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1.
B. C. Schmidt François Holtz Bruno Scaillet Michel Pichavant 《Contributions to Mineralogy and Petrology》1997,126(4):386-400
Solidus temperatures of quartz–alkali feldspar assemblages in the haplogranite system (Qz-Ab-Or) and subsystems in the presence
of H2O-H2 fluids have been determined at 1, 2, 5 and 8 kbar vapour pressure to constrain the effects of redox conditions on phase relations
in quartzofeldspathic assemblages. The hydrogen fugacity (f
H2) in the fluid phase has been controlled using the Shaw membrane technique for moderately reducing conditions (f
H2 < 60 bars) at 1 and 2 kbar total pressure. Solid oxygen buffer assemblages in double capsule experiments have been used to
obtain more reducing conditions at 1 and 2 kbar and for all investigations at 5 and 8 kbar. The systems Qz-Or-H2O-H2 and Qz-Ab-H2O-H2 have only been investigated at moderately reducing conditions (1 and 5 kbar) and the system Qz-Ab-Or-H2O-H2 has been investigated at redox conditions down to IW (1 to 8 kbar). The results obtained for the water saturated solidi are
in good agreement with those of previous studies. At a given pressure, the solidus temperature is found to be constant (within
the experimental precision of ± 5°C) in the f
H2 range of 0–75 bars. At higher f
H2, generated by the oxygen buffers FeO-Fe3O4 (WM) and Fe-FeO (IW), the solidus temperatures increase with increasing H2 content in the vapour phase. The solidus curves obtained at 2 and 5 kbar have similar shapes to those determined for the
same quartz - alkali feldspar assemblages with H2O-CO2- or H2O-N2-bearing systems. This suggests that H2 has the behaviour of an inert diluent of the fluid phase and that H2 solubility in aluminosilicate melts is very low. The application of the results to geological relevant conditions [HM (hematite-magnetite) > f
O2 > WM] shows that increasing f
H2 produces a slight increase of the solidus temperatures (up to 30 °C) of quartz–alkali feldspar assemblages in the presence
of H2O-H2 fluids between 1 and 5 kbar total pressure.
Received: 4 March 1996 / Accepted: 22 August 1996 相似文献
2.
An expression is derived for the calculation of time-integrated metamorphic fluid fluxes in two or more dimensions in rocks
undergoing multivariant reactions under conditions of varying pressure, temperature and angle of flow. This calcuation requires
knowledge of mineral assemblages, modes and compositions, which are obtained from isobaric T-X
CO2 pseudosections constructed using the program THERMOCALC and compared with those observed in east central Vermont. THERMOCALC is capable of reproducing peak mineral assemblages, modes, compositions and the observed reaction sequences within the system
KCaNaFMASCH for two kyanite grade pelitic carbonate rocks from a Barrovian style regional metamorphic terrain in east central
Vermont, U.S.A. Calculation of fluid fluxes for decarbonation reactions under conditions of horizontal, layer-parallel flow
produces time-integrated fluid flux figures of the order of 108 moles m−2. Allowance for possible cross-layer flow from adjacent dehydrating pelites reduces this figure significantly, with episodic
cross-layer fluxes of the order of 105 moles m−2 being capable of driving the observed decarbonation. Chlorite bearing carbonate protoliths would have initially dehydrated
with increasing temperature, a process requiring down-temperature fluid flow to produce the assemblages currently observed.
Received: 28 January 1998 / Accepted: 20 September 1998 相似文献
3.
Periclase formed in steeply dipping marbles from the Beinn an Dubhaich aureole, Scotland, and the Silver Star aureole, Montana,
by the reaction dolomite = periclase + calcite + CO2. Equilibrium between rock and fluids with X
CO
2 < 1 requires that reaction was infiltration-driven. Brucite pseudomorphs after periclase occur in the Beinn an Dubhaich aureole
either as bed-by-bed replacement of dolomite or in a lens along the contact between dolomite and a pre-metamorphic dike. Transport
theory predicts that infiltration drove both periclase reaction and 18O-depletion fronts which moved at significantly different velocities along the flow path. The distributions of brucite and
18O-depleted rocks are identical in surface exposures, thus indicating upward flow. Time-integrated flux (q) was <500 mol/cm2 and the fluid source was magmatic. Because periclase and its hydrated equivalent brucite are unaltered to dolomite by retrograde
reactions, the exposure of brucite marbles accurately images the flow paths of peak metamorphic fluids. In the Silver Star
aureole brucite pseudomorphs after periclase exclusively occur in tabular bodies that are beds with elevated Mg/Ca. The spatial
pattern of 18O-depletion requires upward vertical fluid flow. Estimated prograde q ≈ 103–104 mol/cm2 and the fluid source was magmatic. Low Mg/Ca, 18O-depleted, brucite-free rocks pose a dilemma because the periclase reaction front should have traveled ≈18 times further
through them than the isotope alteration front. The dilemma is resolved by reaction textures that indicate periclase and
brucite were destroyed in low Mg/Ca rocks by infiltration-driven retrograde carbonation reactions. Values of retrograde q were ≈103–104 mol/cm2. Brucite (after periclase) was preserved only in high Mg/Ca layers where periclase developed in greater abundance. The geometry
of brucite marbles at Silver Star thus reflects the location of high Mg/Ca beds rather than the geometry of fluid flow. Retrograde
reactions must be considered before the mineralogical record of prograde fluid flow can correctly be interpreted. In both
aureoles fluid flow, mineral reaction, and isotope depletion were structurally controlled by bedding and lithologic contacts.
Received: 30 July 1996 / Accepted: 21 March 1997 相似文献
4.
Meta-sedimentary rocks including marbles and calcsilicates in Central Dronning Maud Land (CDML) in East Antarctica experienced
a Pan-African granulite facies metamorphism with peak metamorphic conditions around 830 ± 20 °C at 6.8 ± 0.5 kbar which was
accompanied by the post-kinematic intrusion of huge amounts of syenitic (charnockitic) magmas at 4.5 ± 0.7 kbar. The marbles
and calcsilicates may represent meta-evaporites as indicated by the occurrence of metamorphic gypsum/anhydrite and Cl-rich
scapolite that formed in the presence of saline fluids with X
NaCl in the range 0.15–0.27. The marbles and calcsilicates bear biotite, tremolite and/or hornblende and humite group minerals
(clinohumite, chondrodite and humite) which are inferred to have crystallized at about 650 °C and 4.5 kbar. The syenitic intrusives
contain late-magmatic biotite and amphibole (formed between 750 and 800 °C) as well as relictic magmatic fayalite, orthopyroxene
and clinopyroxene. Two syenite and two calcsilicate samples contain fluorite. Corona textures in the marbles and calcsilicates
suggest very low fluid-rock ratios during the formation of the retrograde (650 °C) assemblages. Biotite in all but two syenite
samples crystallized at log(f
H
2
O/f
HF) ratios of 2.9 ± 0.4, while in the calcsilicates, both biotite and humite group minerals indicate generally higher log(f
H
2
O/f
HF) values of up to 5.2. A few samples, though, overlap with the syenite values. Log(f
H
2
O/f
HCl) derived from biotite covers the range 0.5–2.6 in all rock types. Within a single sample, the calculated values for both
parameters vary typically by 0.1 to 0.8 log units. Water and halogen acid fugacities calculated from biotite-olivine/orthopyroxene-feldspar-quartz
equilibria and the above fugacity ratios are 1510–2790 bars for H2O, 1.3–5.3 bars for HF and 7–600 bars for HCl. The results are interpreted to reflect the reaction of relatively homogeneous
magmatic fluids [in terms of log(f
H
2
O
/f
HF)] derived from the late-magmatic stages of the syenites with both earlier crystallized, still hotter parts of the syenites
and with adjacent country rocks during down-temperature fluid flow. Fluorine is successively removed from the fluid and incorporated
into F-bearing minerals (close to the syenite into metamorphic fluorite). In the course of this process log(f
H
2
O
/f
HF) increases significantly. Chlorine preferably partitions into the fluid and hence log(f
H
2
O
/f
HCl) does not change markedly during fluid-rock interaction.
Received: 28 November 1997 / Accepted: 27 April 1998 相似文献
5.
Burkhard C. Schmidt François Holtz Michel Pichavant 《Contributions to Mineralogy and Petrology》1999,136(3):213-224
The water solubility in haplogranitic melts (normative composition Ab39Or32Qz29) coexisting with H2O-H2 fluids at 800 and 950 °C and 1, 2 and 3 kbar vapour pressure has been determined using IR spectroscopy. The experiments were
performed in internally heated pressure vessels and the hydrogen fugacity (f
H2) was controlled using the double capsule technique and oxygen buffer assemblages (WM and IW). Due to the limited lifetimes
of these oxygen buffers the water solubility was determined from diffusion profiles (concentration-distance profiles) measured
with IR spectroscopy in the quenched glasses. The reliability of the experimental strategy was demonstrated by comparing the
results of short- and long-duration experiments performed with pure H2O fluids. The water solubility in Ab39Or32Qz29 melts equilibrated with H2O-H2 fluids decreases progressively with decreasing f
H2O, as f
H2 (or X
H2) increases in the fluid phase. The effect of H2 on the evolution of the water solubility is similar to that of CO2 or another volatile with a low solubility in the melt and can be calculated in a first approximation with the Burnham water
solubility model. Recalculation of high temperature water speciation for AOQ melts coexisting with H2O-H2 fluids at 800 °C, 2 kbar suggests that the concentrations of molecular H2O are proportional to f
H2O (calculated using available mixing models), indicating Henrian behaviour for the solubility of molecular H2O in haplogranitic melts.
Received: 29 June 1998 / Accepted: 10 March 1999 相似文献
6.
I. Kenis Ph. Muchez G. Verhaert A. Boyce M. Sintubin 《Contributions to Mineralogy and Petrology》2005,150(1):102-118
Fluid inclusions in quartz veins of the High-Ardenne slate belt have preserved remnants of prograde and retrograde metamorphic
fluids. These fluids were examined by petrography, microthermometry and Raman analysis to define the chemical and spatial
evolution of the fluids that circulated through the metamorphic area of the High-Ardenne slate belt. The earliest fluid type
was a mixed aqueous/gaseous fluid (H2O–NaCl–CO2–(CH4–N2)) occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic
area. In the central part of the metamorphic area (epizone), in addition to this mixed aqueous/gaseous fluid, primary and
isolated fluid inclusions are also filled with a purely gaseous fluid (CO2–N2–CH4). During the Variscan orogeny, the chemical composition of gaseous fluids circulating through the Lower Devonian rocks in
the epizonal part of the slate belt, evolved from an earlier CO2–CH4–N2 composition to a later composition enriched in N2. Finally, a late, Variscan aqueous fluid system with a H2O–NaCl composition migrated through the Lower Devonian rocks. This latest type of fluid can be observed in and outside the
epizonal metamorphic part of the High-Ardenne slate belt. The chemical composition of the fluids throughout the metamorphic
area, shows a direct correlation with the metamorphic grade of the host rock. In general, the proportion of non-polar species
(i.e. CO2, CH4, N2) with respect to water and the proportion of non-polar species other than CO2 increase with increasing metamorphic grade within the slate belt. In addition to this spatial evolution of the fluids, the
temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of
the basin. In addition to the maturity of the metamorphic fluids, the salinity of the aqueous fluids also shows a link with
the metamorphic grade of the host-rock. For the earliest and latest fluid inclusions in the anchizonal part of the High-Ardenne
slate belt the salinity varies respectively between 0 and 3.5 eq.wt% NaCl and between 0 and 2.7 eq.wt% NaCl, while in the
epizonal part the salinity varies between 0.6 and 17 eq.wt% NaCl and between 3 and 10.6 eq.wt% for the earliest and latest
aqueous fluid inclusions, respectively. Although high salinity fluids are often attributed to the original sedimentary setting,
the increasing salinity of the fluids that circulated through the Lower Devonian rocks in the High-Ardenne slate belt can
be directly attributed to regional metamorphism. More specifically the salinity of the primary fluid inclusions is related
to hydrolysis reactions of Cl-bearing minerals during prograde metamorphism, while the salinity of the secondary fluid inclusions
is rather related to hydration reactions during retrograde metamorphism. The temporal and spatial distribution of the fluids
in the High-Ardenne slate belt are indicative for a closed fluid flow system present in the Lower Devonian rocks during burial
and Variscan deformation, where fluids were in thermal and chemical equilibrium with the host rock. Such a closed fluid flow
system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform δ180 values of both the veins and their host rock demonstrate a rock-buffered fluid flow system. 相似文献
7.
Martin J. Gole Stephen J. Barnes Robin E. T. Hill 《Contributions to Mineralogy and Petrology》1987,96(2):151-162
The Agnew nickel sulfide deposit is spatially associated with a lenticular body of ultramafic rocks which shows a concentric zonation in metamorphic mineralogy. Olivine + tremolite + chlorite + cummingtonite ±enstatite assemblages occur at the margin of the ultramafic lens, giving way to olivine + anthophyllite, olivine + talc and olivine + antigorite assemblages successively inwards. These rocks are interpreted as having crystallized from komatiitic lavas, and exhibit a spectrum of compositions from those of original flow tops to pure olivine adcumulates. The relative modal abundances of metamorphic olivine, tremolite and chlorite reflect original proportions of cumulus olivine and komatiite liquid in the protolith. Peak metamorphic conditions are estimated at 550° C, based on garnet-biotite thermometry, at a maximum pressure of 3 kb. This temperature falls within the narrow range over which metamorphic olivine may co-exist with enstatite, anthophyllite, talc or antigorite depending upon the fugacity of water in the metamorphic fluid. The observed mineralogical zonation is therefore attributed to infiltration by CO2-rich fluids, generated by decarbonation of talc-carbonate rocks formed during pre-metamorphic marginal alteration of the ultramafic lens. Metamorphic fluids were essentially binary mixtures of water and CO2, with minor H2S having a maximum partial pressure less than 1 percent of total pressure. Enstatite-bearing assemblages formed in the presence of CO2-rich fluids at fluid: rock volume ratios close to one, while anthophyllite, talc and antigorite bearing assemblages formed in the presence of progressively more water-rich fluids at progressively lower fluid-rock ratios. 相似文献
8.
Abstract C-O-H fluid produced by the equilibration of H2O and excess graphite must maintain the atomic H/O ratio of water, 2:1. This constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric-isothermal conditions. The O2, H2O and CO2 fugacities (fo2, fH2O and fCO2) of such fluids have been estimated from equations of state and fit as a function of pressure and temperature. These fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration, e.g. pelitic lithologies. Because there are no compositional degrees of freedom for graphite-saturated fluids produced entirely by dehydration, the variance of the dehydration process is not increased in comparison with that in non-graphitic systems. Thus, compositional ‘buffering’of C-O-H fluids by dehydration equilibria, a common petrological model, requires that redox reactions, decarbonation reactions or external, H/O ± 2, fluid sources perturb the evolution of the metamorphic system. Such perturbations are not likely to be significant in metapelitic environments, but their tendency will be to increase the fO2 of the fluid phase. At high metamorphic grades, pyrite desulphidation reactions may cause a substantial reduction of fH2O and slight increases in fO2 and fCO2 relative to sulphur-free fluid. At low metamorphic grade, sulphur solubility in H/O ± 2 fluids is so low that pyrite decomposition must occur by sulphur-conserving reactions that cause iron depletion in silicates, a common feature of sulphidic pelites. With increasing temperature and sulphur solubility, pyrite desulphidation may be driven by dehydration reactions or infiltration of H2O-rich fluids. The absence of magnetite and the assemblages carbonate + aluminosilicate or pyrite + pyrrhotite + ilmenite from most graphitic metapelites is consistent with an H/O = 2 model for GCOH(S) fluid. For graphitic rocks in which such a model is inapplicable, a phase diagram variable that defines the H/O ratio of GCOH(S) fluid is more useful than the conventional fO2 variable. 相似文献
9.
Fluid infiltration and regional metamorphism of the Waits River Formation, north-east Vermont, USA 总被引:2,自引:0,他引:2
Abstract The Siluro-Devonian Waits River Formation of north-east Vermont was deformed, intruded by plutons and regionally metamorphosed during the Devonian Acadian Orogeny. Five metamorphic zones were mapped based on the mineralogy of carbonate rocks. From low to high grade, these are: (1) ankerite-albite, (2) ankerite-oligoclase, (3) biotite, (4) amphibole and (5) diopside zones. Pressure was near 4.5kbar and temperature varied from c. 450° C in the ankerite-albite zone to c. 525° C in the diopside zone. Fluid composition for all metamorphic zones was estimated from mineral equilibria. Average calculated χco2[= CO2/(CO2+ H2O)] of fluid in equilibrium with the marls increases with increasing grade from 0.05 in the ankerite-oligoclase zone, to 0.25 in the biotite zone and to 0.44 in the amphibole zone. In the diopside zone, χCO2 decreases to 0.06. Model prograde metamorphic reactions were derived from measured modes, mineral chemistry, and whole-rock chemistry. Prograde reactions involved decarbonation with an evolved volatile mixture of χCO2 > 0.50. The χCO2 of fluid in equilibrium with rocks from all zones, however, was generally <0.40. This difference attests to the infiltration of a reactive H2O-rich fluid during metamorphism. Metamorphosed carbonate rocks from the formation suggests that both heat flow and pervasive infiltration of a reactive H2O-rich fluid drove mineral reactions during metamorphism. Average time-integrated volume fluxes (cm3 fluid/cm2 rock), calculated from the standard equation for coupled fluid flow and reaction in porous media, are (1) ankerite-oligoclase zone: c. 1 × 104; (2) biotite zone: c. 3 × 104; (3) amphibole zone: c. 10 × 104; and diopside zone: c. 60 × 104. The increase in calculated flux with increasing grade is at least in part the result of internal production of volatiles from prograde reactions in pelitic schists and metacarbonate rocks within the Waits River Formation. The mapped pattern of time-integrated fluxes indicates that the Strafford-Willoughby Arch and the numerous igneous intrusions in the field area focused fluid flow during metamorphism. Many rock specimens in the diopside zone experienced extreme alkali depletion and also record low χCO2. Metamorphic fluids in equilibrium with diopside zone rocks may therefore represent a mixture of acid, H2O-rich fluids given off by the crystallizing magmas, and CO2-H2O fluids produced by devolatilization reactions in the host marls. Higher fluxes and different fluid compositions recorded near the plutons suggest that pluton-driven hydrothermal cells were local highs in the larger regional metamorphic hydrothermal system. 相似文献
10.
O. V. Avchenko K. V. Chudhenko I. A. Aleksandrov V. O. Khudolozhkin 《Geochemistry International》2011,49(2):139-153
The paper presents thermodynamic models for mineral solid solutions used in physicochemical simulations with the SELECTOR-C
program package (PP) in application to metamorphic mineral-forming processes. It is demonstrated that the simulated FeO and
MgO distribution in the mineral pairs garnetbiotite, garnet-orthopyroxene, orthopyroxene-biotite, orthopyroxene-olivine, garnet-cordierite,
garnetclinopyroxene, and clinopyroxene-orthopyroxene in the model samples satisfactorily corresponds to available experimental
and empirical data. Simulations of naturally occurring mineral associations are employed to demonstrate the capabilities of
the new version of the SELECTOR-C PP as a tool for studying the evolution of mineral assemblages at varying P-T conditions and fluid regime, the perfectly mobile and inert behaviors of certain fluid components during the origin of mineral
associations are demonstrated, the pseudosection method applied over a broad P-T range is used to trace systematic variations in the composition of mineral associations in granulite-facies metabasites and
metapelites, and the upper limit of plagioclase stability is estimated for these rocks at pressures of 11–12 kbar. Principal
differences are elucidated in the effect of rocks rich and poor in Fe3+ on the percolation of metamorphic fluid through them: Fe3+-rich rocks retain their own redox potential at a certain level by buffering reactions, whereas Fe3+-poor rocks rapidly exhaust their buffer capacity and acquire the redox potential of the inflowing external fluid. This allowed
us to evaluate the logfO2 at no higher than −17 (at T = 700°C and P = 6.8 kbar). Our simulation of the equilibrium of natural rock samples provides good reasons to believe that natural mineral
assemblages can be formed at low fluid/rock ratios of no higher than 0.01–0.06. 相似文献
11.
Geothermometric constraints on auriferous shear zones of the Renco mine in the Northern Marginal Zone of the late-Archaean,
granulite-facies Limpopo Belt in southern Zimbabwe indicate that deformation and associated mineralization occurred at temperatures
of at least 600 °C up to more likely 700 °C. Mid- to upper-amphibolite facies conditions during mineralization correspond
to the regional-scale retrogression of granulite facies wall rocks during the late-Archaean thrusting of high-grade metamorphic
rocks of the Northern Marginal Zone onto low- to medium-grade granite-greenstone terrains of the Zimbabwe craton. Mineral
assemblages indicate that the ore fluid was moderately oxidized with log fO2 values between 10−17 and 10−18 bars with high H2S activities of 0.25–0.75. Elements enriched in the shear zones include Au, S, Fe, Cu, Mo, Bi, Te, Ni, Co, and H2O, Au and Cu being the most enriched. Geochemically, Au correlates with Cu but not with S, which, together with the fact that
gold is only rarely intergrown or in direct contact with sulfides, possibly indicates a transport of gold as a chloride complex.
The siting of gold along fractures or within implosion breccias suggests that gold was precipitated due to fluid immiscibility
induced by catastrophic fluid pressure drops during seismic slip events. Fluid inclusions are predominantly CO2 (±CH4 ± N2)-rich, but petrographic work indicates that fluid inclusions have undergone extensive post-entrapment modifications due to
the pervasive recrystallization of mineral textures in the high-temperature shear zones. The mineralized shear zones are enriched
in 18O compared to wall-rock enderbites, which is interpreted to represent an influx of externally derived fluids of probably metamorphic
origin. Based on temporal and spatial relationships between mineralization, late-Archaean overthrusting of the Northern Marginal
Zone onto the Zimbabwe craton, and coeval amphibolite-facies hydration of granulites, we suggest that the Renco mineralization
formed in a mid-crustal environment from metamorphic fluids that were generated from dehydration of subcreted greenstone terrains
of the Zimbabwe craton.
Received: 27 October 1998 / Accepted: 13 August 1999 相似文献
12.
Small volumes (in the cm3 range) of a talc-kyanite schist exhibit mosaic equilibria characterized by mineral assemblages conventionally attributed
to vastly different pressure temperature conditions of metamorphism. On the basis of petrographic and microprobe studies these
assemblages are attributed to three consecutive stages of metamorphism of a chemically exceptional rock composition falling
largely into the model system MgO-Al2O3-SiO2-H2O. Stage 1 typified by Mg chlorite-quartz-talc and some paragonite was followed during stage 2 by talc-kyanite, Mg gedrite-quartz,
and the growth of large dravites. In stage 3 pure Mg cordierite formed with or without corundum and/or talc, and kyanite was
partly converted into sillimanite. Pressures and temperature during this final stage of metamorphism were probably near 5–6
kb, 640 ° C.
The preservation of this succession of mineral assemblages related to each other through isochemical reactions suggests that
the main factors governing the metamorphic history of this whitheschist were compositional changes of the coexisting fluids
with time, whereas pressure temperature variations may be subordinate. In the Sar e Sang area such chemical variations of
the metamorphic fluids are probably caused by progressive metamorphism and mobilization of a former evaporite deposit.
Microprobe analyses of the phases gedrite and talc indicate variable degrees of sodium incorporation into these phases according to the substitution NaAl→Si. 相似文献
13.
F. Masoudi B. Mehrabi M. Rezai Aghdam B. W. D. Yardley 《Journal of the Geological Society of India》2009,73(3):407-418
In the Sanandaj-Sirjan zone of metamorphic belt of Iran, the area south of Hamadan city comprises of metamorphic rocks, granitic
batholith with pegmatites and quartz veins. Alvand batholith is emplaced into metasediments of early Mesozoic age. Fluid inclusions
have been studied using microthermometry to evaluate the source of fluids from which quartz veins and pegmatites formed to
investigate the possible relation between host rocks of pegmatites and the fluid inclusion types. Host minerals of fluid inclusions
in pegmatites are quartz, andalusite and tourmaline. Fluid inclusions can be classified into four types. Type 1 inclusions
are high salinity aqueous fluids (NaCleq >12 wt%). Type 2 inclusions are low to moderate salinity (NaCleq <12 wt%) aqueous fluids. Type 3 and 4 inclusions are carbonic and mixed CO2-H2O fluid inclusions. The distribution of fluid inclusions indicate that type 1 and type 2 inclusions are present in the pegmatites
and quartz veins respectively in the Alvand batholith. This would imply that aqueous magmatic fluids with no detectable CO2 were present during the crystallization of these pegmatites and quartz veins. Types 3 and 4 inclusions are common in quartz
veins and pegmatites in metamorphic rocks and are more abundant in the hornfelses. The distribution of the different types
of fluid inclusions suggests that CO2 fluids generated during metamorphism and metamorphic fluids might also contribute to the formation of quartz veins and pegmatites
in metamorphic terrains. 相似文献
14.
Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA 总被引:1,自引:0,他引:1
John M. Ferry Sorena S. Sorensen Douglas Rumble III. 《Contributions to Mineralogy and Petrology》1998,130(3-4):358-378
The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and
amount of fluid flow during contact metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite
(Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically.
At the peak of metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward.
Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope
composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point
at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (<1615 mol/cm2). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm2. The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic
model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from
the fluid source along contacts between limestone and more siliceous rocks point to strong control of flow geometry at the
0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict
correctly fundamental aspects of contact metamorphic fluid flow.
Received: 27 January 1997 / Accepted: 2 October 1997 相似文献
15.
John M. Ferry 《Contributions to Mineralogy and Petrology》1996,124(3-4):235-254
Siliceous dolomites and limestones contain abundant retrograde minerals produced by hydration-carbonation reactions as the
aureole cooled. Marbles that contained periclase at the peak of metamorphism bear secondary brucite, dolomite, and serpentine;
forsterite-dolomite marbles have retrograde tremolite and serpentine; wollastonite limestones contain secondary calcite and
quartz; and wollastonite-free limestones have retrograde tremolite. Secondary tremolite never appears in marbles where brucite
has replaced periclase or in wollastonite-bearing limestones. A model for infiltration of siliceous carbonates by CO2-H2O fluid that assumes (a) vertical upwardly-directed flow, (b) fluid flux proportional to cooling rate, and (c) flow and reaction
under conditions of local equilibrium between peak temperatures and ≈400 °C, reproduces the modes of altered carbonate rocks,
observed reaction textures, and the incompatibility between tremolite and brucite and between tremolite and wollastonite.
Except for samples from a dolomite xenolith, retrograde time-integrated flux recorded by reaction progress is on the order
of 1000 mol fluid/cm2 rock. Local focusing of flow near the contact is indicated by samples from the xenolith that record values an order of magnitude
greater. Formation of periclase, forsterite, and wollastonite at the peak of metamorphism also required infiltration with
prograde time-integrated flux approximately 100–1000 mol/cm2. The comparatively small values of prograde and retrograde time-integrated flux are consistent with lack of stable isotope
alteration of the carbonates and with the success of conductive thermal models in reproducing peak metamorphic temperatures
recorded by mineral equilibria. Although isobaric univariant assemblages are ubiquitous in the carbonates, most formed during
retrograde metamorphism. Isobaric univariant assemblages observed in metacarbonates from contact aureoles may not record physical
conditions at the peak of metamorphism as is commonly assumed.
Received: 19 September 1995 / Accepted: 14 March 1996 相似文献
16.
为了探讨接触变质带内变碳酸盐岩变质过程CO2释放的数量和排放CO2的物理、化学及地质条件,根据递进变质反应和时间积分流体通量模型,定量分析和定量计算了双山地区变碳酸盐岩在接触变质作用中释放CO2的通量。计算结果得到CO2的通量值为0.729×104~2.446×104 mol/cm2,CO2的来源以接触变质反应释放为主;CO2的生成释放与变质程度呈正相关关系。自白云石带至方解石带变质流体中XCO2不断升高,但钙铝榴石带由于岩浆水影响,流体通量最高而XCO2急剧下降。 相似文献
17.
A detailed petrological analysis of the marble assemblages observed within the M2 metamorphic complex on Naxos is presented. Two distinct periods of mineral growth are documented; the first is associated with prograde M2 metamorphism and the second with retrograde M2 metamorphism occurring during ductile extensional thinning of the complex. The textural and miner-alogical characteristics and the carbon and oxygen isotope compositions of each generation are described, and the P-T-X
CO
2 conditions at which these two mineral generations were stable, and the compositions of the fluids present during metamorphism are characterised. Whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution, the retrograde mineral generation is shown to have grown as a result of the infiltration of a water-rich fluid phase that transported silica, Al2O3, Na2O and FeO into the host rocks. This observation, together with the stable isotope compositions of the retrograde calcite, and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas (T>600° C) of the metamorphic complex, suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures. The existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on Naxos, because many of the unusually low 18O compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde M2 fluids, rather than with prograde fluids. 相似文献
18.
The subduction of hydrated oceanic lithosphere potentially transports large volumes of water into the upper mantle; however,
despite its potential importance, fluid–rock interaction during high-pressure metamorphism is relatively poorly understood.
The stable isotope and major element geochemistry of Pennine ophiolite rocks from Italy and Switzerland that were metamorphosed
at high pressures are similar to that of unmetamorphosed ophiolites, suggesting that they interacted with little pervasive
fluid during high-pressure metamorphism. Cover sediments also have oxygen isotope ratios within the expected range of their
protoliths. In the rocks that escaped late greenschist-facies retrogression, different styles of sub-ocean-floor alteration
may be identified using oxygen isotopes, petrology, and major or trace element geochemistry. Within the basalts, zones that
have undergone high- and low-temperature sub-ocean-floor alteration as well as relatively unaltered rocks can be distinguished.
Serpentinites have δ18O and δ2H values that suggest that they were formed by hydration on or below the ocean floor. The development of high-pressure metamorphic
mineralogies in metagabbros occurred preferentially in zones that underwent sub-ocean-floor alteration and which contained
hydrated, fine-grained, reactive assemblages. Given that the transformation of blueschist-facies metabasic rocks to eclogite-facies
assemblages involves the breakdown of hydrous minerals (e.g. lawsonite, zoisite, and glaucophane), and will thus liberate
considerable volumes of fluids, metamorphic fluid flow must have been strongly channelled. High-pressure (quartz+calcite±omphacite±glaucophane±titanoclinohumite)
veins that cut the ophiolite rocks represent one possible channel; however, stable isotope and major element data suggest
that they were not formed from large volumes of exotic fluids. Fluids were more likely channelled along faults and shear zones
that were active during high-pressure metamorphism. Such strong fluid channelling may cause fluids to migrate toward the accretionary
wedge, especially along the slab–mantle interface, which is probably a major shear zone. This may preclude all but a small
fraction of the fluids entering the mantle wedge to flux melting. Additionally, because fluids probably interact with relatively
small volumes of rock in the channels, they cannot "scavenge" elements from the subducting slab efficiently.
Received: 28 January 1999 / Accepted: 2 February 1999 相似文献
19.
Wouter Heijlen Peter W.U. Appel Andy Horsewell 《Geochimica et cosmochimica acta》2006,70(12):3075-3095
Fluid inclusions in quartz globules and quartz veins of a 3.8-3.7 Ga old, well-preserved pillow lava breccia in the northeastern Isua Greenstone Belt (IGB) were studied using microthermometry, Raman spectrometry and SEM Cathodoluminescence Imaging. Petrographic study of the different quartz segregations showed that they were affected by variable recrystallization which controlled their fluid inclusion content. The oldest unaltered fluid inclusions found are present in vein crystals that survived dynamic and static recrystallization. These crystals contain a cogenetic, immiscible assemblage of CO2-rich (+H2O, +graphite) and brine-rich (+CO2, +halite, +carbonate) inclusions. The gas-rich inclusions have molar volumes between 44.8 and 47.5 cm3/mol, while the brine inclusions have a salinity of ∼33 eq. wt% NaCl. Modeling equilibrium immiscibility using volumetric and compositional properties of the endmember fluids indicates that fluid unmixing occurred at or near peak-metamorphic conditions of ∼460 °C and ∼4 kbar. Carbonate and graphite were precipitated cogenetically from the physically separated endmember fluids and were trapped in fluid inclusions.In most quartz crystals, however, recrystallization obliterated such early fluid inclusion assemblages and left graphite and carbonate as solid inclusions in recrystallized grains. Intragranular fluid inclusion trails in the recrystallized grains of breccia cementing and crosscutting quartz veins have CO2-rich assemblages, with distinctly different molar volumes (either between 43.7 and 47.5 cm3/mol or between 53.5 and 74.1 cm3/mol), and immiscible, halite-saturated H2O-CO2-NaCl(-other salt) inclusions. Later intergranular trails have CH4-H2 (XH2 up to ∼0.3) inclusions of variable density (ranging from 48.0 to >105.3 cm3/mol) and metastable H2O-NaCl(-other salt?) brines (∼28 eq. wt% NaCl). Finally, the youngest fluid inclusion assemblages are found in non-luminescent secondary quartz and contain low-density CH4 (molar volume > 105.33 cm3/mol) and low-salinity H2O-NaCl (0.2-3.7 eq. wt% NaCl). These successive fluid inclusion assemblages record a retrograde P-T evolution close to a geothermal gradient of ∼30 °C/km, but also indicate fluid pressure variations and the introduction of highly reducing fluids at ∼200-300 °C and 0.5-2 kbar. The quartz globules in the pillow fragments only contain sporadic CH4(+H2) and brine inclusions, corresponding with the late generations present in the cementing and crosscutting veins. We argue that due to the large extent of static recrystallization in quartz globules in the pillow breccia fragments, only these relatively late fluid inclusions have been preserved, and that they do not represent remnants of an early, seafloor-hydrothermal system as was previously proposed.Modeling the oxidation state of the fluids indicates a rock buffered system at peak-metamorphic conditions, but suggests a change towards fluid-graphite disequilibrium and a logfH2/fH2O above the Quartz-Fayalite-Magnetite buffer during retrograde evolution. Most likely, this indicates a control on redox conditions and on fluid speciation by ultramafic rocks in the IGB.Finally, this study shows that microscopic solid graphite in recrystallized metamorphic rocks from Isua can be deposited inorganically from a fluid phase, adding to the complexity of processes that formed reduced carbon in the oldest, well-preserved supracrustal rocks on Earth. 相似文献
20.
《International Geology Review》2012,54(12):1074-1093
The mineral-fluid equilibria that govern silica redistribution by aqueous fluids in subduction zones were evaluated at constant pressure and temperature in the model system MgO-SiO2-H2O (MSH). At <20 kbar and <1000° C, model H2O-SiO2 fluids liberated via devolatilization in subducting crust will be buffered at or near quartz saturation along any specified subduction P-T path, whereas fluids in equilibrium with model metaperidotites, ranging from dunite to orthopyroxenite protoliths, have silica concentrations significantly below quartz saturation. Isothermalisobaric flow of fluid from the slab to the mantle wedge therefore drives metasomatic reactions that increase the bulk silica content of metaperidotites and decrease the silica content of the fluid. The potential for silica metasomatism increases with depth for all subduction paths and model bulk compositions. At a given depth, the capacity for silica metasomatism increases with temperature and with abundance of forsterite relative to enstatite. Water-rock ratios required to produce metasomatic mineral assemblages decrease with increasing pressure and temperature. Mineral assemblages diagnostic of silica metasomatism at shallow subduction levels require water-rock ratios of >100 moles fluid/cm3 rock; but at depth, flow of only several moles fluid/cm3 rock is sufficient to produce assemblages characteristic of silica metasomatism. Decreasing temperature with time in most subduction zones suggests that the potential for silica metasomatism is greatest at early stages of convergence. Subducted ultramafic rocks showing evidence of high-temperature silica metasomatism therefore may provide windows into early subduction processes. In general, temporal changes in subduction parameters favoring increasing temperatures will enhance the potential for silica metasomatism, whereas those leading to lower temperatures should be expected to decrease the capacity for silica transfer with time. 相似文献