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1.
Nineteen USGS GRSs were analyzed with a Dupont 903-H Moisture Analyzer at 110°C and 1000°C to obtain H2O-and H2O+, and by thermal neutron induced gamma-ray spectrometry to obtain total H2O. The values are compared with the current literature and the two techniques evaluated. Except for QLO-1 by coulometry, no significant differences were obtained when the results were compared to the the literature.  相似文献   

2.
The equilibrium constant, K a, of the association reaction to form ion pairs from charged solute species in supercritical solutions can be calculated from a model based on published equations. Log K a at constant pressure is a linear function of the inverse in the dielectric constant of the fluid times temperature. The dielectric properties of H2O and CO2 at supercritical pressures and temperatures can also be evaluated using the Kirkwood equation. Using Looyenga mixing rules, the dielectric constant of H2O–CO2 mixtures can be obtained and the change in log K a with addition of CO2 in aqueous solutions evaluated. These changes in log K a with addition of CO2 are consistent with measured changes of log K a with addition of Ar in supercritical H2O–Ar solutions.
Log K a of KCl and NaCl increase to an increasing extent as the mole fraction of CO2 increases in H2O–CO2 solutions. For instance, at 2 kbar and constant temperature between 400 and 600° C, log K a of KCl increases by about two orders of magnitude whilst that of NaCl increases by over four orders of magnitude as the CO2 mole fraction increases from 0.0 to 0.35. Such changes in log K a will have dramatic effects on the solubility of minerals in CO2-rich environments.  相似文献   

3.
Abstract Nearly pure CO2 fluid inclusions are abundant in migmatites although H2O-rich fluids are predicted from the phase equilibria. Processes which may play a role in this observation include (1) the effects of decompression on melt, (2) generation of a CO2-bearing volatile phase by the reaction graphite + quartz + biotite + plagioclase = melt + orthopyroxene + CO2-rich vapour, (3) selective leakage of H2O from CO2+ H2O inclusions when the pressure in the inclusion exceeds the confining pressure during decompression, and (4) enrichment of grain-boundary vapour in CO2 by subsolidus retrograde hydration reactions.  相似文献   

4.
Differential thermal analysis, pH determination and ion chromatography were used to investigate the interference of chlorine in the determination of combined water (H2O+) by the Penfield tube gravimetric method. The magnitude of the chlorine interference was quantified and a correction method was proposed to obtain accurate results for H2O+. The method was applied to the determination of H2O+ in deep sea sediments containing chlorine and certified reference materials of oceanic polymetallic nodules.  相似文献   

5.
Abstract Andalusite-bearing veins formed during contact metamorphism in the aureole of the Vedrette di Ries tonalite. In the veins, quartz crystals that are completely armoured by andalusite or that occur in strain shadow areas contain three generations of fluid inclusions: low-salinity H2O-CO2-CH4 mixtures with CH4/(CO2+ CH4) ± 0.35 (type A); low-salinity aqueous fluids (type B); H2O-free, CO2-CH4 fluids with the same carbonic speciation as A (type C). Carbonic types A and C typically have a dark appearance, which is attributed to graphite coatings on inclusion walls. Microstructural analysis of the host quartz and calculated densities indicate that type A inclusions were likely trapped during vein formation. These inclusions underwent strain-assisted re-equilibration during cooling that resulted in density increases without change of composition. After the rocks had cooled below about 350 ° C, type C inclusions appear to have formed from one of the immiscible fractions after unmixing of the H2O-CO2-CH4 fluid mixtures. Aqueous type B inclusions, apparently trapped between 225 and 350 ° C, could represent an independent fluid, or could be the H2O-rich fraction of unmixed type A fluids. Taking account of the uncertainties, the composition and density of the complex type A inclusion fluids are in good agreement with the properties of primary fluids calculated from the petrological data. The fluid inclusion data support the model of vein formation by hydrofracturing as a result of dehydration of graphitic metapelites. These new results also demonstrate the importance of considering strain in the interpretation of metamorphic fluid inclusions.  相似文献   

6.
Calc-silicate granulites from the Bolingen Islands, Prydz Bay, East Antarctica, exhibit a sequence of reaction textures that have been used to elucidate their retrograde P–T path. The highest temperature recorded in the calc-silicates is represented by the wollastonite- and scapolite-bearing assemblages which yield at least 760°C at 6 kbar based on experimental results. The calc-silicates have partially re-equilibrated at lower temperatures (down to 450°C) as evidenced by the successive reactions: (1) wollastonite + scapolite + calcite = garnet + CO2, (2) wollastonite + CO2= calcite + quartz, (3) wollastonite + plagioclase = garnet + quartz, (4) scapolite = plagioclase + calcite + quartz, (5) garnet + CO2+ H2O = epidote + calcite + quartz, and (6) clinopyroxene + CO2+ H2O = tremolite + calcite + quartz.
The reaction sequence observed indicates that a CO2 was relatively low in the wollastonite-bearing rocks during peak metamorphic conditions, and may have been further lowered by local infiltration of H2O from the surrounding migmatitic gneisses on cooling. Fluid activities in the Bolingen calc-silicates were probably locally variable during the granulite facies metamorphism, and large-scale CO2 advection did not occur.
A retrograde P–T path, from the sillimanite stability field ( c. 760°C at 6 kbar) into the andalusite stability field ( c. 450°C at <3 kbar), is suggested by the occurrence of secondary andalusite in an adjacent cordierite–sillimanite gneiss in which sillimanite occurs as inclusions in cordierite.  相似文献   

7.
Results of electron microprobe and microthermometric studies of samples collected from the Bouvet Triple Junction Region (BTJR) during a joint Russian-Italian geological expedition on the R/V Academician Nikolaj Strakhov (1994) have revealed new data on the composition of basaltic magmas and oceanic hydrothermal fluids connected with magmatic processes. Detailed analysis of basaltic glasses shows that the modem Mid-Atlantic Ridge (MAR) rift valley is composed of normal mid-ocean ridge basalts with low concentrations of K2 O and TiOz (N-MORB), while its flanks are more enriched with these components approaching E-MORB. A marked influence of the Bouvet hot spot volcanism on magma generation on the South-West Indian Ridge (SWIR) near Bouvet Island is observed. Basaltic melts in this area belong to alkalic and transitional series and have maximum contents of K2O, TiO2, H2O.
Microthermometric analyses of fluid inclusions in the samples from the BTJR have revealed major differences in the oceanic hydrothermal fluid systems on the MAR and near SWIR, which depends on the peculiarities of magma. In the area of the MAR (with dry melts) only H2O solution inclusions in quartz were found; thus, seawater is probably the only primary source of hydrothermal fluids (NaCl + MgCl2+ H2O; T = 170–200°C). In the SWIR area (with the high content of water in melts) syngenetic liquid CO2 and H2O solution inclusions in quartz indicate the influence of the magmatic fluid component on the ore-forming water/carbon dioxide solutions (NaCl + CaC12+ H2O + CO2; T = 200–310 °C; P = 900–1700 bar).  相似文献   

8.
Abstract. Laser Raman microprobe analysis was performed on the fluid inclusions from the Honko-Sanjin zone in the Hishikari epithermal gold deposit, southern Kyushu, Japan. Gas concentrations of fluid inclusions through the zone were below detection limits (e.g., 5 mmole/kg H2O for CO2), with an exception at shallow portion in which the CO2/N2 mole ratio was determined to be 5.3. Boiling of hydrothermal solutions probably separated gases from ore fluids at the deep portion of the deposit, and migration of gases to shallow portion resulted in CO2-rich steam-heated water and related acid alteration.  相似文献   

9.
Three rock reference samples. W-2, DNC-1, and BIR-1, were analysed five times over several months by classical chemical methods using a Youden Square as the experimental design. A significant variation for the data classified by months was found for SiO2, CaO, H2O-, and TiO2 among the 15 constituents determined. Nevertheless, most standard deviations for the five data for each oxide in any sample, as well as the error standard deviations from the analyses of variance, are less than or approximately equal to the allowable difference between duplicate determinations traditionally used as limits of error. We also determined nine constituents in three portions each of two samples, W-2 and DNC-1, the six portions being analysed concurrently. F ratios for 16 comparisons of the variances of the five data for an oxide obtained over several months and of the three data determined as a group were significant for only one oxide, total iron as Fe2O3 in W-2. We conclude that, if a chemist analyses rock samples carefully, the variation of the determinations will be the same for portions analysed as a group, or analysed over a time interval.  相似文献   

10.
The results are given for all the determinations made by the co-operating laboratories of major elements in the six NIMROC rock samples (granite, syenite, lujavrite, norite, pyroxenite and dunite) prepared by the National Institute for Metallurgy in 1966. Relevant statistical data are given for the sets of results for each major constituent, and recommended values for all constituents except Al203, Na20, K20and CO2 in dunite, Fe2O3, MgO and CO2 in the granite, Fe23 and CO2 in the norite and CO2 in the pyroxenite.
This report and that on the trace and minor elements issued in 1978 complete the revision of the recommended values. It is suggested that analysts should concentrate rather on those constituents for which the results have shown such a wide scatter that they can be of no usc for reference purposes, than on those for which the ualues are fairly well established.  相似文献   

11.
Abstract Late Archaean orthogneisses and aluminous and iron-rich metasedimentary rocks intruded by anorthosite and a ferrodiorite-granite suite were completely recrystallized during Proterozoic granulite facies metamorphism. Geobarometry and geothermometry indicate P-T conditions of around 7.5kbar. 700°C, with a CO2-rich fluid phase and logfO2 at or below -16. A two-stage high-grade history of near isochemical corona growth is preserved in metasediments with the reaction cycle opx + plag + H2O → hbl+gar+SiO2→ opx+plag+H2O. End product compositions resemble those of the initial phases, and the only mobile components were SiO2 and/or H2O. The coronas reflect shortlived fluctuations in chemical activity at essentially constant P and T, contrary to simple progressive change in equilibrium parameters recorded by most corona-bearing textures.  相似文献   

12.
Abstract Scapolite, wollastonite, calcite, diopside, grossular-andradite garnet and sphene occur in calc-silicate rocks in the granulite terrain of the Arunta Block, central Australia. This assemblage buffers the CO2 activity at a low value, so that any coexisting fluid phase must be H2O rich and CO2 poor ( X co2 = 0.2-0.3). In contrast, the H2O activity in the surrounding felsic and mafic granulites was low. Thus fluid activities during granulite facies metamorphism were locally buffered in various rock units and fluid flow appears to have been restricted or fluid may have been absent. Late retrograde rims of garnet and garnet-quartz separate phases formed in the high-grade stage. Formation of these rims would have required either an influx of water-rich fluid or a decrease in pressure. Evidence from the surrounding granulites shows that in one locality, the calc-silicate rocks had undergone late isobaric hydration; in another locality, minor uplift had occurred soon after peak P-T conditions. In both, scapolite had partly broken down to plagioclase-calite. A calc silicate rock from the granulite terrain of Enderby Land, Antarctica, contains scapolite, wollastonite, calcite, diopside, quartz and sphene; this assemblage also indicates low CO2 activities. In this rock, wollastonite has broken down to calcite-quartz, to indicate isobaric cooling without influx of hydrous fluid.  相似文献   

13.
Abstract Two Archaean synvolcanic stocks with contact aureoles occur in the Wawa greenstone belt near Wawa, Ontario, Canada. The Gutcher Lake and Jubilee stocks consist mainly of granitoid trondhjemite with feldspar laths mottled by white mica + calcite + epidote and rimmed by clear albite. Biotite is partly or wholly pseudomorphosed by chlorite + sphene; some epidote is partly altered to calcite + chlorite. The granitoid phase grades into a foliated phase of quartz + albite + white mica + calcite + chlorite near fracture zones traversing the stocks.
The alteration of the Gutcher Lake stock along its foliated margin involved addition of K2O, H2O + CO2, MnO, plus Rb; loss of CaO plus Sr; and a shift in Fe+2/Fet from 0.66 to 0.81. The alteration of the Jubilee stock along the Darwin Shear involved addition of H2O + CO2; loss of Sr; and no significant shift in Fe+2/Fet. The greenschist alteration also modified the contact aureoles bordering both stocks.
One interpretation is that regional metamorphism in the Archaean overprinted a greenschist assemblage on both stocks. The alteration was intense near fracture zones and sporadic remote from fractures. Lower integrated water to rock ratios along the Darwin Shear compared to the margin of the Gutcher Lake stock may explain the comparatively lower perturbation of the element abundances and redox state of iron.  相似文献   

14.
A sequence of regional metamorphic isograds indicating a range from prehnite-pumpellyite to lower amphibolite facies was mapped in metabasites near Flin Flon, Manitoba. The lowest grade rocks contain prehnite + pumpellyite and are cut by younger brittle faults containing epidote + chlorite + calcite. Isobaric temperature- X CO2 and pressure-temperature (constant X CO2) diagrams were calculated to quantify the effects of CO2 in the metamorphic fluid on the stability of prehnite-pumpellyite facies minerals in metabasites containing excess quartz and chlorite. Prehnite and, to a lesser extent, pumpellyite are stable only in fluids with X co2 <0.002. For X co2>0.002, epidote + chlorite + calcite assemblages are stable. Our calculated phase relations are consistent with regional metamorphism in the Flin Flon area in the presence of an H2O-rich fluid and a more CO2-rich fluid in the later fault zones. We believe that the potential effects of small amounts of CO2 in the metamorphic fluid should be assessed when considering the pressure-temperature implications of mineral assemblages in low-grade metabasites.  相似文献   

15.
Two main types of karst formation are commonly known: the surficial meteoric one and the subsurface (hypogenic) karst, related to both carbonic (H2CO3) and sulphuric (H2S) acids. Nevertheless, a third, less well studied type exists that is referred to here as CO2-regime related karst. This article describes Pleistocene phreatic cave spar from the diapiric Jabal Madar dome in Northern Oman. These caverns and their precipitates probably represent examples of CO2-related karsting and subsequent calcite precipitation. Phreatic calcites form at the interface between two fundamentally different diagenetic and hydrogeological domains: the deep-seated, hydrothermal and the near-surficial, meteoric–vadose one. Changes in the ratio between hydrothermal upwelling and meteoric influx are recorded in the geochemistry and mineralogy of these calcites making them uncommon archives of two contrasting realms.  相似文献   

16.
Calcite and quartz veins have formed, and are forming, in steeply dipping fissures in the actively rising Alpine Schist metamorphic belt of New Zealand. The fluids that deposited these minerals were mostly under hydrostatic pressure almost down to the brittle-ductile transition, which has been raised to 5-6 km depth by rapid uplift. Some fluids were trapped under lithostatic pressures. Fluids in the fissure veins were immiscible H2O + NaCl-CO2 mixtures at 200-350 C. Bulk fluid composition is 15-20 mol% CO2 and <4.3 total mol CH4+ N2+ Ar/100mol H2O. Water hydrogen isotopic ratio δDH2O in the fissure veins spans -29 to -68‰, δ18OH2O -0.7 to 8.5‰, and bulk carbon isotopic ratio δ13C ranges from -3.7 to -11.7‰. The oxygen and hydrogen isotopic data suggest that the water has a predominantly meteoric source, and has undergone an oxygen isotope shift as a result of interaction with the host metamorphic rock. Similar fluids were present during cooling and uplift. Dissolved carbon is not wholly derived from residual metamorphic fluids; part may be generated by oxidation of graphite.  相似文献   

17.
Carbon sources in arc volcanism, with implications for the carbon cycle   总被引：1，自引：0，他引：1  
New CO2/3 He data from the East Sunda Arc (Indonesia) confirm earlier observations that arc volcanic gases have higher CO2/3 He ratios than MOR environments.On average, > 80% of arc volcanic CO2 is recycled, exogene carbon. Addition of a few percent of carbonate-bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases, but can not explain the He isotope observations. The CO2/3He in arc volcanoes is not strongly dependent on the composition of modem trough sediments (e.g. deep sea clays vs carbonate-rich sequences), and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of, arcs. The sum of globally deep-subducted sediment and slab carbon exceeds the estimated arc CO2 flux, and approximately 3.5 teramole of carbon may return annually to the mantle in convergent zones. The modem combined processes of MOR volcanism, slab alteration, and subduction volcanism do not produce a substantial carbon flux into the exosphere, and rate-changes in ocean floor spreading are unlikely to cause major changes in atmospheric CO2 as a result of changes in the volcanic CO2 fluxes. Intense pulses of flood basalt volcanism, however, may alter the CO2 contents of the atmosphere over the course of a millenium or so, and influence global climate.  相似文献   

18.
Two impure ultrahigh-pressure (UHP) marbles, a calcite marble with the peak assemblage Grt + Phe + Cpx + Rt + (Arg) and a dolomite marble with the peak assemblage Crn + Chl + Rt + Dol (±Arg), from the same lens from the polymetamorphic complex of the Brossasco-Isasca Unit (BIU) (southern Dora-Maira Massif) have been petrologically investigated and modelled by calculating P – T phase-diagram projections for H2O–CO2 mixed-volatile systems. Thermobarometric data obtained from the calcite marble suggest Alpine peak conditions in the diamond stability field (4.0 GPa at 730 °C), and allow reconstruction of the earlier portion of the Alpine retrograde P – T path, which is characterized by a significant decompression coupled with a moderate and continuous cooling to 650 °C at 2.50 GPa. The modelled fluid compositions at peak conditions point to 0.025 ≤  X (CO2) ≤ 0.10 and X (CO2) ≤ 0.0012 in the calcite marble and dolomite marble, respectively, suggesting fluid heterogeneity at the local scale and an internally buffered fluid evolution of the studied impure marbles. The lack of micro-diamond in the BIU marbles is explained by the very-low X (CO2) values, which favoured relatively high f O2-conditions, preventing the formation of diamond at the UHP peak metamorphic conditions.  相似文献   

19.
Calcsilicate granulites of probable Middle Proterozoic age ( c .1000–1100  Ma) in the vicinity of Battye Glacier, northern Prince Charles Mountains, East Antarctica, contain prograde metamorphic assemblages comprising various combinations of wollastonite, scapolite, clinopyroxene, An-rich plagioclase, calcite, quartz, titanite and, rarely, orthoclase, ilmenite, phlogopite and graphite. Comparison of the prograde assemblages with calculated and experimentally determined phase relations in the simple CaO–Al2O3–SiO2–CO2–H2O system suggests peak metamorphism at ≥835 °C in the presence (in wollastonite-bearing assemblages at least) of a CO2-bearing fluid ( X CO≥0.3) at a probable pressure of 6–7  kbar.
Well-preserved retrograde reaction textures represent: (1) breakdown of scapolite to anorthite+calcite±quartz; (2) formation of grossular–andradite garnet and, locally, (3) epidote, both principally by reactions involving scapolite breakdown products and clinopyroxene; (4) local coupled replacement of clinopyroxene and ilmenite by hornblende and titanite, respectively; and finally (5) local sericitization of prograde and retrograde plagioclase. These retrograde reactions are interpreted to be the result of cooling and variable infiltration by H2O-rich fluids, possibly derived from crystallizing pegmatitic intrusions and segregations that may be partial melts, which are common throughout the area.  相似文献   

20.
The carbonate-carbon (CO2) content of forty-one geochemical reference samples has been determined by coulometric method following acid treatment of the sample for releasing CO2. The method is superior to the conventional methods in speed, accuracy, sensitivity, specificity, and the coverage of CO2 range. The results on NBS limestone samples agree well with the certified values. The precision of the method is 0.5 % r.s.d., and the practical detection limit is 10 ppm C.  相似文献   

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