Bridging the water solubility and ion diffusivity in the mantle silicates by a thermodynamic model

Mineralogy and Petrology - Water solubility in Mg-endmember silicates is suggested to correlate with cation diffusivity. This study proposes a thermodynamic model by introducing the concept of...     

Experimental and thermodynamic study of heterogeneous and homogeneous equilibria in the system NaAlSiO4-SiO2

Internally consistent thermodynamic datasets available at present call for a further improvement of the data for nepheline (Holland and Powell 1988; Berman 1991). Because nepheline is a common rock-forming mineral, an attempt has been made to improve on the present state of knowledge of its thermodynamic properties. To achieve that goal, two heterogeneous reactions involving nepheline, albite, jadeite and a-quartz in the system NaAlSiO₄-SiO₂ have been reversed bylong duration runs in the range 460 ≤ T(°C) ≤ 960 and 10 ≤ P(kbar) ≤ 22. Given sufficiently long run times, thealbite run products approach internal equilibrium with respect to their Al,Si order-disorder states. Using appropriate thermochemical, thermophysical, and volumetric data, Landau expansion for albite, and the relevant reaction reversals, a refined thermodynamic dataset (Δ_fH_i⁰ and S_i⁰) has been derived for nepheline, jadeite, a-quartz, albite, and monalbite. Our refined data agree very well with theircalorimetric counterparts, but have smaller uncertainties. The refined dataset for Δ_fH_i⁰ and S_i⁰, including their uncertainties and correlation, help generate the NaAlSiO₄-SiO₂ phase diagram including 2a confidence interval for eachP-T curve (Fig. 5). Editorial responsibility: W. Schreyer     

复合胎体金刚石钻头试验研究

为解决坚硬岩层钻进效率低下,研究设计一种复合胎体金刚石钻头,在软岩层进尺快,在硬岩层亦能获得相对较高的钻进速度,突破了单靠降低胎体硬度的传统设计理念,获得了满意钻进效率。     

利用热液金刚石压腔开展黑钨矿结晶实验的初步研究

钨是一种工业用途广泛的稀有金属,主要产于热液型矿床。确定钨元素迁移和沉淀的物理化学条件对于揭示热液型钨矿床的形成机制具有重要意义。本文应用新型热液金刚石压腔(HDAC-VT)开展了(Fe,Mn)WO_4-Li_2CO_3-H2O体系的原位观测结晶实验,9组实验结果表明,黑钨矿晶体的结晶温度集中在560~500℃,结晶压力主要集中在400~200MPa。黑钨矿的溶解度随体系内CO_2组分相对含量的增加而增加;碳酸锂的结晶导致CO_2组分的减少,诱发黑钨矿的快速结晶,这指示出CO_2组分对钨的迁移和沉淀具有重要作用。含矿流体中CO_2组分的散逸可能是黑钨矿沉淀富集成矿的重要因素之一。     

Experimental study of stability and crystallization peculiarities of tourmaline in hydrothermal conditions

Doklady Earth Sciences -     

超细FeCoCu粉末在金刚石钻头中的试验研究

文章介绍了超细FeCoCu预合金粉末应用于金刚石钻头胎体中的试验研究。通过基础性试验测试表明：在663Cu含量为30%的前提下,在金刚石钻头胎体组成成分中添加FeCoCu预合金粉末,通过调节其与WC粉末的配比关系,能够有效地调节钻头胎体硬度,适应不同的地层。通过回归分析得到了胎体硬度与FeCoCu粉末加量的数学关系式,由此关系式可预测胎体硬度或计算FeCoCu粉末加量。经过野外实际钻进试验证明：添加了FeCoCu粉末的金刚石钻头胎体综合性能具有较大的提高,为后续钻头耐磨性研究提供了经验积累。     

Formation of metastable graphite inclusions during diamond crystallization in model systems

Metastable graphite inclusions have been studied in diamond, forsterite, and orthopyroxene synthesized in silicate-carbonate-fluid and aqueous chloride systems at 6.3–7.5 GPa and 1400–1600°C. The graphite inclusions were studied using optic microscopy and Raman spectroscopy. It has been established that graphite in diamond and liquidus silicate minerals is represented by a highly ordered variety. Depending on parameters of runs, the graphite inclusions are hexagonal, irregular polygonal, or rounded in shape. The morphology of graphite inclusions involving metastable graphite in run products is compared with previously established crystallization sequence of carbon phases. It has been revealed that the protogenetic graphite inclusions in diamond are rounded, and this shape was caused by dissolution of the newly formed graphite. Polygonal graphite inclusions are syngenetic and represented by metastable graphite that crystallized contemporaneously with diamond.     

Experimental modeling of the interaction of subducted carbonates and sulfur with mantle silicates

Experimental studies in the system Fe,Ni–olivine–carbonate–S (P = 6.3 GPa, T = 1050–1550°C, t = 40–60 h) aimed at modeling of the interaction of subducted carbonates and sulfur with rocks of the silicate mantle and at investigation of the likely mechanism of the formation of mantle sulfides were performed. It is shown that an association of olivine + orthopyroxene + magnesite + pyrite coexisting with a sulfur melt/fluid with dissolved Fe, Ni, and O is formed at T ≤ 1250°C. An association of low-Fe olivine, orthopyroxene, and magnesite and two immiscible melts of the carbonate and S–Fe–Ni–O compositions are formed at T ≥ 1350°C. It is shown that the reduced S-bearing fluids may transform silicates and carbonates, extract metals from the solid-phase matrix, and provide conditions for generation of sulfide melts.     

Diamond crystallization in the Fe-Co-S-C and Fe-Ni-S-C systems and the role of sulfide-metal melts in the genesis of diamond

Diamond crystals 0.1–0.8 carats were synthesized in experiments conducted in a BARS split-sphere multianvil high-pressure apparatus in the systems Fe-Co-S-C and Fe-Ni-S-C at a pressure of 5.5 GPa and temperature of 1300°C. The microtextures of the samples and the phases accompanying diamond (carbides, graphite, monoslufide solid solution, pentlandite, and taenite) are examined in much detail, the properties of metal-sulfide-carbon alloys are discussed, and issues related to the genesis of sulfide inclusions in diamonds and graphite crystallization in the diamond stability field are considered. The experiments demonstrate that diamonds can be synthesized and grow in pre-eutectic metal-sulfide melts with up to 14 wt % sulfur at relatively low P-T parameters, which correspond to the probable temperatures and pressures of natural diamond-forming processes at depths of approximately 150 km in the Earth’s upper mantle.     

Experimental constraints on crystallization differentiation in a deep magma ocean

Major and trace element mineral/melt partition coefficients are presented for phases on the liquidus of fertile peridotite at 23-23.5 GPa and 2300 °C. Partitioning models, based on lattice-strain theory, are developed for cations in the ‘8-fold’ sites of majorite and Mg-perovskite. Composition-dependant partitioning models are made for cations in the 12-fold site of Ca-perovskite based on previously published data. D^min/melt is extremely variable for many elements in Ca-perovskite and highly correlated with certain melt compositional parameters (e.g. CaO and Al₂O₃ contents). The 8-fold sites in Mg-perovskite and majorite generally have ideal site radii between 0.8 and 0.9 Å for trivalent cations, such that among rare-earth-elements (REE) D^min/melt is maximum for Lu. Lighter REE become increasingly incompatible with increasing ionic radii. The 12-fold site in Ca-perovskite is larger and has an ideal trivalent site radius of ∼1.05 Å, such that the middle REE has the maximum D^min/melt. Trivalent cations are generally compatible to highly compatible in Ca-perovskite giving it considerable leverage in crystallization models. Geochemical models based on these phase relations and partitioning results are used to test for evidence in mantle peridotite of preserved signals of crystal differentiation in a deep, Hadean magma ocean.Model compositions for bulk silicate Earth and convecting mantle are constructed and evaluated. The model compositions for primitive convecting mantle yield superchondritic Mg/Si and Ca/Al ratios, although many refractory lithophile element ratios are near chondritic. Major element mass balance calculations effectively preclude a CI-chondritic bulk silicate Earth composition, and the super-chondritic Mg/Si ratio of the mantle is apparently a primary feature. Mass balance calculations indicate that 10-15% crystal fractionation of an assemblage dominated by Mg-perovskite, but with minor amounts of Ca-perovskite and ferropericlase, from a magma ocean with model peridotite-based bulk silicate Earth composition produces a residual magma that resembles closely the convecting mantle.Partition coefficient based crystal fractionation models are developed that track changes in refractory lithophile major and trace element ratios in the residual magma (e.g. convecting mantle). Monomineralic crystallization of majorite or Mg-perovskite is limited to less than 5% before certain ratios fractionate beyond convecting mantle values. Only trace amounts of Ca-perovskite can be tolerated in isolation due to its remarkable ability to fractionate lithophile elements. Indeed, Ca-perovskite is limited to only a few percent in a deep mantle crystal assemblage. Removal from a magma ocean of approximately 13% of a deep mantle assemblage comprised of Mg-perovskite, Ca-perovskite and ferropericlase in the proportions 93:3:4 produces a residual magma with a superchondritic Ca/Al ratio matching that of the model convecting mantle. This amount of crystal separation generates fractionations in other refractory lithophile elements ratios that generally mimic those observed in the convecting mantle. Further, the residual magma is expected to have subchondritic Sm/Nd and Lu/Hf ratios. Modeling shows that up to 15% crystal separation of the deep mantle assemblage from an early magma ocean could have yielded a convecting mantle reservoir with ¹⁴³Nd/¹⁴⁴Nd and ¹⁷⁶Hf/¹⁷⁷Hf isotopic compositions that remain internal to the array observed for modern oceanic volcanic rocks. If kept in isolation, the residual magma and deep crystal piles would grow model isotopic compositions that are akin to enriched mantle 1 (EM1) and HIMU reservoirs, respectively, in Nd-Hf isotopic space.     

Radio-colouration of diamond: a spectroscopic study

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with ≥10¹⁵ He ions per cm². The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 × 10^?3 Å^?3 (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 °C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of ~2.4 ± 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10^?6 Å^?3 (or 0.000006 dpa) and is suppressed at moderate defect densities of ~5 × 10^?4 Å^?3 (or ~0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 °C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.     

Experimental investigation of the stability of a chloroborate complex and thermodynamic description of aqueous species in the B-Na-Cl-O-H system up to 350°C

The solubility of chlorargyrite, AgCl_cr, was experimentally studied in NaCl solutions (0.1, 0.2, and 0.5 m) as a function of the concentration of boric acid (up to 5 m) at 70–300°C and saturated water vapor pressure. The experimental data indicated the existence of the chloroborate species B(OH)₃Cl⁻. The published data on the thermodynamic properties of aqueous complexes in the B-Na-Cl-O-H system were analyzed. The obtained HKF parameters of aqueous species can be used to calculate equilibria in the system up to 350°C. Original Russian Text ? N.N. Akinfiev, M.V. Voronin, A.V. Zotov, V.Yu. Prokof’ev, 2006, published in Geokhimiya, 2006, No. 9, pp. 937–949.     

Monitoring the crystallization of water-saturated granitic melts in real time using the hydrothermal diamond anvil cell

Critical aspects of the crystallization dynamics of H₂O-saturated melts of a typical granitic composition as well as granitic melts enriched in lithium (8800 ppm) were investigated in real-time experiments using the hydrothermal diamond anvil cell at 480–700 °C and 220–960 MPa. Complete crystallization of the charges was achieved within 5–118 h with average crystal growth rates ranging from 3 to 41 cm/year for quartz and from 18 to 58 cm/year for alkali feldspars, demonstrating that crystals formed from a silicate melt in the presence of a coexisting aqueous phase crystallize rapidly. The combination of substantial nucleation delays, low nucleation densities, and rapid growth rates for quartz and alkali feldspars led to the formation of euhedral megacrysts of these minerals in the vicinity of clusters comprised of much smaller muscovite or α-spodumene crystals. Subsolidus replacement processes initiated during crystal–fluid interactions after the silicate melt was consumed were directly observed in the experiments. The experimental results underscore the important role of water as a medium for the transport of essential elements such as Si, Al, Na, and K from the silicate melt to the newly formed crystals, and provide important insights into the crystallization of miarolitic pegmatites.     

Physicochemical formation conditions of natural diamond deduced from experimental study of the eclogite-carbonatite-sulfide-diamond system

A diagram of the syngenesis of diamond, silicate, carbonate, and sulfide minerals and melts is compiled based on experimental data on phase relations in the heterogeneous eclogite-carbonate-sulfidediamond system at P = 7 GPa. Evidence is provided that silicate and carbonate minerals are paragenetic, whereas sulfides are xenogenic with respect to diamond. Diamond and paragenetic phases are formed in completely miscible carbonate-silicate growth melts with dissolved elemental carbon. Coherent data of physicochemical experiment and mineralogy of primary inclusions in natural diamonds allows us to prove the mantle-carbonatite theory of diamond origin. The genetic classification of primary inclusions in natural diamonds is based on this theory. The phase diagrams of syngenesis are applicable to interpretation of diamond and syngenetic minerals formation in natural magma sources. They ascertain physicochemical mechanism of natural diamond formation and conditions of entrapment of paragenetic and xenogenic mineral phases by growing diamonds.     

Experimental study of a biotite-bearing granitic system under water-saturated and water-undersaturated conditions

Phase relationships in haplogranitic melts containing ferromagnesian minerals were investigated in the temperature range 760–850°C, atP _total=2 kbar, =0.25 1.00, and at NNO buffer conditions. The compositions of coexisting biotite, orthopyroxene, magnetite and granitic melt were determined by electron microprobe. Biotite was the only Fe–Mg mineral in the starting material. It disappeared in water-undersaturated melts at temperatures above 830°C and in melts saturated with water above 810°C. Magnetite was present in all runs. Orthopyroxene became stable between 780 and 800°C. The Mg/(Mg+Fe) ratios of biotite (0,63–0,72) and orthopyroxene (0,63–0,71) are similar in water-saturated and undersaturated melts at comparable temperatures and increase slightly with increasing temperature. The solubility of Mg in haplogranitic melts is very low (0,07–0,24 wt% MgO). It increases slightly with temperature and is independent of the prevailing water activity. The solubility of Fe is low (0,91–1,37 wt% FeO); it also increases with increasing temperature, and it is higher in water-saturated than in water-undersaturated melts.     

Experimental study of phase relations in a lithium-bearing fluorine-rich haplogranite and nepheline syenite system

Phase relations were investigated in the model water-saturated system Si-Al-Na-Li-F-O at high fluorine contents, a temperature of 800°C, and a pressure of 1 kbar. The obtained aluminosilicate melts are widely variable from quartz- to nepheline-normative compositions with agpaitic indexes both higher and lower than one. Various fluoride, aluminofluoride, and oxide phases were observed in the equilibrium assemblage depending on the melt composition: quartz and cryolite associate with the silica richest aluminosilicate melts, topaz and corundum coexist with peraluminous melts, and villiaumite was observed in highly peralkaline melts. Extensive immiscibility between aluminosilicate and aluminofluoride melts was observed in the system. Aluminofluoride melt coexists with quartz- and nepheline-normative aluminosilicate melts with agpaitic indexes (K _a) of 0.7–1.4. The composition of aluminosilicate melt in equilibrium with aluminofluoride melt ranges from 33 to 70 wt % SiO₂, from 12 to 24 wt % Al₂O₃, and from 5 to 16 wt % alkalis. The aluminofluoride melt is variable in composition, its Al/Na ratio ranges from 20/80 to 40/60 depending on the composition of the equilibrium aluminosilicate melt. The experimental aluminosilicate melts equilibrated with cryolite, topaz, and aluminofluoride melt coincide in major component proportions with the bulk compositions of cryolite- and topaz-bearing granites and melt inclusions in minerals.     

Fluid regime and diamond formation in the reduced mantle: Experimental constraints

The composition and potential diamond productivity of C–O–H fluids that could exist in the reduced regions of the Earth’s upper mantle and in the mantles of Uranus and Neptune were studied in experiments at 6.3 GPa and 1400–1600 °C and durations of 15–48 h. Hydrogen fugacity in the fluid phase was controlled by the Mo–MoO₂ or Fe–FeO buffers, using a specially modified double-capsule method. The oxygen fugacity in the samples was controlled by adding different amounts of water, stearic acid, anthracene, and docosane to a graphite charge. At high P–T conditions, the degree of decomposition of the heavy hydrocarbons added to the charge was 99.9%. The composition of the fluids coexisting with graphite/diamond in the buffered experiments varied from H₂O  H₂ > CH₄ (at fO₂ somewhat lower than the “water maximum”) to H₂ > CH₄ > (C₂H₄ + C₂H₆)>C₃H₈ (in C–H system). In the C–H system the maximum concentrations of major species in the synthesized fluid were: H₂ = 79 mol.% and CH₄ = 21 mol.%. The composition of the H₂-rich fluids, which were synthesized at 6.3 GPa and 1400–1600 °C for the first time, differs considerably from that of the ultra-reduced CH₄-rich fluids stable at 2.0–3.5 GPa and 1000–1300 °C. Thermodynamic calculations of the reduced C–O–H fluids at the P–T conditions of the experiments revealed CH₄-rich compositions (CH₄  H₂ > (C₂H₄ + C₂H₆)>C₃H₈), which however drastically differed from the synthesized compositions. The rates of diamond nucleation and growth in the experiments depended on the fluid composition. Diamond crystallization had a maximum intensity in the pure aqueous fluids, while in the H₂-rich fluids no diamond formation was observed. Only metastable graphite precipitated from the ultra-reduced fluids. The type of the initial hydrocarbon used for the fluid generation did not affect this process.