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1.
Boom Clay is studied as a potential host formation for the disposal of high-and intermediate level long-lived radioactive waste in Belgium. In such a geological repository, generation of gases (mainly H2 from anaerobic corrosion) will be unavoidable. In order to make a good evaluation of the balance between gas generation vs. gas dissipation for a particular waste form and/or disposal concept, good estimates for gas diffusion coefficients of dissolved gases are essential. In order to obtain an accurate diffusion coefficient for dissolved hydrogen in saturated Boom Clay, diffusion experiments were performed with a recently developed through-diffusion set-up for dissolved gases. Due to microbial activity in the test set-up, conversion of hydrogen into methane was observed within several experiments. A complex sterilisation procedure was therefore developed in order to eliminate microbiological disturbances. Only by a combination of heat sterilisation, gamma irradiation and the use of a microbial inhibitor, reliable, reproducible and accurate H2(g) diffusion coefficients (measured at 21 °C) for samples oriented parallel (Deff = 7.25 × 10−10 m2/s and Deff = 5.51 × 10−10 m2/s) and perpendicular (Deff = 2.64 × 10−10 m2/s) to the bedding plane were obtained. 相似文献
2.
Pure-iron end-member hibbingite, Fe2(OH)3Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe2(OH)3Cl(s), the pure-iron end-member of hibbingite (FeII, Mg)2(OH)3Cl(s), and Fe(OH)2(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe2(OH)3Cl(s) + 3H+ ? 3 H2O + 2 Fe2+ + Cl?,the solubility constant of Fe2(OH)3Cl(s) at infinite dilution and 25 °C has been found to be log10 K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)2(s) + 2H+ ? 2 H2O + Fe2+,the solubility constant of Fe(OH)2 at infinite dilution and 25 °C has been found to be log10 K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe2(OH)3Cl(s) and Fe(OH)2(s), the Na+–Fe2+ pair Pitzer interaction parameter θNa+/Fe2+ has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)2(s) to Fe2(OH)3Cl(s). Additionally, when Fe2(OH)3Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations. 相似文献
3.
《Comptes Rendus Geoscience》2018,350(8):476-486
In this study, the model H(i) = 109.6103 + C1 × F1(i) + C2 × F2(i) + … + C33 × F33(i) obtained from depth modelling based on 33 recent benthic foraminifer species distribution, has been applied to the fossil benthic foraminifers from the borehole GDEC-4-2 drilled at a water depth of 491 m, in the East-Corsica basin, covering the last 550,000 years. The obtained variations of the paleo-depths show a medium correlation with the oscillations of the relative sea level and also with the fluctuations of the oxygen isotopic ratio (δ18O G. bulloides and δ18O C. pachyderma–C. wuellerstorfi). This newly developed transfer function is accompanied by an error margin of ± 86 m, suggesting that this model will probably be more suitable for a time scale of the order of a million years where sea level variations are recorded with larger amplitudes. Without considering these problems related to amplitudes, it also turns out that the “eustatic” signal of the microfauna is accompanied by a “trophic” signal, which should not to be neglected, especially at a millennial scale time resolution. Thus, the application of this method would require taking into account the bottom trophic effects strongly controlling the distribution of benthic foraminifer assemblages. 相似文献
4.
Pristine diorite drill cores, obtained from the Äspö Hard Rock Laboratory (HRL, Sweden), were used to study the retention properties of fresh, anoxic crystalline rock material towards the redox-sensitive uranium. Batch sorption experiments and spectroscopic methods were applied for this study. The impact of various parameters, such as solid-to-liquid ratio (2–200 g/L), grain size (0.063–0.2 mm, 0.5–1 mm, 1–2 mm), temperature (room temperature and 10 °C), contact time (5–108 days), initial U(VI) concentration (3 × 10−9 to 6 × 10−5 M), and background electrolyte (synthetic Äspö groundwater and 0.1 M NaClO4) on the U(VI) sorption onto anoxic diorite was studied under anoxic conditions (N2). Comparatively, U(VI) sorption onto oxidized diorite material was studied under ambient atmosphere (pCO2 = 10−3.5 atm). Conventional distribution coefficients, Kd, and surface area normalized distribution coefficients, Ka, were determined. The Kd value for the U(VI) sorption onto anoxic diorite in synthetic Äspö groundwater under anoxic conditions by investigating the sorption isotherm amounts to 3.8 ± 0.6 L/kg which corresponds to Ka = 0.0030 ± 0.0005 cm (grain size 1–2 mm). This indicates a weak U sorption onto diorite which can be attributed to the occurrence of the neutral complex Ca2UO2(CO3)3(aq) in solution. This complex was verified as predominating U species in synthetic Äspö groundwater by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Compared to U sorption at room temperature under anoxic conditions, U sorption is further reduced at decreased temperature (10 °C) and under ambient atmosphere. The U species in aqueous solution as well as sorbed on diorite were studied by in situ time-resolved attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. A predominant sorbing species containing a UO2(CO3)34− moiety was identified. The extent of U sorption onto diorite was found to depend more on the low sorption affinity of the Ca2UO2(CO3)3(aq) complex than on reduction processes of uranium. 相似文献
5.
《Applied Geochemistry》2005,20(5):961-972
The temperature dependence of the self-diffusion of HTO, 22Na+ and 36Cl− in Opalinus Clay (OPA) was studied using a through-diffusion technique, in which the temperature was gradually increased in the steady state phase of the diffusion. The measurements were done on samples from two different geological locations. The dependence of the effective diffusion coefficient on temperature was found to be of an Arrhenius type in the temperature range between 0 and 70 °C. A slight difference between the two locations could be observed. The average value of the activation energy of the self-diffusion of HTO in OPA was 21.1 ± 1.6 kJ mol−1, and 21.0 ± 3.5 and 19.4 ± 1.5 kJ mol−1 for 22Na+ and 36Cl−, respectively. The measured values for HTO are slightly higher than the values found for the bulk liquid water (HTO: 18.8 ± 0.4 kJ mol−1). This indicates that the structure of the confined water in OPA might be slightly different from that of bulk liquid water. Also for Na+ and Cl−, slightly higher values than in bulk liquid water (Na+: 18.4 kJ mol−1; Cl−: 17.4 kJ mol−1) were observed.The Stokes–Einstein relationship, based on the temperature dependency of the viscosity of bulk water, could not be used to describe the temperature dependence of the diffusion of HTO in OPA. This additionally indicates the slightly different structure of the pore water in OPA. 相似文献
6.
7.
A series of methane (CH4) adsorption experiments on bulk organic rich shales and their isolated kerogens were conducted at 35 °C, 50 °C and 65 °C and CH4 pressure of up to 15 MPa under dry conditions. Samples from the Eocene Green River Formation, Devonian–Mississippian Woodford Shale and Upper Cretaceous Cameo coal were studied to examine how differences in organic matter type affect natural gas adsorption. Vitrinite reflectance values of these samples ranged from 0.56–0.58 %Ro. In addition, thermal maturity effects were determined on three Mississippian Barnett Shale samples with measured vitrinite reflectance values of 0.58, 0.81 and 2.01 %Ro.For all bulk and isolated kerogen samples, the total amount of methane adsorbed was directly proportional to the total organic carbon (TOC) content of the sample and the average maximum amount of gas sorption was 1.36 mmol of methane per gram of TOC. These results indicate that sorption on organic matter plays a critical role in shale-gas storage. Under the experimental conditions, differences in thermal maturity showed no significant effect on the total amount of gas sorbed. Experimental sorption isotherms could be fitted with good accuracy by the Langmuir function by adjusting the Langmuir pressure (PL) and maximum sorption capacity (Γmax). The lowest maturity sample (%Ro = 0.56) displayed a Langmuir pressure (PL) of 5.15 MPa, significantly larger than the 2.33 MPa observed for the highest maturity (%Ro > 2.01) sample at 50 °C.The value of the Langmuir pressure (PL) changes with kerogen type in the following sequence: type I > type II > type III. The thermodynamic parameters of CH4 adsorption on organic rich shales were determined based on the experimental CH4 isotherms. For the adsorption of CH4 on organic rich shales and their isolated kerogen, the heat of adsorption (q) and the standard entropy (Δs0) range from 7.3–28.0 kJ/mol and from −36.2 to −92.2 J/mol/K, respectively. 相似文献
8.
Porphyry Cu deposits occurred in the southern West Junggar of Xinjiang, NW China and are represented by the Baogutu and newly-discovered Jiamantieliek porphyry Cu deposits. Petrographical and geochemical studies show that both Jiamantieliek and Baogutu ore-bearing intrusions comprise main-stage diorite stock and minor late-stage diorite porphyry dikes and are the calc-alkaline intermediate intrusions. Based on U–Pb zircon SHRIMP analyses, the Jiamantieliek intrusion formed in 313 ± 4 Ma and 310 ± 5 Ma, while, based on U–Pb zircon SIMS analyses, the Baogutu intrusion formed in 313 ± 2 Ma and 312 ± 2 Ma. Rocks in the Jiamantieliek intrusion are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) with negative Nb anomaly. Their isotopic compositions (εNd(t) = +1.6 to +3.4, (87Sr/86Sr)i = 0.70369–0.70401, (207Pb/204Pb)i = 15.31–5.41) suggest a mixing origin from depleted to enriched mantle sources. In the Baogutu intrusion, the rocks are similar to those of the Jiamantieliek intrusion. Their Sr-Nd-Pb isotopic composition (εNd(t) = +4.4 to +6.0, (87Sr/86Sr)i = 0.70368–0.70385, (207Pb/204Pb)i = 15.34–5.42) shows a more depleted mantle source. These features suggest generation in an island arc. The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. A larger contribution of calc-alkaline magma would be required to generate the Jiamantieliek intrusion, which may reflect the development of magma arc maturation towards the western section of the southern West Junggar. 相似文献
9.
Silvio Mollo Mario Gaeta Carmela Freda Tommaso Di Rocco Valeria Misiti Piergiorgio Scarlato 《Lithos》2010,114(3-4):503-514
The main effect of magma–carbonate interaction on magma differentiation is the formation of a silica-undersaturated, alkali-rich residual melt. Such a desilication process was explained as the progressive dissolution of CaCO3 in melt by consumption of SiO2 and MgO to form diopside sensu stricto. Magma chambers emplaced in carbonate substrata, however, are generally associated with magmatic skarns containing clinopyroxene with a high Ca-Tschermak activity in their paragenesis. Data are presented from magma–carbonate interaction experiments, demonstrating that carbonate assimilation is a complex process involving more components than so far assumed. Experimental results show that, during carbonate assimilation, a diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution is formed and that Ca-Tschermak/diopside and hedenbergite/diopside ratios increase as a function of the progressive carbonate assimilation. Accordingly, carbonate assimilation reaction should be written as follows, taking into account all the involved magmatic components:CaCO3solid + SiO2melt + MgOmelt + FeOmelt + Al2O3melt → (Di–Hd–CaTs)sssolid + CO2fluidThe texture of experimental products demonstrates that carbonate assimilation produces three-phases (solid, melt, and fluid) whose main products are: i) diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution; ii) silica-undersaturated CaO-rich melt; and iii) C–O–H fluid phase. The silica undersaturation of the melt and, more importantly, the occurrence of a CO2-rich fluid phase, must be taken into account as they significantly affect partition coefficients and the redox state of carbonated systems, respectively. 相似文献
10.
The relationship among subducted oxidized oceanic crust and oxidation state of the subarc mantle, and arc magmas is one of the important aspects to evaluate convergent margin tectonics. However details of the oxidized mass transferred from buried oceanic crust to the overlying subarc mantle wedge remain obscure. Here we investigate the Songduo eclogites from south Tibet formed by the subduction of the paleo-Tethyan oceanic crust, and identify an abrupt decrease in pyrope and increase in almandine contents from the mantle to rim of garnet grains. This is coupled with a decrease in the Fe3 + content of epidote and Fe3 +/(Fe2 ++ Fe3 +) ratios from garnet core to rim domains, as well as speciation of calcite, a new mineral phase, in the rock matrix. Minor sulfates occur only as inclusions in garnet core domains, whereas sulfides are confined to the matrix as an accessory mineral phase. Aegirine augite occurs as relics or inclusions in garnet and omphacite. These features clearly suggest that oxidized components, Fe3 + and S6 +, were reduced as Fe2 + and S2 −, respectively, at the subduction zone. Thermodynamic modeling in the P–T-log10fO2 space using updated Perplex_X programs further revealed that the Songduo eclogites experienced oxygen fugacity variation of up to 8 log10 units, with decreasing pressure. Petrological observations further suggest that the strong redox processes took place, after breaking of garnet, during the initial exhumation of the eclogites. CO2 and minor sulfur are subsequently transferred from the cold oceanic subduction zone to the overlying mantle wedge, partially released by arc volcanoes to atmosphere. Our study presents a case of C and S recycling between the Earth's exterior and interior. 相似文献
11.
Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10?6–1 × 10?4 M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO3), and pCO2 (0–5%) in the presence or absence of 1 × 10?2–1 × 10?4 M citric acid, 1 × 10?2–1 × 10?4 M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10?6–1 × 10?4 M U(VI) in 0.01 M NaNO3 were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10?5 and 1 × 10?4 M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10?6 M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ～3 to 7 and decreases from pH ～7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO2 greatly diminishes U(VI) sorption between pH ～5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH. 相似文献
12.
Orogenic gold mineralization in the Amalia greenstone belt is hosted by oxide facies banded iron-formation (BIF). Hydrothermal alteration of the BIF layers is characterized by chloritization, carbonatization, hematization and pyritization, and quartz-carbonate veins that cut across the layers. The alteration mineral assemblages consist of ankerite-ferroan dolomite minerals, siderite, chlorite, hematite, pyrite and subordinate amounts of arsenopyrite and chalcopyrite. Information on the physico-chemical properties of the ore-forming fluids and ambient conditions that promoted gold mineralization at Amalia were deduced from sulfur, oxygen and carbon isotopic ratios, and fluid inclusions from quartz-carbonate samples associated with the gold mineralization.Microthermometric and laser Raman analyses indicated that the ore-forming fluid was composed of low salinity H2O-CO2 composition (~3 wt% NaCl equiv.). The combination of microthermometric data and arsenopyrite-pyrite geothermometry suggest that quartz-carbonate vein formation, gold mineralization and associated alteration of the proximal BIF wall rock occurred at temperature-pressure conditions of 300 ± 30 °C and ∼2 kbar. Thermodynamic calculations at 300 °C suggest an increase in fO2 (10−32–10−30 bars) and corresponding decrease in total sulfur concentration (0.002–0.001 m) that overlapped the pyrite-hematite-magnetite boundary during gold mineralization. Although hematite in the alteration assemblage indicate oxidizing conditions at the deposit site, the calculated low fO2 values are consistent with previously determined high Fe/Fe + Mg ratios (>0.7) in associated chlorite, absence of sulfates and restricted positive δ34S values in associated pyrite. Based on the fluid composition, metal association and physico-chemical conditions reported in the current study, it is confirmed that gold in the Amalia fluid was transported as reduced bisulfide complexes (e.g., Au(HS)2−). At Amalia, gold deposition was most likely a combined effect of increase in fO2 corresponding to the magnetite-hematite buffer, and reduction in total sulfur contents due to sulfide precipitation during progressive fluid-rock interaction.The epigenetic features coupled with the isotopic compositions of the ore-forming fluid (δ34SΣS = +1.8 to +2.3‰, δ18OH2O = +6.6 to +7.9‰, and δ13CΣC = −6.0 to −7.7‰ at 300–330 °C) are consistent with an externally deep-sourced fluid of igneous signature or/and prograde metamorphism of mantle-derived rocks. 相似文献
13.
The polymetallic Mykonos vein system in the Cyclades, Greece, consists of 15 tension-gashes filled with barite, quartz, pyrite, sphalerite, chalcopyrite and galena in ca. 13.5 Ma, I-type, Mykonos monzogranite. Zones of silica and chlorite–muscovite alteration are associated with the veins and overprint pervasive silicification, phyllic and argillic alteration that affected large parts of the monzogranite. The mineralization cements breccias and consists of an early barite–silica–pyrite–sphalerite–chalcopyrite assemblage followed by later argentiferous galena. A combination of fluid inclusion and stable isotope data suggests that the barite and associated mineralization were deposited from fluids containing 2 to 17 wt.% NaCl equivalent, at temperatures of ~ 225° to 370 °C, under a hydrostatic pressure of ≤ 100 bars. The mineralizing fluids boiled and were saturated in H2S and SO2.Calculated δ18OH2O and δDH2O, initial 87Sr/86Sr isotope compositions and the trace and REEs elements contents are consistent with a model in which the mineralizing fluids were derived during alteration of the Mykonos intrusion and subsequently mixed with Miocene seawater. Heterogeneities in the calculated δ34SSO4− 2 and δ34SH2S compositions of the ore fluids indicate two distinct sources for sulfur, namely of magmatic and seawater origin, and precipitation due to reduction of the SO4− 2 during fluid mixing. The physicochemical conditions of the fluids were pH = 5.0 to 6.2, logfS2 = − 13.8 to − 12.5, logfO2 = − 31.9 to − 30.9, logfH2S(g) = − 1.9 to − 1.7, logfTe2 = − 7.9 and logα(SO4− 2(aq)/H2S(aq)) = + 2.6 to + 5.5. We propose that retrograde mesothermal hydrothermal alteration of the Mykonos monzogranite released barium and silica from the alkali feldspars. Barite was precipitated due to mixing of SO4− 2-rich Miocene seawater with the ascending Ba-rich magmatic fluid venting upwards in the pluton. 相似文献
14.
This is the first report of osumilite occurring as fine isolated inclusions within garnet porphyroblasts, as observed in garnet–sillimanite gneiss from Rundvågshetta, Lützow-Holm Complex, East Antarctica. The osumilite is characterized by high Si content (10.60 and 10.95 atoms based on 30 oxygens per formula unit), low Al content (2.99 and 3.82), a high content of M site-occupying cations (2.51 and 3.03), and high XMg values (about 0.81). We also report a spinel + quartz association found as inclusions within garnet porphyroblasts. Spinel grains, which are in direct contact with quartz and are spatially associated with sillimanite, show extremely high Zn contents (XZnSpl = 0.33 ? 0.46) and high XMg values (0.45–0.54). The garnet is rimmed by sillimanite, K-feldspar, plagioclase, and quartz. Biotite and cordierite are found only as inclusions within garnet porphyroblasts, where biotite coexists with spinel–quartz or with rutile. Porphyroblastic garnet contains rutile needles and has low XMg values (about 0.36). The sillimanite contains a high Fe content (about 1.2 wt.% Fe2O3).The occurrence of osumilite and spinel + quartz indicates a clockwise pressure–temperature path of ultrahigh-temperature metamorphism, involving the following events: (1) the Rundvågshetta granulites suffered prograde metamorphism within the kyanite and sapphirine + quartz fields; (2) subsequent retrograde metamorphism, involving near-isothermal decompression, occurred in the orthopyroxene + sillimanite + quartz field; (3) the granulites passed through the garnet + cordierite + sillimanite + quartz field during decreasing temperature; (4) the granulites entered the osumilite stability field at around 8 kbar and 950 °C; and (5) the granulites retain a final record of retrograde metamorphism within the biotite + sillimanite + K-feldspar and quartz field at 6.1 kbar and about 830 °C. 相似文献
15.
CO2, CH4, and N2 adsorption and gas-induced swelling were quantified for block Blind Canyon, Pittsburgh #8 and Pocahontas Argonne Premium coals that were dried and structurally relaxed at 75 °C in vacuum. Strain measurements were made perpendicular and parallel to the bedding plane on ~ 7 × 7 × 7 mm3 coal blocks and gravimetric sorption measurements were obtained simultaneously on companion coal blocks exposed to the same gaseous environment. The adsorption amount and strain were determined after equilibration at P ≤ 1.8 MPa. There is a strong non-linear correlation between strain and the quantity of gas adsorbed and the results for all gases and coals studied follow a common pattern. The dependence of the coal matrix shrinkage/swelling coefficient (Cgc) on the type and quantity of gas adsorbed is seen by plotting the ratio between the strain and the adsorbate concentration against the adsorbate concentration. In general, Cgc increases with increasing adsorbate concentration over the range of ~ 0.1 to 1.4 mmol/g. Results from the dried block coals are compared to CO2 experiments using native coals with an inherent level of moisture as received. The amount of CO2 adsorbed using native coals (assuming no displacement of H2O by CO2) is significantly less than the dried coals. The gas-induced strain (S) and adsorption amount (M) were measured as a function of time following step changes in CO2, CH4, and N2 pressure from vacuum to 1.8 MPa. An empirical diffusion equation was applied to the kinetic data to obtain the exponent (n) for time dependence for each experiment. The data for all coals were pooled and the exponent (n) evaluated using an ANOVA statistical analysis method. Values for (n) near 0.5 were found to be independent on the coal, the gas or type of measurement (e.g., parallel strain, perpendicular strain, and gas uptake). These data support the use of a Fickian diffusion model framework for kinetic analysis. The kinetic constant k was determined using a unipore diffusion model for each experiment and the data were pooled for ANOVA analysis. For dry coal, statistically significant differences for k were found for the gases (CO2 > N2 > CH4) and coals (Pocahontas >Blind Canyon > Pittsburgh #8) but not for the method of the kinetic measurement (e.g., strain or gas uptake). For Blind Canyon and Pittsburgh #8 coal, the rate of CO2 adsorption and gas-induced strain for dry coal was significantly greater than that of the corresponding native coal. For Pocahontas coal the rates of CO2 adsorption and gas-induced strain for dry and native coal were indistinguishable and may be related to its low native moisture and minimal amount of created porosity upon drying. 相似文献
16.
The Shangdan suture zone (SSZ) is the main collisional boundary between the North China Craton and the South China Craton, along which discontinuous Paleozoic ophiolites and subduction–accretion related volcanic arc assemblages occur. Here we report the petrology, geochemistry, geochronology and phase equilibria modeling of garnet amphibolite from the Songshugou ophiolite which is one of the largest ophiolite outcrops in the northern side of the SSZ. From petrological studies, we identify: (1) prograde stage, defined by garnet + clinopyroxene + calcic amphibole + ilmenite + rutile + epidote + plagioclase + quartz; (2) peak stage with garnet + clinopyroxene + ilmenite + rutile + quartz; and (3) retrograde stage with amphibole + plagioclase + titanite + ilmenite. Our pseudosection analysis defines stability of the peak assemblage at 750–850 °C, 15–19 kbar and traces a clockwise P–T path in the system Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCFMASHTO), suggesting high pressure (HP) metamorphism. Subsequently, the rocks experienced rapid decompression and cooling. LA-ICP-MS U-Pb analyses of zircons from the garnet amphibolite yield a weighted mean 206Pb/238U age of 515 ± 12 Ma. This Early Paleozoic metamorphic age represents the emplacement time of the Songshugou ophiolite, and suggests that the HP metamorphism is possibly related to the northward deep subduction of the Shangdan oceanic crust in Early Paleozoic. 相似文献
17.
《Comptes Rendus Geoscience》2007,339(14-15):872-884
Now extinct, short-lived radioactive nuclides, such as 7Be (T1/2 = 53 days), 10Be (T1/2 = 1.5 Ma), 26Al (T1/2 = 0.74 Ma), 36Cl (T1/2 = 0.3 Ma), 41Ca (T1/2 = 0.1 Ma), 53Mn (T1/2 = 3.7 Ma) and 60Fe (T1/2 = 1.5 Ma), were present in the protosolar nebula when the various components of meteorites formed. The presence of these radioactive isotopes requires a ‘last-minute’ origin, either nucleosynthesis in a massive star dying close in space and time to the nascent solar system or production by local irradiation of part of the protosolar disk by high-energy solar cosmic rays. In this review, we list: (i) the different observations indicating the existence of multiple origins for short-lived radioactive nuclides, namely 7Be, 10Be and 36Cl for irradiation scenario and 60Fe for injection scenario; (ii) the constraints that exist on their distribution (homogeneous or heterogeneous) in the accretion disk; (iii) the constraints they brought on the timescales of nebular processes (from Ca–Al-rich inclusions to chondrules) and of the accretion and differentiation of planetesimals. 相似文献
18.
The Xiadong Alaskan-type complex shares much in common with typical Alaskan-type complexes worldwide, while showing some unique features in terms of mineral compositions. Olivine from the Xiadong dunites is characterized by extremely high Fo component of 91.7–96.7 and anomalously negative correlation of Fo with NiO, while chromite is featured by high 100 × Fe3+/(Fe3+ + Cr + Al) (>70), high 100 × Fe2+/(Fe2+ + Mg) (>70), high 100 × Cr/(Cr + Al) (>90), low MnO (<0.6 wt%) and TiO2 contents (<0.5 wt%). To investigate these particular features, we conducted petrographic observation and mineral composition analyses for the Xiadong dunite. A number of Fe and/or Ni sulfides and alloys occurring as inclusions in olivine and chromite indicate that base metal mineral segregation took place prior to crystallization of olivine and chromite and probably induced Fe and Ni depletions in olivine. The FeO and MgO variations in profile analyses from chromite to adjacent olivine are compatible with Fe-Mg exchange. The diffusion mechanism of Fe from olivine to chromite and Mg from chromite to olivine may have elevated both Fo of olivine and 100 × Fe2+/(Mg + Fe2+) ratio of chromite and further enhanced the decoupling of Fo and NiO in olivine. We thus suggest that base metal mineral segregation and Fe-Mg exchange play important roles in the extreme compositions of the Xiadong dunite. The Ni depletion of olivine and degree of Fe-Mg exchange between olivine and chromite may be used as indicators of mineralization in mafic-ultramafic intrusions. 相似文献
19.
The interaction of groundwater with cement in a geological disposal facility (GDF) for intermediate level radioactive waste will produce a high pH leachate plume. Such a plume may alter the physical and chemical properties of the GDF host rock. However, the geochemical and mineralogical processes which may occur in such systems over timescales relevant for geological disposal remain unclear. This study has extended the timescale for laboratory experiments and shown that, after 15 years two distinct phases of reaction may occur during alteration of a dolomite-rich rock at high pH. In these experiments the dissolution of primary silicate minerals and the formation of secondary calcium silicate hydrate (C–S–H) phases containing varying amounts of aluminium and potassium (C–(A)–(K)–S–H) during the early stages of reaction (up to 15 months) have been superseded as the systems have evolved. After 15 years significant dedolomitisation (MgCa(CO3)2 + 2OH− → Mg(OH)2 + CaCO3 + CO32−(aq)) has led to the formation of magnesium silicates, such as saponite and talc, containing variable amounts of aluminium and potassium (Mg–(Al)–(K)–silicates), and calcite at the expense of the early-formed C–(A)–(K)–S–H phases. This occured in high pH solutions representative of two different periods of cement leachate evolution with little difference in the alteration processes in either a KOH and NaOH or a Ca(OH)2 dominated solution but a greater extent of alteration in the higher pH KOH/NaOH leachate. The high pH alteration of the rock over 15 years also increased the rock’s sorption capacity for U(VI). The results of this study provide a detailed insight into the longer term reactions occurring during the interaction of cement leachate and dolomite-rich rock in the geosphere. These processes have the potential to impact on radionuclide transport from a geodisposal facility and are therefore important in underpinning any safety case for geological disposal. 相似文献
20.
Lukáš Krmíček Jan Cempírek Aleš Havlín Antonín Přichystal Stanislav Houzar Michaela Krmíčková Petr Gadas 《Lithos》2011,121(1-4):74-86
A peralkaline, ultrapotassic dyke found at ?ebkovice (T?ebí? district, western Moravia) is a mineralogically extreme member of a dyke swarm occurring along the south-eastern border of the Moldanubian Region of the Bohemian Massif. The dyke shows a simple zoning, with a very fine-grained marginal zone grading into a medium-grained central zone. It has a primary mineral assemblage of microcline and potassic amphiboles, with accessory apatite and altered phlogopite. The microcline exhibits an unusual red luminescence colour and pronounced substitution of Fe3+ for Al, with measured contents of Fe2O3 up to 8.5 wt.% (0.31 apfu Fe3+). Amphiboles have very high K (up to 0.99 apfu) and Si contents; their compositions follow an alkaline fractionation trend from potassic-richterite to potassic-magnesio-arfvedsonite, characterized by an increase of Na/K and a decrease of Ca, Mg, Fe2+ and Ti via heterovalent substitutions [B]Ca + [C](Mg,Fe2+) → [B]Na + [C]Fe3+ and Ti + Mg → 2Fe3+. The most evolved apatite is significantly enriched in SrO (up to 9.7 wt.%; 0.49 apfu Sr). The core of the dyke and late veinlets contain unique late- to post-magmatic Ba–Ti–Zr-bearing mineral assemblages of baotite, henrymeyerite, titanite, rutile, benitoite and bazirite. Anhedral baotite fills interstices distributed inhomogeneously in the dyke centre; it is locally replaced by a Ba-bearing titanite + henrymeyerite + rutile + quartz assemblage. Henrymeyerite (the second record in a lamproite) shows variable Fe/Ti ratios and represents a solid solution of the hepta- and hexatitanate components. Euhedral crystals of benitoite and bazirite are enclosed in the late-stage quartz–titanite–apatite veinlets in the fine-grained margin of the intrusion. In terms of a mineralogical–genetic classification, the ?ebkovice dyke can be considered as a new high-silica (~ 57 wt.% SiO2) variety of lamproite (variety ?ebkovice), and represents a unique expression of post-collisional potassic magmatism on the south-eastern border of the Bohemian Massif. The peralkaline dykes from this area show mineralogical and geochemical features similar to those of silica-rich orogenic lamproites emplaced at destructive plate margins. In terms of the modern classification of lamproites, the ?ebkovice dyke is the first lamproite recognised in the Variscan orogenic belt. 相似文献