a decrease in W siderophility at higher pressures that supports the qualitative behavior predicted by the WWO-IW buffer difference, and agrees with findings of others. Comparing the competing effects of temperature and pressure the results here indicate that pressure exerts a greater effect on W metal-silicate partitioning. [ABSTRACT FROM AUTHOR]

We present high-pressure experiments up to 8 GPa that constrain the solidus and liquidus of a composition, Fe0.69Ni0.23Cu0.01S1.00, typical of upper mantle sulfide. Solidus and liquidus brackets of this monosulfide are parameterized according to a relation similar to the Simon-Glatzel equation, yielding, respectively, T (°C) = 1015.1 [P(GPa)/1.88 + 1]0.206 and T (°C) = 1067.3 [P(GPa)/1.19 + 1]0.149 (1 ≤ P ≤ 8). The solidus fit is accurate within ±15 °C over the pressure intervals 1–3.5 GPa and within ±30 °C over the pressure intervals 3.5–8.0 GPa. The solidus of the material examined is cooler than the geotherm for convecting mantle, but hotter than typical continental geotherms, suggesting that sulfide is molten or partially molten through much of the convecting upper mantle, but potentially solid in the continental mantle. However, the material examined is one of the more refractory among the spectrum of natural mantle sulfide compositions. This, together with the solidus-lowering effects of O and C not constrained by the present experiments, indicates that the experimentally derived melting curves are upper bounds on sulfide melting in the Earth’s upper mantle and that the regions where sulfide is molten are likely extensive in both the convecting upper mantle and, potentially, the deeper parts of the oceanic and continental lithosphere, including common source regions of many diamonds. [ABSTRACT FROM AUTHOR]

Elasticity of single-crystal San Carlos olivine has been derived from sound velocity and density measurements at simultaneous high pressure–temperature conditions up to 20 GPa and 900 K using in situ Brillouin spectroscopy and single-crystal X-ray diffraction in externally-heated diamond anvil cells. These experimental results are used to evaluate the combined effect of pressure and temperature on full elastic constants of single-crystal olivine to better understand its velocity profiles and anisotropies in the deep mantle. Analysis of the results shows that the shear moduli display strong concave behaviors as a function of pressure at a given high temperature, while the longitudinal modulus, C 11 , and the off-diagonal moduli, C 12 and C 13 , exhibit greater temperature dependence at higher pressures than at relatively lower pressures. Using a finite-strain theory and thermal equation of state modeling for a pyrolitic mantle composition along an expected mantle geotherm, our results show that the magnitude of the V P and V S jumps at the 410-km depth are 6% and 6.4%, respectively, which are greater than that found in seismic observations, suggesting a mantle olivine content of 40–50 vol%, which is less than what is expected for the pyrolite model. Our modeled velocity profiles for a metastable olivine wedge in the subduction slabs along a representative cold slab geotherm are 6% and 10% lower than those of wadsleyite and ringwoodite, respectively, at corresponding depths of the normal mantle. Our modeled results also show that metastable olivine in the cold slabs could have strong V P and V S anisotropies. The maximum V P anisotropy is estimated to be 19–22% at transition zone depth, whereas the maximum V S splitting is 13–23% and increases with depth. As a result, the presence of a metastable olivine wedge at the transition zone depth would exhibit a seismic signature of low velocity and strong seismic anisotropy which are consistent with recent seismic observations for various locations of the slabs and can be used as mineral physics constraints for future seismic detections of the metastable olivine wedges in the deep mantle. [ABSTRACT FROM AUTHOR]

The hydrogen isotopic composition of melt inclusions trapped in phenocrysts during their crystallization and growth in a magma may contribute to a better understanding of the water cycle between the atmosphere, the hydrosphere and the lithosphere. Such understanding relies on the knowledge of the hydrogen isotopic fractionation factors between aqueous fluids, silicate melts, and minerals at temperature and pressure conditions relevant to the Earth's interior. Significant D/H fractionation between silicate melts and aqueous fluids was reported at hundreds of MPa and °C by using in situ measurements in hydrothermal diamond anvil cell (HDAC) experiments ( Mysen, 2013a, 2013b , Am. Mineral. 98, 376–386 and 1754–1764). However, the available dataset is focused on fluids and melts with D/H ratios close to unity. The relevance of such data for natural processes that involve per mil variations of δ D-values may not always be clear. To address such concerns, the effect of the bulk D/H ratio on hydrogen isotope partitioning between water-saturated silicate melts and coexisting silicate-saturated aqueous fluids has been determined in the Na 2 O–Al 2 O 3 –SiO 2 –H 2 O–D 2 O system. To this end, in situ Raman spectroscopic measurements were performed on fluids and melts with bulk D/H ratios from 0.05 to 2.67 by using an externally-heated diamond anvil cell in the 300–800 °C and 200–1500 MPa temperature and pressure range, respectively. In these pressure/temperature ranges, the D/H ratios of fluids in equilibrium with melt barely change with temperature (in average Δ H fluid = 0.47 ± 1.15 kJ / mol ). In contrast, the D/H ratios of coexisting melts display strong dependence on temperature (average Δ H melt = 7.18 ± 1.27 kJ / mol ). The temperature-dependence of the D/H fractionation factor between melt and fluid ( α fluid - melt = D / H fluid / D / H melt ) is comparable in all the experiments and can be written: 1000 ⋅ ln ⁡ ( α fluid - melt ) = 263 ( ± 26 ) ⋅ T − 2 – 126 ( ± 48 ) . Therefore, the α fluid-melt is independent of the bulk D/H ratio of the melt + fluid system. Experimentally determined α fluid-melt using D-enriched fluids, therefore, can be applied to natural systems. It follows that for water-saturated magma strong isotopic fractionation of D and H between water dissolved in magmas and deep aqueous fluids may occur. The δ D-values in melt inclusions in phenocrysts in such water-saturated magma will reflect such fluid/melt fractionation effects. A likely result is underestimation of the δ D isotopic composition of slab fluids based on δ D-values in melt inclusions. The temperature-dependent hydrogen isotope fractionation must be taken into account in the modeling of slab fluid–magma interaction in the mantle wedge. [ABSTRACT FROM AUTHOR]

The geochemical signatures of “adakites” are usually attributed to high-pressure ( ≥ 50 km ) partial melting of mafic rocks, and accordingly the occurrence of adakitic magmas in continental settings is frequently used as an indicator of a thickened or foundered lower crust at the time of magma emplacement. These premises are built on experiments and modeling using an MORB-like source, but the probable source of continental “adakites” (i.e., continental lower crust) is compositionally different from MORB. To elucidate the effect of source inheritance and pressure on resultant melts, geochemical analyses and trace-element modeling have been carried out on Jurassic adakitic rocks from the northern part of the North China Craton. The results show that these continental adakitic melts can be generated at depths less than 40 km, and their “adakitic” signature is most likely inherited from their source rocks. Such conclusions can be applied to the Mesozoic adakitic magmas from the interior of the North China Craton. Only the “adakites” from collisional orogens (i.e., Tibet, Dabie UHP belt) require crustal melting at depths greater than 50 km, consistent with collision-induced crustal thickening in these areas. This study therefore highlights the importance of source composition when defining the formation conditions of magmatic rocks in general, and in particular questions the common use of “adakites” as an indicator of specific geodynamic situations. [ABSTRACT FROM AUTHOR]

In the atmospheric boundary layer, under high pressure conditions and negligible geostrophic winds, problems associated with pollution are the most critical. In this situation local winds play a major role in the evaluation of the atmospheric dynamics at small scales and in dispersion processes. These winds originate as a result of nonuniform heating of the soil, either when it is homogeneous or in discontinuous terrain in the presence of sea and/or slopes. Depending on the source of the thermal gradient, local winds are classified into convective boundary layer, sea and land breezes, urban heat islands, and slope currents. Local winds have been analyzed by (i) simple analytical models; (ii) numerical models; (iii) field measurements; (iv) laboratory measurements through which it is impossible to completely create the necessary similarities, but the parameters that determine the phenomenon can be controlled and each single wind can be separately analyzed. The present paper presents a summary of laboratory simulations of local winds neglecting synoptic winds and the effects of Coriolis force. Image analysis techniques appear suitable to fully describe both the individual phenomenon and the superposition of more than one local wind. Results do agree with other laboratory studies and numerical experiments. [ABSTRACT FROM AUTHOR]

Two vertically pointing S-band radars (coastal and inland) were operated in western Washington during two winters to monitor brightband snow-level altitudes. Similar snow-level characteristics existed at both sites, although the inland site exhibited lower snow levels by ~70 m because of proximity to cold continental air, and snow-level altitude changes were delayed there by several hours owing to onshore translation of weather systems. The largest precipitation accumulations and rates occurred when the snow level was largely higher than the adjacent terrain. A comparison of these observations with long-term operational radiosonde data reveals that the radar snow levels mirrored climatological conditions. The inland radar data were used to assess the performance of nearby operational freezing-level forecasts. The forecasts possessed a lower-than-observed bias of 100-250 m because of a combination of forecast error and imperfect representativeness between the forecast and observing points. These forecast discrepancies increased in magnitude with higher observed freezing levels, thus representing the hydrologically impactful situations where a greater fraction of mountain basins receive rain rather than snow and generate more runoff than anticipated. Vertical directional wind shear calculations derived from wind-profiler data, and concurrent surface temperature data, reveal that most snow-level forecast discrepancies occurred with warm advection aloft and low-level cold advection through the Stampede Gap. With warm advection, forecasts were too high (low) for observed snow levels below (above) 1.25 km MSL. An analysis of sea level pressure differences across the Cascades indicated that mean forecasts were too high (low) for observed snow levels below (above) 1.25 km MSL when higher pressure was west (east) of the range. [ABSTRACT FROM AUTHOR]

Previous studies have argued that the strength of the South Atlantic subtropical high pressure system, referred to as the South Atlantic anticyclone (SAA), modulates sea surface temperature (SST) anomalies in the eastern equatorial Atlantic. Using ocean and atmosphere reanalysis products, it is shown here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic via anomalous tropical wind power. This modulation in the timing and amplitude of seasonal cold tongue development manifests itself via SST anomalies peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events, the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA-induced wind power variations south of the equator influence eastern equatorial Atlantic SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations. [ABSTRACT FROM AUTHOR]

Evolved, highly olivine-normative diabase dikes of the Central Atlantic Magmatic Province (CAMP) crosscut 6 active quarries in the Georgia Piedmont. Chill zone and dike interior samples were collected to study the magmatic evolution of these dikes. Plagioclase phenocrysts (An60-An52 for the most evolved dike) dominate the chill margin mineralogy of these dikes with only trace olivine microphenocrysts (Fo71-Fo67 for the most evolved dike). The evolved compositions of these dikes, evidenced by low Mg# (44-55), Ni (66-118 ppm), and Cr (<5-43 ppm), are consistent with olivine and chromian spinel fractionation. They are also characterized by high contents of incompatible major and trace elements. Moreover when bulk compositions are plotted on projections of high pressure phase relationships relevant to MORB basalts, the Georgia diabases plot along projections of multiphase saturation surfaces at ~1 GPa consistent with multiple saturation with olivine, plagioclase and clinopyroxene. Major element variations as shown on Pearce element and related plots are also consistent with fractionation of olivine + plagioclase + clinopyroxene. These observations are rationalized in a model that includes high pressure (~1 GPa) fractionation of olivine, spinel, plagioclase, and augite from the parent magmas of these dikes. These olivine-normative, evolved diabase dikes studied in the Georgia Piedmont (Norcross, Keystone Blue, Camak, Bolingbroke, Jackson County, and Sparta), for which we propose the name 'Georgia-Type' dikes, are different from other CAMP dikes in the southeastern US, and they are interpreted to represent more evolved olivine-normative dikes than dikes previously studied in this province. [ABSTRACT FROM AUTHOR]

Highlights: [•] Discussing the exhumation processes of high-pressure rocks in the West African Craton (2.2–2.0Ga). [•] Thickening of the crust by buckling leading to burial of sedimentary rocks. [•] Partial melting of the mid to lower crust and development of gravitational instabilities. [•] Exhumation controlled by large-scale folding and re-melting of felsic material. [Copyright &y& Elsevier]

The pressure-dependent elastic properties of the Fe-S system are important to understand the dynamic properties of the Earth's interior. We have therefore undertaken a first-principles study of the structural and elastic properties of FeS polymorphs under high pressure using a method based on plane-wave pseudopotential density function theory. The lattice constants, elastic constants, zero-pressure bulk modulus, and its pressure derivative of pyrite are in good agreement with the previous experiments and theoretical approaches; the lattice constants of marcasite are also consistent with the available experimental data. Calculations of the elastic constants of pyrite and marcasite have been determined from 0 to 200 GPa. Based on the relationship between the calculated elastic constants and the pressure, which can provide the stability of mineral, it would appear that pyrite is stable, whereas marcasite is unstable when the pressure rises above 130 GPa. Static lattice energy calculations predict the marcasite-to-pyrite phase transition to occur at 5.4 GPa at 0 K. [ABSTRACT FROM AUTHOR]

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Abstract: The abundances and distribution of incompatible trace elements in low-Ca pyroxene are important to the interpretation of the thermal and chemical evolution of the lunar magma ocean and cumulate mantle. We conducted high pressure (2GPa) and high temperature (1340–1450°C) experiments to constrain trace elements partitioning between low-Ca pyroxene and a wide range of lunar picritic melt compositions (TiO2 =1.6–16.6wt%) under reducing conditions imposed by graphite-lined molybdenum capsules. We show that addition of TiO2 in the melt decreases rare earth element (REE) and Y partition coefficients in low-Ca pyroxene and quantified this effect through a parameterized lattice strain model. Together with published high quality partitioning data of tetravalent high field strength elements (HFSEs) in the literature, we also developed a parameterized lattice strain model for Ti, Hf and Zr partitioning in low-Ca pyroxene. Partition coefficients of REE and HFSE are positively correlated with Al and Ca abundances in low-Ca pyroxene and negatively correlated with temperature. HFSE partition coefficients show an inverse correlation with Fe content in low-Ca pyroxene. As examples of lunar applications, we estimated REE and HFSE partition coefficients in low-Ca pyroxene close to the multiple saturation points of lunar picritic melts, and found small variations of these partition coefficients in low-Ca pyroxene from individual lunar picritic melts. Constant REE and HFSE partition coefficients can be used in melting models exploring the petrogenesis of individual picritic melts. On the other hand, large variations in estimated REE and HFSE partition coefficients for low-Ca pyroxene are expected during lunar magma ocean crystallization, underscoring the significance of temperature-composition dependent REE and HFSE partition coefficients for understanding lunar magma ocean evolution. [Copyright &y& Elsevier]

Abstract: Garnet from diamondiferous granulites of Ceuta (Betic–Rif cordillera, Spain and Morocco) contains a variety of inclusion types. To better understand the evolution of these rocks during the ultrahigh pressure event, two samples (1 and 2) were selected for the detailed study of garnet. Primary inclusions of apatite, quartz, coesite, rutile and retrograded pyroxene, and exsolution microstructures of rutile characterize garnet from sample 1, whereas exsolution microstructures of quartz, coesite, apatite and rutile, and inclusions formed from a melt characterize garnet from sample 2, indicating that peak metamorphic conditions were recorded by sample 2. In contrast, the chemical patterns of garnet suggest an inverse situation. Garnet from sample 1 has high Ca- and low Mn contents and high XMg, characteristic of growth at high pressure and temperature whereas garnet from sample 2 shows high Mn and low Ca contents and low XMg, characteristic of garnet formed at lower temperature and pressure. The contrasting compositions are interpreted as reflecting differences in the position of the metamorphic path followed by both samples relative to the solidus: Garnets from sample 1 are interpreted as formed below the solidus whereas garnets from sample 2 are interpreted as formed in the presence of a melt, which caused notable enrichment of garnet in Mn and depletion in Ca relative to garnet from sample 1. Due to extensive low-pressure Hercynian melting that caused generalized migmatization and melt mobilization, whole-rock composition of the samples notably changed, thus preventing the accurate estimation of the physical conditions characterizing the older ultrahigh pressure event. Estimations based on experimental determinations of the phosphorous solubility in garnet suggest that peak pressure conditions were on the order of 6–7GPa, which put the origin of the studied crustal rocks at depths greater than 200km. [Copyright &y& Elsevier]

Ultrahigh-pressure (UHP) layered eclogites from the Shuanghe area, Dabie Mountains display the peak assemblage garnet, Na-rich omphacite (Jd60), and minor amounts of coesite, rutile, Si-rich phengite (Si=3.58p.f.u) and apatite. Zr-in-rutile thermometry provides evidence for peak metamorphic conditions of ~650–700°C, which combined with garnet–clinopyroxene–phengite barometry yields a peak pressure of 3.5–4GPa. Three different types of polyphase inclusions that formed after peak conditions are identified in garnet. The first type consists of a symplectitic intergrowth of zoisite+quartz±amphibole associated with epidote and exhibits a rectangular shape. These inclusions are interpreted to have formed during decompression of the UHP rocks as pseudomorphs after prograde to peak lawsonite. The second type of polyphase inclusions contains approximately equal amounts of K-feldspar and quartz. These inclusions are usually surrounded by radial fractures and exhibit regular negative crystal shapes. The observed gradual breakdown of peak metamorphic phengite resulting in these types of inclusions suggests that phengite melting at an advanced stage of exhumation at ~1.5–2GPa and ~750–800°C occurred. The third type of polyphase inclusions displays irregular shapes and preserves the retrograde mineral assemblage amphibole+plagioclase+quartz+biotite+K-feldspar, which likely formed during late stage fluid influx that is also responsible for the replacement of phengite by biotite as well as omphacite by amphibole+plagioclase. The trace element composition of K-feldspar+quartz inclusions has been determined in-situ by LA-ICP-MS and is characterized by a strong enrichment in LILE and a moderate enrichment in LREE with respect to HREE and a depletion in HFSE. The presence of melts assisted in the recrystallization of the eclogites and resulted in the segregation of garnet+quartz-rich and omphacite-rich domains. Field observations show that the melting is very limited and no interconnected network of partial melts formed. Thus, the low degree of partial melting did not result in a chemical differentiation of the subducted rocks but likely influenced the rheology of the eclogites during exhumation. [ABSTRACT FROM AUTHOR]

Abstract: An integrated study of petrology, geochronology and geochemistry was performed for ultrahigh-pressure metamorphic gneisses in the Sulu orogen. The results are used to elucidate the polyphase growth of such metamorphic minerals as zircon, titanite and garnet in response to pressure–temperature changes and fluid/melt action during continental collision. This provides insights into the property of metamorphic fluid/melt and their effects on trace element mobility. A combined result from REE patterns, mineral inclusions and Ti-in-zircon temperatures indicates three stages of zircon growth. Prograde growth occurred at ~237Ma primarily at eclogite-facies, retrograde growth at ~222Ma mostly at eclogite-facies, and the last growth at ~205Ma at granulite-facies. The three stages of zircon growth are deciphered by distinct REE patterns and trace element compositions, reflecting the differences in the property of metamorphic fluid/melt. The episodic growth of metamorphic zircon is primarily dictated by the episodic concentration of Zr and Si in metamorphic fluid/melt. Relict domains of magmatic titanite are distinguished from metamorphosed and metamorphic domains by their distinctive REE patterns and trace element compositions. The metamorphic titanite exhibit variably elevated Nb contents and Nb/Ta ratios, suggesting Nb/Ta fractionation due to breakdown of amphibole and/or biotite during metamorphism. Polyphase growth of garnet is suggested by an integrated analysis of mineral inclusions, and major and trace elements in large garnet grains. Trace element abundances vary in different zones of garnet, which is ascribed to changes in the paragenesis and composition of matrix minerals involved in garnet-forming reactions at different P–T conditions. Therefore, the metamorphic growth of zircon, titanite and garnet would have occurred not only during prograde subduction but also during retrograde exhumation in the continental collision zones. Both metamorphic dehydration and partial melting would have taken place episodically during the collisional orogeny. The breakdown of hydrous minerals at high- to ultrahigh-pressure conditions is a key to fluid liberation and element supply for the growth of these accessory minerals. [Copyright &y& Elsevier]

Abstract: The Makbal Complex in the western Tianshan Mountains of Kazakhstan and Kyrgyzstan consists of HP/UHP metasedimentary host rocks which enclose various HP mafic blocks or boudins. These mafic rocks comprise rare eclogites (sensu stricto and sensu lato), garnet amphibolites (retrograded eclogites) and a newly discovered glaucophanite (glaucophane–garnet–omphacite bearing rock). So far the Makbal Complex has been interpreted to predominantly consist of continental lithologies and the mafic rocks were considered as dismembered dikes intruding continental metasediments. This interpretation is mainly based on the geological relationship and bulk rock chemistry of the different rock types. It was further suggested that the continental lithologies of the Makbal Complex underwent eclogite-facies metamorphism in a former subduction zone. In the present study we combined conventional geothermometry, P–T pseudosection modeling and major and trace element whole rock geochemistry for different mafic samples (glaucophanite and eclogites (sensu lato)) in order to shed light on both the metamorphic evolution and the protoliths of the mafic HP rocks in the Makbal Complex. Prograde to peak-pressure clockwise P–T paths of glaucophanite and eclogites (sensu lato) were modeled using garnet isopleth thermobarometry. The results show that the glaucophanite and eclogite (sensu lato) samples experienced similar prograde P–T paths and slightly different peak metamorphic conditions at ~560°C at 2.4GPa for the former and between ~520°C at 2.2GPa and ~555°C at ~2.5GPa for the latter, corresponding to burial depths between 70 and 85km. Whole rock major and trace element analyses and petrological evidence imply that the various rock types at the Makbal Complex most likely originated from different precursor rocks. Eclogites (sensu lato) are believed to represent strongly retrogressed former eclogite-facies rocks that had never been eclogites (sensu stricto, i.e. >70 vol.% garnet and omphacite) due to an unfavorable alkali-poor bulk composition (Na2O <1wt.%). The four high-pressure mafic samples investigated in this study originated from oceanic crust (Zr/Hf ratio of 33 to 35) which contradicts all previous studies suggesting a continental protolith for all mafic HP/UHP rocks at Makbal. The present study indicates that the mafic high-pressure rocks represent incoherent segments of exhumed oceanic crust. Juxtaposition of different mafic oceanic (this study) and continental rocks is suggested to be due to buoyancy-driven exhumation of the metasedimentary host rock in the subduction channel where dismembered fragments of the subducted oceanic crust were captured in different depths. [Copyright &y& Elsevier]

The Rhodope Domain in NE Greece is comprised of different tectonometamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates. The Kechros Complex represents the lowermost tectonic unit in East Rhodope, and contains a metamorphic suite of Na–Al-rich leucocratic rocks (i.e., alkali feldspar granites, alkali syenites and syenites) within the Virsini antigorite serpentinite. Based on the calculated P–T pseudosection and superimposed isopleths for a meta-syenite, we have determined a peak pressure and temperature of 1.55±0.03GPa and 550±25°C, suggesting HP metamorphism for leucocratic rocks enclosed in the Virsini serpentinized peridotites. The retrograde conditions suggest a prolonged exhumation history, with equilibration conditions first at P 1.1±0.03GPa and T 580±20°C and then at P 0.55±0.04GPa and T 430±30°C. The P–T conditions suggest an early rapid uplift event followed by a late-stage exhumation period, characterized by rapid cooling at relatively isobaric conditions. Similar metamorphic signatures are also recorded in continental rocks of the Kechros complex (i.e., orthogneisses, metapelites), suggesting that crustal and mantle rocks underwent a common Alpine tectonometamorphic evolution. The exact ages of HP metamorphism in the Kechros Complex are not well constrained, however, a Rb–Sr age of 37Ma from a neighboring orthogneiss records a stage of exhumation that may be contemporaneous with the Eocene HP metamorphism (49–55Ma; i.e., recorded in the Nestos Shear Zone of Central Rhodope). We interpret this to be the result of the eventual closure of the Axios/Vardar Ocean and subsequent subduction of the Apulian continental crust (a promontory of the Africa continent) under the southern margin of the European continent in the late Cretaceous and early Tertiary. [ABSTRACT FROM AUTHOR]

Abstract: Quartz c-axis fabric, finite strain, and kinematic vorticity analyses were carried out in well-exposed quartz mylonites to investigate the heterogeneous nature of ductile deformation within the Eghlid deformed area in the High Pressure–Low Temperature (HP–LT) Sanandaj–Sirjan metamorphic belt (Zagros Mountains, Iran). This belt belongs to a sequence of tectonometamorphic complexes with low- to high-grade metamorphic rocks affected by a polyphase deformation history. Asymmetric quartz c-axis fabrics (type I) confirm a localized top-to-the-southeast sense of shear. Quantitative finite strain analysis in the XZ, XY and YZ principal planes of the finite strain ellipsoid demonstrate that the strain ratio increases towards the thrust planes of the Zagros Thrust System. Kinematic vorticity analysis of deformed quartz grains showed sequential variation in the kinematic vorticity number from ∼0.5 to ∼0.8 between the thrust sheets. Such vorticity numbers show that both simple and pure shear components contribute to the deformation. Our results show that simple shear dominated deformation near the thrust faults, and pure shear dominated deformation far from them. Quartz c-axis opening angles suggest deformation temperatures range between 450°±50°C and 600°±50°C, which yield greenschist to amphibolite facies conditions during ductile deformation. [Copyright &y& Elsevier]

Abstract: Five domains (microplates) have been recognized by seismic anisotropy in the mantle lithosphere of the Bohemian Massif. The mantle domains correspond to major crustal units and each of the domains bears a consistent fossil olivine fabric formed before their Variscan assembly. The present-day mantle fabric indicates that this process consisted of at least three oceanic subductions, each followed by an underthrusting of the continental lithosphere. The seismic anisotropy does not detect remnants of the oceanic subductions, but it can trace boundaries of the preserved continental domains subsequently underthrust along the paths of previous oceanic subductions. The most robust continent–continent collision was followed by westward underthrusting of the Brunovistulian mantle lithosphere, still detectable by seismic anisotropy more than 100km beneath the Moldanubian mantle lithosphere. Major occurrences of the high-pressure/ultra high-pressure (HP–UHP) rocks follow the ENE and NNE oriented sutures and boundaries of the mantle–lithosphere domains mapped from three-dimensional modeling of body-wave anisotropy. The HP–UHP rocks are products of oceanic subductions and the following underthrusting of the continental crust and mantle lithosphere exhumed along the mantle boundaries. The close relation of the mantle sutures and occurrences of the HP–UHP rocks near the paleosubductions testifies for models interpreting the granulite–garnet peridotite association by oceanic/continental subduction/underthrusting followed by the exhumation of deep-seated rocks. Our findings support the bivergent subduction model of tectonic development of the central part of the Bohemian Massif. The inferences from seismic anisotropy image the Bohemian Massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric. The collisional mantle boundaries, blurred by tectonometamorphic processes in easily deformed overlying crust, served as major exhumation channels of the HP–UHP rocks. [Copyright &y& Elsevier]

Abstract: Despite extensive studies of calc-silicate rocks of the Kokchetav massif, there is no satisfactory explanation of the origin of potassium-bearing clinopyroxene in alkali poor metamorphic rocks. In this paper we report the finding of potassium-bearing clinopyroxene with prograde zonation (K2O increases from core to rim) from diamond-grade, but diamond-free UHP calc-silicate rocks of the Kokchetav massif. We believe that the crystallization of potassium-bearing clinopyroxene started on the prograde stage and slightly prior to the peak of UHP metamorphism. Thus, prograde metamorphic history is only traceable in diamond-free UHP calc-silicate rocks, while in diamond-bearing UHPM rocks it is completely reset. Fluid and polyphase solid inclusions, originally representing melt inclusions, occur in the core of potassium-bearing clinopyroxene and imply that melt and fluid may coexist in calc-silicate rocks even at 1000–1100°C and 6–7GPa. [Copyright &y& Elsevier]

Abstract: In this study, we link zircon U and LA-ICP-MS geochronology and the Luic composition of eclogites and their host gneisses/schists with whole-rock geochemistry of eclogites in the Dulan area to constrain their protoliths and metamorphic relationships. U suggests that the protolith of one of the eclogites was a Neoproterozoic mafic intrusive rock (828±58Ma) and the protolith of enclosing orthogneiss was an early-Neoproterozoic granitoid (923±12Ma). Detrital zircons from Grt-bearing mica-schists yield ages of 0.9–2.5Ga, with a dominant range of 1.0–1.8Ga, indicating sedimentary sources from Neoproterozoic to Neoarchean crust and a depositional age ≤0.9Ga. The matching metamorphic ages of eclogites (438±5Ma, 436±4Ma) and their country rocks (Grt-bearing mica-schists: 438±4Ma, 439±8Ma; orthogneiss: 427±8Ma) indicate that all studied samples experienced coeval Early Paleozoic HP/UHP metamorphism. The Und Hf isotopic compositions of the inherited magmatic zircon cores of an eclogite sample (ε Hf (800)=2.6–9.2, TDM1 =1.0–1.3Ga, TDM2 =1.1–1.4Ga) suggest that the protolith may be derived from Neoproterozoic depleted mantle with variable proportions of an older crustal component. The magmatic zircon cores of the orthogneiss (εHf (900)=−7.3 to −0.2; TDM2 =1.8–2.1Ga) suggest that the parental magma was derived from a Paleoproterozoic crustal source. Hf isotopic compositions of the detrital zircons from the metasediments (εHf(t)=−19.4 to +10.6) suggest three crust formation and reworking events: (1) Archean (TDM2 =2.7–2.9Ga) juvenile crust reworked at ~2.5Ga; (2) early Paleoproterozoic (TDM2 =2.3–2.5Ga) juvenile crust reworked at ~1.8Ga; and (3) late Paleoproterozoic (TDM2 =1.5–1.9Ga) juvenile crust reworked in the Neoproterozoic. Whole-rock geochemical data suggest that the protoliths of the Dulan eclogites were probably derived from a continental rift or an incipient oceanic basin rather than a large, long-lived ocean basin. Thus, combined with field relationships, petrology, geochemistry, zircon U and the Luic analysis presented in this paper and reported from previous studies, we suggest that the Dulan eclogites and their country rocks experienced a common UHP metamorphism during Late Ordovician deep continental subduction. [Copyright &y& Elsevier]

Abstract: Whole rock trace element and isotopic compositions of different HP–LT metamorphic rocks of the Ile de Groix were analysed to characterise geochemical fingerprints during subduction and exhumation in a late Palaeozoic HP metamorphic terrain. Massive metabasites of hydrothermally altered enriched mid-ocean ridge basalt (E-MORB) origin are in association with banded metabasic rocks of volcano-sedimentary origin and metapelites. Fluid-rock interactions that likely occurred during seafloor hydrothermal alteration and early subduction metasomatism increased δ18O values, as well as K2O, Na2O, MgO, and LILE contents and decreased CaO contents of metabasites. Most metabasites have retained their early-subduction and pre-HP trace element and isotopic composition, even for rocks metamorphosed to lower eclogite-facies P–T conditions. Micaschists also preserved apparent pelitic protolith trace element values and oxygen isotopic compositions. During retrograde metamorphism related to the exhumation, metabasites were rehydrated by fluids in equilibrium with the host rock compositions, which were likely derived from the basic rocks. This style of fluid–rock interaction formed a greenschist facies mineral assemblage. Metabasites that underwent pervasive alteration by seafloor hydrothermal and metasomatism processes prior to peak metamorphism, show greater effects of retrogression and albitisation, probably because they were richer in H2O and Na2O. The variety of metamorphic assemblages on the Ile de Groix is thus directly related to the pre-HP rock composition. The extent of retrogression in the western part of the Ile de Groix primarily reflects stronger metasomatic intensities than in the eastern part. [Copyright &y& Elsevier]

Abstract: The first evidence for ultrahigh-pressure (UHP) metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides is recorded by kyanite-bearing eclogite, found in a basic dyke within a garnet peridotite body exposed close to the lake Friningen in northern Jämtland (central Sweden). UHP metamorphic conditions of ~3GPa and 800°C, within the stability field of coesite, are constrained from geothermobarometry and calculated phase equilibria for the peak-pressure assemblage garnet+omphacite+kyanite+phengite. A prograde metamorphic evolution from a lower P–T (1.5–1.7GPa and 700–750°C) stage during subduction is inferred from inclusions of pargasitic amphibole, zoisite and kyanite in garnet cores. The post-UHP evolution is constrained from breakdown textures, such as exsolutions of kyanite and silica from the Ca-Eskola clinopyroxene. Near isothermal decompression of eclogite to lower crustal levels (~0.8–1.0GPa ) led to formation of sapphirine, spinel, orthopyroxene and diopside at granulite facies conditions. Published age data suggest a Late Ordovician (460–445Ma) age of the UHP metamorphism, interpreted to be related to subduction of Baltoscandian continental margin underneath an outboard terrane, possibly outermost Laurentia, during the final stages of closure of the Iapetus Ocean. The UHP rocks were emplaced from the hinterland collision zone during Scandian thrusting of the nappes onto the Baltoscandian foreland basin and platform. The record of P–T conditions and geochonological data from UHP rocks occurring within the allochthonous units of the Scandinavian Caledonides indicate that Ordovician UHP events may have affected much wider parts of the orogen than previously thought, involving deep subduction of the continental crust prior to final Scandian collision between Baltica and Laurentia. [Copyright &y& Elsevier]

Abstract: The survey of high-P metamorphic rocks in Antarctica can help clarify the geodynamic evolution of the continent by pointing out palaeo-suture zones and constraining the age of subduction and collision events. There are eclogite-facies rocks along the eastern margin of the ‘Mawson block’ (e.g., in the Nimrod Glacier region and George V Land). Some of these have been long forgotten (George V Land; Eyre Peninsula in Australia). Stillwell (1918) described rocks from George V Land containing glaucophane, lawsonite, garnet coronas and symplectites possibly after omphacite. These high-P rocks were apparently involved in the Nimrod-Kimban orogenic cycle and therefore provide a record of convergence along the eastern margin of the Mawson block at ~1700Ma; they could represent one of the oldest blueschist-facies imprint. Many terranes in East Antarctica underwent a tectonometamorphic evolution during the Grenvillian (1300–900Ma) and/or the Pan-African (600–500Ma) orogenies, corresponding to the amalgamation of Rodinia and Gondwana, respectively. High-P relicts have been described or are suspected to occur in these terranes. Garnet-bearing coronitic metagabbros, in some cases possibly containing omphacite, are common in Dronning Maud Land and the Rayner Complex. They formed under high-P granulite-facies or eclogite-facies conditions and recall similar metabasites from the Grenville mobile belt of Canada. Note that some reconstructions of the Rodinia supercontinent consider these two Antarctic regions as an extension of the Grenvillian belt of Canada. Other eclogite-facies metamorphic rocks and ophiolites (Shackleton Range and possibly Sverdrupfjella) belong to the Pan-African mobile belt extending from Tanzania to East Antarctica. Since the Cambrian, the terranes of West Antarctica have been accreted along the palaeo-Pacific margin of Gondwana/Antarctica during several subduction-accretion orogenies. The ultrahigh-P metamorphic rocks of Northern Victoria Land formed through the accretion of an arc-backarc system during the Cambrian-Ordovician Ross orogeny; eclogites of the same orogeny also exist in Tasmania and Australia. Lastly, on the western edge of the Antarctic Peninsula, the Mesozoic–Cenozoic Andean orogeny generated a subduction-accretionary complex containing blueschist-facies rocks. [Copyright &y& Elsevier]

Abstract: Carbonation reaction with silicate minerals that are common components of the host rock and cap rock within geological storage reservoirs and the associated structural deformation were investigated for better understanding of the geochemical reactions associated with geologic CO2 storage. Exposure of a model expanding clay, Wyoming montmorillonite, SWy-2, to high-pressure CO2 resulted in the formation of a mineral carbonate phase via dry CO2–clay mineral interactions at two different temperatures. The experimental evidence suggests that the properties of CO2 fluid at 70°C provide more favorable conditions for carbonate formation at the clay surface less accessible to CO2 at 22°C. The carbonation reaction occurred predominantly within the first couple of days of exposure to the fluid and then proceeded slower with continuing exposure. As compared to the as-received clay under the same ambient conditions, the (001) basal spacing of the clay bearing carbonates (after the CO2 exposure) was slightly expanded at a relative humidity (RH) level of 12% but it was slightly collapsed at the RH level of 40%. Experimental observations suggest that the carbonation reaction occurs at the external surface as well as internal surface (interlayer) of the clay particles. [Copyright &y& Elsevier]

Abstract: High-pressure (HP) rocks at Tehuitzingo, on the western margin of the HP belt within the Paleozoic Acatlán Complex (southern México), occur in a klippe that was thrust over low-grade clastic rocks. The youngest detrital zircon cluster in the low-grade rocks yielded U-Pb ages of 481±16Ma, which provide an older limit for deposition. The HP rocks are composed of metabasites, serpentinite, granite (482±3Ma) and mica schist (youngest concordant detrital zircon: 433±3Ma). The schist and granite are inferred to be high-grade equivalents of lower Paleozoic, low-grade rocks exposed elsewhere in the Acatlán Complex, from which they are inferred to have been removed by subduction erosion. Mineral analyses indicate that the subducted rocks underwent HP metamorphism and polyphase deformation at depths of ~50km (~16kbar and 750°C: eclogite facies). Subsequent retrogression passed through epidote-amphibolite to greenschist facies, which was synchronous with W-vergent thrusting over the low-grade clastic rocks. Deposition of the low-grade rocks and thrusting are bracketed between either 481–329Ma (Ordovician-Mississippian), and was followed by F3 synformal folding. Cooling through ca. 385°C is indicated by 329±1 and 316–317±2Ma, 40Ar/39Ar muscovite plateau ages in HP rocks, which are 5–17 my younger than those of the adjacent Piaxtla eclogites suggesting younger exhumation. The petrology, P-T conditions and ages of the Piaxtla Suite is consistent with an extrusion channel within the Acatlán Complex along the active western margin of Pangea during the Carboniferous. Detrital zircon populations in the low-grade psammite (ca. 481, 520–650, 720, 750, 815, 890, 1050 and 2750Ma) and the HP schist (ca. 457–480, 534, 908, 954–1150, 1265, 1845 and 2035Ma) indicate derivation from the Ordovician Acatlán granitoids, Neoproterozoic Brasiliano orogens, 900–750Ma Goiás arc (Amazonia), 1–1.3Ma Oaxaquia, and more ancient sources in Oaxaquia/Amazonia. [Copyright &y& Elsevier]

Abstract: Although at 1atm pressure the oxidation state of W in silicate melts is 6+at oxygen fugacities from air down to several logfO2 units below Fe-FeO (IW) equilibrium, Cottrell et al. (2009) suggested that, at pressures above 6GPa, W becomes predominantly 4+in this oxygen fugacity range. Wade and Wood (2005), using a similar, but expanded metal-silicate partitioning dataset found, however, no evidence for an oxidation state change. In order to resolve the issue we collected tungsten L3 edge XANES spectra of a series of synthetic tungsten- bearing glass standards and of silicates from a range of high-pressure (1.5 to 25GPa) metal/silicate partitioning experiments. Glass standards were made at 1atm pressure and equilibrated at oxygen fugacities spanning a range from approximately 5.5 log units below the Fe-FeO buffer (IW-5.5) to Air. Metal-silicate partitioning experiments were performed at oxygen fugacities between IW-6.2 and IW-1 and at pressures between 1.5 and 25GPa. At low pressures and oxygen fugacities above IW-3.5, W exists in the silicate melt almost exclusively as W6+ (identical L3-edge energy to WO3) with the progressive reduction to W4+ completed by about IW-6. The XANES spectra of W from experiments at 6, 7 and 25GPa are completely consistent with those from 1atm and 1.5GPa experiments and with that of WO3. We conclude that there is no change of oxidation state with increasing pressure to 25GPa and that modelling of the oxygen-fugacity dependence of core formation requires use of a+6 oxidation state of W. [Copyright &y& Elsevier]

The formation and exhumation of high and ultrahigh- pressure, (U)HP, rocks of crustal origin appears to be ubiquitous during Phanerozoic plate subduction and continental collision events. Exhumation of (U)HP material has been shown in some orogens to have occurred only once, during a single short-lived event; in other cases exhumation appears to have occurred multiple discrete times or during a single, long-lived, protracted event. It is becoming increasingly clear that no single exhumation mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. Subduction zone style and internal force balance change in both time and space, responding to changes in width, steepness, composition of subducting material and velocity of subduction. In order for continental crust, which is relatively buoyant compared to the mantle even when metamorphosed to (U)HP assemblages, to be subducted to (U)HP conditions, it must remain attached to a stronger and denser substrate. Buoyancy and external tectonic forces drive exhumation, although the changing spatial and temporal dominance of different driving forces still remains unclear. Exhumation may involve whole-scale detachment of the terrane from the subducting slab followed by exhumation within a subduction channel (perhaps during continued subduction) or a reversal in motion of the entire plate (eduction) following the removal of a lower part of the subducting slab. Weakening mechanisms that may be responsible for the detachment of deeply subducted crust from its stronger, denser substrate include strain weakening, hydration, melting, grain size reduction and the development of foliation. These may act locally to form narrow high-strain shear zones separating stronger, less-strained crust or may act on the bulk of the subducted material, allowing whole-scale flow. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Future research directions include identifying temporal and spatial changes in exhumation mechanisms within different tectonic environments, and determining the factors that influence those changes. [ABSTRACT FROM AUTHOR]

Changshaling Structural Belt is an important oil and gas exploration area in Jiudong Basin, and abnormal high pressure is universal in the zone. The paper proposes a new three-dimensional (3D)pore pressure calculation method based on single point hypothesis, which can use 3D interval velocity data to estimate 3D pore pressure. The novel method was applied to the 3D pore pressure calculation and analysis of Changshaling Structural Belt. Firstly, the pore pressure profile and model parameters of several key exploratory wells were established. Secondly, the 3D interval velocity data of the structural belt was obtained by seismic inversion. Further, the computer program was developed, and it was used to calculate the 3D pore pressure of Changshaling Structural Belt. Finally, with the 3D pressure results of Changshaling Structural Belt, the pore pressure distribution of this zone was systematically analyzed, with positive results. [ABSTRACT FROM AUTHOR]

Abstract: High-pressure mafic granulites from the Jiaobei massif in the southern segment of the Jiao-Liao-Ji Belt (JLJB) situating in the Eastern Block of the North China Craton (NCC) were examined based on an integrated study of petrology, mineral chemistry and pseudosection modeling. Microstructural relationships of the high-pressure mafic granulites indicate four metamorphic stages, including the pre-peak (M1) stage indicated by garnet core+inclusion-phase minerals of hornblende+clinopyroxene+plagioclase+quartz±epidote±rutile, the peak (M2) stage featured by garnet mantle/rim+matrix-phase minerals of clinopyroxene+plagioclase+quartz±rutile, the post-peak (M3) stage characterized by the clinopyroxene+plagioclase+orthopyroxene symplectite, and the retrograde (M4) stage represented by the hornblende+plagioclase symplectite and symplectic clinopyroxene+ilmenite+quartz. By applying the THERMOCALC (Version 3.33) technique in the NCFMASHTO system, the P–T conditions are estimated at 9.4–9.8kbar and 690–702°C for the pre-peak (M1) stage, 13.1–15.1kbar and 780–890°C for the peak (M2) stage, 7.8–8.4kbar and 820–880°C for the post-peak (M3) stage and the 6.4–7.2kbar and 690–760°C for the retrograde (M4) stage. These mineral assemblages and their P–T conditions define a clockwise P–T path for the high-pressure mafic granulites in the Jiaobei massif, suggesting that the rocks underwent near-isothermal decompression and subsequent cooling after the peak metamorphism, which implies that the southern segment of the JLJB must have experienced subduction-/collision-related tectonic processes at ca. 1.93–1.90Ga. Therefore, the Jiao-Liao-Ji Belt may represent another Paleoproterozoic collisional belt along which the Longgang and Langrim Blocks amalgamated to form the Eastern Block of the North China Craton. [Copyright &y& Elsevier]