首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Freezing was used in the jointing section of two shields (diameter 3.14 m) which ran across at right angles and at 25-m depth under the crossing of main roads for the construction of a 2.4-m diameter sewer tunnel. The object of freezing was to create a frozen barrier to prevent the inflow of water and fine sand into the area to be excavated.

Thirty-five freeze pipes (length about 7 m) were placed from one shield conically in the direction of the flank of another shield with freeze pipes attached to its inside wall. The cooling unit was placed on unoccupied land at about 60 m distant from the jointing section and the freeze pipes were connected with the cooling unit by supply and return pipelines.

The cooling unit had a cooling capacity of 79,000 kcal/h at an evaporation temperature of −27°C and a condensation temperature of +40°C. Freezing was continued for 180 days and the CaCl2 brine temperature was −25 to −30°C. These works were accomplished without the sinking of shaft and the use of injection, in complete safety with no traffic restriction on the road surface.  相似文献   


2.
The thermal expansivities of eight sodium aluminosilicate liquids were derived from the slope of new volume data at low temperatures (713−1072 K) combined with the high temperature (1300−1835 K) volume measurements of Stein et al. (1986) on the same liquids. Melt compositions range from 47−71 wt% SiO2, 0−31 wt% A1203, and 17−33 wt% Na2O; the volume of albite supercooled liquid at 1092 K was also determined. The low temperature volumes were derived from measurements of the glass density of each sample at 298 K, followed by measurements of the glass thermal expansion coefficient from 298 K to the respective glass transition interval. This technique takes advantage of the fact that the volume of a glass is equal to the volume of the corresponding liquid at the limiting fictive temperature (Tf), and that Tf can be approximated as the onset of the rapid rise in thermal expansion at the glass transition in a heating curve (Moynihan, 1995). No assumptions were made regarding the equivalence of enthalpy and volume relaxation through the glass transition. The propagated error on the volume of each supercooled liquid at Tf is 0.25%. Combination of these low temperature data with the high temperature measurements of Stein et al. (1986) allowed a constant thermal expansivity of each liquid to be derived over a wide temperature interval (763−1001 degrees) with a fitted 1σ error of 0.6–4.6%; in every case, no temperature dependence to dV/dTliq could be resolved. Calibration of a linear model equation leads to fitted values ± 1σ (units of cm3/mole) for (26.91 ± .04), (37.49 ± .12), (26.48 ± .06) at 1373 K, and (7.64 ± .08 × 10-3 cm3/mole-K). The results indicate that neither Si02 nor Al2O3 contribute to the thermal expansivity of the liquids, and that dV/dTliq is independent of temperature between 713–1835 K over a wide range of liquid composition. Calculated volumes based on this model recover both low and high temperature measurements with a standard deviation <0.25%, whereas values of dV/dTliq can be predicted within 5.6%.  相似文献   

3.
The maximum potential temperature of the Archaean mantle is poorly known, and is best constrained by the MgO contents of komatiitic liquids, which are directly related to eruptive temperatures. However, most Archaean komatiites are significantly altered and it is difficult to assess the composition of the erupted liquid. Relatively fresh lavas from the SASKMAR suite, Belingwe Greenstone Belt, Zimbabwe (2.7 Ga) include chills of 25.6 wt.% MgO, and olivines ranging to Fo93.6, implying eruption at around 1520°C. A chill sample from Alexo Township, Ontario (also 2.7 Ga) is 28 wt.% MgO, and associated olivines range to Fo94.1, implying eruption at 1560°C. However, inferences of erupted liquids containing 32–33 wt.% MgO, from lavas in the Barberton Greenstone Belt, South Africa (3.45 Ga) and from the Perseverance Complex, Western Australia (2.7 Ga) may be challenged on the grounds that they contain excess (cumulate) olivine, or were enriched in Mg during alteration or metamorphism. Re-interpretation of olivine compositions from these rocks shows that they most likely contained a maximum of 29 wt.% MgO corresponding to an eruption temperature of 1580°C. This composition is the highest liquid MgO content of an erupted lava that can be supported with any confidence. The hottest modern magma, on Gorgona Island (0.155 Ga) contained 18–20% MgO and erupted at circa 1400°C.

If 1580°C is taken as the temperature of the most magnesian known eruption, then the source mantle from which the liquids rose would have been at up to 2200°C at pressures of 18 GPa corresponding to a mantle potential temperature of 1900°C. These temperatures are in excess of the mantle temperatures predicted by secular cooling models, and thus komatiites can only be formed in hot rising convective jets in the mantle. This result requires that Archaean mantle jets may have been 300°C hotter than the Archaean ambient mantle temperature. This temperature difference is similar to the 200–300°C temperature difference between present day jets and ambient mantle temperatures. An important subsidiary result of this study is the confirmation that spinifex rocks may be cumulates and do not necessarily represent liquid compositions.  相似文献   


4.
Cylindrical specimens of fine Ottawa sand (A.S.T.M. designation C-109), compacted at the optimum moisture content and saturated before unidirectional freezing, have been tested in uniaxial compression at a cold room temperature of —5.5°C and strain rates between 10−7 and 10−2 s−1. The results agree with an extrapolation of data obtained by Sayles and Epanchin [1], but are much higher than those obtained by both Goughnour and Andersland [2] and Perkins and Ruedrich [3] at strain rates below 10−5 s−1. There is evidence that this may be due to variation in total moisture (ice) content, the conditions under which the specimens were frozen (closed system or an open system) and to the end effects at the platen—specimen interface.  相似文献   

5.
One of the more promising techniques in soft ground tunneling through urbanized areas is the use of artificially frozen ground for temporary tunnel support. This paper describes the general design considerations involved in the ground freezing method. Various factors are discussed which influence the selection of the freezing temperature, the thickness of the frozen zones and the spacing of the freeze pipes. The time required to achieve freezing is discussed in addition to the amount and rate of frost heave caused by the freezing.

To illustrate the applicability of the freezing method, various considerations in the design of an 8-ft. diameter tunnel in upstate New York, a 75-ft. diameter tunnel in Georgia, and a 12 1/2-ft. diameter tunnel in Washington, D.C. are discussed. All three of the tunnels were to pass immediately beneath mainline railroad tracks. A laboratory testing program was implemented to determine the effects of the repetitive train loads on the zone of frozen soil around the tunnel perimeter. Stress-controlled repeated load triaxial tests were performed on both undisturbed and remolded samples frozen from temperatures of −7°C for the New York tunnel to −10°C for the Atlanta and Washington tunnels. Static testing consisted of both quick triaxial tests and creep tests on frozen samples of the various soil types.

It was found that there was little difference between the cumulative strain response from repeated load tests and static tests for the low frequencies investigated (one-quarter to one-half cycles per minute). Hyperbolic stress—strain functions were developed to simulate the stress—strain relationship for various cumulative loading times.

The stresses and strains in the frozen soil tunnel configuration were computed by the finite element method, using both linear and hyperbolic stress—strain functions. Tangent modulus values were varied to reflect the decreasing modulus with increasing loading time. The analyses indicated that zones of frozen soil of approximately 3 ft. thick were required for both the New York and Washington tunnels. However, high tensile stresses were calculated for the Atlanta tunnel, precluding the use of the freezing method.  相似文献   


6.
We investigate the use of a ductile material with temperature-sensitive viscosity for thermomechanical modelling of the lithosphere. First, we consider the scaling of mechanical and thermal properties. For a normal field of gravity, the balance of stresses and body forces sets the stress scale, in proportion to the linear dimensions and the densities. The equation of thermal conduction sets the time scale. The activation enthalpy for creep sets the temperature scale; but the thermal expansivity provides an additional constraint on this temperature scale.

Gum rosin appears to be a suitable material for lithospheric modelling. We have measured its flow properties, at various temperatures, in a specially designed rotary viscometer with unusually low machine friction. The rosin is almost Newtonian. Strain rate depends upon stress to the power n, where 1.0 <n < 1.14. The viscosity varies over 5 orders of magnitude, from about 102 Pa s at 80°C, to about 107 Pa s at 40°C. The activation enthalphy is thus about 250 kJ/mol. Measured with a needle probe, the thermal conductivity is 0.113 ± 0.001 W m−1K−1; the thermal diffusivity, (6±3) ×10−7 m2 s−1. Calculated from X-ray profiles, the thermal expansivity is about 3 × 10−4 K−1. These thermal and mechanical properties make gum rosin suitable for thermomechanical models, where linear dimensions scale down by a factor of 106; time, by 1011; viscosity, by 1017; and temperature change, by 101.  相似文献   


7.
Within the framework of Pitzer's specific interaction model, interaction parameters for aqueous silica in concentrated electrolyte solutions have been derived from Marshall and co-authors amorphous silica solubility measurements. The values, at 25°C, of the Pitzer interaction parameter (λSiO2(aq)−i) determined in this study are the following: 0.092 (i = Na+), 0.032 (K+), 0.165 (Li+), 0.292 (Ca2+, Mg2+), −0.139 (SO42−), and −0.009 (NO3). A set of polynomial equations has been derived which can be used to calculate λSiO2(aq)−i for these ions at any temperature up to 250°C. A linear relationship between the aqueous silica-ion interaction parameters (λSiO2(aq)−i) and the surface electrostatic field (Zi/re,i) of ions was obtained. This empirical equation can be used to estimate, in first approximation, λSiO2(aq)−i if no measurements are available. From this parameterisation, the calculated activity coefficient of aqueous silica is 2.52 at 25°C and 1.45 at 250°C in 5 m NaCl solution. At lower concentrations, e.g. 2 m NaCl, the activity coefficient of silica is 1.45 at 25°C and 1.2 at 250°C. Hence, in practice, it is necessary to take into account the activity coefficient of aqueous silica (λSiO2(aq)≠1) in hydrothermal solutions and basinal brines where the ionic strength exceeds 1. A comparison of measured [Marshall, W.L., Chen, C.-T.A., 1982. Amorphous silica solubilities, V. Prediction of solubility behaviour in aqueous mixed electrolyte solutions to 300°C. Geochim. Cosmochim. Acta 46, 289–291.] and computed amorphous silica solubility, using this parameterisation, shows a good agreement. Because the effect of individual ions on silicate and silica polymorph solubilities are additive, the present study has permitted to derive Pitzer interaction parameters that allow a precise computation of γSiO2(aq) in the Na---K---Ca---Mg---Cl---SO4---HCO3---SiO2---H2O system, over a large range of salt concentrations and up to temperatures of 250°C.  相似文献   

8.
Strain-controlled cyclic triaxial tests were performed on a one-size silica (Ottawa) sand artificially frozen into 71.1-mm-diameter cylindrical samples. Ice-saturated samples with three different sand contents were tested under the following conditions: axial strains ranging from 3 × 10−3 to 3 X 10−2%, confining pressures from zero to 1.378 MPa, frequencies of 0.05–5.0 cps and temperatures from −1 to −10 °C.

Test equipment included (1) an MTS electrohydraulic closed-loop testing system which applies the load to the sample, (2) a triaxial cell completely immersed in a low-temperature coolant for temperature control, (3) a refrigeration unit for control of the coolant temperature and constant coolant circulation and (4) measuring devices including an LVDT and load cell, together with recording devices such as a digital multimeter, an oscilloscope, a strip-chart recorder and a minicomputer.

Test results indicate that the dynamic Young's modulus increases with increasing frequency, confining pressure and sand content, but decreases with increasing strain and temperature. The damping ratio decreases with increasing frequency, sand content and lower temperatures. The influence of confining pressures and axial strain on the damping ratio are less explicit for the ranges considered. The experimental results are compared with data from other sources.  相似文献   


9.
A detailed fluid inclusion study has been carried out on the hydrocarbon-bearing fluids found in the peralkaline complex, Lovozero. Petrographic, microthermometric, laser Raman and bulk gas data are presented and discussed in context with previously published data from Lovozero and similar hydrocarbon-bearing alkaline complexes in order to further understand the processes which have generated these hydrocarbons. CH4-dominated inclusions have been identified in all Lovozero samples. They occur predominantly as secondary inclusions trapped along cleavage planes and healed fractures together with rare H2O-dominant inclusions. They are consistently observed in close association with either arfvedsonite crystals, partially replaced by aegirine, aegirine crystals or areas of zeolitization. The majority of inclusions consist of a low-density fluid with CH4 homogenisation temperatures between −25 and −120 °C. Those in near-surface hand specimens contain CH4+H2 (up to 40 mol%)±higher hydrocarbons. However, inclusions in borehole samples contain CH4+higher hydrocarbons±H2 indicating that, at depth, higher hydrocarbons are more likely to form. Estimated entrapment temperatures and pressures for these inclusions are 350 °C and 0.2–0.7 kbar. A population of high-density, liquid, CH4-dominant inclusions have also been recorded, mainly in the borehole samples, homogenising between −78 and −99 °C. These consist of pure CH4, trapped between 1.2 and 2.1 kbar and may represent an early CH4-bearing fluid overprinted by the low-density population. The microthermometric and laser Raman data are in agreement with bulk gas data, which have recorded significant concentrations of H2 and higher hydrocarbons up to C6H12 in these samples. These data, combined with published isotopic data for the gases CH4, C2H6, H2, He and Ar indicate that these hydrocarbons have an abiogenic, crustal origin and were generated during postmagmatic, low temperature, alteration reactions of the mineral assemblage. This would suggest that these data favour a model for formation of hydrocarbons through Fischer–Tropsch type reactions involving an early CO2-rich fluid and H2 derived from alteration reactions. This is in contrast to the late-magmatic model suggested for the formation of hydrocarbons in the similar peralkaline intrusion, Ilímaussaq, at temperatures between 400 and 500 °C.  相似文献   

10.
Anders Lindh 《Lithos》1972,5(4):325-343
Phase relations in the system FeO---Fe2O3---TiO2, at temperatures ranging between 300°C and 700°C, have been investigated experimentally with special refference to the reaction Fe3O4 + TiO2 = Fe2O3 + FeTiO3. Pressure was varied between 500 and 2000 bars but its effect was negligible. Magnetite and rutile are the stable assemblage at temperatures above 550 dgC, and hematite and ilmenite are stable for lower temperatures. The equilibrium oxygen fugacity is estimated to be 10−17.5 bars at equilibrium temperature. It is suggested that intermediate hematite-ilmenite solid solutions are inhomogeneous, consisting of ‘domains’ of hematite and ilmenite. The ‘domains’ are too small to be resolved by X-ray diffraction techniques. The top of the solvus curve in the hematite-ilmenite solution corresponds to a temperature of 660°C. Regular solution theory is not applicable to the solid solution.  相似文献   

11.
We have determined cooling rates of orthopyroxene crystals from two Mg-suite lunar samples (gabbronorite 76255 and troctolite 76535) and one terrestrial sample (orthopyroxenite SC-936 from the Stillwater Complex), on the basis of their Fe–Mg ordering states. In addition, a cooling rate of 76255 was determined by modeling the formation of exsolution lamellae in pyroxenes. The M1–M2 site occupancies of the orthopyroxene crystals were determined by single crystal X-ray diffraction and the rate constant for the ordering reaction was used along with calibrations of the equilibrium intracrystalline fractionation of Fe and Mg as a function of temperature to calculate cooling rates. The closure temperatures (TC) of cation ordering are 525 °C for 76255, 500 °C for 76535 and 350 °C for SC-936 corresponding to cooling rates of 4 × 10−2 °C/year at the closure temperature for the lunar samples and 10−6 °C/year for the Stillwater sample. A cooling rate for 76255, determined by simulating the exsolution process, is 1.7 × 10−2 °C/year at a closure temperature for exsolution of 700 °C. The Fe–Mg ordering cooling rate determined for 76535 reflects a complex thermal history superimposed on the initial plutonic provenance established for this sample [McCallum, I.S., Schwartz, J.M., 2001. Lunar Mg suite: thermobarometry and petrogenesis of parental magmas. J. Geophys. Res. 106, 27969–27983]. The preservation of a crystallization age of 4.51 Ga and a metamorphic age of 4.25 Ga for 76535 is consistent with a model in which excavation of this sample from the lower lunar crust took place while the sample was at a temperature above the closure temperatures for the Sm–Nd, U–Pb and Ar–Ar isotopic systems. Temperatures in excess of the isotopic closure temperatures (i.e., >600 °C) in the lower lunar crust were maintained by heat diffusing from concentrations of U- and Th-rich KREEP material at the base of the crust. On the other hand, 76255 formed at a much shallower depth in the lunar crust (2 km) and was well below its isotopic closure temperatures at the time of excavation, most likely during the Serenitatis basin-forming impact event. Both lunar samples were reheated during transport to the surface and deposition in hot ejecta blankets. The reheating was short lived but apparently sufficient to redistribute Fe and Mg in M sites in orthopyroxenes. For the lunar samples, the cooling rates based on Fe–Mg ordering represent final stage cooling within an ejecta blanket.  相似文献   

12.
Marcasite precipitation from hydrothermal solutions   总被引:3,自引:0,他引:3  
Pyrite and marcasite were precipitated by both slow addition of aqueous Fe2+ and SiO32− to an H2S solution and by mixing aqueous Fe2+ and Na2S4 solutions at 75°C. H2S2 or HS2 and H2S4 or HS4 were formed in the S2O32− and Na2S4 experiments, respectively. Marcasite formed at pH < pK1 of the polysulfide species present (for H2S2, pK1 = 5.0; for H2S4, pK1 = 3.8 at 25°C). Marcasite forms when the neutral sulfane is the dominant polysulfide, whereas pyrite forms when mono-or divalent polysulfides are dominant. In natural solutions where H2S2 and HS2 are likely to be the dominant polysulfides, marcasite will form only below pH 5 at all temperatures.

The pH-dependent precipitation of pyrite and marcasite may be caused by electrostatic interactions between polysulfide species and pyrite or marcasite growth surfaces: the protonated ends of H2S2 and HS2 are repelled from pyrite growth sites but not from marcasite growth sites. The negative ions HS2 and S22− are strongly attracted to the positive pyrite growth sites. Masking of 1πg* electrons in the S2 group by the protons makes HS2 and H2S2 isoelectronic with AsS2− and As22−, respectively ( et al., 1981). Thus, the loellingitederivative structure (marcasite) results when both ends of the polysulfide are protonated.

Marcasite occurs abundantly only for conditions below pH 5 and where H2S2 was formed near the site of deposition by either partial oxidation of aqueous H2S by O2 or by the reaction of higher oxidation state sulfur species that are reactive with H2S at the conditions of formation e.g., S2O32− but not SO42−. The temperature of formation of natural marcasite may be as high as 240°C ( and , 1985), but preservation on a multimillion-year scale seems to require post-depositional temperatures of below about 160°C ( , 1973; and , 1985).  相似文献   


13.
In this paper the first fluid-inclusion data are presented from Late Archaean Scourian granulites of the Lewisian complex of mainland northwest Scotland. Pure CO2 or CO2-dominated fluid inclusions are moderately abundant in pristine granulites. These inclusions show homogenization temperatures ranging from − 54 to + 10 °C with a very prominent histogram peak at − 16 to − 32 °C. Isochores corresponding to this main histogram peak agree with P-T estimates for granulite-facies recrystallization during the Badcallian (750–800 °C, 7–8 kbar) as well as with Inverian P-T conditions (550–600 °C, 5 kbar). The maximum densities encountered could correspond to fluids trapped during an early, higher P-T phase of the Badcallian metamorphism (900–1000 °C, 11–12 kbar). Homogenization temperatures substantially higher than the main histogram peak may represent Laxfordian reworking (≤ 500 °C, < 4 kbar). In the pristine granulites, aqueous fluid inclusions are of very subordinate importance and occur only along late secondary healed fractures. In rocks which have been retrograded to amphibolite facies from Inverian and/or Laxfordian shear zones, CO2 inclusions are conspicuously absent; only secondary aqueous inclusions are present, presumably related to post-granulite hydration processes. These data illustrate the importance of CO2-rich fluids for the petrogenesis of Late Archaean granulites, and demonstrate that early fluid inclusions may survive subsequent metamorphic processes as long as no new fluid is introduced into the system.  相似文献   

14.
Status report on stability of K-rich phases at mantle conditions   总被引:1,自引:0,他引:1  
George E. Harlow  Rondi Davies 《Lithos》2004,77(1-4):647-653
Experimental research on K-rich phases and observations from diamond inclusions, UHP metamorphic rocks, and xenoliths provide insights about the hosts for potassium at mantle conditions. K-rich clinopyroxene (Kcpx–KM3+Si2O6) can be an important component in clinopyroxenes at P>4 GPa, dependent upon coexisting K-bearing phases (solid or liquid) but not, apparently, upon temperature. Maximum Kcpx content can reach 25 mol%, with 17 mol% the highest reported in nature. Partitioning (K)D(cpx/liquid) above 7 GPa=0.1–0.2 require ultrapotassic liquids to form highly potassic cpx or critical solid reactions, e.g., between Kspar and Di. Phlogopite can be stable to about 8 GPa at 1250 °C where either amphibole or liquid forms. When fluorine is present, it generally increases in Phl upon increasing P (and probably T) to about 6 GPa, but reactions forming amphibole and/or KMgF3 limit F content between 6 and 8 GPa. The perovskite KMgF3 is stable up to 10 GPa and 1400 °C as subsolidus breakdown products of phlogopite upon increasing P. (M4)K-substituted potassic richterite (ideally K(KCa)Mg5Si8O22(OH,F)2) is produced in K-rich peridotites above 6 GPa and in Di+Phl from 6 to 13 GPa. K content of amphibole is positively correlated with P; Al and F content decrease with P. In the system 1Kspar+1H2O K-cymrite (hydrous hexasanidine–KAlSi3O8·nH2O–Kcym) is stable from 2.5 GPa at 400 to 1200 °C and 9 GPa; Kcym can be a supersolidus phase. Formation of Kcym is sensitive to water content, not forming within experiments with H2O2O>Kspar. Phase X, a potassium di-magnesium acid disilicate ((K1−xn)2(Mg1−nMn3+)2Si2O7H2x), forms in mafic compositions at T=1150–1400 °C and P=9–17 GPa and is a potential host for K and H2O at mantle conditions with a low-T geotherm or in subducting slabs. The composition of phase-X is not fixed but actually represents a solid solution in the stoichiometries □2Mg2Si2O7H2–(K□)Mg2Si2O7H–K2Mg2Si2O7 (□=vacancy), apparently stable only near the central composition. K-hollandite, KAlSi3O8, is possibly the most important K-rich phase at very high pressure, as it appears to be stable to conditions near the core–mantle boundary, 95 GPa and 2300 °C. Other K-rich phases are considered.  相似文献   

15.
The gas and redox chemistry of 100–300 °C geothermal fluids in Iceland has been studied as a function of fluid temperature and fluid composition. The partial pressures of CO2 in dilute (mCl<500 ppm) and saline (mCl>500 ppm) geothermal fluids above 200 °C are controlled by the mineral buffer clinozoisite+prehnite+calcite+quartz. Two buffers are considered to control the H2S and H2 partial pressures above 200 °C depending on fluid salinity, epidote+prehnite+pyrite+pyrrhotite for dilute fluids and pyrite+prehnite+quartz+magnetite+anhydrite+clinozoisite+quartz for saline fluids. Below 200 °C, the partial pressures of CO2, H2S and H2 also seem to be buffered but other minerals must be involved. Zeolites are expected to replace prehnite and epidote. Redox potential calculated on the assumption of equilibrium for the H+/H2 redox couple decreases in dilute geothermal fluids with increasing temperature from about −0.5 V at 100 °C to −0.8 V at 300 °C, whereas saline geothermal fluids at 250 °C display a redox potential of about −0.45 V. A systematic discrepancy between redox couples of about 0.05–0.09 V is observed in the redox potential for the dilute geothermal fluids, whereas redox potentials agree within 0.02–0.04 V for saline geothermal waters. The discrepancies in the calculated redox potential for dilute geothermal fluids are thought to be due to a general lack of equilibrium between CH4, CO2 and H2 and between H2S, SO4 and H2. It is, accordingly, concluded that an overall equilibrium among redox species has not been reached for dilute geothermal fluids whereas it appears to be more closely approached for the saline geothermal fluids. The latter conclusion is based on limited database and should be treated with care. Since the various redox components are not in an overall equilibrium in geothermal fluids in Iceland these fluids cannot be characterised by a unique hydrogen fugacity, oxygen fugacity or redox potential at a given temperature and pressure.  相似文献   

16.
The Berriedale Limestone formed at about 80°S paleolatitude and contains many glacial dropstones. It formed during a period of major Gondwana deglaciation.

The Berriedale Limestone contains mostly bryozoans, brachiopods and bivalves, with some intraclasts and rare pellets. The faunal diversity is low and the fauna are similar to the modern cold-water foramol faunal assemblage. Micrite, microspar and spar occur as equant to well developed rhombs of calcite. The coarse spar cements are bored and are ruptured by dropstones, indicating submarine origin of low-Mg calcite at water-temperatures of around 3°C. The mixing zone cementation was preceded by erosion of early formed crystals. The eroded crystals occur as inclusions in mixing zone cements.

The fauna are characterized by heavy δ13C and light δ18O. The whole-rock field of δ18O-δ13C falls at the edge of “Normal Marine Limestone” and deviates to lighter δ18O values (down to −16.7‰ PDB). Lightest δ18O values ( −22‰ PDB) of fresh-water sparry calcite cement are similar to those in the Early Permian continental tillites, suggesting that the Permian sea was diluted by isotopically light melt waters. Micrite δ18O values (−9.2 to −12.6‰ PDB) are within the range of whole-rock values. The δ18O values of calcite in shales are lighter than limestone values.

The δ18O values of the fauna give an unrealistic range of sea-water temperatures because the fauna have equilibrated with variable amounts of melt waters. However, calculated original δ18O values of the fauna indicate temperatures < 4°C. The heaviest δ18O of fauna gives cold temperatures of 9°C (with δw −2.8‰) and −3°C (with δw −6‰). The lightest values of sparry calcite cements (−22‰ PDB) indicate that the limestone reacted with cold melt waters.

The δ18O of Permian sea is estimated to be about +1.2‰ and was diluted by melt waters as light as −27‰ SMOW.  相似文献   


17.
Maximum homogenization temperatures of fluid inclusions (Thmax) in halite (laboratory-grown crystals and modern samples, Death Valley, CA) match maximum brine temperatures during halite precipitation. Maximum brine temperatures during halite precipitation in Death Valley, late April, 1993 (34.4°C) agree with Thmax (34°C) and correlate well with average maximum air temperatures in April (31.3°C) and May (37.6°C). Thmax may be used for paleoclimate interpretations based on the close relationship between saline lake temperatures and average air temperatures from modern settings. Lower homogenization temperatures, demonstrably below the temperatures at which halite grew, are interpreted to reflect collapse of some fluid inclusion walls due to the pressure difference between the inside and outside of inclusions. By only using Thmax, the problems of anomalously low homogenization temperatures due to possible collapse of fluid inclusions are avoided. Halite samples from 30 stratigraphic intervals, 90 to 0 m (100 to 0 ka), Core DV93-1, Death Valley, CA, were used to measure homogenization temperatures of fluid inclusions. Virtually all homogenization temperatures from Core DV93-1 are below the modern Thmax of 34°C (halite precipitation late April, 1993). Lacustrine halites, deposited in a perennial saline lake 35 to 10 ka, have Thmax between 19°C and 30°C, which suggests brine temperatures approximately 4°C to 15°C below modern late April values. Ephemeral saline lake halites precipitated 60 to 35 ka have Thmax between 23°C and 28°C, 6 to 11°C below modern values. The highest Thmax value in the 100 ka record (up to 35°C) is from a halite sample formed approximately 100 ka in a climate regime somewhat colder than the modern.  相似文献   

18.
Carbonic inclusions   总被引:17,自引:0,他引:17  
The paper gives an overview of the phase relations in carbonic fluid inclusions with pure, binary and ternary mixtures of the system CO2–CH4–N2, compositions, which are frequently found in geological materials. Phase transitions involving liquid, gas and solid phases in the temperature range between −192°C and 31°C are discussed and presented in phase diagrams (PT, TX and VX projections). These diagrams can be applied for the interpretation of microthermometry data in order to determine fluid composition and molar volume (or density).  相似文献   

19.
Janos L. Urai 《Tectonophysics》1985,120(3-4):285-317
Cylindrical samples of polycrystalline carnallite (KMgCl3, 6H2O) were deformed in a triaxial apparatus at 60°C, at confining pressures between 0.1 and 31 MPa and at strain rates between 10−4 and 10−8 s−1. In a number of cases, small amounts of saturated carnallite brine were added. Samples without added brine deform by intracrystalline slip, mechanical twinning, cracking, and by frictional sliding on crack surfaces. Stress-strain curves of these samples are strongly dependent on confining pressure. Addition of brine has a dramatic effect on both microstructural development and mechanical properties. Grain-boundary migration is strongly enhanced. At lower strain rates, additional intracrystalline effects start to appear, together with the onset of solution transfer. Rapid compaction in samples deformed with added brine causes high fluid pressures to develop. At higher strain rates addition of brine results in a decrease of the flow stress by a factor of two. This weakening will increase even further at strain rates below about 10−9 s−1, when solution transfer becomes rate controlling. It is argued that deformation of carnallite in nature is adequately described by the flow law found for samples deformed with added brine.  相似文献   

20.
Paolo Ferla  Carmelina Meli   《Lithos》2007,99(3-4):266-288
Tourmalinite and tourmaline-rich rocks associated with Fe-carbonate–graphite phyllite, strata-bound polymetallic sulphide deposits, metabasite and marble were studied, for information on the mechanism of tourmaline formation in the pre-Hercynian low-grade metamorphic sequence of the Mandanici Unit in the Peloritani Mountains of Sicily, southern Italy. The major and trace element compositions of the tourmaline rocks suggest the existence of a sedimentary protolith with pre-metamorphic black shale and bedded chert. Boron was interpreted to be accumulated in a restricted sedimentary basin, between platform carbonate formations, with abundant organic matter and Fe–Al–Ti-rich laterite–bauxite soil-derived clastic supply, under a continental volcano-tectonic extensional regime accompanied by a local convective hydrothermal system along faults. Petrographic, crystal–chemical and δ11B isotopic data are compatible with a model of marine sediment dewatering at temperatures below 200 °C, which caused the removal of boron from clay. Metamorphism led to the development of tourmaline in an Al–Ti-rich environment, in equilibrium with other minerals such as ilmenite, albite and muscovite. The upper temperature of metamorphism (almost 375 °C), estimated on the basis of δ11B, fits geothermometric results from Δ13Ccarbonate–graphite on associated rocks. The estimated value of δ11B in the tourmalinite protolith, − 7.5‰ , is also compatible with continental-derived Al-rich sediments.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号