Determination of zircon/melt trace element partition coefficients from SIMS analysis of melt inclusions in zircon   总被引：3，自引：0，他引：3  

J.B Thomas  R.J BodnarN Shimizu  A.K Sinha 《Geochimica et cosmochimica acta》2002,66(16):2887-2901

Partition coefficients (^zircon/meltD_M) for rare earth elements (REE) (La, Ce, Nd, Sm, Dy, Er and Yb) and other trace elements (Ba, Rb, B, Sr, Ti, Y and Nb) between zircon and melt have been calculated from secondary ion mass spectrometric (SIMS) analyses of zircon/melt inclusion pairs. The melt inclusion-mineral (MIM) technique shows that D_REE increase in compatibility with increasing atomic number, similar to results of previous studies. However, D_REE determined using the MIM technique are, in general, lower than previously reported values. Calculated D_REE indicate that light REE with atomic numbers less than Sm are incompatible in zircon and become more incompatible with decreasing atomic number. This behavior is in contrast to most previously published results which indicate D > 1 and define a flat partitioning pattern for elements from La through Sm. The partition coefficients for the heavy REE determined using the MIM technique are lower than previously published results by factors of ≈15 to 20 but follow a similar trend. These differences are thought to reflect the effects of mineral and/or glass contaminants in samples from earlier studies which employed bulk analysis techniques.D_REE determined using the MIM technique agree well with values predicted using the equations of Brice (1975), which are based on the size and elasticity of crystallographic sites. The presence of Ce⁴⁺ in the melt results in elevated D_Ce compared to neighboring REE due to the similar valence and size of Ce⁴⁺ and Zr⁴⁺. Predicted ^zircon/meltD values for Ce⁴⁺ and Ce³⁺ indicate that the Ce⁴⁺/Ce³⁺ ratios of the melt ranged from about 10⁻³ to 10⁻². Partition coefficients for other trace elements determined in this study increase in compatibility in the order Ba < Rb < B < Sr < Ti < Y < Nb, with Ba, Rb, B and Sr showing incompatible behavior (D_M < 1.0), and Ti, Y and Nb showing compatible behavior (D_M > 1.0).The effect of partition coefficients on melt evolution during petrogenetic modeling was examined using partition coefficients determined in this study and compared to trends obtained using published partition coefficients. The lower D_REE determined in this study result in smaller REE bulk distribution coefficients, for a given mineral assemblage, compared to those calculated using previously reported values. As an example, fractional crystallization of an assemblage composed of 35% hornblende, 64.5% plagioclase and 0.5% zircon produces a melt that becomes increasingly more enriched in Yb using the D_Yb from this study. Using D_Yb from Fujimaki (1986) results in a melt that becomes progressively depleted in Yb during crystallization.  相似文献   

Zonation des éléments en traces au cours de la croissance des cristaux dans les bains silicatés: l'exemple de Rb,Cs, Sr et Ba dans le système Qz-Ab-Or-H₂O     

M. Lagache  J.P. Carron 《Geochimica et cosmochimica acta》1982,46(11):2151-2158

An indirect method was used to study Na, K, Rb, Cs, Sr and Ba partition coefficients between crystals and silicate melt. Equilibria between a hydrothermal solution and the melt at 800°C and 2 kb and between a hydrothermal solution and crystals at 750°C and 2 kb were separately achieved.For major element partitioning (Na and K), the results obtained here are in good agreement with those of Tuttle and Bowen (1958) which allow us to follow crystal evolution during a fractional crystallization process where the growth of zoned crystals takes place.For minor elements Rb, Cs, Sr, Ba, melt/aqueous solution partition coefficients depend on Na/K as well as the silica content of the melt. These effects are rather small for Rb and Cs, but are much more important for the alkaline earths. The feldspar/aqueous solution partition coefficients also depend on Na/K.The variations of the partition coefficients feldspar/melt are complex in the part of the Qz-Ab-Or diagram located below the cotectic line.During fractional crystallization following the Rayleigh law (assuming that there are no kinetic phenomena) Sr (D > 10) is almost totally removed from the melt in the early stages whereas Cs (D < 0.1) remains in the melt during the whole process. Rb and Ba have partition coefficients closer to unity. The variation of these coefficients, due to changes in bulk composition of liquid and crystals during fractional crystallization, can lead to complex zoning with possible concentration maxima at some stages. Similar phenomena can be expected in non-ideal natural solid solutions, even if no discontinuities can be detected in the physicochemical evolution of the parent magma.  相似文献   

Partitioning of Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺ between olivine and silicate melts: compositional dependence of partition coefficient   总被引：1，自引：0，他引：1  

Eiichi Takahashi 《Geochimica et cosmochimica acta》1978,42(12):1829-1844

Partitioning of Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺ and Mg²⁺ between olivine and silicate melts has been determined near the join (Mg_0.5·-Fe_0.5)₂SiO₄-K₂O 4SiO₂ and for seven different basaltic compositions. The experiments were made at 1 atm total pressure, 1500-1100°C, and under moderate to reducing oxygen fugacities. The concentration factor, defined as K^MO = (MO)^ol/(MO)^liq (molar ratio), increases markedly for all the cations studied as the olivine component of the liquid decreases. Much of the increase in K^MO is considered as due to the compositional effect of the coexisting liquid: the temperature effect on K^MO is probably opposite to the compositional effect (K^MO decreases as temperature decreases).The partition coefficient K^MO-MgO = (MO/MgO)^ol/(MO/MgO)^liq for the reaction, M_ol²⁺ + Mg_liq²⁺ = M_liq²⁺ + Mg_ol²⁺. is relatively constant over a wide range of SiO₂ content of the liquid, except in the case of Ni²⁺. The partition coefficients have similar ranges both in synthetic and natural rock systems: K^NiO-MgO = 1.8–3.0, K^CoO-MgO = 0.6–0.8, K^FeO-MgO = 0.27–0.38, and K^MnO-MgO = 0.23–0.32. There is a systematic variation in the partition coefficient K^MO-MgO with the composition of liquid; K^MO-MgO increases with increasing SiO₂ content of melt. The partition coefficients for Co²⁺, Fe²⁺ and Mn²⁺ are useful to test the equilibration of olivine with magma of a wide compositional range.  相似文献   

Experimental rare earth element partition coefficients for garnet,clinopyroxene and amphibole coexisting with andesitic and basaltic liquids     

I.A. Nicholls  K.L. Harris 《Geochimica et cosmochimica acta》1980,44(2):287-308

The partitioning of La, Sm, Dy, Ho and Yb between garnet, calcic clinopyroxene, calcic amphibole and andesitic and basaltic liquids has been studied experimentally. Glasses containing one or more REE in concentrations of 500–2000 ppm were crystallized at pressures of 10–35 kbar, and temperatures of 900–1520°C. Water was added to stabilize amphibole and to allow study of partition coefficients over wide temperature ranges. Major element and REE contents of crystal rims and adjacent glass were determined by EPMA, with limits of detection for individual REE of 100–180 ppm. Measured partition coefficients, D_REE^Cryst-liq, are independent of REE concentration over the concentration ranges used.D-values show an inverse dependence on temperature, best illustrated for garnet. At a given temperature, they are almost always higher for equilibria involving andesitic liquid. Garnet shows by far the greatest range of D-values, with e.g. D_La < 0.05 and D_Yb ~ 44 for andesitic liquid at 940°C. D_Yb falls to ~ 12 at 1420°C. D_Sm^Ga-liq also correlates negatively with temperature and positively with the grossular content of garnet. Patterns of D_ree^Cryst-Liq for calcic clinopyroxenes and amphiboles are sub-parallel, with D-values for amphibole generally higher. Both individual D-values and patterns for the crystalline phases studied are comparable with those determined for phenocryst-matrix pairs in natural dacites, andesites and basalts.D-values and patterns are interpreted in terms of the entry of REE³⁺ cations into mineral structures and liquids of contrasted major element compositions. The significance of the partition coefficients for models of the genesis of andesitic and Hy-normative basaltic magmas is assessed. Most magmas of these types in island arcs are unlikely to be produced by melting of garnet-bearing sources such as eclogite or garnet lherzolite.  相似文献   

Electron paramagnetic resonance study of the site preferences of Gd³⁺ and Eu²⁺ in polycrystalline silicate and aluminate minerals     

Richard V. Morris 《Geochimica et cosmochimica acta》1975,39(5):621-634

Electron paramagnetic resonance (EPR) measurements were made on Gd³⁺ and Eu²⁺ ions in polycrystalline samples to determine the nature of the sites occupied by those ions in mineral structures. Both Gd³⁺ and Eu²⁺ ions were incorporated at Ca²⁺ structural sites in β-Ca₂SiO₄, pseudo-CaSiO₃, CaMgSiO₄, CaMgSi₂O₆, hex-CaAl₂Si₂O₈, CaAl₂O₄, and Ca₃Al₂O₆. For tri-CaAl₂Si₂O₈, Eu²⁺ was incorporated at a Ca²⁺ site and Gd³⁺ was incorporated at a site where the crystalline electric field was disordered. That difference in behavior may contribute to the anomalous behavior of Eu in plagioclase feldspar. Both Gd³⁺ and Eu²⁺ were incorporated as aggregates or clusters of those ions in Mg₂SiO₄ and clino-MgSiO₃.  相似文献   

Experimental determination of REE partition coefficients between amphibole and basaltic to andesitic liquids at high pressure     

T.H. Green  N.J. Pearson 《Geochimica et cosmochimica acta》1985,49(6):1465-1468

Amphibole/liquid partition coefficients for the REE(D^amph/liq_REE) obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy REE. Five new experimentally determined sets of D_REE (La, Sm, “Eu²⁺”, Ho, Lu)and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole, over a range of temperature, pressure and oxygen fugacity. The partition coefficients increase significantly with decreasing temperature, and increase slightly with increasing oxygen fugacity. Pressure does not appear to have a major effect, although one data set suggests increased pressure lowers D^amph/liq_REE in a basaltic composition.  相似文献   

Co-precipitation of Sr2+ and Ba2+ with aragonite by membrane diffusion of CO2 between 10 and 50 °C     

《Chemical Geology》2004,203(1-2):139-151

Aragonite is precipitated by a new CO₂-diffusion technique from a Ca²⁺–Mg²⁺–Cl⁻ solution between 10 and 50 °C. Crystallisation of aragonite instead of calcite occurs by maintaining a [Mg²⁺]/[Ca²⁺] ratio of 2 in the fluid. The dissolved inorganic carbon (DIC) is received by diffusion of CO₂ through a polyethylene membrane (diffusion coefficient: D_CO2=10^−6.4 cm² s⁻¹ at 19 °C). It is suggested that significant amounts of DIC may be transferred by diffusion of CO₂ in natural systems if the CO₂ gradient is high. The CO₂-diffusion technique is used as a kind of simple mixed flow reactor for the co-precipitation of barium and strontium with aragonite. The distribution coefficients of Ba²⁺ and Sr²⁺ decrease from 10 to 50 °C according to D_Ba,a*=2.42−0.03595T (°C) and D_Sr,a*=1.32−0.005091T (°C). At 25 °C, the distribution coefficients are D_Ba,a*=1.5±0.1 and D_Sr,a*=1.19±0.03. The effect of temperature on D_Ba,a* is about one order of magnitude higher versus that on D_Sr,a*. Thus, Ba²⁺ may be a potential paleotemperature indicator if the composition of the solution is known.  相似文献   

Trace element partitioning between apatite and silicate melts   总被引：7，自引：0，他引：7  

Stefan Prowatke  Stephan Klemme 《Geochimica et cosmochimica acta》2006,70(17):4513-4527

We present new experimental apatite/melt trace element partition coefficients for a large number of trace elements (Cs, Rb, Ba, La, Ce, Pr, Sm, Gd, Lu, Y, Sr, Zr, Hf, Nb, Ta, U, Pb, and Th). The experiments were conducted at pressures of 1.0 GPa and temperatures of 1250 °C. The rare earth elements (La, Ce, Pr, Sm, Gd, and Lu), Y, and Sr are compatible in apatite, whereas the larger lithophile elements (Cs, Rb, and Ba) are strongly incompatible. Other trace elements such as U, Th, and Pb have partition coefficients close to unity. In all experiments we found D_Hf > D_Zr, D_Ta ≈ D_Nb, and D_Ba > D_Rb > D_Cs. The experiments reveal a strong influence of melt composition on REE partition coefficients. With increasing polymerisation of the melt, apatite/melt partition coefficients for the rare earth elements increase for about an order of magnitude. We also present some results in fluorine-rich and water-rich systems, respectively, but no significant influence of either H₂O or F on the partitioning was found. Furthermore, we also present experimentally determined partition coefficients in close-to natural compositions which should be directly applicable to magmatic processes.  相似文献   

Partitioning of trace elements between rutile and silicate melts: Implications for subduction zones   总被引：9，自引：0，他引：9  

Stephan Klemme  Stefan Prowatke  Detlef Günther 《Geochimica et cosmochimica acta》2005,69(9):2361-2371

Mineral/melt trace element partition coefficients were determined for rutile (TiO₂) for a large number of trace elements (Zr, Hf, Nb, Ta, V, Co, Cu, Zn, Sr, REE, Cr, Sb, W, U, Th). Whilst the high field strength elements (Zr, Hf, Nb, Ta) are compatible in rutile, other studied trace elements are incompatible (Sr, Th, REE). In all experiments we found D_Ta > D_Nb, D_Hf > D_Zr and D_U > D_Th. Partition coefficients for some polyvalent elements (Sb, W, and Co) were sensitive to oxygen fugacity. Melt composition exerts a strong influence on HFSE partition coefficients. With increasing polymerization of the melt, rutile/melt partition coefficients for the high field strength elements Zr, Hf, Nb and Ta increase about an order of magnitude. However, D_Nb/D_Ta and D_Hf/D_Zr are not significantly affected by melt composition. Because D_U ? D_Th, partial melting of rutile-bearing eclogite in subducted lithosphere may cause excesses of ²³⁰Th over ²³⁸U in some island arc lavas, whereas dehydration of subducted lithosphere may cause excesses of ²³⁸U over ²³⁰Th. From our partitioning results we infer partition coefficients for protactinium (Pa) which we predict to be much lower than previously anticipated. Contrary to previous studies, our data imply that rutile should not significantly influence observed ²³¹Pa-²³⁵U disequilibria in certain volcanic rocks.  相似文献   

Partitioning of trace elements between carbonate-silicate melts and mantle minerals: Experiment and petrological consequences     

A. V. Girnis  V. K. Bulatov  Y. Lahaye  G. P. Brey 《Petrology》2006,14(5):492-514

The partitioning of a number of trace elements (Ba, Nb, Zr, Y, REE, etc.) between orthopyroxene, garnet, and carbonate-silicate melt was experimentally studied using a belt apparatus at pressures of 3.5–4.2 GPa and temperatures of 1300–1500°C. The experimental products were investigated by electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The experimental melts varied from carbonatitic (～5 wt % SiO₂) at low temperatures (1300–1350°C) to kimberlitic compositions (30 wt % SiO₂) at high temperatures (1500°C). The partition coefficients of most elements between orthopyroxene and melt (D _i ^Opx/L ) and garnet and melt (D _i ^Grt/L ) were almost independent of melt composition (temperature). The D _i ^Opx/L values ranged from <0.01 for the most incompatible Ba and light REE to 0.02–0.08 for moderately incompatible Zr, Y, and heavy REE. The D _i ^Grt/L values were approximately an order of magnitude higher, ～0.07 for light REE, 0.7 for Y, and 1.5 for Yb. The character of D _i ^Grt/L variations in the systems studied is in general similar to that established for silicate melts without volatile components. However, the differences in the behavior of moderately incompatible and compatible elements (e.g., light and heavy REE) in the experimental systems are less pronounced compared with CO₂-free systems. Considering carbonate-silicate and silicate melts as possible agents of mantle metasomatism, it can be concluded that the former can efficiently transport heavy REE, and the latter have a greater affinity for Nb, Ba, and light REE. A characteristic feature of mantle rocks enriched by carbonate-silicate melts is high Ba/La ratio coupled with relatively weakly fractionated REE distribution patterns. It was shown that the high degrees of enrichment observed in natural kimberlites can be explained by a two-stage scenario, including a preliminary invasion of carbonate-silicate melt into depleted harzburgites in the lower parts of the lithosphere and subsequent very low degree melting.  相似文献   

Geochemistry of the shawmere anorthosite complex,kapuskasing structural zone,Ontario     

E. Craig Simmons  Gilbert N. Hanson  S.B. Lumbers 《Precambrian Research》1980,11(1):43-71

The Archean Shawmere Anorthosite Complex, at the southern end of the Kapuskasing Structural Zone, consists dominantly of anorthosite (An_{65 –85}) with minor gabbroic and ultramafic units, which are completely enclosed and cut by tonalites. Both the anorthosites and the tonalites are themselves cut by narrow dikes of gabbroic anorthosite. All of the rocks have undergone high grade metamorphism and are recrystallized so that few igneous textures remain.The anorthosites, gabbros and ultramafic rocks of this complex are cumulates which contain calcic plagioclase (An_65–95) and have atomic Mg/(Mg + Fe²⁺) ratios (Mg#) greater than 0.6; less than 3 ppm Rb; 150–210 ppm Sr; and less than 60 ppm Ba. REE abundanees range from 0.2 to 10 times chondritic and exhibit both light-enriched and light-depleted REE patterns. The lower Mg^# for the samples having more enriched light REE indicates substantial fractions of ferromagnesian minerals crystallized in addition to plagioclase during fractional crystallization, suggesting that the parent magma was basaltic, and not anorthositic. The ranges in Sr, Ba and REE abundances required for the magmas are typical of those for tholeiitic basalts from Archean greenstone belts. Thus the Shawmere Anorthosite Complex may represent cumulates of a crustal-level magma chamber which could have been the immediate source of basic Archean volcanics.One gabbroic anorthositic dike sample has a steeply fractionalted REE pattern with heavy REE abundances less than chondrites and a large positive Eu anomaly. The proposed interpretations is that this rock formed by partial melting of mafic cumulates, perhaps those of the Shawmere Anorthosite Complex itself.  相似文献   

Microscope-photometric methods for non-destructive Fe²⁺ – Fe³⁺ determination in chloritoids (Fe²⁺, Mn²⁺, Mg)₂ (Al,Fe³⁺)₄ Si₂O₁₀(OH)₄     

Ulf Hålenius  Klaus Langer 《Lithos》1980,13(3):291-294

Six natural chloritoid crystals with Fe²⁺ and Fe³⁺ contents ranging from 4.15 to 12.81 and from 0.411 to 0.849g-atoms/l, respectively, as determined by means of microprobe and Mössbauer techniques, served as reference material to develop non-destructive microscope-spectrophotometric methods for quantitative Fe²⁺ – Fe³⁺ determinations in chloritoids from unpolarized spectra of (001) platelets. Fe²⁺ concentrations in g-atom/l can be obtained from [ [Fe³⁺]=C₁xD₁/t where D₁ = log₁₀(I_0/I at 28,000 cm^-1 and t=crystal thickness in cm; C₁ is a conttant that may be influenced somewhat by experimental conditions and is found to be 0.002289 with the experimental set-up used in this study. Fe²⁺ concentrations in g-atom/l can be obtained from [Fe²⁺]=C₁xD₁/D₁-C₃ with D₂=log₁₀(I₀/I) at 16,300 cm^?1 and constants C₄ = 45.36 and C₅ = 3.540. Due to the uncertainties in absorbance measurements, D₁ and D₂ and the thickness measurements, the accuracies are ±0.05 and ±0.15 g-atom/l for [Fe³⁺] and [Fe²⁺], respectively. The determinations may be carried out on chloritoid grains in normal thin sections with an areal resolution of ～10 μm.  相似文献   

Rare-earth distribution in alkali rocks from Oki-Dogo Island,Japan     

Hiroshi Nagasawa 《Contributions to Mineralogy and Petrology》1973,39(4):301-308

Rare-earth, Sr and Ba abundances were determined for three basalts, one mugearite, one trachyandesite and five trachytes from Dogo, Oki Islands, Japan and Ca-rich clinopyroxene and feldspar phenocryst samples separated from them. It is concluded that rareearth, Sr and Ba abundance patters for basalts and three trachytes could be explained by crystallization differentiation of olivine basalt magma, while those for other samples suggest more complicated process of magma production. Calculated Eu²⁺ to total Eu ratios in the magmas showed a increasing trend with differentiation. It is found that Yb and Lu partition coefficients were larger than those of lighter rare earths for clinopyroxenes in trachytes suggesting preferential substitution of the heavy rare-earth ions for Mg-site in the clinopyroxenes.  相似文献   

Evolution of major mineral compositions and trace element abundances during fractional crystallization of a model lunar composition     

Michael J. Drake 《Geochimica et cosmochimica acta》1976,40(4):401-411

The evolution of major mineral compositions and trace element abundances during fractional crystallization of a model lunar magma ocean have been calculated. A lunar bulk composition consistent with petrological constraints has been selected. Major mineral compositions have been calculated using published studies of olivine-melt, plagioclase-melt, and pyroxene-olivine equilibria. Trace element abundances have been calculated using experimentally-determined partition coefficients where possible. In the absence of experimental determinations, published partition coefficients obtained by analyzing phase separates from porphyritic volcanic rocks have been used. Trace elements studied are La, Sm, Eu, Lu, Rb, Sr( Eu²⁺), Ni, Co, and Cr.The first mineral to crystallize is olivine, which varies in composition from Fo₉₈ at the liquidus to Fo₉₅ at 50% solidification. Orthopyroxene crystallizes from 50 to 60% solidification with a restricted composition range of En₉₅-En₉₃. Plagioclase and Ca-rich clinopyroxene (X_Wo arbitrarily set equal to 0.5) co-crystallize during the final 40% solidification. Plagioclase changes in composition from An₉₇ to approximately An₉₃, while clinopyroxene evolves from En₄₆ to approximately En₄₀. The concomitant evolution of major element abundances in the melt is also discussed.The concentration of Ni in the melt decreases rapidly because solid-melt partition coefficients are significantly greater than unity at all stages of crystallization. The concentration of Cr in the melt increases slowly during olivine crystallization, then drops precipitously during the crystallization of orthopyroxene and clinopyroxene. The concentration of Co in the melt decreases slowly during olivine and orthopyroxene crystallization, after which it returns slowly to its initial concentration. Rubidium and Sr are not fractionated relative to one another until the onset of plagioclase crystallization. Ratios of Rb/Sr, normalized to their initial concentrations in the magma, do not rise above 10 until 95% of the magma has solidified. The ratios of Eu/Sm and La/Lu, normalized to their initial concentrations in the magma, remain essentially unfractionated until the onset of crystallization of clinopyroxene plus plagioclase, at which point the normalized La/Lu ratio increases to approximately 1.3 at 100% solidification and the normalized Eu/Sm ratio decreases to approximately 0.2 at 100% solidification.The model calculations are used to place approximate constraints on the bulk composition of the primitive Moon. Consideration of the effect on plagioclase composition of the activities of NaO_0.5 and SiO₂ in the melt suggests that the primitive Moon contained less than 0.4 wt % NaO_0.5 and approximately 42–43 wt % SiO₂. Concentrations of the REE in model lunar anorthosites are consistent with the returned samples. Concentrations of the REE in several model ‘highland basalts’ (considered to be representative of the average lunar terrae) are too low when compared with returned samples. Several possible explanations of this discrepancy are considered. The possible role of spinel in a twostage geochemical evolution of mare basalt liquids is discussed.  相似文献   

Laser Ablation ICPMS study of trace element partitioning between plagioclase and basaltic melts: an experimental approach   总被引：3，自引：1，他引：3  

Mario Aigner-Torres  Jon Blundy  Peter Ulmer  Thomas Pettke 《Contributions to Mineralogy and Petrology》2007,153(6):647-667

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.  相似文献   

Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: effects of major element composition, water, and temperature     

Chenguang Sun  Yan Liang 《Contributions to Mineralogy and Petrology》2012,163(5):807-823

The distribution of rare earth elements (REE) between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. REE and Y partition coefficients from a given cpx-melt partitioning experiment can be quantitatively described by the lattice strain model. We analyzed published REE and Y partitioning data between cpx and basaltic melts using the nonlinear regression method and parameterized key partitioning parameters in the lattice strain model (D ₀, r ₀ and E) as functions of pressure, temperature, and compositions of cpx and melt. D ₀ is found to positively correlate with Al in tetrahedral site (Al ^T ) and Mg in the M2 site (Mg^M2) of cpx and negatively correlate with temperature and water content in the melt. r ₀ is negatively correlated with Al in M1 site (Al^M1) and Mg^M2 in cpx. And E is positively correlated with r ₀. During adiabatic melting of spinel lherzolite, temperature, Al ^T , and Mg^M2 in cpx all decrease systematically as a function of pressure or degree of melting. The competing effects between temperature and cpx composition result in very small variations in REE partition coefficients along a mantle adiabat. A higher potential temperature (1,400°C) gives rise to REE partition coefficients slightly lower than those at a lower potential temperature (1,300°C) because the temperature effect overwhelms the compositional effect. A set of constant REE partition coefficients therefore may be used to accurately model REE fractionation during partial melting of spinel lherzolite along a mantle adiabat. As cpx has low Al and Mg abundances at high temperature during melting in the garnet stability field, REE are more incompatible in cpx. Heavy REE depletion in the melt may imply deep melting of a hydrous garnet lherzolite. Water-dependent cpx partition coefficients need to be considered for modeling low-degree hydrous melting.  相似文献   

Kimberlite petrogenesis: Insights from clinopyroxene-melt partitioning experiments at 6 GPa in the CaO-MgO-Al₂O₃-SiO₂-CO₂ system     

Shantanu Keshav  Alexandre Corgne  Michael Bizimis  Yingwei Fei 《Geochimica et cosmochimica acta》2005,69(11):2829-2845

In this experimental study, we examine the mineral-melt partitioning of major and trace elements between clinopyroxene and CO₂-rich kimberlitic melts at a pressure of 6 GPa and temperatures of 1410°C and 1430°C. The melts produced contain ∼ 28 wt% dissolved CO₂, and are saturated with olivine and clinopyroxene. To assess the effects of temperature, crystal and melt compositions on trace element partitioning, experiments were performed in the model CaO-MgO-Al₂O₃-SiO₂-CO₂ system. Our results reveal that all the elements studied, except Al, Mg, Si, and Ga, are incompatible in clinopyroxene. Partition coefficients show a considerable range in magnitude, from ∼ 10⁻³ for D_U and D_Ba to ∼ 2.5 for D_Si. The two experimental runs show similar overall partitioning patterns with the D values being lower at 1430°C. Rare earth elements display a wide range of partition coefficients, D_La (0.012-0.026) being approximately one order of magnitude lower than D_Lu (0.18-0.23). Partition coefficients for the 2+ and 3+ cations entering the M2-site exhibit a near-parabolic dependence on radius of the incorporated cations as predicted from the lattice strain model. This underlines the contribution made by the crystal structure toward controlling the distribution of trace elements. Using data obtained in this study combined with that in the published literature, we also discuss the effects that other important parameters, namely, melt composition, pressure, and temperature, could have on partitioning.Our partition coefficients have been used to model the generation of the Group I (GI) kimberlites from South Africa. The numerical modeling shows that kimberlitic melts can be produced by ∼0.5% melting of a MORB-type depleted source that has been enriched by small-degree melts originating from a similar depleted source. This result suggests that the source of GI kimberlites may be located at the lithosphere-asthenosphere transition. Percolation of small degree melts from the asthenosphere would essentially create a metasomatic horizon near the bottom of the non-convecting sublithospheric mantle. Accumulation of such small degree melts together with the presence of volatiles and conductive heating would trigger melting of the ambient mantle and subsequently lead to eruption of kimberlitic melts. Additionally, our model shows that the GI source can be generated by metasomatism of a 2 Ga old MORB source ca. 1 Ga ago. Assuming that MORB-type mantle is the most depleted source of magmas on earth, then this is the oldest age at which the GI source could have existed. However, this age most likely reflects the average age of a series of metasomatic events than that of a single event.  相似文献   

Actinide crystal-liquid partitioning for clinopyroxene and Ca₃(PO₄)₂     

T. Benjamin  W.R. Heuser  D.S. Burnett  M.G. Seitz 《Geochimica et cosmochimica acta》1980,44(9):1251-1264

Using fission and alpha track radiography techniques, we have measured partition coefficients (D) for the actinide elements Th, U and Pu between diopsidic clinopyroxene, whitlockite [β-Ca₃ (PO₄)₂] and silicate liquid at 20kbar. Equilibrium partitioning at the crystal-liquid interface is assumed, and corrections for actinide zoning have been applied to the measured D values. Reproducibility for both actinide and minor element D values is carefully examined as a criterion for crystal-liquid interface equilibrium. The data are mostly compatible with interface equilibrium except for experiments at high cooling rates ( ? 30 deg/hr). Partition coefficients for Th/U/Pu of about 0.002/0.002/0.06 are measured for clinopyroxene and 1.2/0.5/3.4 for whitlockite. At an oxygen fugacity of 10^?8.5, Pu is much more readily incorporated into the crystalline phases than is U or Th because of the importance of trivalent Pu. The D_Pu(cpx) is similar to D(cpx) of the light rare earths supporting the concept of Pu/(rare earth) dating.  相似文献   

The use of vein fluorite as probe for paleofluid REE and Sr-Nd isotope geochemistry: The Santa Catarina Fluorite District, Southern Brazil   总被引：1，自引：0，他引：1  

Ricardo Sallet  Robert Moritz 《Chemical Geology》2005,223(4):227-248

Fluorite can be used as a probe for the source of Sr and REE, as well as for the Sr and Nd isotope systematics of mineralizing solutions, allowing characterization of the composition, oxidation state and sources of the fluids. The ⁸⁷Sr / ⁸⁶Sr ratios in vein fluorite from the Santa Catarina Fluorite District, southern Brazil, are low (0.720 to 0.745) relative to those of the majority of host granites at the time of mineralization (90 Ma), but are similar to those of less abundant and less evolved Sr- and Ca-rich granites and plagioclases of the heterogeneous Pedras Grandes granite association. Major contributions of Sr from the unradiogenic Parana Basin rocks (⁸⁷Sr / ⁸⁶Sr_{90 Ma} = 0.705 to 0.718) are unlikely, considering the radiogenic character of the lower ⁸⁷Sr / ⁸⁶Sr end-member in fluorite mixing lines. Estimated fluorite fluid partition coefficients (K_d^Sr-Ca = 0.019 and D^Sr ≈ 600) indicate a Sr / Ca ratio in the fluorite-forming solution of 0.012, and Sr contents of 0.05 to 0.25 ppm, which are similar to those of present-day granitic geothermal waters. Initial Nd isotopic compositions of the vein fluorites (0.5120 to 0.512) are similar to those of the Pedras Grandes granites. The ¹⁴³Nd / ¹⁴⁴Nd_{90 Ma} of the evolved granites of the Tabuleiro granite association, their accessory fluorites and the Parana Basin rocks are considerably more radiogenic (0.5120 to 0.5127) and these are thus considered to be unlikely sources of the fluids. The REE patterns of vein fluorites, normalized to upper continental crust, show a range of LREE-depleted patterns, with highly variable positive and negative Eu anomalies. The host Pedras Grandes granites show flat to slightly depleted UCC normalized LREE patterns with strong negative Eu anomalies. Depletion of the LREE in fluorites resulted from the mobility of HREE fluoride complexes during fluid migration. A REE fractionation model based on ionic potential ratios indicates that Eu³⁺ was stable during fluid migration and fluorite precipitation. The coexistence of pyrite and Eu³⁺ in the mineralizing fluids is consistent with low pH and oxygen fugacities near the hematite-magnetite buffer.  相似文献   

The determination of SO₄^2-, NaSO₄^-, and MgSO₄⁰ tracer diffusion coefficients and their application to diagenetic flux calculations     

Kenneth R Applin  Antonio C Lasaga 《Geochimica et cosmochimica acta》1984,48(10):2151-2162

Sulfur-35 was used to monitor the non-steady-state tracer diffusion of the free sulfate ion and sulfate ion-pairs in aqueous solutions of MgSO₄ and Na₂SO₄. Diffusion coefficients were derived from radiotracer flux measurements taken over ionic strengths ranging from 0.001 to 0.7. The experimental tracer diffusion coefficient is a function of the diffusion coefficients of the free sulfate ion and the sulfate ion-pairs as well as the ion pair equilibrium constant. The free sulfate ion tracer diffusion coefficient was determined independently from both the MgSO₄ and Na₂SO₄, experiments and found to be 1.11 and 1.08 (in units of 10^-5cm²sec^-1, ± 10%, respectively. These values closely agree with that calculated from the Nernst expression, 1.07 sx 10^-5cm²sec^-1. The tracer diffusion coefficients of MgSO₄⁰ and NaSO₄^- were determined to be 0.85 and 1.23 sx 10^-5cm²sec^-1, respectively. These numbers are in reasonable agreement with the earlier work on mutual diffusion coefficients by Rard and Miller (1979b) (D_MgSO4^o = 0.65, D_naso4^- = 1.19) and Harned and Hudson (1951)D_MgSO4⁰ = (0.70). A modified version of the theoretical equation developed by Pikal (1971) is proposed for predicting the tracer diffusion coefficients of many ion-pairs relevant to seawater. Many of these predicted values are found to be within 10–20% of the empirical values extracted from mutual diffusion data. The experimental and theoretical diffusion coefficient data are used to calculate revised coupled diffusion coefficients, D^g, according to the model of Lasaga (1979).  相似文献