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1.
The carbon isotopic fractionation between CO2 vapour and sodamelilite (NaCaAlSi2O7) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag2C2O4 was the source of CO2 and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined by stepped heating and the 13C of coexisting vapour was determined directly by capsule piercing. CO2 solubility in SM displays a complex behavior with temperature. At pressures up to 10 kbars CO2 dissolves in SM to form carbonate ion complexes and the solubility data suggest slight negative temperature dependence. Above 20 kbars CO2 reacts with SM to form immiscible Na-rich silicate and Ca-rich carbonate melts and CO2 solubility in Na-enriched silicate melt rises with increasing temperature above the liquidus. Measured values for carbon isotopic fractionation between CO2 vapour and carbonate ions dissoived in sodamelilite melt at 1200°–1400° C and 5–30 kbars average 2.4±0.2, favouring13C enrichment in CO2 vapour. The results are maxima and are independent of pressure and temperature. Similar values of 2 are obtained for the carbon isotopic fractionation between CO2 vapour and carbonate melts at 1300°–1400° C and 20–30 kbars.  相似文献   

2.
Chemical weathering and resulting water compositions in the upper Ganga river in the Himalayas were studied. For the first time, temporal and spatial sampling for a 1 year period (monthly intervals) was carried out and analyzed for dissolved major elements, trace elements, Rare Earth Elements (REE), and strontium isotopic compositions. Amounts of physical and chemical loads show large seasonal variations and the overall physical load dominates over chemical load by a factor of more than three. The dominant physical weathering is also reflected in high quartz and illite/mica contents in suspended sediments. Large seasonal variations also occur in major elemental concentrations. The water type is categorized as HCO3––SO42––Ca2+ dominant, which constitute >60% of the total water composition. On an average, only about 5–12% of HCO3– is derived from silicate lithology, indicating the predominance of carbonate lithology in water chemistry in the head waters of the Ganga river. More than 80% Na+ and K+ are derived from silicate lithology. The silicate lithology is responsible for the release of low Sr with extremely radiogenic Sr (87Sr/86 Sr>0.75) in Bhagirathi at Devprayag. However, there is evidence for other end-member lithologies for Sr other than carbonate and silicate lithology. Trace elements concentrations do not indicate any pollution, although presence of arsenic could be a cause for concern. High uranium mobilization from silicate rocks is also observed. The REE is much less compared to other major world rivers such as the Amazon, perhaps because in the present study, only samples filtered through <0.2 m were analysed. Negative Eu anomalies in suspended sediments is due to the excess carbonate rock weathering in the source area.  相似文献   

3.
Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO4 solutions. Single-crystal XRD refinement with R1=0.0232 for the unique observed reflections (|Fo| > 4F) and wR2=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, Vo=160.11(4) cm3, and fractional positions for all atoms except the H in the H3O groups. The chemical composition of this sample is described by the formula (H3O)0.91Fe2.91(SO4)2[(OH)5.64(H2O)0.18]. The enthalpy of formation (Hof) is –3694.5 ± 4.6 kJ mol–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H2O, and -MgSO4. The entropy at standard temperature and pressure (So) is 438.9±0.7 J mol–1 K–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (Cp) data between 273 and 400 K were fitted to a Maier-Kelley polynomial Cp(T in K)=280.6 + 0.6149T–3199700T–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol–1. Speciation and activity calculations for Fe(III)–SO4 solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the Cp data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in Cp, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H3O)Fe3(SO4)2(OH)6 was estimated: Gof= –3226.4 ± 4.6 kJ mol–1, Hof=–3770.2 ± 4.6 kJ mol–1, So=448.2 ± 0.7 J mol–1 K–1, Cp (T in K)=287.2 + 0.6281T–3286000T–2 (between 273 and 400 K).  相似文献   

4.
KAlSi3O8 sanidine dissociates into a mixture of K2Si4O9 wadeite, Al2SiO5 kyanite and SiO2 coesite, which further recombine into KAlSi3O8 hollandite with increasing pressure. Enthalpies of KAlSi3O8 sanidine and hollandite, K2Si4O9 wadeite and Al2SiO5 kyanite were measured by high-temperature solution calorimetry. Using the data, enthalpies of transitions at 298 K were obtained as 65.1 ± 7.4 kJ mol–1 for sanidine wadeite + kyanite + coesite and 99.3 ± 3.6 kJ mol–1 for wadeite + kyanite + coesite hollandite. The isobaric heat capacity of KAlSi3O8 hollandite was measured at 160–700 K by differential scanning calorimetry, and was also calculated using the Kieffer model. Combination of both the results yielded a heat-capacity equation of KAlSi3O8 hollandite above 298 K as Cp=3.896 × 102–1.823 × 103T–0.5–1.293 × 107T–2+1.631 × 109T–3 (Cp in J mol–1 K–1, T in K). The equilibrium transition boundaries were calculated using these new data on the transition enthalpies and heat capacity. The calculated transition boundaries are in general agreement with the phase relations experimentally determined previously. The calculated boundary for wadeite + kyanite + coesite hollandite intersects with the coesite–stishovite transition boundary, resulting in a stability field of the assemblage of wadeite + kyanite + stishovite below about 1273 K at about 8 GPa. Some phase–equilibrium experiments in the present study confirmed that sanidine transforms directly to wadeite + kyanite + coesite at 1373 K at about 6.3 GPa, without an intervening stability field of KAlSiO4 kalsilite + coesite which was previously suggested. The transition boundaries in KAlSi3O8 determined in this study put some constraints on the stability range of KAlSi3O8 hollandite in the mantle and that of sanidine inclusions in kimberlitic diamonds.  相似文献   

5.
The two-liquid field between alkali-carbonate liquids and phonolite or nephelinite magmas from the Oldoinyo Lengai volcano has been determined between 0.7 and 7.6 kb and 900°–1,250° C. The miscibility gap expands with increase in and decrease in temperature. Concomitantly there is a rotation of tie-lines so that the carbonate liquids become richer in CaO. The element distribution between the melts indicates that a carbonate liquid equivalent in composition to Oldoinyo Lengai natrocarbonatite lava would have separated from a phonolitic rather than a nephelinitic magma. CO2-saturated nephelinites coexist with carbonate liquids much richer in CaO than the Lengai carbonatites, but even so these liquids have high alkali concentrations. If the sövites of hypabyssal and plutonic ijolite-carbonatite complexes originated by liquid immiscibility, then large quantities of alkalis have been lost, as is suggested by fenitization and related phenomena. The miscibility gap closes away from Na2O-rich compositions, so that the tendency to exsolve a carbonatite melt is greater in salic than in mafic silicate magmas. The two-liquid field does not approach kimberlitic compositions over the range of pressures studied, suggesting that the globular textures observed in many kimberlite sills and dykes may be the result of processes other than liquid immiscibility at crustal pressures.  相似文献   

6.
The behaviour of synthetic Mg-ferrite (MgFe2O4) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K0=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by a0+a1*(T–298)+a2/(T–298)2, where a0=9.1(1) 10–6 K–1, a1=4.9(2) 10–9 K–2 and a2= 5.1(5) 10–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol–1 and =–17.6(± 1.2) kJ mol–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe2O4, which shows that the high-pressure transition from spinel to orthorombic CaMn2O4-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe2O3.  相似文献   

7.
Densities of 21 silicate liquids have been determined from 1,000 ° to 1,600 ° C. The compositions studied contain from two to eight oxide components and have the following ranges in composition (mole %): SiO2, 35–79%; TiO2, 4–36%; Al2O3, 5–25%; FeO, 11–41%; MgO, 7–28%; CaO, 7–35%; Na2O, 5–50%; and K2O, 4–20%. The compositions thus cover the upper range observed in magmas for each oxide. Precision for each determination of liquid density is always better than ±1%.Volumes/gfw (gram formula weight) calculated from the density measurements and the chemical compositions of the analyzed liquids have been combined with data on 96 silicate liquids reported in the literature. From this data set we derive, by using multiple linear regression, partial molar volumes of the components SiO2, TiO2, A12O3, FeO, MgO, CaO, Na2O, and K2O at five temperatures. The standard deviation of the multiple regression is 1.8% of the molar volumes, which is considered about equal to the total errors due to compositional and instrumental uncertainties.These derived partial molar volumes have been used to calculate volumes/gfw of natural silicate liquids which are found to agree within 1% of the measured values. No compositional dependence of the partial molar volumes can be detected within the error considered to be typical of the measurements. This is further supported by the close agreement between the calculated volumes of CaMgSi2O6 and Fe2SiO2 liquids derived from the initial slopes of their fusion curves and their heats of fusion, and the volumes obtained by summing the respective partial molar volumes. The experimental data indicate that silicate liquids mix ideally with respect to volume, over the temperature and composition range of this data set.  相似文献   

8.
Infrared spectroscopy has been used to study the speciation of CO2 in glasses near the NaAlO2-SiO2 join quenched from melts held at high temperatures and pressures. Absorption bands resulting from the antisymmetric stretches of both molecular CO2 (2,352 cm–1) and CO 3 2– (1,610 cm–1 and 1,375 cm–1) are observed in these glasses. The latter are attributed to distorted Na-carbonate ionic-complexes. Molar absorptivities of 945 liters/mole-cm for the molecular CO2 band, 200 liters/mole-cm for the 1,610 cm–1 band, and 235 liters/mole-cm for the 1,375 cm–1 band have been determined. These molar absorptivities allow the quantitative determination of species concentrations in the glasses with a precision on the order of several percent of the amount present. The accuracy of the method is estimated to be ±15–20% at present.The ratio of molecular CO2 to CO 3 2– in sodium aluminosilicate glasses varies little for each silicate composition over the range of total dissolved CO2 content (0–2%), pressure (15–33 kbar) and temperature (1,400–1,560° C) that we have studied. This ratio is, however, a strong function of silicate composition, increasing both with decreasing Na2O content along the NaAlO2-SiO2 join and with decreasing Na2O content in peraluminous compositions off the join.Infrared spectroscopic measurements of species concentrations in glasses provide insights into the molecular level processes accompanying CO2 solution in melts and can be used to test and constrain thermodynamic models of CO2-bearing melts. CO2 speciation in silicate melts can be modelled by equilibria between molecular CO2, CO 3 2– , and oxygen species in the melts. Consideration of the thermodynamics of such equilibria can account for the observed linear relationship between molecular CO2 and carbonate concentrations in glasses, the proposed linear relationship between total dissolved CO2 content and the activity of CO2 in melts, and observed variations in CO2 solubility in melts.  相似文献   

9.
We have investigated the effect of Fe on the stabilities of carbonate (carb) in lherzolite assemblages by determining the partitioning of Fe and Mg between silicate (olivine; ol) and carbonates (magnesite, dolomite, magnesian calcite) at high pressures and temperatures. Fe enters olivine preferentially relative to magnesite and ordered dolomite, but Fe and Mg partition almost equally between disordered calcic carbonate and olivine. Measurement of K d (X Fe carb X Mg ol /X Fe ol X Mg carb ) as a function of Fe/ Mg ratio indicates that Fe–Mg carbonates deviate only slightly from ideality. Using the regular solution parameter for olivine W FeMg ol of 3.7±0.8 kJ/mol (Wiser and Wood 1991) we obtain for (FeMg)CO3 a W FeMg carb of 3.05±1.50 kJ/mol. The effect of Ca–Mg–Fe disordering is to raise K d substantially enabling us to calculate W CaMg carb -W CaFe carb of 5.3±2.2 kJ/mol. The activity-composition relationships and partitioning data have been used to calculate the effect of Fe/Mg ratio on mantle decarbonation and exchange reactions. We find that carbonate (dolomite and magnesian calcite) is stable to slightly lower pressures (by 1 kbar) in mantle lherzolitic assemblages than in the CaO–MgO–SiO2(CMS)–CO2 system. The high pressure breakdown of dolomite + orthopyroxene to magnesite + clinopyroxene is displaced to higher pressures (by 2 kbar) in natural compositions relative to CMS. CO2. We also find a stability field of magnesian calcite in lherzolite at 15–25 kbar and 750–1000°C.  相似文献   

10.
In contrast to adjacent volcanic centers of the modern central Aleutian arc, Seguam Island developed on strongly extended arc crust. K-Ar dates indicate that mid-Pleistocene, late-Pleistocene, and Holocene eruptive phases constitute Seguam. This study focuses on the petrology of the mid-Pleistocene, 1.07–07 Ma, Turf Point Formation (TPF) which is dominated by an unusual suite of porphyritic basalt and basaltic andesite lavas with subordinate phenocryst-poor andesite to rhyodacite lavas. Increasing whole-rock FeO*/MgO from basalt to dacite, the anhydrous Plag+Ol+Cpx±Opx±Mt phenocryst assemblage, groundmass pigeonite, and the reaction Ol+Liq=Opx preserved in the mafic lavas indicate a tholeiitic affinity. Thermometry and comparison to published phase equilibria suggests that most TPF basalts crystallized Plag+Ol+Cpx±Mt at 1160°C between about 3–5 kb (±1–2% H2O), andesites crystallized Plag+Cpx+Opx±Mt at 1000°C between 3–4 kb with 3–5% H2O, and dacites crystallized Plag +Cpx±Opx±Mt at 1000°C between 1–2 kb with 2–3% H2O. All lavas crystallized at f o 2 close to the NNO buffer. Mineral compositions and textures indicate equilibrium crystallization of the evolved lavas; petrographic evidence of open-system mixing or assimilation is rare. MgO, CaO, Al2O3, Cr, Ni, and Sr abundances decrease and K2O, Na2O, Rb, Ba, Zr, and Pb increase with increasing SiO2 (50–71%). LREE enrichment [(Ce/Yb)n=1.7±0.2] characterizes most TPF lavas; total REE contents increase and Eu anomalies become more negative with increasing SiO2. Relative to other Aleutian volcanic centers, TPF basalts and basaltic andesites have lower K2O, Na2O, TiO2, Rb, Ba, Sr, Zr, Y, and LREE abundances. 87Sr/86Sr ratios (0.70361–0.70375) and ratios of 206Pb/204Pb (18.88–18.97), 207Pb/204Pb (15.58–15.62), 208Pb/204Pb (38.46–38.55) are the highest measured for any suite of lavas in the oceanic portion of the Aleutian arc. Conversely, Nd values (+5.8 to+6.7) are among the lowest from the Aleutians. Sr, Nd, and Pb ratios are virtually constant from basalt through rhyodacite, whereas detectable isotopic heterogenity is observed at most other Aleutian volcanic centers. Major and trace element, REE, and Sr, Nd, and Pb isotopic compositions are consistent with the basaltic andesitic, andesitic, dacitic, and rhyodacitic liquids evolving from TPF basaltic magma via closed-system fractional crystallization alone. Fractionation models suggest that removal of 80 wt% cumulate (61% Plag, 17% Cpx, 12% Opx, 7% Ol, and 3% Mt) can produce 20 wt% rhyodacitic residual liquid per unit mass of parental basaltic liquid. Petrologic and physical constraints favor segregation of small batches of basalt from a larger mid-crustal reservoir trapped below a low-density upper crustal lid. In these small magma batches, the degree of cooling, crystallization, and fractionation are functions of the initial mass of basaltic magma segregated, the thermal state of the upper crust, and the magnitude of extension. Tholeiitic magmas erupted at Seguam evolved by substantially different mechanisms than did calc-alkaline lavas erupted at the adjacent volcanic centers of Kanaga and Adak on unextended arc crust. These variable differentiation mechanisms and liquid lines of descent reflect contrasting thermal and mechanical conditions imposed by the different tectonic environments in which these centers grew. At Seguam, intra-arc extension promoted eruption of voluminous basalt and its differentiates, unmodified by interaction with lower crustal or upper mantle wallrocks.  相似文献   

11.
Hydrochemistry of groundwater in Chithar Basin, Tamil Nadu, India was used to assess the quality of groundwater for determining its suitability for drinking and agricultural purposes. Physical and chemical parameters of groundwater such as electrical conductivity, pH, total dissolved solids (TDS), Na+, K+, Ca2+, Mg2+, Cl–, HCO3–, CO32–, SO42–, NO–3, F–, B– and SiO2 were determined. Concentrations of the chemical constituents in groundwater vary spatially and temporarily. Interpretation of analytical data shows that mixed Ca–Mg–Cl, Ca–Cl and Na–Cl are the dominant hydrochemical facies in the study area. Alkali earths (Ca2+, Mg2+) and strong acids (Cl–, SO42–) are slightly dominating over alkalis (Na+, K+) and weak acids (HCO3–, CO32–). The abundance of the major ions is as follows: Na+ Ca2+ Mg2+ > K+ = Cl– > HCO3–> SO42– > NO3– > CO32– . Groundwater in the area is generally hard, fresh to brackish, high to very high saline and low alkaline in nature. High total hardness and TDS in a few places identify the unsuitability of groundwater for drinking and irrigation. Such areas require special care to provide adequate drainage and introduce alternative salt tolerance cropping. Fluoride and boron are within the permissible limits for human consumption and crops as per the international standards.  相似文献   

12.
The intramolecular kinetic oxygen isotope fractionation between CO2 and CO32− during reaction of phosphoric acid with natural smithsonite (ZnCO3) and cerussite (PbCO3) has been determined between 25 and 72°C. While cerussite decomposes in phosphoric acid within a few hours at 25°C, smithsonite reacts very slowly with the acid at 25°C providing yields of CO2 < 25% after 2 weeks. The low yields result in a low precision for oxygen isotope measurements of the acid-liberated CO2 (±1.65‰, 1σ, n = 9). The yield and reproducibility of oxygen isotope values of the acid-liberated CO2 from smithsonite can be improved, the latter to ∼±0.15‰, by increasing the reaction temperature to 50°C for 12 h or to 72°C for 1 h. Our new phosphoric acid fractionation factor for natural cerussite at 25°C deviates significantly from a previously published value on synthetic material. The temperature dependence of the oxygen isotope factionation factor, α between acid-liberated CO2 and carbonate at 25 to 72°C is given by the following equations
  相似文献   

13.
CO2 solubility has a slight negative temperature dependence in olivine melilitite at 30 kb with 9% CO2 dissolved at 1,450 °C, 8.5% at 1,550 °C and 8.3% at 1,650° C. CO2 is dissolved as the carbonate molecule (CO 3 2– ) only. Feldspar melts (albite-anorthite) dissolve much less CO2 at 30 kb (around 2%) with a slight increase with increasing anorthite content. A CO2 absorption peak in infrared spectra of albite-rich glasses diappears in favour of the CO 3 2– peak with increasing anorthite content. It is inferred that CO2 was present as CO 3 2– in albite-rich melts also, but reverts to CO2 during quenching because of bonding differences related to Ca2+ and Na+ in the melts.  相似文献   

14.
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.  相似文献   

15.
To further our knowledge of the effects of volatile components on phase relationships in aluminosilicate systems, we determined the vapor saturated solidi of albite, anorthite, and sanidine in the presence of CO2 vapor. The depression of the temperature of the solidus of albite by CO2 decreases from 30° C at 10 kbar, to 10° C at 20 kbar, to about 0 at 25 kbar, suggesting that the solubility of CO2 in NaAlSi3O8 liquid in equilibrium with solid albite decreases with increasing pressure and temperature. In contrast, CO2 lowers the temperature of the solidus of anorthite by 30° C at 14 kbar, and by 70dg C at 25 kbar. This contrasting behavior of albite and anorthite is also reflected in the behavior of melting in the absence of volatile components. Whereas albite melts congruently to a liquid of NaAl-Si3O8 composition to pressures of 35 kbar, anorthite melts congruently to only about 10 kbar and, at higher pressures, incongruently to corundum plus a liquid that is enriched in SiO2 and CaO and depleted in Al2O3 relative to CaAl2Si2O8.The tendency toward incongruent melting with increasing pressure in albite and anorthite produces an increase in the activity of SiO2 component in the liquid ( ). We predict that this increases the ratio of molecular CO2/CO 3 2– in these liquids, but the experimental results from other workers are mutually contradictory. Because of the positive dP/dT of the albite solidus and the negative dP/dT of the anorthite solidus, we propose that a negative temperature derivative of the solubility of molecular CO2 in plagioclase liquids may partly explain the decrease in solubility of carbon with increasing pressure in near-solidus NaAlSi3O8 liquids, which is in contrast to that in CaAl2Si2O8 liquid. Also, reaction of CO2 with NaAlSi3O8 liquid to form CO 3 2– that is complexed with Na+ must be accompanied by a change in Al3+ from network-former to network-modifier, as Na+ is no longer abailable to charge-balance Al3+ in a network-forming role. However, when anorthite melts incongruently to corundum plus a CaO-rich liquid, the complexing of CO 3 2– with the excess Ca2+ in the liquid does not require a change in the structural role of aluminum, and it may be more energetically favorable.The depression of the temperature of the solidus of sanidine resulting from the addition of CO2 increases from 50° C at 5 kbar to 170° C at 15 kbar. In marked contrast to the plagioclase feldspars, sanidine melts incongruently to leucite plus a SiO2-rich liquid up to the singular point at 15 kbar. Above this pressure, sanidine melts congruently, resulting in a decrease in the with increasing pressure in the interval up to 15 kbar. Above this pressure, the congruent melting of sanidine results in a lower and nearly constant relative to those of albite and anorthite, and CO2 produces a nearly constant freezing-point depression of about 170° C. Because of the low at pressures above the singular point, we infer that most of the carbon dissolves as CO 3 2– , resulting in a low CO2/ CO 3 2– , but a high total carbon content.The principles derived from the studies of phase equilibria in these chemically simple systems provide some information on the structural and thermal properties of magmas. We propose that the is an important parameter in controlling the speciation of carbon in these feldspathic liquids, but it certainly is not the only factor, and it may be relatively less significant in more complex compositions. In addition, our phase-equilibria approach does not provide direct thermal and structural information as do calorimetry and spectroscopy, but the latter have been used primarily on glasses (quenched liquids) and cannot be used in situ to derive direct information on liquids at elevated pressures, as can our method. Hopefully, the results of all of these approaches can be integrated to yield useful results.Institute of Geophysics and Planetary Physics, Contribution No. 2744  相似文献   

16.
The petrochemistry of kimberlites from Yakutia and Lesotho has been studied using a silicate melt model with the SiO2, CO2 and H2O derivatives as the main anions.A model has been developed, according to which the dissolution of H2O in an ultramafic melt results in orthosilicates (H2SiC 4 -2 , H3SiO 4 – , H4SiO4 etc.) rather than metasilicates, while the dissolution of CO2 produces additional hydrocarbonate complexes. It suggests that at high PCO 2 1 , and where the orthosilicic calcium salt clusters are likely to be present in the magma, the kimberlite melt can break down into carbonate and silicate liquids. Therefore, the composition of kimberlite magma will be determined by the H2O/CO2 ratio under the relatively constant fluid pressure. This can be seen from the distinct fluidrs trend in the H2O-CO2-SiO2 diagram for the Yakutia and Lesotho diamond-bearing kimberlites. The H2O/CO2 ratio changes with the liquidus temperature along this trend (Perchuk and Vaganov 1977) which suggests that liquid immiscibility predominates over the simple CO2 solubility in the melts of kimberlite composition. The well-known Boyd's diagrams for the equilibrium PT-conditions in peridotites have been applied along with new experimental data to natural Cpx and Opx, and the PT-parameters were correlated for peridotite inclusions in kimberlite pipes in Yakutia and Lesotho. The liquidus temperatures for the extrapolated area of these correlations gave depths (pressures) at which kimberlite magmas are formed (200–250 km).The hypothesis on SiO2 partitioning between the melt and the fluid was used to calculate the composition of dry initial kimberlite which characterised the average mantle composition: SiO2 — 45.12; TiO2 — 2.49; Al2O3 — 3.58; Cr2O3 — 0.12; FeO — 9.32; MnO — 0.16; CoO — 0.11; MgO — 23.47; CaO — 13.44; Na2O — 0.20; K2O — 1.12; P2O5 — 0.69; S — 0.18; sum — 100 wt.%. This kimberlite is close to wehrlite in composition.  相似文献   

17.
The Wolyu mine is one of the largest vein-type gold-silver-bearing epithermal systems in the Youngdong district and is the first gold-silver deposit in Korea found to contain significant germanium, in the form of argyrodite (Ag8GeS6). Mineralized veins (78.9 ± 1.2 Ma) crosscutting Late Cretaceous hostrock tuff and quartz porphyry (81.5 ± 1.8 Ma) consist of three stages of quartz and carbonates, the first of which contains pyrite, basemetal sulfides and Au-Ag-minerals. Stage I Au-Ag-Ge-mineralized veins show a systematic variation of mineral assemblage with time: (1) quartz + pyrite; (2) quartz + pyrite + sphalerite + electrum + argentite; (3) carbonate + quartz + sphalerite + electrum + argentite; (4) carbonate + native silver + argentite + Ag-sulfosalts + argyrodite + sphalerite. Calculated values of temperature and sulfur activity are: assemblage (1), 360-280°C and 10–7-10–10; (2), 280-210°C and 10–10-10–14; (3), 210-180°C and 10–14-10–16; (4), 180-155°C and 10–17-10–18. These data, the frequent association of gold with sulfides, and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition. Hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time. Within the main Ag-Au-Ge mineralization, D and 18O values decrease with the transition from quartz to carbonate deposition (from -78 and –2.8% to –90 and –8.7%., respectively), indicating increasing involvement (mixing) of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow ( 370–600 m) Wolyu epithermal system.  相似文献   

18.
Samples of granitic rock from south-central Maine contain primary igneous minerals altered by hydrothermal fluids. The reaction mechanisms (by which the over-all mineralogical change during the alteration was accomplished) involve several different mineral-fluid reactions at different reaction sites in the rock. The reactions involve both molecular and charged species in solution. The different reaction sites correspond to alteration of different primary igneous minerals. Biotite is partially converted to chlorite+sphene; microcline to muscovite; plagioclase to various combinations of muscovite, epidote, and calcite. The different reaction sites are linked by exchange of ions: some reaction sites produce ions consumed at other sites and vice versa. Physical conditions during the hydrothermal event are estimated from mineralogical and thermochemical data: P = 3,500 (±300) bars; T =425 ° (± 25 °)C. The fluid was characterized by X CO 2 = 0–0.13; ln([K+]/[H+ ]) = 10.0; ln([Ca2+]/[H+]2)=9.1; ln([Na+]/[H+]) = 10.5; Fe/(Fe+Mg) = 0.95. Amounts of secondary minerals in altered rock, when compared to the inferred mineral reactions that formed them, indicate that small but significant amounts (0.01–0.3mol/ 1,000cm3 altered rock) of CO2, H2O, H+, and K+ were added to the granites by fluids during the alteration, as well as lesser amounts (< 0.01–0.03 mol/1,000cm3 altered rock) of Mg2+, Fe2+, Fe3+, Mn2+, Na+, and Ti4+. The sole element leached from the granitic rocks during alteration was Ca in amounts 0.1–0.3 mol/1,000 cm3 rock. By estimating the composition of the hydrothermal fluids before and after reaction with the granites and by measuring the amount of material added to or subtracted from the granites during the alteration, the amount and volume of hydrothermal fluid involved can be calculated. Two independent calculations require minimum volumes in the range 100–1,000 cm3 fluid/1,000cm3 altered rock to participate in the hydrothermal event.  相似文献   

19.
To explore the effect of bulk composition on the solidus of carbonated eclogite, we determined near-solidus phase relations at 3 GPa for four different nominally anhydrous, carbonated eclogites. Starting materials (SLEC1, SLEC2, SLEC3, and SLEC4) were prepared by adding variable proportions and compositions of carbonate to a natural eclogite xenolith (66039B) from Salt Lake crater, Hawaii. Near-solidus partial melts for all bulk compositions are Fe–Na calcio-dolomitic and coexist with garnet + clinopyroxene + ilmenite ± calcio-dolomitic solid solution. The solidus for SLEC1 (Ca#=100 × molar Ca/(Ca + Mg + FeT)=32, 1.63 wt% Na2O, and 5 wt% CO2) is bracketed between 1,050°C and 1,075°C (Dasgupta et al. in Earth Planet Sci Lett 227:73–85, 2004), whereas initial melting for SLEC3 (Ca# 41, 1.4 wt% Na2O, and 4.4 wt% CO2) is between 1,175°C and 1,200°C. The solidus for SLEC2 (Ca# 33, 1.75 wt% Na2O, and 15 wt% CO2) is estimated to be near 1,100°C and the solidus for SLEC3 (Ca# 37, 1.47 wt% Na2O, and 2.2 wt% CO2) is between 1,100°C and 1,125°C. Solidus temperatures increase with increasing Ca# of the bulk, owing to the strong influence of the calcite–magnesite binary solidus-minimum on the solidus of carbonate bearing eclogite. Bulk compositions that produce near-solidus crystalline carbonate closer in composition to the minimum along the CaCO3-MgCO3 join have lower solidus temperatures. Variations in total CO2 have significant effect on the solidus if CO2 is added as CaCO3, but not if CO2 is added as a complex mixture that maintains the cationic ratios of the bulk-rock. Thus, as partial melting experiments necessarily have more CO2 than that likely to be found in natural carbonated eclogites, care must be taken to assure that the compositional shifts associated with excess CO2 do not unduly influence melting behavior. Near-solidus dolomite and calcite solid solutions have higher Ca/(Ca + Mg) than bulk eclogite compositions, owing to Ca–Mg exchange equilibrium between carbonates and silicates. Carbonates in natural mantle eclogite, which have low bulk CO2 concentration, will have Ca/Mg buffered by reactions with silicates. Consequently, experiments with high bulk CO2 may not mimic natural carbonated eclogite phase equilibria unless care is taken to ensure that CO2 enrichment does not result in inappropriate equilibrium carbonate compositions. Compositions of eclogite-derived carbonate melt span the range of natural carbonatites from oceanic and continental settings. Ca#s of carbonatitic partial melts of eclogite vary significantly and overlap those of partial melts of carbonated lherzolite, however, for a constant Ca-content, Mg# of carbonatites derived from eclogitic sources are likely to be lower than the Mg# of those generated from peridotite.  相似文献   

20.
OH structure of metamorphic fluids has been studied by high temperature infrared (IR) microspectroscopy on natural fluid inclusions contained in quartz veins, over the temperature range 25–370 °C. Blueschist-facies veins from Tinos island core complex (Cyclades, Greece) display H2O–NaCl–CaCl2–CO2 inclusions whereas greenschist-facies veins contain H2O–NaCl ± CO2 inclusions. From 25 to 370 °C, peak positions of OH stretching IR absorption bands increase quasi-linearly with slopes of 0.25 and 0.50 cm–1 °C–1 for inclusions trapped under blueschist and greenschist conditions, respectively. Extrapolation to 400 °C yield peak positions of 3,475 cm–1 for blueschist inclusions and 3,585 cm–1 for greenschist inclusions. Because the smaller wave number indicates the shorter hydrogen-bond distance between water molecules, fluids involved in the greenschist event have a loose structure compared with blueschist fluids. We suggest that these properties might correspond to a low wetting angle of fluids. This would explain the high mobility of aqueous fluids suggested by structural observation and stable isotope analysis.Editorial responsibility: J. Hoefs  相似文献   

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