Soil and lake sediments are important paleoclimate archives often forming a source-sink setting. To better understand magnetic properties in such settings, we studied red soil on low-magnetic bedrock and subrecent sediments of Caohai Lake (CL) in Heqing Basin, China. Red soil is the only important source material for the CL sediments, it is highly magnetic with susceptibilities (chi) of similar to 10(-5) m(3)/kg. The red soil is dominated by pedogenic nano-magnetite (similar to 10-15 nm) arranged in aggregates of similar to 100 nm, with particle interaction that causes a wide effective grain size distribution in the superparamagnetic (SP) range tailing into stable single-domain behavior. Transmission electron microscopy and broadband frequency chi(f) suggest partial disintegration of the aggregates and increased alteration of the nanoparticles to hematite during transfer of red soil material to CL. This shifts the domain state behavior to smaller effective magnetic grain sizes, resulting in lower chi(fd)% and chi values, and a characteristic change of chi(f). The SP-stable single-domain distribution of the aggregates in red soil could be climate dependent, and the ratio of saturation remanence to chi is a potential bedrock-specific paleoclimate proxy reflecting it. Magnetic properties of the CL sediments are controlled by an assemblage of nanoparticle aggregates and larger-sized bedrock-derived magnetite. The results challenge the validity of the previous paleoclimate interpretation from the 168-m-long Core-HQ (900-30 ka) in Heqing Basin. Disintegration of aggregates could lead to SP behavior with low chi(fd)% without extinction of individual magnetite nanoparticles, and the chi(fd)%-based assumption of SP magnetite dissolution may be wrong.

A new on-line Raman System, which was installed at the M3-beamline at the UNILAC, GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt was used for first "in situ" spectroscopic measurements. Calcite and malachite samples were irradiated in steps between 1 x 10(9) and 1 x 10(12) ions/cm(2) with Au ions (calcite) and Xe ions (malachite) at an energy of 4.8 MeV/u. After irradiation, calcite revealed a new Raman band at 437 cm(-1) and change of the full width at half maximum for the 1087 cm(-1) Raman band.The Raman bands of malachite change significantly with increasing fluence. Up to a fluence of 7 x 10(10) ions/cm(2), all existing bands decrease in intensity. Between 8 x 10(10) and 1 x 10(11) ions/cm(2) a broad Cu2O band between 110 and 220 cm(-1) occurs, which superimposes the pre-existing Raman bands. Additionally, a new broad band between 1000 and 1750 cm(-1) is formed, which is interpreted as a carbon coating. In contrast to the Cu2O band, the carbon band vanished when further irradiating the-sample.The installations as well as first in situ measurements at room temperature are presented. (C) 2015 Elsevier B.V. All rights reserved.

Data for the solubility of minerals in aqueous solutions at high pressures and temperatures are essential for our understanding of fluid properties, mass transport and growth/dissolution processes of minerals in Earth's crust and upper mantle. Almost all available data on mineral solubility above 0.5 GPa have been obtained by ex situ quench methods in piston-cylinder-type apparatus. To exploit the obvious advantages of direct in situ solubility determinations in diamond anvil cells, we have developed simple in situ mass-loss approaches to calculate the mass of the observed crystal at any given pressure and temperature condition. This strategy combines the advantages of in situ and ex situ experiments while circumventing their disadvantages. In the present paper we describe a method that takes advantage of the tendency of crystals to approach an idiomorphic habit during hydrothermal diamond-anvil-cell runs. It can also be used for cleavage fragments. Using a modified version of the Kristall 2000 software designed for crystal drawing, the three-dimensional habit of a crystal can be modelled based on a two-dimensional digital image. This three-dimensional model allows the crystal volume and therefore its mass to be determined by measuring the exact length of just one crystal edge. The accuracy of this method is demonstrated by modelling the mass of various mineral grains of different shapes, morphologies, masses, densities and complexities, and comparing the modelled values to their actual weight. Modelled mass calculations are within 1 sigma = 0.38 % based on the Gaussian Error propagation for crystals varying from 0.2 to 38 mg. This method can be used not only for solubility experiments, but also in all situations where the crystalline sample is accessible only by optical methods.

First principles molecular dynamics simulations have been carried out at various temperatures and pressures starting with either Ca(2+) or CaO in a reactive volume of 63 H(2)O molecules. In the case of aqueous Ca(2+), the ion is surrounded by six H(2)O molecules in the first hydration shell at 300 K/0.3 GPa, with rare exchange between first and second hydrations shells. At 900 K/0.9 GPa, the coordination number in the first hydration shell fluctuates between six and eight, the average being 7.0. CaO immediately reacts with the surrounding H(2)O molecules to form Ca(2+) + 2OH(-). The hydroxyl ions form transient Ca(OH)(+) and Ca(OH)(2) complexes and have a mean residence time in the first coordination shell of Ca(2+) of 6 ± 4 ps at 500 K and 3 ± 3 ps at 900 K, respectively. At 500 K/0.5 GPa, the time-averaged relative concentrations of the transient Ca(2+), Ca(OH)(+), and Ca(OH)(2) species are 14%, 55%, and 29%, while at 900 K/0.9 GPa, they are 2%, 34%, and 63%.

A novel diamond-anvil cell (DAC) design has been constructed and tested for in situ applications at high-pressure (HP) operations and has proved to be suitable even for HP sample environments at non-ambient temperature conditions. The innovative high-precision guiding mechanism, comparable to a dog clutch, consists of perpendicular planar sliding-plane elements and is integrated directly into the base body of the cylindrically shaped DAC. The combination of two force-generating devices, i.e., mechanical screws and an inflatable gas membrane, allows the user to choose independently between, and to apply individually, two different forcing mechanisms for pressure generation. Both mechanisms are basically independent of each other, but can also be operated simultaneously. The modularity of the DAC design allows for an easy exchange of functional core-element groups optimized not only for various analytical in situ methods but also for HP operation with or without high-temperature (HT) application. For HP-HT experiments a liquid cooling circuit inside the specific inner modular groups has been implemented to obtain a controlled and limited heat distribution within the outer DAC body.

The method of fission-track dating is highly established in thermochronology to define the range of temperature rocks have been exposed to in the past. As carbonate rocks are abundant in Earth’s crust, our new approach tries to apply the fission-track thermochronology to calcite dominated rock formations. First steps of this project include defining suitable etching agent and specifying etching conditions. Different etching recepies [1-3] have been tested with respect to their effectiveness. As the uranium content of natural calcite is highly variable, we simulated natural fission fragments of U by using accelerated heavy ions. The experiments were performed with annealed natural calcite crystals irradiated with 11.1 MeV/u U or Au ions at the UNILAC. Fluences between 10 and 10 ions/cm were applied. During irradiation, the surface of some calcite crystals was covered with a hexagonal mask to create irradiated and nonirradiated sites next to each other (Fig. 1). Agents tested for etching are formic acid (CH2O2), sodium hydroxide (NaOH), hydrochloric acid (HCl), and a 1:1 mixture of ethylenediaminetetraacetic acid (EDTA) and 5% acetic acid, the latter showing best results so far.

There is a distinct need for predictive equations of state for supercritical aqueous solutions, both for understanding fluids in deeper levels of Earth’s crust or in subduction zones, as well as in experimental work on mineral solubility. Here we develop a semi-empirical approach introduced by Gerya & Perchuk (1997) based on the P-T partition function of statistical thermodynamics, using experimental data on quartz and wollastonite solubility, as well as data on speciation of dissolved solution components derived from first principles molecular dynamics simulations. Two approaches are possible, differing in the degree of explicit information provided on the nature of the solution modelled and also in the amount of basic data needed to implement them. Both have their potential fields of application. A “simple” model using only the semi-empirical formulation for the H 2 O solvent is useful if independent data on speciation are lacking, overall neutrality of the dissolving species can be assumed, and the number of components is relatively low. Computation is fairly straightforward, because the system can be treated as a simple “mixing” problem, and adopted effective dissolved species are characterized by conventional thermodynamic properties that allow interpolation and extrapolation of fitted experimental solubility data. Application to the system CaO–SiO 2 –H 2 O shows that experimental data on fluids coexisting with wollastonite + quartz/coesite can be successfully modelled up to 900 °C and 4 GPa. This simple semi-empirical formulation can lay the groundwork for an “internally consistent data set” allowing descriptions of fluids in relatively simple fluid-rock systems at high pressures. With the addition of independent data on actual speciation, and an optimized model for the dissociation of H 2 O from available literature data, the semi-empirical approach can be extended to a comprehensive description of aqueous solutions in the CaO–SiO 2 –H 2 O system. Both models have one positive feature in common. Because standard thermodynamic properties for dissolved species, oxides or fictive aggregates/clusters can be derived, solutions of arbitrary compositions can be modelled from data obtained from experiments in which fluids are saturated with a given solid phase or phases.

The microporous framework structure of (Mg1−xFex)2Al4Si5O18 (=cordierite) has been subject to a comparative study on the effect of structural alterations originating from exposure to high-energy heavy ions. Oriented samples (with x=0.061, 0.122, and 0.170) were irradiated with swift 124Xe, 197Au and 96Ru ions with 11.1MeV per nucleon energy and fluences of 1×1012 and 1×1013ions/cm2. Irradiated and non-irradiated samples were investigated by means of X-ray diffraction, Mössbauer spectroscopy and optical absorption spectroscopy. Structural investigations reveal an essentially unchanged Al,Si ordering, which appears to be unaffected by irradiation. The most remarkable macroscopic change is the ion-beam induced colouration, which could be assigned to electronic charge transfer transitions involving the Fe cations. Mössbauer spectra indicate an increased amount of [4]Fe3+ for the irradiated sample. The most noticeable structural alteration concerns irradiation-induced dehydration of extra-framework H2O, which is accompanied by a reduction in the molar volume by ∼0.2vol%.

The Erzgebirge dome in the Central European Variscides is a stack of crustal slices including some high- and ultrahigh-pressure rocks related to continent–continent collision. One such slice is the Mica-Schist/Eclogite Unit, in which the predominantly metasedimentary country rocks appear to record maximum metamorphic pressures of at most 11–13 kbar, whereas volumetrically minor eclogite lenses within the unit indicate pressures up to 27 kbar. In the present study, the P – T evolution of rocks found in calc–silicate reaction zones between eclogite and country rock marble near the locality Stumpelfelsen, a crag composed of eclogite near the village of Hammerunterwiesenthal, has been established via conventional geothermobarometry. A metasomatic marble–eclogite interchange can be documented for the earliest stages of prograde metamorphism. Significant amounts of fluorine infiltrated the metabasic rocks from the marbles, leading to fluorine-bearing amphibole as well as phengite, and even fluorine-rich growth zones in garnet with 0.62 wt.% F and 1.2 wt.% OH. This appears to be the first description of a F-bearing member of an almandine–grossular solid solution poor in andradite component. The P – T path of the eclogite–marble reaction zone reaches a maximum pressure of 26 kbar at 520–640 °C, just below the quartz–coesite transition. The exhumation path can be traced to 10 kbar and 450–600 °C, where it is then coincident with the published P – T paths of the mica schists and orthogneisses of the Mica-Schist/Eclogite Unit. This study indicates that the Stumpelfelsen eclogite lens and the surrounding metasedimentary country rock of the area must share a common high-pressure metamorphic history. The critical question arising for future studies is how much of the Mica-Schist/Eclogite Unit has actually “travelled the high-pressure eclogite route”, and how much of it was never subducted to pressures greater than 11–13 kbar.

Although the titanomagnetite-ilmenite thermo-oxybarometer has been widely used to provide information on temperature and oxygen fugacity during magmatic and metamorphic processes, the available formulations yield unsatisfactory results; for example, at high temperature and low to moderate fO(2) (i.e. in conditions relevant to crystallization in basic and intermediate rocks). We present a new version of this thermo-oxybarometer based on numerical fits of a large experimental dataset comprising new results in the Fe-Ti-Al-Mg-O system and those of literature studies. Our new subsolidus experimental results at temperatures in the range 1100-1300 degrees C under low to moderate fO(2) conditions show that the addition of Mg and/or Al in the concentration ranges that are usual in Fe-Ti oxides from basic magmatic rocks can be accommodated by simple projections. We have taken advantage of this fact and performed numerical fits to generate empirical formulations. With the resulting expressions we can retrieve temperature values from X(usp)(') and X(ilm)(') (projected mole fractions) of titanomagnetite-ilmenite(ss) pairs and fO(2) values from X(usp)(') and T. The present thermo-oxybarometer model is designed for assemblages of titanomagnetite and hemoilmenite (with the R (3) over bar space group), with the usual low Al(2)O(3), Cr(2)O(3), MgO and MnO contents (less than about 6 wt %), which equilibrated at high temperatures (T >= 800 degrees C) and low to moderate oxygen fugacities (-4<Delta NNO<+2, where NNO is the nickel-nickel oxide buffer). Tests of our model by using the compositions of titanomagnetite-ilmenite(ss) pairs in products of liquidus experiments conducted at known T-fO(2) conditions ( literature data and new results) show that the calculated values reproduce the experimental ones within +/- 70 degrees C, and in most cases within +/- 50 degrees C. The estimates of the oxygen fugacity are mostly within +/- 0.4 log units. This is a significant improvement compared with the previous models.

The solubility of a natural grossular-rich garnet of composition Ca 2.86 Fe 2+ 0.07 Mg 0.07 Fe 3+ 0.10 Al 1.90 Si 3.00 O 12 has been experimentally determined in pure water at pressures from 1 to 5 GPa and temperatures ranging from 400 to 800 °C with the weight-loss technique in piston–cylinder apparatus. Grossular dissolves congruently in this pressure–temperature region. The amount of dissolved grossular increases with both increasing pressure and temperature and ranges from 0.1 to 7.0 wt.%. In comparison to available data on other phases in the CaO–Al 2 O 3 –SiO 2 system, the solubility of grossular is considerably lower than that of quartz (SiO 2 ) or wollastonite (CaSiO 3 ), but higher than that of corundum (Al 2 O 3 ) at comparable pressure–temperature conditions. Using a model based on the familiar correlation between the equilibrium constant of a dissolution reaction and the density of water, ρ H 2 O, we suggest that the following expression provides an acceptable description of the solubility of pure grossular, Ca 3 Al 2 Si 3 O 12 , in water for the above pressure–temperature range: \[log\ (\mathit{m}_{grs})\ =\ 0.8639\ {-}\ 3519.71{\ast}\mathit{T}^{{-}1}\ +\ 676921.07{\ast}\mathit{T}^{{-}2}\ +\ 4502.85{\ast}\mathit{T}^{{-}3}\ +\ log{\rho}_{H_{2}O}{\ast}\ (7.2557\ +\ 773.65{\ast}\mathit{T}^{{-}1}\ {-}\ 106080.98{\ast}\mathit{T}^{{-}2}),\] where m grs is the molality of dissolved grossular and T is in °C. Uncertainties estimated from the outer bounds of experimental data scatter indicate a maximum of ±0.045 mol grs /kg H 2 O. Comparison with available experimental solubility data on quartz, wollastonite, corundum and kyanite provides indirect evidence for the presence of aqueous Al–Si-species.

Thermochemical characterization of Ca4La6(SiO4)6(OH)2a synthetic La- and OH-analogous of britholite: implication for monazite and LREE apatites stabilityIn this contribution, monazite (LREEPO4) solubility is addressed in a chemical system involving REE-bearing hydroxylapatite, (Ca, LREE)10(PO4,SiO4)6(OH)2. For this purpose, a synthetic (La)- and (OH)-analogous of britholite, Ca4La6(SiO4)6(OH)2, was synthesised and its thermodynamic properties were measured. Formation enthalpy of -14,618.4±31.0 kJ·mol-1was obtained by high-temperature drop-solution calorimetry using a Tian-calvet twin calorimeter (Bochum, Germany) at 975 K using lead borate as solvent. Heat capacities (Cp) were measured in the 143-323 K and 341-623 K ranges with an automated Perkin-Elmer DSC 7. For calculations of solubility diagrams at 298 K, the GEMS program was used because it takes into account solid solutions. In conditions representative of those expected in nuclear waste disposal, calculations show that La-monazite is stable from pH = 4 to 9 with a minimum of solubility at pH = 7. La-bearing hydroxylapatite precipitates at pH > 7 with a nearly constant composition of 99% hydroxylapatite and 1% La-britholite. Each mineral buffers solution at extremely low lanthanum concentrations (log{La} = 10-10-10-15mol·kg-1for pH = 4 to 13). In terms of chemical durability, both La-monazite and La-rich apatite present low solubility, a requisite property for nuclear-waste forms.

Recent systematic studies of mineral solubilities in water to high pressures up to 50 kbar call for a suitable thermodynamic formalism to allow realistic fitting of the experimental data and the establishment of an internally consistent data base. The very extensive low-pressure ( 2 in H 2 O has in the last few years been extended to 20 kbar and 1300°C, providing an excellent experimental basis for testing new approaches. In addition, solubility experiments with different SiO 2 -buffering phase assemblages and in situ determinations of Raman spectra for H 2 O-SiO 2 fluids have provided both qualitative and quantitative constraints on the stoichiometry and quantities of dissolved silica species. We propose a thermodynamic formalism for modeling both absolute silica solubility and speciation of dissolved silica using a combination of the chain reaction approach and a new Gibbs free energy equation of water based on a homogeneous reaction formalism. For a given SiO 2 -buffer ( e.g. , quartz) and the coexisting H 2 O-SiO 2 fluid both solubility and speciation of silica can be described by the following two reactions: - monomer-forming standard reaction: \[\mathrm{SiO_{2(s)} {+} 2(H_{2}O)L {=} (SiO_{2}){\bullet}(H_{2}O)_{2}}\] - polymer-forming chain reaction: \[\mathrm{(SiO_{2})_{n{-}1}{\bullet}(H_{2}O)_{n} {+} (SiO_{2}){\bullet}(H_{2}O)_{2} {=} (SiO_{2})_{n}{\bullet}(H_{2}O)_{n{+}1} {+} (H_{2}O)_{L},}\] where 2 ≤ n ≤ ∞, and (H 2 O) L stands for “liquid-like” (associated, clustered) water molecules in the aqueous fluid. We show that reactions (A) and (B) lead to the simplified relationships Δ G ° (mono)r, P,T = Δ H ° (mono),r − T Δ S ° (mono),r + Δ Cp ° (mono),r [ T − 298.15 - T ln( T /298.15)] + Δ V ° (mono),r ( P − 1), and Δ G ° (poly),r, P,T = Δ H ° (poly),r − T Δ S (poly),r + Δ V ° (poly),r ( P − 1) (where the Δ G ° r, P,T , are the standard molar Gibbs free energy changes in reactions (A) and (B) as a function of pressure P and temperature T ; the Δ H ° r , Δ S ° r , Δ Cp ° r , and Δ V ° r are standard molar enthalpy, entropy, isobaric heat capacity and volume changes, respectively, in reactions (A) and (B) at reference temperature T o = 298.15 K and pressure T o = 1 bar) that provide excellent descriptions of the available H 2 O-SiO 2 data set in terms of both SiO 2 solubility and silica speciation. Discrepancies between directly determined solubility data and data obtained from in situ Raman spectra are ascribed to (i) possible experimental problems of equilibration and (ii) inherent difficulties of interpreting Raman spectra of dilute H 2 O-SiO 2 solutions. In agreement with recent findings, our model indicates that dissolved silica in quartz-buffered aqueous solutions is considerably polymerized, exceeding 20–25 % at all temperatures above 400°C.

Recent systematic studies of mineral solubilities in water to high pressures up to 50 kbar call for a suitable thermodynamic formalism to allow realistic fitting of the experimental data and the establishment of an internally consistent data base. The very extensive low-pressure (< 5 kbar) experimental data set on the solubility of SiO(2) in H(2)O has in the last few years been extended to 20 kbar and 1300 degrees C, providing an excellent experimental basis for testing new approaches. In addition, solubility experiments with different SiO(2)-buffering phase assemblages and in situ determinations of Raman spectra for H(2)O-SiO(2) fluids have provided both qualitative and quantitative constraints on the stoichiometry and quantities of dissolved silica species. We propose a thermodynamic formalism for modeling both absolute silica solubility and speciation of dissolved silica using a combination of the chain reaction approach and a new Gibbs free energy equation of water based on a homogeneous reaction formalism. For a given SiO(2)-buffer (e.g., quartz) and the coexisting H(2)O-SiO(2) fluid both solubility and speciation of silica can be described by the following two reactions: monomer-forming standard reaction: SiO(2)(s) + 2(H(2)O)L = (SiO(2))center dot(H(2)O)(2) (A) polymer-forming chain reaction: (SiO(2))(n-1)center dot(H(2)O)(n) + (SiO(2))center dot(H(2)O)(2) = (SiO(2))(n)center dot(H(2)O)(n+1) + (H(2)O)(L), (B) where 2 <= n <= infinity, and (H(2)O)(L) stands for "liquid-like" (associated, clustered) water molecules in the aqueous fluid. We show that reactions (A) and (B) lead to the simplified relationships Delta G degrees((Mono),r,PT) = Delta H degrees((mono),r) - T Delta S degrees((mono),r) + Delta Cp((mono),r) [T - 298.15 - Tln(T/298.15)] + Delta V degrees((mono),r)(P - 1), and Delta G degrees((poly),rP,T) = Delta H degrees((poly)j) - T Delta S degrees((poly),r) + Delta V degrees((poly)j) (P - 1) (where the Delta G degrees(r,P,T), are the standard molar Gibbs free energy changes in reactions (A) and (B) as a function of pressure P and temperature T; the Delta H degrees(r), Delta S degrees(r), Delta Cp degrees(r) and Delta V degrees(r) are standard molar enthalpy, entropy, isobaric heat capacity and volume changes, respectively, in reactions (A) and (B) at reference temperature T(o) = 298.15 K and pressure P(o) = 1 bar) that provide excellent descriptions of the available H(2)O-SiO(2) data set in terms of both SiO(2) solubility and silica speciation. Discrepancies between directly determined solubility data and data obtained from in situ Raman spectra are ascribed to (i) possible experimental problems of equilibration and (ii) inherent difficulties of interpreting Raman spectra of dilute H(2)O-SiO(2) solutions. In agreement with recent findings, our model indicates that dissolved silica in quartz-buffered aqueous solutions is considerably polymerized, exceeding 20-25 % at all temperatures above 400 degrees C.

isostructural Mg-phosphate, phosphoellenbergerite. Ellenbergerite, (Mg,Ti,Zr, )2Mg6Al6Si8O28(OH)10 is a hexagonal nesosilicate (space group P63) with a dense and rigid structure based on single chains of face-sharing (Mg,Ti,Zr, )O6 octahedra and double chains of face-sharing MgO6 and AlO6 octahedra, both running parallel to the hexagonal axis. The formula of the phosphate end-member can, ideally, be expressed as follows Mg14P8O30(OH)8 if one ignores minor vacancies in the octahedral single chain. Therefore the substitution leading from the silicate to the phosphate end-member is primarily PMgSi1Al-1 (for 6 out of 8 Si); additional mechanism must involve protons, tetravalent cations, and vacancies in the octahedral single chain. The silicate end-member is expected to be stable up to ca. 3.5 GPa whereas the stability field of the phosphate end-member, although stable down to lower pressure, extends to much higher pressures. So far, PVT data have only been collected on a natural ellenbergerite specimen close to the silicate end-member composition [1,2] in a diamond anvil-cell (DAC). We report here data on the compressibility of the synthetic silicate collected using the MAX80 multi-anvil press installed on the F 2.1 beamline for comparison to the DAC dataset (Figure 1).