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1.
On the basis of fluid inclusion evidence, pervasive influx of deep-seated CO2-rich fluids has been invoked to account for mid- to upper amphibolite facies (M2B) metamorphism on the island of Naxos (Cyclades, Greece). In this paper, mineral devolatilization and melt equilibria are used to constrain the composition of both syn- and post-peak-M2B fluids in the deepest exposed levels of the metamorphic complex. The results indicate that peak-M2B fluids were spatially and compositionally heterogeneous throughout the high-grade core of the complex, whereas post-peak-M2B fluids were generally water-rich. The observed heterogeneities in syn-M2B fluid composition are inconsistent with pervasive CO2-flushing models invoked by previous workers on the basis of fluid inclusion evidence. It is likely that few CO2-rich fluid inclusions on Naxos preserve fluids trapped under peak metamorphic conditions. It is suggested that many of these inclusions have behaved as chemically open systems during the intense deformation that accompanied the uplift of the metamorphic complex. A similar process may explain the occurrence of some CO2-rich fluid inclusions in granulite facies rocks.  相似文献   

2.
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   

3.
Abstract Quartz-hosted, synthetic CO2-H2O fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory-simulated metamorphic re-equilibration at 650, 750 and 825°C and 1.5 kbar total pressure with fO2 defined by the C-CH4 buffer. Microthermometry and Raman spectroscopy show that the initial CO2-H2O inclusions become CO2-CH4-H2-H2O
inclusions after diffusive influx of hydrogen from the reducing confining medium. Measurable changes are observed in inclusion compositions after only 15 days of re-equilibration, implying significant hydrogen mobility at still lower temperatures over geological time spans. Results of synthetic inclusion re-equilibrium experiments have profound implications for the interpretation of natural fluid-inclusion data; failure to account for potential hydrogen migration in inclusions from high-temperature geological environments may lead to erroneous estimates of P-T, and/or the compositions of metamorphic fluids.  相似文献   

4.
Abstract Fluids, some of which are CO2-rich (up to 40 mol.% CO2) and some of which are highly saline (up to 18 wt% NaCl equivalent), are trapped as fluid inclusions in quartz-calcite (∼ metallic minerals) veins which cross-cut the pumpellyite-actinolite to amphibolite facies rocks of the Alpine Schist. Fluids were commonly trapped as immiscible liquid-vapour mixes in quartz and calcite showing open-space growth textures. Fluid entrapment occurred at fluid pressures near 500 bars (possibly as low as 150 bars) at temperatures ranging from 260 to 330° C. Saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low-density CO2-rich fluid. Calcite deposited by these fluids has δ13C ranging from – 8.4 to – 11.5 and δ18O from + 4 to + 13. Isotopic data, fluid compositions and mode of occurrence suggest that the fluids are derived from high-grade metamorphic rocks. Fluid interaction with wall-rock has caused biotite crystallization and/or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks.
Fluid penetration through the rock is almost pervasive in many areas where permeability, probably related to Alpine Fault activity, has focussed fluids on a regional scale into fractured rocks. The fluid flow process is made possible by high uplift-rates (in excess of 10 mm/year) bringing hot rocks near to the surface.  相似文献   

5.
Abstract Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic zone (CTZ) of the southern Abitibi region in north-western Quebec. At McWatters, the CTZ contains slices of metavolcanic units bounded by corridors of highly strained and altered rocks. Mineral assemblages of the metabasites record the metamorphic evolution of the CTZ.
The McWatters metabasalts and metagabbros have similar chemistry but different mineral assemblages consisting of variable amounts of actinolite, hornblende, chlorite, albite, epidote, quartz, carbonates, titanite, biotite, rutile, magnetite, ilmenite and sulphides. The different mineral assemblages, which coexist in a single tectonic slice, can be divided into three types, characterized by (A) presence of hornblende and actinolite, (B) presence of actinolite and epidote, and (C) absence of amphibole and epidote. Partial replacements indicate that these mineral assemblages are not in equilibrium. The hornblende of the least altered and deformed samples of the type A assemblage is a relict of a prograde metamorphic event, contemporaneous with the development of the main schistosity. The prograde conditions are estimated at P = 5 kbar, T = 475° C with low Pf . The more altered and deformed samples of the type C assemblage record a later retrograde metamorphic event. Conditions of the later event are estimated at P = 4 kbar, T = 400° C with higher Pf . Widespread calcite precipitation occurred during a later episode. The diversity of the mineral assemblages results from permeability variations along the high-strain zones of the CTZ.  相似文献   

6.
One-dimensional advection-dispersion models predict that characteristic δ18O vs. distance and δ18O vs. δ13C profiles should be produced during isothermal metamorphic fluid flow under equilibrium conditions. However, the patterns of isotopic resetting in rocks that have experienced fluid flow are often different from the predictions. Two-dimensional advection-dispersion simulations in systems with simple geometries suggest that such differences may be as a result of fluid channelling and need not indicate disequilibrium, high dispersivities, or polythermal flow. The patterns of isotopic resetting are a function of: (1) the permeability contrast between more permeable layers ('channels') and less permeable layers ('matrix'); (2) the width and spacing of the channels; (3) the width and spacing of discrete fractures; and (4) the orientation of the pressure gradient with respect to layering. In fractured systems, the efficiency of isotopic transport depends on the fracture aperture and the permeability of the surrounding rock. Resetting initially occurs along and immediately adjacent to the fractures, but with time isotopic resetting because of flow through the rock as a whole increases in importance. Application of the one-dimensional advection-dispersion equations to metamorphic fluid flow systems may yield incorrect estimates of fluid fluxes, intrinsic permeabilities, dispersivities, and permeability contrasts unless fluid flow occurred through zones of high permeability that were separated by relatively impermeable layers.  相似文献   

7.
A spatial association is observed between the size distribution of garnet porphyroblasts and the size distribution of quartz veins in greenschist facies metapelites from Troms, North Norway. The size distribution of quartz veins reflects the flow regime of metamorphic fluids. The hypothesis that the flow regime of metamorphic fluids is also responsible for the size distribution of garnet crystals was tested by ascribing empirical acceleration parameters to the nucleation and growth rates of garnet crystals.
In regions where fluid flow was interpreted as pervasive', acceleration parameters for nucleation were high, whereas in regions where fluid flow was interpreted as channelled', acceleration parameters for growth were high. Accelerated crystal growth is further implied from the chemical zoning and crystal morphologies of garnets collected near discrete veins.
This spatial association may imply that fluid flow can be instrumental in controlling garnet crystallization. Fluid flow could affect garnet crystallization kinetics by facilitating thermal advection and/or mass transfer. In the study area, rhodochrosite (MnCO3) veins provide evidence for mass transfer of Mn by fluid flow. An influx of Mn would expand the stability field of garnet to lower temperatures. The resulting thermal overstep could accelerate nucleation and/or growth of garnets.
The corollary of this study is that size distributions and chemical zoning of garnets, or other porphyroblast phases, can be used to study metamorphic fluid flow.  相似文献   

8.
The field relations from a quarry at Nuliyam, South India, illustrate dehydration of an amphibolite facies gneiss to granulite facies charnockite by CO2 influx, over a scale of 30 m. Both the calc-silicate source of the fluids and the full extent of their penetration into the gneiss are preserved in a continuous section. Fluid flow is by a hydraulic fracture mechanism, but is thought to be pervasive. The sharp reaction front predicted by the continuum mechanical theory for advective fluid transport is not observed. The front spreading is on too large a scale for either diffusive or dispersive control and is due to local kinetic disequilibrium between the fluid and rock, although the divariant nature of the reaction may also have a limited effect. The time-integrated fluid flux varies from the instantaneous porosity at the fluid front to 20 vol. % adjacent to the calc-silicate. Carbon isotope budgets suggest that decarbonation of the calc-silicate by a Rayleigh fractionation process provides a sufficient source for the CO2 influxing into the gneiss. Graphite abundances vary from 0.01 to 0.1% (by weight), it is principally derived by precipitation from the fluid and may be modelled from phase equilibria. Carbon isotope fronts coincide with the reaction front on the scale of sampling, although isotopic disequilibrium between graphite and inclusion-CO2 also implies local fluid-rock disequilibrium.  相似文献   

9.
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   

10.
Abstract. Primary fluid inclusions in quartz and carbonates from the Kanggur gold deposit are dominated by aqueous inclusions, with subsidiary CO2-H2O inclusions that have a constant range in CO2 content (10–20 vol %). Microthermometric results indicate that total homogenization temperatures have a wide but similar range for both aqueous inclusions (120 to 310C) and CO2-H2O inclusions (140 to 340C). Estimates of fluid salinity for CO2-H2O inclusions are quite restricted (5.9∼10.3 equiv. wt% NaCl), whereas aqueous inclusions show much wider salinity ranging from 2.2 to 15.6 equivalent wt %NaCl.
The 6D values of fluid inclusions in carbonates vary from -45 to -61 %, in well accord with the published δD values of fluid inclusions in quartz (-46 to -66 %). Most of the δ18O and δD values of the ore-forming fluids can be achieved by exchanged meteoric water after isotopic equilibration with wall rock by fluid/rock interaction at a low water/rock ratio. However, the exchanged meteoric water alone cannot explain the full range of δ18O and δD values, magmatic and/or meta-morphic water should also be involved. The wide salinity in aqueous inclusions may also result from mixing of meteoric water and magmatic and/or metamorphic water.  相似文献   

11.
增强型地热系统(EGS)中高温岩石与流体之间的对流换热特征一直以来是干热岩(HDR)研究的重要基础内容。岩石导热热阻对裂隙对流换热特征具有重要影响。为研究其具体影响,综合运用理论解析与数值模拟2种研究方法,通过对解析解讨论以及建立数值模型,研究两平行光滑平板之间的换热规律。结果表明：流体速度、传热边界层充分发展时,局部努塞尔特准数Nux为定值,与其他因素无关;局部对流换热系数hx仅与流体热导率k和裂隙开度e有关,与其他因素无关。上下平板壁面热流恒定时,Nux为8.235;温度恒定时,Nux为7.54。然后建立多组导热热阻不同的岩石裂隙对流换热数值模型,发现岩石导热热阻增大,温度场进口段延长,对流换热系数h增大。岩石长度显著影响进口段占比,进而影响h的大小。h随着长度增大而减小;当岩石长度足够长时,进口段占比足够小,此时除k与e之外的参数对h基本没影响。并且发现实验室常用岩石长度为100 mm,而典型EGS工程中裂隙长度是米级的,建议室内实验重视岩石长度对裂隙对流换热特征的影响。  相似文献   

12.
本文通过对巴西典型金-矽卡岩矿床的解剖，探讨了成矿流体来源、组成演化，以及流体和岩石之间的质量转移程度和机理的信息，揭示金成矿过程中成矿流体演化的规律。研究认为，成矿作用两阶段的成矿流体分别为变质流体和大气降水，它们在开放系统中水岩质量比分别为0．02，2．11，并且获得矽卡岩可能是由围岩转向岩体方向的变质流体交代形成的认识。  相似文献   

13.
Dehydration and melting reactions generate large volumes of fluid in the crust and upper mantle, and play an important role in subduction zone seismicity. The fluid pathway must evolve from isolated pockets in low porosity, low permeability rock, coalescing to interconnected permeable pathways to the surface. When fluid pressures generated from a dehydration or melting reaction are sufficient to induce hydrofracture, then hydrofracture significantly influences the porosity–permeability structure within the dehydrating/melting horizon. If a low fluid-pressure boundary is introduced to the dehydrating rock, then fluid will be driven from the rock along the evolved permeable network toward that boundary. The resulting pressure reduction can then accelerate the dehydration reaction and further drive the flow. The sudden introduction of a low fluid-pressure boundary may occur by the co-seismic (dilatant) rupturing of a pressure seal that connects different fluid pressure states. This mechanism is invoked to explain the observed post-seismic evolution of wave velocities (Vp/Vs) following the 1995 Antofagasta, Chile earthquake. We show experimental results and introduce a conceptual and numerical model that reflects this scenario. The model couples the mechanical and thermodynamic effects of fluid pressure with devolitization kinetics, and is quantitatively consistent with experimental studies of the dehydration of gypsum and serpentine. The experimental results show that dehydration is controlled by access to a free (drained) boundary. The model provides a mechanistic explanation for the experimental observations and has applications in understanding the role of transient transport networks on the large-scale behavior of dehydrating and melting systems.  相似文献   

14.
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   

15.
天然气水合物开采涉及传热、水合物分解相变、多相渗流和地层变形4个物理过程。多相渗流过程伴随着对流传热,影响传热效率;多相渗流过程影响孔隙压力的消散速率,引起有效应力改变而影响地层变形;多相渗流过程影响传热的效率和孔隙压力的消散速率,使温度和压力条件发生变化,影响水合物的分解。多相渗流过程中,某相流体的有效渗透率不仅与该相流体的饱和度有关,还与地层绝对渗透率有关。地层绝对渗透率是多相渗流过程的关键参数之一。概述不同贮存状态水合物、地层孔隙率、水合物饱和度和地层有效应力对地层绝对渗透率影响的研究内容。以国内外天然气水合物地层绝对渗透率研究成果为基础,将来的研究重点主要包括粉细砂、黏土类地层和各向异性地层多相渗流研究,以及地层有效应力对绝对渗透率影响研究。  相似文献   

16.
This study presents new data on the deformational and metamorphic history of previously unstudied Cambrian high-pressure metamorphic rocks exposed on the remote south coast of Tasmania. The Red Point Metamorphic Complex consists of two blocks of high-pressure, medium-grade metamorphic rocks including pelitic schist and minor garnet-bearing amphibolite, which are faulted against a sequence of low-grade phyllite and quartzite. The Red Point Metamorphic Complex records five phases of deformation, all of which except the first are expressed at a mesoscopic scale in both the medium- and low-grade rocks. Peak metamorphic conditions in the high-pressure epidote–amphibolite facies is recorded by medium-grade schist and amphibolite and was synchronous with the second major deformation event, which produced a pervasive schistosity and mesoscale isoclinal folds. The juxtaposition of the low- and medium-grade rocks is interpreted to have first occurred prior to the development of upright, opening folding associated with the third deformation. However, the present contacts between the two contrasting metamorphic sequences formed during widespread faulting and ductile-shear zone development associated with the fourth and fifth deformation events. The new data from the Red Point Metamorphic Complex provide insights into the structural and metamorphic history experienced by the medium-grade rocks of Tasmania during the Cambrian Tyennan Orogeny. This study demonstrates that Cambrian medium-grade metamorphic rocks are more widespread throughout Tasmania than previously realised, which represents an important step towards understanding the large-scale architecture of the Tyennan Orogen.  相似文献   

17.
The 5-km deep Chinese Continental Scientific Drilling Main Hole penetrated a sequence of ultrahigh pressure (UHP)-metamorphic rocks consisting mainly of eclogite, gneiss and garnet-peridotite with minor schist and quartzite. Zircon separates taken from thin layers of schist and gneiss within eclogite were investigated. Cathodoluminescence images of zircon grains show that they have oscillatory zoned magmatic cores and unzoned to patchy zoned metamorphic rims. Zircon rims contain rare coesite and calcite inclusions whereas cores contain inclusions of both low- P minerals (e.g. feldspar, biotite and quartz) and coesite and other eclogite-facies minerals such as phengite and jadeite. The zircon cores give highly variable 206Pb/238U ages ranging from 760 to 431 Ma for schist and from 698 to 285 Ma for gneiss, and relatively high but variable Th/U ratios (0.16–1.91). We suggest that the coesite and other eclogite facies mineral inclusions in zircon cores were not magmatic but formed through metasomatic processes caused by fluids during UHP metamorphism, and that the fluids contain components of SiO2, Al2O3, K2O, FeO, MgO, Na2O and H2O. Metasomatism of the Sulu UHP rocks during continental subduction to mantle depths has partly altered magmatic zircon cores and reset isotopic systems. This study provides key evidence that mineral inclusions within magmatic zircon domains are not unequivocal indicators of the formation conditions of the respective domain. This finding leads us to conclude that the routine procedure for dating of metamorphic events solely based on the occurrence of mineral inclusions in zoned zircon could be misleading and the data should be treated with caution.  相似文献   

18.
Ijolite-carbonatite complexes are ubiquitously surrounded of an aureole of metasomatically altered rocks. The process of alteration is termed fenitization and is generally caused by peralkaline fluids emanating from cooling alkaline, i.e. ijolite and carbonatite magmas. Ijolites and carbonatites normally occur together and attempts to determine the source of the fenitizing fluids may therefore lead to controversial, if not erroneous, conclusions.
Mineralogical and chemical data of fenites from Oldoinyo Lengai (Tanzania), Fen (Norway), and Alnö (Sweden) are reviewed in the present paper in order to reveal the main factors controlling the fenitization around ijolite and carbonatite. Despite the overall alkaline nature of the process, variables such as XCO2 of the fluid, activity gradients of SiO2, Al2O3 and CaO, FeO/MgO ratio, f O2 and temperature gradients may differ, producing distinctive patterns of fenitization around the two magmatic sources. The ijolitic-type fluid has low XCO2, high activities of alkalies, SiO2 and Al2O3, and low activity of CaO. The f O2 evolves along the hm-mt buffer conditions and the temperature falls gradually with distance from the magmatic source. The carbonatitic-type fluid has high XCO2, high activities of alkalies and CaO, and low activities of SiO2 and Al2O3. Temperatures and f O2 are initially high, but decrease sharply with distance from the source. Moreover, the CO2-rich fluid may complex and transport the REE.  相似文献   

19.
Metasomatic tremolite-rich mylonites are widespread in imbricate thrust slices of ultramafic rocks of the ophiolitic Ingalls Complex in Washington State. Protoliths for these amphibolite-facies mylonites were peridotite and serpentinite. Abundant syntectonic tremolite veins in the ultramafites record narrowly channelized flow of infiltrating fluids, whereas metasomatic mylonite zones record more pervasive flow. Fluids were probably released mainly by prograde devolatization reactions within serpentinite and mafic ophiolitic rocks that experienced earlier hydrothermal metamorphism.Olivine apparently deformed by dislocation creep in the mylonites. In the tremolite-rich rocks, locally preserved amphibole porphyroclasts deformed mainly by microfracturing. Acicular tremolites, which dominate the mylonites, form syntectonic overgrowths on porphyroclasts and probably record diffusive mass transfer which may have accompanied cataclasis. Acicular tremolites subsequently were folded and define both post-crystalline crenulations and polygonal arcs.Fluid flow, deformation and metamorphism were apparently complexly interrelated in the imbricate zone. Thrusts juxtaposed contrasting rock types that were sources and sinks for fluids, and shear zones focused fluid flow. Metamorphism probably facilitated deformation through the release of fluids during dehydration reactions. High fluid pressure may have led to hydraulic fracturing and may have controlled strain softening in the tremolitic mylonite zones as it favored microcracking and diffusive mass transfer over dislocation creep. Infiltrating metasomatic fluids probably play an important role in the evolution of shear zones in many ultramafic bodies during medium-grade metamorphism.  相似文献   

20.
Liqiang Yang    Jun Deng    Chunying Guo    Jing Zhang    Shaoqing Jiang    Bangfei Gao    Qingjie Gong    Qingfei Wang 《Resource Geology》2009,59(2):181-193
The Dayingezhuang gold deposit is located in the central part of the Zhaoping Fault Zone, which is one of the most important gold-hosting faults in the Jiaodong gold province of China. Dayingezhuang is a typical large-scale shear zone-hosted disseminated gold deposit with superimposed silver mineralization. Fluid inclusion (FI) petrography and microthermometry, and analysis of oxygen and hydrogen isotopes for fluid inclusions were conducted to determine the characteristics of the ore-forming fluids and the processes of silver mineralization. Microthermometry data of FI indicated that ore-forming fluids are characterized by low salinity and low density. Homogenization pressures of FI are estimated at 20 × 105–220 × 105 Pa. The change in ore-forming fluids from K2SO4 type to NaCl type indicates the superposition of two hydrothermal mineralizing events. Ore-forming fluids were dominated by magmatic components in the early mineralization period, and affected by meteoric waters in the late period. Gold may have been transported as Au-S or Au-Cl complexes, whereas silver was transported as Ag-Cl complexes. Early fluid boiling and later fluid mixing are thought to be two of the main factors causing the deposition and superimposing of gold and silver to form the large deposit.  相似文献   

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