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1.
Fluid inclusions have been studied in three pegmatite fields in Galicia, NW Iberian Peninsula. Based on microthermometry
and Raman spectroscopy, eight fluid systems have been recognized. The first fluid may be considered to be a pegmatitic fluid
which is represented by daughter mineral (silicates)-rich aqueous inclusions. These inclusions are primary and formed above
500 °C (dissolution of daughter minerals). During pegmatite crystallization, this fluid evolved to a low-density, volatile-rich
aqueous fluid with low salinity (93% H2O; 5% CO2; 0.5% CH4; 0.2% N2; 1.3% NaCl) at minimum P–T conditions around 3 ± 0.5 kbar and 420 °C. This fluid is related to rare-metal mineralization. The volatile enrichment may
be due to mixing of magmatic fluids and fluids equilibrated with the host rock. A drop in pressure from 3 ± 0.5 to 1 kbar
at a temperature above 420 °C, which may be due to the transition from predominantly lithostatic to hydrostatic pressure,
is recorded by two-phase, water-rich inclusions with a low-density vapour phase (CO2, CH4 and N2). Another inclusion type is represented by two-phase, vapour-rich inclusions with a low-density vapour phase (CO2, CH4 and N2), indicating a last stage of decreasing temperature (360 °C) and pressure (around 0.5 kbar), probably due to progressive
exhumation. Finally, volatile (CO2)-rich aqueous inclusions, aqueous inclusions (H2O-NaCl) and mixed-salt aqueous inclusions with low Th, are secondary in charac- ter and represent independent episodes of hydrothermal fluid circulation below 310 °C and 0.5 kbar.
Received: 14 October 1999 / Accepted: 5 October 1999 相似文献
2.
The Archean Shawmere anorthosite lies within the granulite facies portion of the Kapuskasing Structural Zone (KSZ), Ontario,
and is crosscut by numerous linear alteration veins containing calcite + quartz ± dolomite ± zoisite ± clinozoisite ± margarite ±paragonite ± chlorite.
These veins roughly parallel the trend of the Ivanhoe Lake Cataclastic Zone. Equilibria involving clinozoisite + margarite + quartz ± calcite
± plagioclase show that the vein minerals were stable at T < 600 °C, XCO2 < 0.4 at P ≈ 6 kbar. The stabilities of margarite and paragonite in equilibrium with quartz are also consistent with T < 600 °C and XCO2 < 0.4 at 6 kbar. Additional assemblages consisting of calcite + clinochlore + quartz + talc + margarite indicate T < 500 °C with XCO2 > 0.9. Thus, vein formation, while clearly retrograde, spanned a range of temperatures, and fluid compositions evolved from
H2O-rich to CO2-rich. The calcite in the retrograde veins has δ18O values that range from 8.4 to 11.2‰ (average = +9.7 ± 0.9‰) and δ13C values that range from −3.9 to −1.6‰ (average = −3.1 ± 0.6‰). These values indicate that the fluids from which calcite precipitated
underwent extensive exchange with the anorthosite and other crustal lithologies. The fluids may have been initially derived
either from devolatilization of metamorphic rocks or crystallization of igneous rocks in the adjacent Abitibi subprovince.
Vein quartz contains CO2-rich fluid inclusions (final melting T = −57.0 to −58.7 °C) that range in size from 5 to 17 μm. Measured homogenization temperatures (T h) range from −44.0 to 14.5 °C, however for most inclusions (46 of S1), T h = −44.0 to −21.1 °C (ρCO2 ≈ 1.13 to 1.05 g/cm3). At 400 to 600 °C, these densities correspond to pressures of 3.5 to 7 kbar, which is the best estimate of pressures of
vein formation. It has been argued that some high density CO2-rich fluid inclusions found in the KSZ were formed during peak metamorphism and thus document the presence of a CO2-rich fluid during peak granulite facies metamorphism (Rudnick et al. 1984). The association of high density CO2-rich fluid inclusions with clearly retrograde veins documents the formation of similar composition and density inclusions
after the peak of metamorphism. Thus, the coincidence of entrapment pressures calculated from fluid inclusion density measurements
with peak metamorphic pressures alone should not be considered strong evidence for peak metamorphic inclusion entrapment.
All fluid inclusion results are consistent with an initially semi-isobaric retrograde P–T path.
Received: 2 April 1996 / Accepted: 15 November 1996 相似文献
3.
B. Cesare 《Contributions to Mineralogy and Petrology》1995,122(1-2):25-33
Equilibrium C–O–H fluid speciation calculations predict that graphite will precipitate from initially graphite saturated
fluid inclusions during cooling and exhumation of metamorphic rocks. In the case that no mass is gained or lost by the inclusions,
the original X
O ratio [O/(O+H)] of the fluid phase must be maintained. Given this closed system constraint, the down-temperature progress
of graphite precipitation can easily be monitored as a function of the varible X
O, and produces some effects that are of significance to fluid inclusion studies: 1. Variation of the H2O : CO2 : CH4 relationship in the graphite-saturated COH fluid, namely increase of X
H2
O and decrease of the carbonic fraction; 2. Decrease of fluid density due to precipitation of graphite, which is denser than
the residual fluid; 3. Alteration of the CO2 : CH4 ratio of the fluid, depending on the initial O : H ratio of the fluid: for X
O>1/3, fluids increase their CO2 : CH4 ratio with decreasing temperature, and vice-versa. This implies that the CO2 : CH4 ratio measured at room T will not represent the trapping value, which is in any case closer to unity. As a consequence of density reduction, isochores
extrapolated from densities observed at room temperature do not pass through the pressure-temperature conditions at which
the inclusion was trapped, with pressure underestimates of up to 2 kbar. Actual P-T trapping conditions are located along the equilibrium “bulk isochore” (curve of constant-X
O, constant-volume) of the fluid. Alteration of the CO2 : CH4 ratio is a mechanism by which a CO2-rich or CH4-rich carbonic phase can be formed from aqueous fluids that are slightly off the neutral X
O=1/3 value. Subsequent segregation of this phase from the aqueous counterpart may account for the formation of pure CO2 and CH4 fluids in the upper crust.
Received: 15 March 1995 / Accepted: 1 June 1995 相似文献
4.
High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids? 总被引:4,自引:0,他引:4
Fluid inclusions were studied in samples from the Ashanti, Konongo-Southern Cross, Prestea, Abosso/Damang and Ayanfuri gold
deposits in the Ashanti Belt, Ghana. Primary fluid inclusions in quartz from mineralised veins of the Ashanti, Prestea, Konongo-Southern
Cross, and Abosso/Damang deposits contain almost exclusively volatile species. The primary setting of the gaseous (i.e. the
fluid components CO2, CH4 and N2) fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids. Microthermometric
and Raman spectroscopic analyses of the inclusions revealed a CO2 dominated fluid with variable contents of N2 and traces of CH4. Water content of most inclusions is below the detection limits of the respective methods used. Aqueous inclusions are rare
in all samples with the exception of those from the granite-hosted Ayanfuri mineralisation. Here inclusions associated with
the gold mineralisation contain a low salinity (<6 eq.wt.% NaCl) aqueous solution with variable quantities of CO2. Microthermometric investigations revealed densities of the gaseous inclusions of 0.65 to 1.06 g/cm3 at Ashanti, 0.85 to 0.98 g/cm3 at Prestea, up to 1.02 g/cm3 at Konongo-Southern Cross, and 0.8 to 1.0 g/cm3 at Abosso/Damang. The fluid inclusion data are used to outline the PT ranges of gold mineralisation of the respective gold deposits. The high density gaseous inclusions found in the auriferous
quartz at Ashanti and Prestea imply rather high pressure trapping conditions of up to 5.4 kbar. In contrast, mineralisation
at Ayanfuri and Abosso/Damang is inferred to have occurred at lower pressures of only up to 2.2 kbar. Mesothermal gold mineralisation
is generally regarded to have formed from fluids characterized by H2O > CO2 and low salinity ( ± 6 eq.wt.%NaCl). However, fluid inclusions in quartz from the gold mineralisations in the Ashanti belt
point to distinctly different fluid compositions. Specifically, the predominance of CO2 and CO2 >> H2O have to be emphasized. Fluid systems with this unique bulk composition were apparently active over more than 200␣km along
strike of the Ashanti belt. Fluids rich in CO2 may present a hitherto unrecognised new category of ore-forming fluids.
Received: 30 May 1996 / Accepted: 8 October 1996 相似文献
5.
The high-pressure granulites of the Uluguru Mountains are part of the Pan-African belt of Tanzania, the metamorphic evolution
of which is characterized by an anticlockwise P-T path. Mineral assemblages that represent distinct metamorphic stages are selected for fluid inclusion studies in order to
deduce the fluid evolution in metapelites and pyroxene granulites from the prograde to the retrograde stage. Fluid inclusion
data improve the petrologically derived P-T path and confirm the anticlockwise evolution. Fluid inclusions in quartz enclosed in garnet porphyroblasts in metapelites
preserve prograde fluids of CO2–N2 composition and later-trapped pure CO2. During isochoric heating at temperatures near the peak of metamorphism, deformation and recrystallization led to fluid homogenization
yielding N2-poor CO2 composition in the metapelites. Near-peak CO2–N2 fluid inclusions in quartz of metapelites and CO2 inclusions in garnet-pyroxene granulites are characterized by perfect negative crystal shape. Garnet formed in veins and
as coronas around orthopyroxene represent the near-isochoric/isobaric cooling stage which is characterized by high-density
CO2-rich fluid inclusions. Up to 15 mol% N2 in some primary CO2 inclusions in corona garnet indicate small-scale fluid heterogeneity during the static garnet growth. The fact that high-density
fluid inclusions are preserved, suggests a shallow dP/dT slope of the uplift path. Nevertheless, some fluid inclusions decrepitated or re-equilibrated and low-density CO2 inclusions were trapped in the garnet-pyroxene granulite while N2–CH4 inclusions formed in the metapelites. Different fluid compositions in metapelite and metabasite argue for an internal control
of the fluid composition by phase equilibria. In shear zones where the pyroxene granulite was transformed into scapolite-biotite
schist, CO2–N2 and low-density N2–CH4 fluid inclusions indicate several stages of tectonic activity and suggest fluid influx from the nearby metapelites. High-
and low-salinity aqueous inclusions observed beside CO2 inclusions in garnet-pyroxene granulites, in vein quartz and shear zones could be of high-grade origin but are mainly re-equilibrated
or re-trapped along healed microfractures during lower-grade stages.
Received: 21 May 1997 / Accepted: 6 October 1997 相似文献
6.
Gold ore-forming fluids of the Tanami region, Northern Australia 总被引:1,自引:0,他引:1
Fluid inclusion studies have been carried out on major gold deposits and prospects in the Tanami region to determine the compositions
of the associated fluids and the processes responsible for gold mineralization. Pre-ore, milky quartz veins contain only two-phase
aqueous inclusions with salinities ≤19 wt% NaCl eq. and homogenization temperatures that range from 110 to 410°C. In contrast,
the ore-bearing veins typically contain low to moderate salinity (<14 wt% NaCl eq.), H2O + CO2 ± CH4 ± N2-bearing fluids. The CO2-bearing inclusions coexist with two-phase aqueous inclusions that exhibit a wider range of salinities (≤21 wt% NaCl eq.).
Post-ore quartz and carbonate veins contain mainly two-phase aqueous inclusions, with a last generation of aqueous inclusions
being very CaCl2-rich. Salinities range from 7 to 33 wt% NaCl eq. and homogenization temperatures vary from 62 to 312°C. Gold deposits in
the Tanami region are hosted by carbonaceous or iron-rich sedimentary rocks and/or mafic rocks. They formed over a range of
depths at temperatures from 200 to 430°C. The Groundrush deposit formed at the greatest temperatures and depths (260–430°C
and ≤11 km), whereas deposits in the Tanami goldfield formed at the lowest temperatures (≥200°C) and at the shallowest depths
(1.5–5.6 km). There is also evidence in the Tanami goldfield for late-stage isothermal mixing with higher salinity (≤21 wt%
NaCl eq.) fluids at temperatures between 100 and 200°C. Other deposits (e.g., The Granites, Callie, and Coyote) formed at
intermediate depths and at temperatures ranging from 240 to 360°C. All ore fluids contained CO2 ± N2 ± CH4, with the more deeply formed deposits being enriched in CH4 and higher level deposits being enriched in CO2. Fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of N2. The one exception is the Tanami goldfield, where the quartz veins were dominated by aqueous inclusions with rare CO2-bearing inclusions. Calculated δ
18O values for the ore fluids range from 3.8 to 8.5‰ and the corresponding δD values range from −89 to −37‰. Measured δ
13C values from CO2 extracted from fluid inclusions ranged from −5.1 to −8.4‰. These data indicate a magmatic or mixed magmatic/metamorphic source
for the ore fluids in the Tanami region. Interpretation of the fluid inclusion, alteration, and structural data suggests that
mineralization may have occurred via a number of processes. Gold occurs in veins associated with brittle fracturing and other
dilational structures, but in the larger deposits, there is also an association with iron-rich rocks or carbonaceous sediments,
suggesting that both structural and chemical controls are important. The major mineralization process appears to be boiling/effervescence
of a gas-rich fluid, which leads to partitioning of H2S into the vapor phase resulting in gold precipitation. However, some deposits also show evidence of desulfidation by fluid–rock
interaction and/or reduction of the ore-fluid by fluid mixing. These latter processes are generally more prevalent in the
higher crustal-level deposits. 相似文献
7.
Summary ?Fluid inclusions from two Mesoproterozoic, metamorphosed layered intrusive complexes, Niquelandia and Barro Alto, Goiás State,
Brazil record multiple fluid influx events from the magmatic to granulitic and retrograde metamorphic stages.
1. The oldest inclusions contain high density CO2 ± N2 ± CH4 and are found as primaries in plagioclase and orthopyroxene in mafic granulite with homogenization temperatures between − 48
and − 28 °C. These inclusions may correspond to the early, magmatic stage. This type was found in samples from both the Niquelandia
and the Barro Alto complexes.
2. Intragranular, relatively high density CO2 + N2 inclusions (Th between − 33 and − 26 °C) together with decrepitated and reequilibrated N2 inclusions (Th between − 160 and − 151 °C) in the rock-forming minerals can be associated with the granulite facies metamorphism. Such inclusions
were found only in the Barro Alto complex.
3. Transgranular, high density, CO2–N2 inclusions (93% CO2 and 7% N2, according to Raman analysis, with Th between − 66.6 and − 50.4 °C) as well as the low density, secondary CO2 ± N2 ± CH4 inclusions (Th between − 13.0 and + 18.7 °C) and the H2O–NaCl–CaCl2 hypersaline inclusions (with halite dissolution temperature between 132 and 354 °C, and Th between 212 and 490 °C) are attributed to different fluid influx events during the retrograde metamorphism. This inclusion
type can be found both in the Niquelandia and in the Barro Alto complexes.
The fluid inclusion textures and compositions show several stages of fluid evolution. The fluid inclusion measurements and
the geothermobarometric data indicate an anticlockwise P-T path for both the Barro Alto and the Niquelandia complexes.
Received October 16, 2000; revised version accepted November 20, 2001 相似文献
8.
G. GIORGETTI M.-L.E FREZZOTTI R. PALMERI E. A. J. BURKE 《Journal of Metamorphic Geology》1996,14(3):307-317
ABSTRACT The metasedimentary sequence of the Deep Freeze Range (northern Victoria Land, Antarctica) experienced high-T/low-F metamorphism during the Cambro-Ordovician Ross orogeny. The reaction Bt + Sil + Qtz = Grt + Crd + Kfs + melt was responsible for the formation of migmatites. Peak conditions were c. 700–750° C, c. 3.5–5 kbar and xH2Oc. 0.5). Distribution of fluid inclusions is controlled by host rock type: (1) CO2-H2O fluid inclusions occur only in graphite-free leucosomes; (2) CO2–CH4± H2O fluid inclusions are the most common type in leucosomes, and in graphite-bearing mesosomes and gneiss; and (3) CO2–N2–CH4 fluid inclusions are observed only in the gneiss, and subordinately in mesosomes. CO2–H2O mixtures (41% CO2, 58% H2O, 1% Nad mol.%) are interpreted as remnants of a synmig-matization fluid; their composition and density are compatible P–T–aH2O conditions of migmatization (c. 750° C, c. 4 kbar, xH2Oc. 0.5). CO2-H2O fluid in graphite-free leucosomes cannot originate via partial melting of graphite-bearing mesosomes in a closed system; this would have produced a mixed CO2–CH4 fluid in the leucosomes by a reaction such as Bt + Sil + Qtz + C ± H2O = Grt + Crd + Kfs + L + CO2+ CH4. We conclude that an externally derived oxidizing CO2-H2O fluid was present in the middle crust and initiated anatexis. High-density CO2-rich fluid with traces of CH4 characterizes the retrograde evolution of these rocks at high temperatures and support isobaric cooling (P–T anticlockwise path). In unmigmatized gneiss, mixed CO2–N2–CH4 fluid yields isochores compatible with peak metamorphic conditions (c. 700–750° C, c. 4–4.5 kbar); they may represent a peak metamorphic fluid that pre-dated the migmatization. 相似文献
9.
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
10.
C. CASQUET 《Journal of Metamorphic Geology》1986,4(2):117-130
Abstract The Berzosa fault is a major ductile shear zone, the Berzosa Shear Zone (BSZ), which separates the ‘Ollo de Sapo’anticline from the inner higher-grade crystalline axis of the Iberian Hercynian Belt. This shear zone is the site of abundant early kinematic quartz (± Al-silicates) segregations, rich in fluid inclusions. Host rocks are medium-grade staurolite schists and sillimanite gneisses. Fluid inclusions in selected quartz segregations across the Berzosa shear zone have been studied by microthermometric methods as well as, in some instances, by Raman analysis. The recorded fluid inclusion history begins at the end of an intense secondary recrystallization period during late-peak metamorphic conditions and lasts until late in the uplift history of the zone. Three types of inclusions have been found, which in a time sequence are: CO2± H2O; H2O+salt (B-type); and, N2+CH4. Three types of B inclusion may be distinguished in turn, depending on whether they were trapped during an earlier dynamic-recovery phase (B1-type), formed later as intergranular trails (B2-type), or were trapped apparently along with N2+CH4 in clusions from a heterogeneous fluid (B3-type). Considerations from isochores confirm that CO2± H2O inclusions were trapped during late-peak and high-T retrograde metamorphic conditions (in the range 650–500°C and 5–2 kbar), whilst N2+CH4 inclusions, along with the B3-type of inclusions, formed at low-pressures (<1 kbar) and temperatures (± 300°C). B2-type inclusions were trapped chronologically between these two in a period in which strong inverse lateral thermal gradients developed in the zone. Inferred P-T paths for the area are convex to the T-axis. 相似文献
11.
Well-formed, texturally-early fluid inclusions in garnets from the Archean Pikwitonei granulite domain, Manitoba, Canada,
have been analyzed using microthermometric methods. The mean CO2 homogenization temperature (to liquid) for inclusions in 12 of 13 samples from the Cauchon Lake-Nelson River area is +15.2°
C (n=125, 2σ=8.2° C), corresponding to a CO2 density of 0.82 g/cm3. Inclusions in the remaining sample have somewhat lower CO2 homogenization temperatures (mean=+5.4° C, n=24). The studied inclusions contain an estimated 10 to 20 vol. percent H2O, with minor amounts of other fluid species such as CH4, N2, and/or H2S. The fluid inclusions were probably trapped during early garnet growth at relatively low pressures (≤5 kbar if at 750° C),
and appear to have undergone only limited or possibly no subsequent re-equilibration. This interpretation is consistent with
the “anti-clock-wise” P-T-t path (heating before loading) determined for the Pikwitonei region by other workers. For such a prograde path, inclusions
entrapped early, at high temperatures but at relatively low pressures, would experience internal underpressures during most
of the subsequent prograde and retrograde phases of metamorphism. The texturally-early fluid inclusions in garnets from the
Pikwitonei region therefore cannot be used to provide direct information about the highest metamorphic temperature and pressure conditions (750° C and 7 kbar). However, the results obtained in this study suggest that texturally-early fluid
inclusions in garnets may, in some cases, retain evidence of the prograde metamorphic path. 相似文献
12.
Phase equilibria in the ternary system H2O-CO2-NaCl were studied at 800 °C and 9 kbar in internally heated gas pressure vessels using a modified synthetic fluid inclusion
technique. The low rate of quartz overgrowth along the `b' and `a' axes of quartz crystals was used to avoid fluid inclusion
formation during heating, prior to attainment of equilibrium run conditions. The density of CO2 in the synthetic fluid inclusions was calibrated using inclusions in the binary H2O-CO2 system synthesised by the same method and measured on the same heating-freezing stage. In the two-phase field, two types
of fluid inclusions with different densities of CO2 were observed. Using mass balance calculations, these inclusions are used to constrain the miscibility gap and the orientation
of two-phase tie-lines in the H2O-CO2-NaCl system at 800 °C and 9 kbar. The equation of state of Duan et al. (1995) approximately describes the P-T section of the ternary system up to about 40 wt% of NaCl. At higher NaCl concentrations the measured solubility of CO2 in the brine is much smaller than predicted by the EOS. A “salting out” effect must be added to the equation of state to
include coulomb interaction in the model of Anderko and Pitzer (1993) and Pitzer and Jiang (1996). The new experimental data
together with published data up to 5 kbar (Shmulovich et al. 1995) encompass practically all subsolidus crustal P-T conditions. A feature of the new experimental results is the large compositional range in the H2O-CO2-NaCl system occupied by the stability fields of halite + CO2-rich fluid ± H2O-NaCl brine. The prediction of halite stability in equilibrium with CO2-rich fluid in deep-crustal rocks is supported by recent petrological and fluid inclusion studies of granulites.
Received: 29 June 1998 / Accepted: 17 March 1999 相似文献
13.
Maria Luce Frezzotti Gianfranco Di Vincenzo Claudio Ghezzo Ernst A. J. Burke 《Contributions to Mineralogy and Petrology》1994,117(2):111-123
Fine-grained peraluminous synkinematic leuco-monzogranites (SKG), of Cambro-Ordovician age, occur as veins and sills (up to 20–30 m thick) in the Deep Freeze Range, within the medium to high-grade metamorphics of the Wilson Terrane. Secondary fibrolite + graphite intergrowths occur in feldspars and subordinately in quartz. Four main solid and fluid inclusion populations are observed: primary mixed CO2+H2O inclusions + Al2SiO5 ± brines in garnet (type 1); early CO2-rich inclusions (± brines) in quartz (type 2); early CO2+CH4 (up to 4 mol%)±H2O inclusions + graphite + fibrolite in quartz (type 3); late CH4+CO2+N2 inclusions and H2O inclusions in quartz (type 4). Densities of type 1 inclusions are consistent with the crystallization conditions of SKG (750°C and 3 kbar). The other types are post-magmatic: densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature (700–550°C). Type 4 inclusions were trapped below 500°C. The SKG crystallized from a magma that was at some stage vapour-saturated; fluids were CO2-rich, possibly with immiscible brines. CO2-rich fluids (±brines) characterize the transition from magmatic to post-magmatic stages; progressive isobaric cooling (T<670°C) led to a continuous decrease off
O
2 can entering in the graphite stability field; at the same time, the feldspars reacted with CO2-rich fluids to give secondary fibrolite + graphite. Decrease ofT andf
O
2 can explain the progressive variation in the fluid composition from CO2-rich to CH4 and water dominated in a closed system (in situ evolution). The presence of N2 the late stages indicates interaction with external metamorphic fluids.Contribution within the network Hydrothermal/metamorphic water-rock interactions in crystalline rocks: a multidisciplinary approach on paleofluid analysis. CEC program: Human Capital and Mobility 相似文献
14.
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
15.
Gold mineralization in the Kolar schist belt of the Dharwar craton occurs dominantly in the form of a sulfide-poor Au-quartz
lode (the Champion lode exposed in the Mysore and other mines) and sulfide-rich auriferous lodes (from the Nundydroog mine).
Fluid inclusion microthermometric experiments were conducted on primary inclusions in quartz intimately associated with Au-mineralization.
Homogenization studies on aqueous-biphase (L + V), aqueous polyphase (L + V+ halite) and aqueous-carbonic (LCO2± VCO2 + Laq) inclusions from the Champion lode furnish a temperature range of 120 to 420 °C. Freezing of aqueous biphase inclusions and
dissolution of halite in the aqueous polyphase inclusions provide salinity of 5 to 50 wt.% NaCl equivalent. Fluid inclusion
thermobarometry from the total homogenization of aqueous-carbonic inclusions and from intersecting isochores of coeval pure-carbonic
(LCO2± VCO2) and pure-aqueous inclusions constrain the P-T path of evolution of the fluid in the Champion lode. Gold precipitation was likely to have been brought about in response
to a sharp fall in pressure with attendant unmixing of liquid-CO2 from the parent H2O-CO2 fluid of possible metamorphic origin. This would imply transportation of gold by some pressure-sensitive complex such as
the Au-carbonyl. Fluid characteristics are different in the sulfide-rich auriferous lodes, as indicated by the virtual absence
of the CO2-bearing and the halite-bearing inclusions. The fluid evolution path, as evident from the crude positive colinearity of temperature
and salinity, is due to mixing of a low (≤200 °C) temperature-low saline (≤7 wt.% NaCl equivalent) fluid with a high temperature
(≥400 °C)-high saline (≥50 wt.% NaCl equivalent) fluid. The lack of CO2 and association of Au with sulfides indicate a different mode of gold transport, as chloride or bisulfide complexing, deposition
of which was possibly brought about by fluid mixing.
Received: 17 April 1997 / Accepted: 30 June 1998 相似文献
16.
Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong gold province, China 总被引:45,自引:0,他引:45
The Sanshandao gold deposit, with total resources of more than 60 t of gold, is located in the Jiaodong gold province, the most important gold province of China. The deposit is a typical highly fractured and altered, disseminated gold system, with high-grade, quartz-sulphide vein/veinlet stockworks that cut Mesozoic granodiorite. There are four stages of veins that developed in the following sequence: (1) quartz-K-feldspar-sericite; (2) quartz-pyrite±arsenopyrite; (3) quartz-base metal sulfide; and (4) quartz-carbonate. Fluid inclusions in quartz and calcite in vein/veinlet stockworks contain C-O-H fluids of three main types. The first type consists of dilute CO2–H2O fluids coeval with the early vein stage. Molar volumes of these CO2–H2O fluid inclusions, ranging from 50–60 cm3/mol, yield estimated minimum trapping pressures of 3 kbar. Homogenization temperatures, obtained mainly from CO2–H2O inclusions with lower CO2 concentration, range from 267–375 °C. The second inclusion type, with a CO2–H2O±CH4 composition, was trapped during the main mineralizing stages. These fluids may reflect the CO2–H2O fluids that were modified by fluid/rock reactions with altered wallrocks. Isochores for CO2-H2O±CH4 inclusions, with homogenization temperatures ranging from 204–325 °C and molar volumes from 55 to 70 cm3/mol, provide an estimated minimum trapping pressure of 1.2 kbar. The third inclusion type, aqueous inclusions, trapped in cross-cutting microfractures in quartz and randomly in calcite, are post-mineralization, and have homogenization temperatures between 143–228 °C and salinities from 0.71–7.86 wt% NaCl equiv. Stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin, most likely sourced from 120–126 Ma mafic to intermediate dikes. This is consistent with the carbonic nature of the fluid, and the cross-cutting nature of those deposits relative to the host Mesozoic granitoid.Editorial handling: R.J. Goldfarb 相似文献
17.
Quartz–carbonate–chlorite veins were studied in borehole samples of the RWTH-1 well in Aachen. Veins formed in Devonian rocks
in the footwall of the Aachen thrust during Variscan deformation and associated fluid flow. Primary fluid inclusions indicate
subsolvus unmixing of a homogenous H2O–CO2–CH4–(N2)–Na–(K)–Cl fluid into a H2O–Na–(K)–Cl solution and a vapour-rich CO2–(H2O, CH4, N2) fluid. The aqueous end-member composition resembles that of metamorphic fluids of the Variscan front zone with salinities
ranging from 4 to 7% NaCl equiv. and maximum homogenisation temperatures of close to 400°C. Pressure estimates indicate a
burial depth between 4,500 and 8,000 m at geothermal gradients between 50 and 75°C/26 MPa, but pressure decrease to sublithostatic
conditions is also indicated, probably as a consequence of fracture opening during episodic seismic activity. A second fluid
system, mainly preserved in pseudo-secondary and secondary fluid inclusions, is characterised by fluid temperatures between
200 and 250°C and salinities of <5% NaCl equiv. Bulk stable isotope analyses of fluids released from vein quartz, calcite,
and dolomite by decrepitation yielded δDH2O values from −89 to −113 ‰, δ13CCH4 from −26.9 to −28.9‰ (VPDB) and δ13CCO2 from −12.8 to −23.3‰ (VPDB). The low δD and δ13C range of the fluids is considered to be due to interaction with cracked hydrocarbons. The second fluid influx caused partial
isotope exchange and disequilibrium. It is envisaged that an initial short lived flux of hot metamorphic fluids expelled from
the epizonal metamorphic domains of the Stavelot–Venn massif. The metamorphic fluid was focused along major thrust faults
of the Variscan front zone such as the Aachen thrust. A second fluid influx was introduced from formation waters in the footwall
of the Aachen thrust as a consequence of progressive deformation. Mixing of the cooler and lower salinity formation water
with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion
characteristics. 相似文献
18.
Scheelite mineralization accompanied by muscovite and albite, and traces of Mo-stolzite and stolzite occurs in epigenetic
quartz vein systems hosted by two-mica gneissic schists, and locally amphibolites, of the Paleozoic or older Vertiskos Formation,
in the Metaggitsi area, central Chalkidiki, N Greece. Three types of primary fluid inclusions coexist in quartz and scheelite:
type 1, the most abundant, consists of mixed H2O-CO2 inclusions with highly variable (20–90 vol.%) CO2 contents and salinities between 0.2 and 8.3 equivalent weight % NaCl. Densities range from 0.79 to 0.99 g/cc; type 1 inclusions
contain also traces (<2 mol%) of CH4. Type 2 inclusions are nearly 100 vol.% liquid CO2, with traces of CH4, and densities between 0.75 and 0.88 g/cc. Type 3 inclusions, the least abundant, contain an aqueous liquid of low salinity
(0.5 to 8.5 equivalent weight% NaCl) with 10–30 vol.% H2O gas infrequently containing also small amounts of CO2 (<2 mol%); densities range from 0.72 to 0.99 g/cc. The wide range of coexisting fluid inclusion compositions is interpreted
as a result of fluid immiscibility during entrapment. Immiscibility is documented by the partitioning of CH4 and CO2, into gas-rich (CO2-rich) type 1 inclusions, and the conformity of end-member compositions trapped in type 1 inclusions to chemical equilibrium
fractionation at the minimum measured homogenization temperatures, and calculated homogenization pressures. Minimum measured
homogenization temperatures of aqueous and gas-rich type 1 inclusions of 220°–250 °C, either to the H2O, or to the CO2 phase, is considered the best estimate of temperature of formation of the veins, and temperature of scheelite deposition.
Corresponding fluid pressures were between 1.2 and 2.6 kbar. Oxygen fugacities during mineralization varied from 10−35 to 10−31 bar and were slightly above the synthetic Ni-NiO buffer values. The fluid inclusion data combined with δ18O water values of 3 to 6 per mil (SMOW) and δ13C CO2− fluid of −1.2 to +4.3 per mil (PDB), together with geologic data, indicate generation of mineralizing fluids primarily by
late- to post-metamorphic devolatilization reactions.
Received: 8 April 1997 / Accepted: 8 July 1997 相似文献
19.
Fluid inclusions from a biotite-garnet schist in the Southern Aravalli Mountain Belt (India) give information on both peak
metamorphic conditions and post-peak metamorphic processes during uplift. A combination of careful petrography, microthermometry
and Raman spectroscopy reveals the presence of at least five generations of enclosed fluids. Lower amphibolite-facies pressure-temperature
conditions of the growth of garnet rims are reproduced by the highest fluid density of the relatively oldest inclusion type
of CO2 (±N2)-rich compositions. A calculated fluid composition in the COH system, in equilibrium with the graphite buffer corresponds
to a CO2-rich fluid at metamorphic conditions. However, the results of these calculations are very sensitive to small fluctuations
in oxygen fugacity and the accuracy of thermodynamic properties of mineral equilibria. Re-equilibration, conceived by specific
size-density distribution and the absence of an aqueous phase in inclusions that contain nahcolite crystals, is monitored
in these inclusions as post-peak metamorphic processes, like partial decrepitation and preferential leakage. The other fluid
types represent heterogeneous fluid trapping of coexisting aqueous NaCl-bearing solutions with CO2-CH4-rich vapour bubbles in healed cracks, and probably the introduction of external fluids containing high salinity aqueous CaCl2-rich solutions in nearly pure N2 vapour bubbles, at lower P-T conditions. This study illustrates that fluid inclusions remain a valuable database of peak metamorphic conditions, moreover,
alterations of the entrapped fluids and surrounding crystals are illustrative for specific exhumation evolutions.
Received: 24 March 1999 / Accepted: 13 January 2000 相似文献
20.
V. S. Shatsky E. Jagoutz N. V. Sobolev O. A. Kozmenko V. S. Parkhomenko M. Troesch 《Contributions to Mineralogy and Petrology》1999,137(3):185-205
Isotopic and geochemical data of the Zerenda series metamorphic rocks from the Kokchetav massif are reported. Some of these
rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism (P > 40 kbar, T = 900–1000 °C). The diamond-bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks.
The REE patterns range from LREE depleted to slightly LREE enriched [chondrite normalized (La/Yb)N– 0.1–5.4] with a negative Eu anomaly. They are depleted in incompatible elements (e.g. Sr, Ba, U, Th) with respect to the
upper crust. In contrast non-diamondiferous rocks of the Zerenda series exhibit normal crustal geochemistry. All rocks of
the Zerenda series have very radiogenic lead isotopes. The measured μ values (238U/204Pb) compared with those calculated for the interval between crust formation and ultrahigh pressure (UHP) metamorphism suggest a decrease by factors of up to 200 during the UHP metamorphism. The Sm-Nd mineral isochrons from the diamond-bearing rocks and other rock types of the Zerenda series give
a Middle Cambrian (524–535 Ma) age of metamorphism. The Nd model ages show that crust formation occurred about 2.3 Ga ago.
Significant fractionation of Sm and Nd and loss of incompatible elements may be due to partial melting of the protoliths.
The Ar-Ar age determinations of secondary biotite and muscovite from the diamond-bearing rocks yield an age of 517 ± 5 Ma.
This cooling age requires a short time interval between UHP metamorphism and uplift to a crustal level. Ultrahigh pressure metamorphism might be a significant source of Pb for the mantle.
We propose that the radiogenic Pb of the oceanic array is the contamination traces of numerous UHP events. Beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using Nd isotopes.
We compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the Sm-Nd system
during very high grade metamorphic events.
Received: 14 August 1998 / Accepted: 1 June 1999 相似文献