Partition of nickel between olivine and sulfide: A test for immiscible sulfide liquids

The partition of Ni between olivine, crystallised from basalt liquids, and iron-nickel monosulfide has been determined experimentally at 1160 and 1050 °C using alumina crucibles in sealed silica glass tubes. The compositional ranges investigated are 83 to 88 mol. % Fo and 5 to 50 mol. % NiS. The average distribution coefficient for the exchange reaction FeS +NiSi_0.5O₂NiS+FeSi_0.5O₂ is remarkably similar to the literature value of 33.2 for 900 °C. It is concluded that within the temperature and pressure range of magmatic olivine crystallisation the exchange reaction is effectively independent of temperature, pressure, olivine composition and composition and physical state of the sulfide.The NiO contents of early magmatic olivine are appreciably greater than the calculated NiO contents for equilibration with any hypothetical iron-rich immiscible sulfide liquid, suggesting that an immiscible sulfide liquid may not be a normal product of upper mantle magmatic processes. Similarly, it appears unlikely that sulfide liquid immiscibility had any role in the genesis of nickel sulfide ores.Olivine from upper mantle and crustal rock associations has characteristic NiO/MgO distributions. Both distributions appear to be the products of extensive fractionation by crystal-liquid processes although the crustal olivine distribution may be complicated by the added factor of heterogeneity of mantle magma source.     

Rare earth partitioning between immiscible carbonate and silicate liquids and CO2 vapor: Results and implications for the formation of light rare earth-enriched rocks

Melting relations at 5 and 20 kbar on the composition join sanidine-potassium carbonate are dominated by a two-liquid region that covers over 60% of the join at 1,300 ° C. At this temperature, the silicate melt contains approximately 19 wt% carbonate component at 5 kbar and 32 wt% carbonate component at 20 kbar. The conjugate carbonate melt contains less than 5 wt% silicate component, and it varies less as a function of temperature than does the silicate melt.Partition coefficients for Ce, Sm, and Tm between the immiscible carbonate and silicate melts at 1,200 ° and 1,300 ° C at 5 and 20 kbar are in favor of the carbonate melt by a factor of 2–3 for light REE and 5–8 for heavy REE. The effect of pressure on partitioning cannot be evaluated independently because of complementary changes in melt compositions.Minimum REE partition coefficients for CO₂ vapor/carbonate melt and CO₂ vapor/silicate melt can be calculated from the carbonate melt/silicate melt partition coefficients, the known proportions of melt, and maximum estimates of the proportion of CO₂ vapor. The vapor phase is enriched in light REE relative to both melts at 20 kbar and enriched in all REE, especially the light elements, at 5 kbar. The enrichment of REE in CO₂ vapor relative to both melts is 3–4 orders of magnitude in excess of that in water vapor (Mysen, 1979) at 5 kbar and is approximately the same as that in water vapor at 20 kbar.Mantle metasomatism by a CO₂-rich vapor enriched in light REE, occurring as a precursor to magma genesis, may explain the enhanced REE contents and light REE enrichment of carbonatites, alkali-rich silicate melts, and kimberlites. Light REE enrichment in fenites and the granular suite of nodules from kimberlites attests to the mobility of REE in CO₂-rich fluids under both mantle and crustal conditions.     

Experimental investigation of K and Na partitioning between miscible liquids

Model silicate melts with variable Al₂O₃ and SiO₂ contents were experimentally saturated with alkalis at a total pressure of 1 atm and temperatures of 1300–1470°C, using the crucible supported loop technique. It was shown that Al₂O₃ content has little influence on the degree of silicate melt saturation with K and Na. In contrast, SiO₂ content strongly affects the solubility of alkalis in silicate melts. Model calculations were performed to evaluate the behavior of alkalis during the contamination/mixing of basic and silicic magmas.     

Element partitioning between olivine and silicate melt under high pressure

Element partitioning between olivine and silicate melt has been investigated at pressures 1–14 GPa, by using a 6–8 type multi-anvil high pressure apparatus. In order to observe systematics in the partitioning of trivalent ions, Li was added to the starting materials in order to increase the concentration of trivalent ions in olivine. With increasing pressure, it was found that partition coefficients of most of the elements gradually decreased. Trivalent ions generally showed parabolic pattern on partition coefficient — ionic radius diagram. When pyrolite-like material was used as the starting material, partition coefficient of Al, D_Al, gradually increased with increase in pressure while the partition coefficients of the other elements decreased, and the D_Al deviated from the parabolic pattern of other trivalent ions. The deviation of D_Al from the D pattern of the other trivalent ions was also found when olivine was employed as main component of the starting material. This result may be ascribed to the compositional change of coexisting silicate melt with increase in pressure.     

Isovalent trace element partitioning between minerals and melts: A computer simulation study

We present a new approach for the rationalisation of trace element partitioning between silicate melts and minerals, which is not based on the empirical, parameterised continuum models in common use. We calculate the energetics of ion substitution using atomistic simulation techniques, which include an explicit evaluation of the relaxation energy (strain energy) contribution to this process. Solution energies are estimated for isovalent impurities in CaO, diopside, orthoenstatite, and forsterite. These show a parabolic dependence on ionic radius, similar to the variation of mineral-melt partition coefficients with ionic radius. The success of the empirical models, which often include only the strain energy, appear to have been due to the partial cancellation of energy terms, and to the empirical fitting of the parameters included in these models. Our approach can be readily extended to aliovalent substitution.     

Peralkaline acid liquids: A petrological study

Electron-microprobe analyses of the feldspars and associated ferromagnesian minerals in the peralkaline volcanics, comendites and pantellerites, are presented together with new data on the major and trace-elements of the rocks and residual glasses. The feldspar phenocrysts in the pantellerites span a narrower range (Or₃₃–Or₃₉) than those of the comendites (Or₃₀–Or₄₆); both sets show only limited increase in Or outwards, and the zoning is greatest in quartz-bearing assemblages. The feldspar microlites in the residual glasses are invariably more potassic (2–4% Or) than their associated phenocrysts. In pantellerites the feldspars become more potassic as the residual liquids become more sodic; thus the most potassic feldspar is found in the most sodic (and peralkaline) pantellerite.Of the ferromagnesian phenocrysts, aenigmatite is the most ubiquitous and is commonly associated with hedenbergite±fayalite, or ferrorichterite; in the later stages of crystallization (groundmass), it is associated with acmite, arfvedsonite and tuhualite. Aside from slight variation in Ti/Fe+Ti ratio, aenigmatite is virtually constant in composition. The pyroxenes from the different assemblages have zones which together almost span the range acmitehedenbergite. Both ferrorichterite and arfvedsonite incorporate F but not Cl, and are slightly potassic. Tuhualite exists as two varieties; one blue and potassic, the other violet and sodic; both varieties reject halogens. Using (estimated) free-energy data, a field in fo₂, T space is postulated in which Fe-Ti oxides are absent; their place is taken by pyroxene and aenigmatite. The no-oxide field will be intercepted by a cooling liquid in which peralkalinity is increasing and in which fo₂ is near but above the FMQ buffer.The characteristic pattern of trace-elements in peralkaline volcanics (e.g., high Nb, Ta, Zr, Mo, Zn, Cd, R.E, etc; low Sr, Ba, Mg) are considered to be as much evidence for the peralkaline (salic) condition as of the genetic process. Several lines of evidence suggest that at liquidus temperatures, peralkaline rhyolites are essentially anhydrous.     

Rare earth and high field strength element partitioning between iron-rich clinopyroxenes and felsic liquids

Rare earth elements are commonly assumed to substitute only for Ca in clinopyroxene because of the similarity of ionic radii for REE³⁺ and Ca²⁺ in eightfold coordination. The assumption is valid for Mg-rich clinopyroxenes for which observed mineral/melt partition coefficients are readily predicted by the lattice strain model for substitution onto a single site (e.g., Wood and Blundy 1997). We show that natural Fe-rich pyroxenes in both silica-undersaturated and silica-oversaturated magmatic systems deviate from this behavior. Salites (Mg# 48–59) in phonolites from Tenerife, ferrohedenbergites (Mg# 14.2–16.2) from the rhyolitic Bandelier Tuff, and ferroaugites (Mg# 9.6–32) from the rhyolitic Rattlesnake Tuff have higher heavy REE contents than predicted by single-site substitution. The ionic radius of Fe²⁺ in sixfold coordination is substantially greater than that of Mg²⁺; hence, we propose that, in Fe-rich clinopyroxenes, heavy REE are significantly partitioned between eightfold Ca sites and sixfold Fe and Mg sites such that Yb and Lu exist dominantly in sixfold coordination. We also outline a REE-based method of identifying pyroxene/melt pairs in systems with multiple liquid and crystal populations, based upon the assumption that LREE and MREE reside exclusively in eightfold coordination in pyroxene. Contrary to expectations, interpolation of mineral/melt partition coefficient data for heavy REE does not predict the behavior of Y. We speculate that mass fractionation effects play a role in mineral/melt lithophile trace element partitioning that is detectable among pairs of isovalent elements with near-identical radii, such as Y and Ho, Zr and Hf, and Nb and Ta.     

Element partitioning during precipitation of aragonite from seawater: A framework for understanding paleoproxies

This study presents the results from precipitation experiments carried out to investigate the partitioning of the alkaline earth cations Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ between abiogenic aragonite and seawater as a function of temperature. Experiments were carried out at 5 to 75 °C, using the protocol of Kinsman and Holland [Kinsman, D.J.J., Holland, H.D., 1969. The coprecipitation of cations with CaCO₃ IV. The coprecipitation of Sr²⁺ with aragonite between 16 and 96 °C. Geochim. Cosmochim. Acta33, 1-17.] The concentrations of Mg Sr and Ba were determined in the fluid from each experiment by inductively coupled plasma-mass spectrometry, and in individual aragonite grains by secondary ion mass spectrometry. The experimentally produced aragonite grains are enriched in trace components (“impurities”) relative to the concentrations expected from crystal-fluid equilibrium, indicating that kinetic processes are controlling element distribution. Our data are not consistent with fractionations produced kinetically in a boundary layer adjacent to the growing crystal because Sr²⁺, a compatible element, is enriched rather than depleted in the aragonite. Element compatibilities, and the systematic change in partitioning with temperature, can be explained by the process of surface entrapment proposed by Watson and Liang [Watson, E.B., Liang, Y., 1995. A simple model for sector zoning in slowly grown crystals: implications for growth rate and lattice diffusion, with emphasis on accessory minerals in crustal rocks. Am. Mineral.80, 1179-1187] and Watson [Watson, E.B., 1996. Surface enrichment and trace-element uptake during crystal growth. Geochim. Cosmochim. Acta60, 5013-5020; Watson, E.B., 2004. A conceptual model for near-surface kinetic controls on the trace-element and stable isotope composition of abiogenic calcite crystals. Geochim. Cosmochim. Acta68, 1473-1488]. This process is thought to operate in regimes where the competition between crystal growth rate and diffusivity in the near-surface region limits the extent to which the solid can achieve partitioning equilibrium with the fluid. A comparison of the skeletal composition of Diploria labyrinthiformis (brain coral) collected on Bermuda with results from precipitation calculations carried out using our experimentally determined partition coefficients indicate that the fluid from which coral skeleton precipitates has a Sr/Ca ratio comparable to that of seawater, but is depleted in Mg and Ba, and that there are seasonal fluctuations in the mass fraction of aragonite precipitated from the calcifying fluid (“precipitation efficiency”). The combined effects of surface entrapment during aragonite growth and seasonal fluctuations in “precipitation efficiency” likely forms the basis for the temperature information recorded in the aragonite skeletons of Scleractinian corals.     

Apatite solubility in carbonatitic liquids and trace element partitioning between apatite and carbonatite at high pressure

We have measured apatite solubility in calcic carbonatitic liquids and determined apatite/melt partition coefficients for a series of trace elements, including the rare earth elements (REE), high field strength elements (HFSE), Rb, Sr, U-Th-Pb. Experiments were performed between 4 and 6 GPa, from 1200 to 1380 °C, using the multianvil apparatus. Trace element concentrations were determined by laser ablation ICP-MS and electron microprobe. In addition, a specific protocol was designed to measure carbon concentration in the apatites, using the electron microprobe. Two starting apatite samples were used in order to test for the effect of apatite chemistry on partitioning behavior.Apatite solubility is lower in calcitic melts by a factor 3-5 compared to dolomitic melts (3-5.5 vs. 10-18 wt.% P₂O₅ in melt). We interpret this difference in terms of solubility product in the liquid and propose an empirical model for apatite saturation that takes into account melt calcium content. We conclude that calcitic melts that may form by melting of carbonated eclogites could be saturated with residual apatite, contrary to dolomitic melts formed in carbonated peridotites.Compatibility behavior of the REE depends on apatite silica content: REE are compatible in apatites containing 3.5-5 wt.% SiO₂, with values between 1.5 and 4, whereas REE are incompatible in apatites containing 0.2 wt.% SiO₂. HFSE, U, Th, and Y are compatible in silica-rich apatite, with while . Strontium is always retained in the melt, with of the order of 0.5. Lead appears to be incompatible in apatite, although this finding is weakened by almost complete Pb loss to sample container. High silica concentration favors REE incorporation in apatite by allowing for charged balanced coupled substitution. Sulfur and carbonate may also favor REE incorporation in apatite. Our results allow to reconcile previously published experimental determinations of REE partitioning. We use our experimentally determined partition coefficients to investigate the impact of residual apatite during partial melting of recycled carbonated material (eclogite + sediments) and discuss how the chemical characteristics of the produced liquids can be affected by residual apatite.     

Minor and trace element partitioning between immiscible ocelli-matrix pairs from lamprophyre dikes and sills,Monteregian Hills petrographic province,Quebec

Many lamprophyre dike and sill rocks in the Monteregian Hills petrographic province of southwestern Quebec contain felsic segregations (ocelli) which have been interpreted as globules of immiscible liquid (Philpotts 1976). Ocelli and matrix material were separated from a number of these rocks and analyzed for major and trace elements. The major element data, when plotted on a Greig diagram, outline a field of possible silicate-liquid immiscibility at higher alumina+alkali content than that previously mapped in iron-rich experimental systems. The trace element data support a liquid immiscibility hypothesis for the formation of these ocelli since high-charge density cations are preferentially concentrated in the matrix (mafic) material, a result which is consistent with theoretical and experimental studies. The distribution of minor and trace elements between ocelli and matrix indicates that several factors control the partitioning of these elements between immiscible felsic and mafic liquids. These factors include the difference in relative polymerization (as measured by the Si∶O ratio) of the two liquids, with an increase in this difference favoring partitioning of the high-charge density cations into the mafic liquid; the concentration of P₂O₅ in the mafic liquid which favors the partitioning of high-charge density cations into this liquid; the presence of a CO₂ vapor (?) phase which favors the partitioning of high-charge density cations into the CO₂ enriched phase; and the presence of solid phases at the onset of immiscibility. These observations indicate that the chemical compositions of two possibly immiscible melts should be known if minor and trace element data are to be used as evidence for silicate-liquid immiscibility.     

Minor and trace element partitioning between immiscible ocelli-matrix pairs from lamprophyre dikes and sills,Monteregian Hills petrographic province,Quebec

Many lamprophyre dike and sill rocks in the Monteregian Hills petrographic province of southwestern Quebec contain felsic segregations (ocelli) which have been interpreted as globules of immiscible liquid (Philpotts 1976). Ocelli and matrix material were separated from a number of these rocks and analyzed for major and trace elements. The major element data, when plotted on a Greig diagram, outline a field of possible silicate-liquid immiscibility at higher alumina+alkali content than that previously mapped in iron-rich experimental systems. The trace element data support a liquid immiscibility hypothesis for the formation of these ocelli since high-charge density cations are preferentially concentrated in the matrix (mafic) material, a result which is consistent with theoretical and experimental studies.The distribution of minor and trace elements between ocelli and matrix indicates that several factors control the partitioning of these elements between immiscible felsic and mafic liquids. These factors include the difference in relative polymerization (as measured by the Si∶O ratio) of the two liquids, with an increase in this difference favoring partitioning of the high-charge density cations into the mafic liquid; the concentration of P₂O₅ in the mafic liquid which favors the partitioning of high-charge density cations into this liquid; the presence of a CO₂ vapor (?) phase which favors the partitioning of high-charge density cations into the CO₂ enriched phase; and the presence of solid phases at the onset of immiscibility. These observations indicate that the chemical compositions of two possibly immiscible melts should be known if minor and trace element data are to be used as evidence for silicate-liquid immiscibility.     

Element partitioning in calcite as a function of solution flow rate: a study on vein calcites from the Harz Mountains

A semi-empirical treatment of isothermal element partitioning caused by flow rate-dependent calcite growth from hydrothermal solutions yields element/Ca ratios that are qualitatively similar to those observed in calcite bands of the Pb-Zn banded ores from the Harz Mountains, Germany. The comparison of the calculations with the analytical results suggests that flow rates varied between episodes of calcite precipitation as well as during formation of individual bands. Based on a flow rate-dependent element partition coefficient, changing element/Ca ratios in precipitates from a hydrotherm are therefore not necessarily indicative of changing compositions of the fluid. The variations in element/Ca ratios to be envisaged could be as much as a factor of three.Notation A defined by Eq. 8 - a, b individual values of any element in Eq. 1 - c concentration in moles/m³ - C ₀ initial concentration moles/m³ - i running parameter - F area of precipitation in m² - k _p rate constant of pth order reaction in s · m³/moles^p - R linear (one-dimensional) growth rate in moles/m² · s - p order of growth reaction - s distance from entry of solution in m - s ₀ vertical extension of a vein in m - t time in s - v flow rate of hydrothermal solution in m/s - v₀ standard flow rate in m/s - _r relative flow rate in multiple of v₀ - fraction of total precipitation - ₀ fraction of precipitation under reference conditions when the hydrothermal solution leaves the vein - defining the sign in Eq. 1 for elements that are en riched (= +1) or impoverished (= -1) - logarithmic partition coefficient in Eq. 10 - (R) logarithmic partition coefficient as a function of variable growth rate - [ ], { } concentration ratios of fluids and solids, respectively - EL/Ca calculated ratio of El/Ca in the calcite surface zone after Eq. 11     

100MPa、850℃和800℃条件下锡在流体与富磷过铝质熔体相间分配的实验研究

利用江西宜春414岩体中的钠长石花岗岩作为实验初始物,制备含不同1〉20s含量（0．27％－7．71％）的实验玻璃,本次实验研究了100MPa、850℃和800℃条件下Sn在流体与富磷过铝质熔体相间的分配。实验结果显示,Sn在流体与熔体相间的分配系数（Dsofluid/mclt）变化于2．10×10^-4－1．36×10^3之间,指示Sn强烈趋向于在富磷过铝质熔体中富集。随体系中P2Os含量从0．27％增至1．91％,Sn在流体与熔体相间的分配系数逐渐增加,当体系中R2O5含量进一步增加时,Sn在两相间的分配系数呈降低的趋势。本次实验结果表明,P可能不是Sn以流体相形式进行搬运的主要络合剂。     

Laser Ablation ICPMS study of trace element partitioning between plagioclase and basaltic melts: an experimental approach

Plagioclase-melt partition coefficients (D) for 34 trace elements at natural concentration levels were determined experimentally in a natural MORB composition at atmospheric pressure using thin Pt-wire loops. Experiments were carried out at three temperatures (1,220, 1,200, and 1,180°C), and at three different oxygen fugacities (fO₂ = IW, QFM, air) in order to assess the effect of fO₂ on the partitioning of elements with multiple valence (Fe, Eu, Cr). Run products were analyzed by laser-ablation ICP-MS. Most trace element Ds increase slightly as temperature decreases, except for D _Zr, D _Fe, D _Eu and D _Cr that vary systematically with fO₂. Applying the Lattice Strain Model to our data suggests the presence of Fe²⁺ entirely in the octahedral site at highly to moderate reducing conditions, while Fe³⁺ was assigned wholly to the tetrahedral site of the plagioclase structure. Furthermore, we provide a new quantitative framework for understanding the partitioning behaviour of Eu, which occurs as both 2+ and 3+ cations, depending on fO₂and confirm the greater compatibility of Eu²⁺, which has an ionic radius similar to Sr, relative to Eu³⁺ in plagioclase and the higher Eu²⁺/ Eu³⁺ under reducing conditions. For petrogenetic basaltic processes, a combined fractionation of Eu²⁺–Sr and Fe–Mg by plagioclase has considerable potential as an oxybarometer for natural magmatic rocks.     

REE partitioning between monazite and garnet: Implications for petrochronology

Rare‐earth element and Y partitioning between garnet and monazite was measured in metamorphic rocks from western Norway to provide more confidence in tying monazite U/Th–Pb dates to P–T conditions recorded in garnet. A subset of samples has low‐Y garnet mantles and low‐Y monazite cores that gave Y‐partitioning temperatures similar to independently determined metamorphic temperatures. In combination with previously published data, these monazite–garnet pairs have temperature‐dependent partitioning of the HREE from Dy to Lu, and nonsystematic partitioning of the LREE from La–Gd. The temperature‐dependent partitioning must be considered when using HREE to assess which portions of garnet and monazite might have coexisted, but experiments are needed to place the dependence on a firm footing.     

An experimental study of the partitioning of Fe and Mg between garnet and orthopyroxene

The partitioning of Fe and Mg between garnet and aluminous orthopyroxene has been experimentally investigated in the pressure-temperature range 5–30 kbar and 800–1,200° C in the FeO-MgO-Al₂O₃-SiO₂ (FMAS) and CaO-FeO-MgO-Al₂O₃-SiO₂ (CFMAS) systems. Within the errors of the experimental data, orthopyroxene can be regarded as macroscopically ideal. The effects of Calcium on Fe-Mg partitioning between garnet and orthopyroxene can be attributed to non-ideal Ca-Mg interactions in the garnet, described by the interaction term:W _CaMg ^ga -W _CaFe ^ga =1,400±500 cal/mol site. Reduction of the experimental data, combined with molar volume data for the end-member phases, permits the calibration of a geothermometer which is applicable to garnet peridotites and granulites: $$T(^\circ C) = \left\{ {\frac{{3,740 + 1,400X_{gr}^{ga} + 22.86P(kb)}}{{R\ln K_D + 1.96}}} \right\} - 273$$ with $$K_D = {{\left\{ {\frac{{Fe}}{{Mg}}} \right\}^{ga} } \mathord{\left/ {\vphantom {{\left\{ {\frac{{Fe}}{{Mg}}} \right\}^{ga} } {\left\{ {\frac{{Fe}}{{Mg}}} \right\}}}} \right. \kern-\nulldelimiterspace} {\left\{ {\frac{{Fe}}{{Mg}}} \right\}}}$$ and $$X_{gr}^{ga} = (Ca/Ca + Mg + Fe)^{ga} .$$ The accuracy and precision of this geothermometer are limited by largerelative errors in the experimental and natural-rock data and by the modest absolute variation inK _D with temperature. Nevertheless, the geothermometer is shown to yield reasonable temperature estimates for a variety of natural samples.