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1.
Comparison of theoretical and analytical equilibrium constants based on the reactions CH4 + 2H2O = CO2 + 4H2, 2NH3 = N2 + 3H2 and iron(II)-aluminium-silicate + 2H2S = FeS2 + H2 + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H2O, CO2, H2S, NH3, H2, N2 and CH4. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.  相似文献   

2.
The application of chemical and isotopic geothermometry to geothermal systems is reviewed, pointing out the uses and limitations of specific reactions in estimating deep temperatures from well, hot-spring and fumarole discharges.At present the most reliable indicators are: the silica-water equilibria; the Na/K ratio; the isotopic distributions Δ2H(H2“H2O), Δ2H(H2“CH4), Δ18O(H2O“HSO?4); and the gas reactions CO2 + 4H2 ? CH4 + 2H2O, and 2NH3 ? N2 + 3H2. Many other qualitative chemical indicators exist.  相似文献   

3.
The Khtada Lake. British Columbia, metamorphic complex consists of high grade amphibolite and metasedimentary units with development of gneiss, migmatite and homogeneous autochthonous plutons. Maximum metamorphic conditions are estimated to have exceeded 5 kbar and 700°C.Fluid inclusions in matrix quartz are highly variable in density and composition, ranging from apparently pure CO2 (gas or liquid or both at room temperature) through CO2 + H2O ± CH4 mixtures to inclusions which are entirely aqueous. They occur along cracks, in groups without planar features and as isolated inclusions. The latter and some which occur in groups, are interpreted to most nearly approximate, in density and composition, the fluids present during the peak of metamorphism.The density and fluid composition data are derived from direct observations of phase changes between ? 180 and + 380°C and from the application of published experimental data in the system CH4-CO2-H2O-NaCl. The most dense, pure CO2 inclusions indicate a pressure of entrapment at 5 kbar, if a temperature of 700°C is assumed. This is in close agreement with the minimum P-T estimates from the mineral assemblages. Methane was positively identified in inclusions in graphite-bearing specimens. Salt content is concluded to be about 5–6 wt% NaCl equivalent in the aqueous phase in both aqueous and CO2 + H2O inclusions. There is evidence of immiscible separation of CO2-rich and H2O-rich fluids at temperatures at least as high as 375°C.  相似文献   

4.
The chemical composition of gas mixtures emerging in thermal areas can be used to evaluate the deep thermal temperatures. Chemical analyses of the gas compositions for 34 thermal systems were considered and an empirical relationship developed between the relative concentrations of H2S, H2, CH4 and CO2 and the reservoir temperature. The evaluated temperatures can be expressed by: t°C = 24775α + β + 36.05 ?273 where α = 2 logCH4CO2 ?log H2CO2?3 log H2SCO2 (concentrations in % by volume) and β = 7 logPco2  相似文献   

5.
Aqueous-carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite (Fe.95Mn.05 WO4) vein within the low-grade metamorphic aureole of the Borne granite (French Massif Central) have been studied by microthermometry and Raman spectrometry. The bulk V?-X properties of the aqueous-carbonaceous inclusions have been derived using the equation of state of Heyenet al. (1982) for the low-temperature CO2-CH4 system. A P-T path has been proposed for their trapping using the equations of state of Jacobs and Kerrick (1981a) for the H2O-CO2-CH4 system. Two main episodes were reconstructed for the history of the aqueous-carbonaceous fluid. (1) Primary H2O-CO2-CH4 vapourrich inclusions in quartz indicated the early circulation of a low-density fluid (65 mole% H2O-34 mole% CO2-1 mole% CH4 and traces of N2: d = 0.35 gcm?3) at around 550° ± 50°C and 700 ± 100 bar. Fluid cooled approximately isobarically to 450°-400°C and was progressively diluted by H2O with a concomitant increase in density. The fO2 of the H2OCO2-CH4 fluid, estimated from the equilibrium CO2 + 2H2O CH4 + 2O2, first ranged from 10?22 to 10?27 bar, close to the Q-F-M buffer. Within analytical errors, these values were consistent with the presence of graphite in equilibrium with the fluid. (2) A drop in PCO2, and therefore a drop in fO2, was recorded by the secondary liquid-rich inclusions in quartz. The inclusions, formed at and below 400°C, were composed of H2O and CH4 only, and fO2 at that stage was below that fixed by the graphite-fluid equilibrium. This second episode in the fluid-rock system could be explained by the drop of temperature below the blocking temperature of the graphite-fluid equilibrium. According to this interpretation, the blocking of the graphite-fluid equilibrium occurred at T ≥ 370°C and probably at 400°C on account of the pressure correction. Mass spectrometric data show that ferberite contains H2O, CO2 and CH4 in fluid inclusions, which lie in the gap of the V?-X properties of the aqueouscarbonaceous fluid in quartz. Deposition of ferberite probably occurred at around 400°C, the previously inferred blocking temperature, resulting from either the drop in PCO2, the drop fO2 and/or the related pH-increase.It is concluded that the existence of a blocking-temperature for the graphite-fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite-bearing rocks.  相似文献   

6.
At pressures which are expected in the earth's crust, the high temperature border of the lawsonite stability field is marked by reaction lawsonite = zoisite + kyanite/andalusite + pyrophyllite + H2O. (1a) The equilibrium data of reaction (1a) have been experimentally determined, and the equilibrium curve is characterized by the following P, T-data: 4 kb; 360±20° C; 5 kb; 375 ±20° C; 7kb;410±20° C. In the P, T diagram the equilibrium curve of reaction lawsonite + quartz = zoisite + pyrophyllite + H2O (6) is very close to the curve of reaction (1a); the distance is smaller than the error stated for curve (1a), i.e. below ±20° C. The stability fields of lawsonite and anorthite + H2O are not adjacent fields in the P, T diagram. This means that no stable reaction of lawsonite to anorthite + H2O can exist. Thus, the CaAl-silicate formed by the decomposition of lawsonite is always zoisite. Further, as shown by experimental determination of reaction calcite + pyrophyllite + H2O = lawsonite + quartz + CO2, (7) lawsonite can coexist with a gas phase only if the CO2 content of the gas phase does not exceed 3±2 Mol-%. This means, for metamorphism of lawsonite glaucophane rocks, that the fluid phase that was present during metamorphism has been quite rich in H2O. Ernst (1971, in press) who applied a different, indirect investigation method when studying the composition of the fluid-attending Franciscan and Sanbagawa metamorphism has come to the result that during metamorphism of lawsonite-glaucophane rocks the fluid phase did not contain more than 1–3 Mol-% of CO2.  相似文献   

7.
Oxygen fugacity (fO2) in the Earth’s mantle has a bearing on the problems of the chemical differentiation of the Earth’s materials and formation of the chemical and phase state of its shells. This paper addresses some problems concerning changes in the redox state of the upper mantle over geologic time and through its depth and the possible influence of fO2 stratification in the interiors on geochemical processes. Among these problems are the formation of fluids enriched in H2O, CO2, CH4,and H2; the possible influence of reduced fluid migration from mantle zones with low fO2 values on reactions in the lithosphere; and the formation of films of silicate liquids with high H2O and CO2 contents, which could be responsible for metasomatic transformations in rocks. The formation of a metallic core and accompanying large-scale melting of the silicate part of the Earth are the early mechanisms of the chemical differentiation of the mantle that must have had an effect on the redox state and the composition of volatile components in planetary materials. The molten metallic and silicate phases were prone to gravitational migration, which affected the formation of the metallic core. Volatile components had to be simultaneously formed in the zones of large-scale melting of the early Earth. The composition of these volatiles was largely controlled by the interaction of hydrogen and carbon, the two major gas-forming elements in the mantle, with melt under low fO2 values. A remarkable feature is that, despite fairly low fO2 values imposed by the presence of a metallic phase, both reduced (CH4 and H2) and oxidized species of hydrogen and carbon (H2O, OH? and CO 3 ?2 ) are stable in the melt. This peculiarity of carbon and hydrogen dissolution in reduced melts may be crucial for the elucidation of mechanisms for the formation of initial amounts of CO2 and H2O connected with incipient melting in the reduced mantle.  相似文献   

8.
We have performed experiments to determine the effects of pressure, temperature and oxygen fugacity on the CO2 contents in nominally anhydrous andesitic melts at graphite saturation. The andesite composition was specifically chosen to match a low-degree partial melt composition that is generated from MORB-like eclogite in the convective, oceanic upper mantle. Experiments were performed at 1–3 GPa, 1375–1550?°C, and fO2 of FMQ ?3.2 to FMQ ?2.3 and the resulting experimental glasses were analyzed for CO2 and H2O contents using FTIR and SIMS. Experimental results were used to develop a thermodynamic model to predict CO2 content of nominally anhydrous andesitic melts at graphite saturation. Fitting of experimental data returned thermodynamic parameters for dissolution of CO2 as molecular CO2: ln(K 0) = ?21.79?±?0.04, ΔV 0?=?32.91?±?0.65 cm3mol?1, ΔH 0?=?107?±?21 kJ mol?1, and dissolution of CO2 as CO3 2?: ln(K 0 ) = ?21.38?±?0.08, ΔV 0?=?30.66?±?1.33 cm3 mol?1, ΔH 0?=?42?±?37 kJ mol?1, where K 0 is the equilibrium constant at some reference pressure and temperature, ΔV 0 is the volume change of reaction, and ΔH 0 is the enthalpy change of reaction. The thermodynamic model was used along with trace element partition coefficients to calculate the CO2 contents and CO2/Nb ratios resulting from the mixing of a depleted MORB and the partial melt of a graphite-saturated eclogite. Comparison with natural MORB and OIB data suggests that the CO2 contents and CO2/Nb ratios of CO2-enriched oceanic basalts cannot be produced by mixing with partial melts of graphite-saturated eclogite. Instead, they must be produced by melting of a source containing carbonate. This result places a lower bound on the oxygen fugacity for the source region of these CO2-enriched basalts, and suggests that fO2 measurements made on cratonic xenoliths may not be applicable to the convecting upper mantle. CO2-depleted basalts, on the other hand, are consistent with mixing between depleted MORB and partial melts of a graphite-saturated eclogite. Furthermore, calculations suggest that eclogite can remain saturated in graphite in the convecting upper mantle, acting as a reservoir for C.  相似文献   

9.
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   

10.
Glassy orthopyroxene granodiorite-tonalite (named pincinite after type locality) was described from basaltic lapilli tuffs of the Pliocene maar near Pinciná village in the Slovakian part of the Pannonian Basin. Two pincinite types exhibit a qualitatively similar mineral composition (quartz, An20–55 plagioclase, intergranular silicic glass with orthopyroxene and ilmenite, ±K-feldspar), but strongly different redox potential and formation PT conditions. Peraluminous pincinite is reduced (6–7% of total iron as Fe3+ in corundum-normative intergranular dacitic glass) and contains ilmenite with 8–10 mol% Fe2O3 and orthopyroxene dominated by ferrosilite. High-density (up to 0.85 g/cm3) primary CO2 inclusions with minor H2, CH4, H2S, CO and N2 (<2 mol% total) are present in Qtz and Plg. Equilibrium PT conditions inferred from the intergranular Opx–Ilm–Glass assemblage and fluid density correspond to 1,170±50°C, 5.6±0.4 kbar, respectively. Metaluminous pincinite is more oxidised (25–27% of total iron as Fe3+ in diopside-normative intergranular glass of rhyolite–trachyte–dacite composition) and contains Fe2O3-rich ilmenite (17–29 mol%) associated with enstatite. Fluid inclusions are composed of CO2–H2O mixtures with up to 38 mol% H2O. Raman spectroscopy revealed H2S along with dominant CO2 in the carbonic phase. Equilibrium PT parameters for the intergranular Opx–Ilm–Glass assemblage correspond to 740±15°C, 2.8±0.1 kbar, respectively. Reducing gas species (<2 mol% total) in the CO2-inclusions of the peraluminous pincinite resulted from hydrogen diffusion due to fH2 gradient imposed during decrease of redox potential from the log fO2 values near QFM during Qtz + Plg growth, to QFM-2 incidental to the superimposed Opx + Ilm assemblage in the intergranular melt. The decrease in oxygen fugacity was recorded also in the metaluminous pincinite, where log fO2 values changed from ~QFM + 2.6 to QFM + 0.4, but hydrogen diffusion did not occur. Absence of OH-bearing minerals, major and trace element abundances (e.g. REE 300–320, Nb 55–57, Th 4–31, Zr 240–300 ppm, FeOtot/MgO up to 11), and Sr–O isotope ratios in the pincinites are diagnostic of high-temperature anorogenic magmas originated by dehydration melting of biotite in quartz-feldspathoid crust (87Sr/86Sr>0.705–0.706, 18O>9 V-SMOW) around alkali basalt reservoir in depths between 17 and 20 km, and around late stage derivatives of the basalt fractionation, intruding the crust up to depths of 10–11 km. Low water activity in the pincinite parental melt was caused by CO2-flux from the Tertiary basaltic reservoirs and intrusions. The anatexis leads to generation of a melt-depleted granulitic crust beneath the Pannonian Basin, and the pincinites are interpreted as equivalents of igneous charnockites and enderbites quenched at temperatures above solidus and unaffected by sub-solidus re-equilibration and metamorphic overprint.  相似文献   

11.
Hydrothermal volatile-solubility and partitioning experiments were conducted with fluid-saturated haplogranitic melt, H2O, CO2, and S in an internally heated pressure vessel at 900°C and 200?MPa; three additional experiments were conducted with iron-bearing melt. The run-product glasses were analyzed by electron microprobe, FTIR, and SIMS; and they contain ??0.12 wt% S, ??0.097 wt% CO2, and ??6.4 wt% H2O. Apparent values of log f O2 for the experiments at run conditions were computed from the [(S6+)/(S6++S2?)] ratio of the glasses, and they range from NNO ?0.4 to NNO?+?1.4. The C?CO?CH?CS fluid compositions at run conditions were computed by mass balance, and they contained 22?C99?mol% H2O, 0?C78?mol% CO2, 0?C12?mol% S, and <3 wt% alkalis. Eight S-free experiments were conducted to determine the H2O and CO2 concentrations of melt and fluid compositions and to compare them with prior experimental results for C?CO?CH fluid-saturated rhyolite melt, and the agreement is excellent. Sulfur partitions very strongly in favor of fluid in all experiments, and the presence of S modifies the fluid compositions, and hence, the CO2 solubilities in coexisting felsic melt. The square of the mole fraction of H2O in melt increases in a linear fashion, from 0.05 to 0.25, with the H2O concentration of the fluid. The mole fraction of CO2 in melt increases linearly, from 0.0003 to 0.0045, with the CO2 concentration of C?CO?CH?CS fluids. Interestingly, the CO2 concentration in melts, involving relatively reduced runs (log f O2????NNO?+?0.3) that contain 2.5?C7?mol% S in the fluid, decreases significantly with increasing S in the system. This response to the changing fluid composition causes the H2O and CO2 solubility curve for C?CO?CH?CS fluid-saturated haplogranitic melts at 200?MPa to shift to values near that modeled for C?CO?CH fluid-saturated, S-free rhyolite melt at 150?MPa. The concentration of S in haplogranitic melt increases in a linear fashion with increasing S in C?CO?CH?CS fluids, but these data show significant dispersion that likely reflects the strong influence of f O2 on S speciation in melt and fluid. Importantly, the partitioning of S between fluid and melt does not vary with the (H2O/H2O?+?CO2) ratio of the fluid. The fluid-melt partition coefficients for H2O, CO2, and S and the atomic (C/S) ratios of the run-product fluids are virtually identical to thermodynamic constraints on volatile partitioning and the H, S, and C contents of pre-eruptive magmatic fluids and volcanic gases for subduction-related magmatic systems thus confirming our experiments are relevant to natural eruptive systems.  相似文献   

12.
After its initial synthesis as the new compound Mg2Al3B2O9(OH) (Daniels et al. 1997) pseudosinhalite has now been discovered as a new mineral. It occurs, together with hydrotalcite, as a replacement product of sinhalite, MgAlBO4, in an impure marble of the contact metasomatic iron boron deposit of Tayozhnoye in the Aldan Shield of Siberia. Its chemical composition determined by electron microprobe is (wt%): Al2O3 46.88; MgO 25.12; FeO 1.99; B2O3 (calculated) 21.75; H2O (calculated) 2.81 giving a total of 98.55 and leading to the empirical formula (Mg2.00 Fe2+ 0.09)Σ=2.09 Al2.94 B2O9(OH). The small deviation from the ideal stoichiometry with (Mg?+?Fe2+):Al?≠?2:3 may be caused by either solid solution towards, or submicroscopic interlayering with lamellae of, the structurally similar mineral sinhalite. The underlying substitution involving also B and H would be (Mg?+?Fe)+?B=Al+2H. Pseudosinhalite is monoclinic, space group P21/c, with a=7.49(1), b=4.33(1), c=9.85(2) Å; β=110.7(1)°; V?=?299(1) Å3; Z?=?2. Calculated density is 3.508?g/cm3. Pseudosinhalite is colourless with white streak and has a vitreous lustre. It is transparent; no fluorescence was detected. There is no cleavage and parting; fractures are concoidal. Optical constants could not be measured properly due to polysynthetic microtwinning, but α<1.72<γ. For synthetic pseudosinhalite α=1.691(1); β=1.713(1); γ=1.730(1); Δ=0.039; 2?V=80°. The temperature of pseudosinhalite formation was below about 400?°C at low pressures and with a hydrous, CO2-bearing fluid participating in the reaction.  相似文献   

13.
The equilibrium conditions of the following reaction 2 zoisite +1 CO2?3 anorthite+1 calcite+1 H2O 2 Ca2Al3[O/OH/SiO4/Si2O7]+1 CO2?3 CaAl2Si2O8+1 CaCO3+1 H2O have been determined experimentally at total pressures of P j= 2000 bars, P f =5000 bars, and P f =7000 bars. Owing to the vertical position of the equilibrium curves in isobaric T- \(X_{{\text{CO}}_{\text{2}} }\) diagrams, the composition of the binary H2O-CO2 fluid phase coexisting with zoisite is independent of temperature in the temperature interval investigated. According to our experiments, orthorhombic zoisite is only stable in equilibrium with a fluid phase at a concentration of CO2 which is less than, respectively, ca. 2 Mol% CO2 at P f =2000 bars, ea. 6 Mol% at P f =5000 bars, and ca. 10 Mol% at P f =7000 bars. Thus, the fluid phase coexisting with zoisite is rich in H2O. While this is independent of temperature the experimental data demonstrate that the influence of pressure cannot be neglected: With increasing pressure the concentration of CO2 of the fluid phase coexisting with zoisite can rise a little. The position of the reaction studied, which is independent of temperature and exhibits small values of \(X_{{\text{CO}}_{\text{2}} }\) ,leads to two important petrogenetic conclusions:
  1. The occurrence of zoisite is an indicator for a CO2-poor and H2O-rich fluid composition during metamorphism of marly calcsilicates.
  2. If the concentration of CO2 of the fluid phase coexisting with zoisite exceeds the equilibrium value of \(X_{{\text{CO}}_{\text{2}} }\) calcite+anorthite+H2O is formed from zoisite+CO2. Thus, a considerable increase in the anorthite-content of plagioelase is possible.
  相似文献   

14.
The occurrence of talc and tremolite in a temperature gradient was investigated in siliceous calcite-dolomite sediments exposed along a strip in the southeastern part of the Damara Orogen. Five bivariant reactions may lead to the formation of talc and tremolite:
  1. 3 dolomite+4 quartz+1 H2O ? 1 talc+3 calcite+3 CO2
  2. 5 talc+6 calcite+4 quartz ? 1 tremolite+6 CO2+2 H2O
  3. 2 talc+3 calcite ? 1 tremolite+1 dolomite+1 CO2+1 H2O
  4. 5 dolomite+8 quartz+1 H2O ? 1 tremolite+3 calcite+7 CO2
  5. 2 dolomite+1 talc+4 quartz ? 1 tremolite+4 CO2.
The common paragenesis of four mineral assemblages tc+cc+dol+qtz1 and tre+tc+ cc+qtz with increasing temperature over an extended area show that the reactions must have taken place along the equilibrium curve or when fluid pressure is not constant along the equilibrium plane of reactions (1) or (2). The described occurrence of the five mineral assemblage tre+tc+cc+dol+qtz can be stable only on the isobaric intersection point, or when P f is variable on the univariant intersection curve of the equilibrium planes of all five reactions. The genetic relations of the described parageneses are illustrated with the help of a phase diagram. Minimum P-T conditions which prevailed during metamorphism in this part of the Damara Orogen have been estimated to be about 590° C and 5 kb.  相似文献   

15.
《Applied Geochemistry》2001,16(7-8):895-910
Coalbed gases in the Lower Silesian Coal Basin (LSCB) of Poland are highly variable in both their molecular and stable isotope compositions. Geochemical indices and stable isotope ratios vary within the following ranges: hydrocarbon (CHC) index CHC=CH4/(C2H6+ C3H8) from 1.1 to 5825, wet gas (C2+) index C2+=(C2H6+ C3H8+ C4H10+ C5H12) / (CH4+ C2H6+ C3H8+ C4H10+ C5H12) 100 (%) from 0.0 to 48.3%, CO2–CH4 (CDMI) index CDMI=CO2/(CO2+ CH4) 100 (%) from 0.1 to 99.9%, δ13C(CH4) from −66.1 to −24.6‰, δD(CH4) from −266 to −117‰, δ13C(C2H6) from −27.8 to −22.8‰, and δ13C(CO2) from −26.6 to 16.8‰. Isotopic studies reveal the presence of 3 genetic types of natural gases: thermogenic (CH4, higher gaseous hydrocarbons, and CO2), endogenic CO2, and microbial CH4 and CO2. Thermogenic gases resulted from coalification processes, which were probably completed by Late Carboniferous and Early Permian time. Endogenic CO2 migrated along the deep-seated faults from upper mantle and/or magma chambers. Minor volumes of microbial CH4 and CO2 occur at shallow depths close to the abandoned mine workings. “Late-stage” microbial processes have commenced in the Upper Cretaceous and are probably active at present. However, depth-related isotopic fractionation which has resulted from physical and physicochemical (e.g. diffusion and adsorption/desorption) processes during gas migration cannot be neglected. The strongest rock and gas outbursts occur only in those parts of coal deposits of the LSCB which are dominated by large amounts of endogenic CO2.  相似文献   

16.
The dissolution of H2O and CO2 in structurally dense, nominally anhydrous and non-carbonate oxide matrices such as MgO and CaO is reviewed. H2O and CO2 are treated as gaseous oxide components which enter into solid solution with the refractory oxide hosts. They form anion complexes associated with cation vacancy sites. Evidence is presented that OH? pairs which derive from the dissolution of H2O are subject to a charge transfer (CT) conversion into peroxy moieties and molecular hydrogen, O 2 2? ... H2. Because the O 2 2? moiety is small (O?-O? distance ≈ 1.5 Å) high pressure probably favors the CT conversion. Mass spectroscopic studies show that molecular H2 may be lost from the solid which retains excess oxygen in the form of O 2 2? , leading to the release of atomic O. The dissociation of O 2 2? moieties into a vacancy-bound O? state and an unbound O? state can be followed by measuring the internal redox reactions involving transition metal impurities, the transient paramagnetism of the O? and their effect on the d.c. conductivity. Evidence is presented that CO2 molecules dissolve dissociatively in the structurally dense oxide matrix, as if they were first to dissociate into CO+O and then to form separate solute moieties CO 2 2? and O 2 2? , both associated with cation vacancy sites. In the CO 2 2? moiety (C-O? distance 1.2–1.3 Å, OCO angle ≈ 130°) the C atom probably sits off center. The transition of the C atom into interstitial sites is accompanied by dissociation of the CO 2 2? moiety into CO? and O?. This transition can be followed by infrared spectroscopy, using OH? as local probes. Further support derives from magnetic susceptibility, thermal expansion, low frequency dielectric loss and low temperature deformation measurements. The recently observed emission of O and Mg atoms besides a variety of molecules such as CO, CO2, CH4, HCN and other hydrocarbons during impact fracture of MgO single crystals is presented and discussed in the light of the other experimental data.  相似文献   

17.
Burnham (1975a, b) has shown that in several alumino-silicate systems Henry's law constant is independent of silicate melt composition up to XmeltH2O = 0.5. He has used this fact to conclude that such silicate melts behave ideally over a wide range of compositions based on the application of the Gibbs-Duhem relation. Unless Henry's law is valid up to XmeltH2O = 1.0, the application of the Gibbs—Duhem relation to three component systems only shows that if one component obeys Henry's law, the other two components follow the two component Gibbs-Duhem equation. There is no thermodynamic requirement of ideality.  相似文献   

18.
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19.
Geochemistry of biotites from granitic rocks,Northern Portugal   总被引：2，自引：0，他引：2  
The biotites from a series of rocks ranging in composition from tonalite to granite have been analysed for both major and trace elements.The relations between chemical composition and paragenesis of the biotites are studied. Most biotites co-exist with potassium feldspar and ilmenite. Variations in composition can be correlated with the occurrence of amphibole, primary muscovite and aluminosilicates in the rocks.Variation diagrams of the trace element contents and element ratios of biotite are compared to those of the host rocks. Fractionation of elements can be defined more accurately as the influence of other mineral phases is eliminated.Variations in the proportions of the octahedrally co-ordinated Al, Ti and Fe3+ are correlated with the conditions of crystallization and comparisons made with biotites from other suites of calc-alkali rocks.In the light of the experimental data available, the petrographic observations and the chemical data it is apparent that biotites crystallized from systems in which fO2 was buffered, its values remaining close to that of the buffer FMQ. From the same data, a temperature of 800°C for fO2 = 10?14to 10?15 bars is deduced as prevalent during the crystallization of the tonalites while for the granites, at a temperature of crystallization of 680°C, fO2 = 10?16to 10?18 bars.A calc-alkali trend of fractionation is therefore apparent with decreasing fO2 while fH2O2 remains relatively high.  相似文献   

20.
Carbon dioxide sequestration in deep aquifers and depleted oilfields is a potential technical solution for reducing green-house gas release to the atmosphere: the gas containment relies on several trapping mechanisms (supercritical CO2, CO2(sc), dissolution together with slow water flows, mineral trapping) and on a low permeability cap-rock to prevent CO2(sc), which is less dense than the formation water, from leaking upwards. A leakproof cap-rock is thus essential to ensure the sequestration efficiency. It is also crucial for safety assessment to identify and assess potential alteration processes that may damage the cap-rock properties: chemical alteration, fracture reactivation, degradation of injection borehole seals, etc. The reactivity of the host-rock minerals with the supercritical CO2 fluid is one of the potential mechanisms, but it is altogether unknown. Reactivity tests have been carried out under such conditions, consisting of batch reactions between pure minerals and anhydrous supercritical CO2, or a two-phase CO2/H2O fluid at 200?°C and 105/160 bar. After 45 to 60 days, evidence of appreciable mineral-fluid reactivity was identified, including in the water-free experiments. For the mixed H2O/CO2 experiments, portlandite was totally transformed into calcite; anorthite displayed many dissolution patterns associated with calcite, aragonite, tridymite and smectite precipitations. For the anhydrous CO2 experiments, portlandite was totally carbonated to form calcite and aragonite; anorthite also displayed surface alteration patterns with secondary precipitation of fibrous calcite. To cite this article: O. Regnault et al., C. R. Geoscience 337 (2005).  相似文献   

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