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A. E. Sveinbjornsdottir M. L. Coleman B. W. D. Yardley 《Contributions to Mineralogy and Petrology》1986,94(1):99-109
The Reykjanes and Krafla geothermal fields are both examples of active high temperature systems and show similar assemblages of alteration minerals, but the fluid at Reykjanes is dominantly sea water whereas that at Krafla is meteoric. Oxygen isotope analyses of surface rock and of drill chip samples from different depths are presented, together with results for the Krafla fluid, which is close to local precipitation (δ 18 O = ?11.9‰, δD= ?86.8‰). Calcite in both systems is apparently in equilibrium with the present deep fluid at the present field temperature, except for the upper 250 m at Reykjanes where the fluid may be more meteoric than at depth. Feldspar gives similar results. Quartz separates at Reykjanes are anomalously lighter than coexisting feldspar and give exceptionally high quartz-fluid temperatures. It is suggested that quartz originally grew when the fluid was more nearly meteoric (? glacial period) and has not re-equilibrated. Bulk-rock 18 O depletion supports this interpretation of the history of the Reykjanes system. Quartz in the Krafla system is mostly in equilibrium at the present field conditions but anomalies occur near the boundary between the upper and lower parts of the system, suggesting that this is not entirely stable. A high fluid:rock ratio (10–100 minimum) is indicated for the Krafla field. 相似文献
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W. M. Yan R. N. Manchester G. Hobbs W. van Straten J. E. Reynolds N. Wang M. Bailes N. D. R. Bhat S. Burke-Spolaor D. J. Champion A. Chaudhary W. A. Coles A. W. Hotan J. Khoo S. Oslowski J. M. Sarkissian D. R. B. Yardley 《Astrophysics and Space Science》2011,335(2):485-498
We report on variations in the mean position angle of the 20 millisecond pulsars being observed as part of the Parkes Pulsar Timing Array (PPTA) project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring in the Earth??s ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in interstellar RM was found with limits typically about 0.1 rad?m?2?yr?1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen. These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar electron density and magnetic field along the line of sight. 相似文献
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An experimental investigation has been carried on the solubility of CO2 in water and 1 M NaCl between 0.3 and 4 MPa, in order to test the validity of the results given by various modelling codes. In addition to experiments with pure fluids, the effect of a range of likely reservoir minerals on CO2–water interactions, including K-feldspar, kaolinite, calcite, Ca-montmorillonite and Na-montmorillonite were also investigated. In addition to measurements of CO2 solubility, the pH of the CO2-saturated suspensions was also measured directly at pressures of up to 1 MPa. The results demonstrate that predictions of CO2 solubility made with PHREEQC and Geochemist’s Workbench agree to within 20% with the experimental value, provided corrections are first made off-line for the fugacity coefficient of CO2, while predictions from standalone models are slightly more accurate. In the presence of mineral suspensions, PHREEQC and Geochemist’s Workbench give good results for calcite and kaolinite but underestimate the pH of montmorillonite-bearing assemblages while slightly overestimating the pH of K-feldspar suspensions. These results are significant because they indicate that CO2-charged fluids reacted with clays may be less acidic than indicated by the models, which will impact predictions of the potential for dissolution of reservoir and cap rock minerals, as well as the potential for leaching of toxic metals. 相似文献
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Emerald mineralisation in Colombia is located in two distinct zones along the borders of the Eastern Cordillera, some 80 km
apart. Mineralisation in the western zone has been dated at ca. 35 Ma whereas in the eastern zone it is 30 Ma older. Crush
leach analysis of the electrolyte chemistry of fluid inclusions contained in emerald, quartz, calcite, dolomite and fluorite
from both zones, demonstrates that in each region brines associated with emerald mineralisation range between two extremes
with many samples yielding intermediate compositions. Fluid 1, found mainly in emerald-hosted fluid inclusions, is dominated
by NaCl with high Cl:Br ratios indicating that the salinity was derived by dissolution of halite, most probably from the local
salt beds. Fluid 2, found notably in quartz hosted-fluid inclusions, is of similar salinity but contains less Na and significant
concentrations of Ca–K–Fe–Cl and other cations. It has lower Cl:Br ratios, more comparable with formation waters, but is inferred
to have obtained part of its salinity by halite dissolution. Bivariate plots of almost all cations have linear or sublinear
trends regardless of the mineral hosting the inclusions or the locality from which the samples originated, demonstrating that
mixing of the two saline fluids has occurred. Because the same two fluids occur in both eastern and western zones, despite
the difference in space and time, it is inferred that fluid compositions were rock controlled by similar interactions with
evaporites and black shales in both instances. It is proposed that beryllium was transported as Be–F complexes in the NaCl-fluid,
and was precipitated as emerald after mixing with the calcic brine caused precipitation of fluorite and parisite.
Received: 9 April 1999 / Accepted: 14 March 2000 相似文献
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Bruce W. D. Yardley 《Contributions to Mineralogy and Petrology》1982,81(4):317-327
Rare but widespread relics of sodic amphibole occur in metabasites and metacherts of the Haast Schists and related Caples Terrane rocks. Present main-stage metamorphic assemblages are frequently chemically equivalent to earlier sodic amphibole bearing assemblages, indicating that these rocks underwent an earlier, higher P/Tmetamorphism prior to formation of the present pumpellyite-actinolite and greenschist facies assemblages. The earlier assemblages were stable during and after early isoclinal folding, but were replaced by the present moderate P/T assemblages prior to the last major fabric-forming deformation. The change in conditions was due to thermal relaxation, probably accompanied by uplift and erosion, and peak metamorphic temperatures were about 350–370° C in the pumpellyite-actinolite zone of the Caples Terrane and near 390° C in the greenschist facies chlorite zone near Queenstown. According to Henley (1975) these greenschist facies rocks attained a pressure of at least 6.4±0.4 kb during their history, but a pressure of 4.6±0.6 kb has been estimated for a chlorite zone rock from Middlemarch, and so the 6.4 kb estimate probably refers to the maximum pressure attained during the earlier, higher P/T metamorphism. Similar changes in metamorphic facies series with time occur in some older and more complex metamorphic belts such as the Caledonides, and this study suggests that it may be possible to interpret particular elements in the metamorphic development of such belts in terms of specific circum-Pacific analogues. 相似文献
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The relative importance of buffering and brine inputs in controlling the abundance of Na and Ca in sedimentary formation waters 总被引：1，自引：0，他引：1
Stephanie Houston Craig SmalleyAdam Laycock Bruce W.D. Yardley 《Marine and Petroleum Geology》2011,28(6):1242-1251
The concentration of Ca in the formation waters of petroleum reservoirs can play a major role in influencing the outcome of a number of processes that are of great significance to the oil industry. For example, formation water Ca concentration affects the risk of carbonate scale formation during production. In order to better understand the concentrations of Ca in formation waters, we have investigated the chemistries of formation waters from a range of onshore and offshore basins worldwide, using published sources, as well as unpublished data held by BP. Although calcium and sodium are the principal cations in almost all formation waters they vary enormously in their relative proportions. We have identified three distinct trends on a plot of XCa (Ca/(Na + Ca)) against Cl. Most data lie on a high-Ca trend, here termed Trend 1, and show an increase in XCa with salinity. We interpret this as tracking equilibration with Ca and Na-bearing minerals, with the ratio (mol Ca/mol Na2) remaining approximately constant irrespective of salinity for chloride-dominated fluids. At very high salinities, Br-enriched bittern brines that have taken part in dolomitisation lie at the Cl-rich end of this trend. Some brines remain Na-dominated up to very high salinities and define a distinct low-Ca trend, Trend 2. These are associated with dissolution of halite beds and are interpreted to arise when the amount of Na in the pore fluid greatly exceeds the amount of Ca available in minerals. We refer to such brines as mass-limited; the sparsity of Ca in the rock-fluid system constrains XCa to a low value. Remarkably few brines lie between these trends. Finally, dilute formation waters show very large variations in XCa and may have bicarbonate as the dominant anion. They define a distinct low-Cl trend, Trend 3. We conclude that the behaviour of Na and Ca in most formation waters reflects equilibration with minerals, and concentrations of Ca in solution are sensitive to pH and PCO2 as well as to chloride concentration. For some brines however, the amount of salts in solution is sufficient to overwhelm the buffering capacity of the wallrocks. 相似文献