首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 984 毫秒
1.
The study of fluid inclusions in high-grade rocks is especially challenging as the host minerals have been normally subjected to deformation, recrystallization and fluid-rock interaction so that primary in- clusions, formed at the peak of metamorphism are rare. The larger part of the fluid inclusions found in metamorphic minerals is typically modified during uplift. These late processes may strongly disguise the characteristics of the ＂original＂ peak metamorphic fluid. A detailed microstructural analysis of the host minerals, notably quartz, is therefore indispensable for a proper interpretation of fluid inclusions. Cathodoluminescence （CL） techniques combined with trace element analysis of quartz （EPMA, LA- [CPMS） have shown to be very helpful in deciphering the rock-fluid evolution. Whereas high-grade metamorphic quartz may have relatively high contents of trace elements like Ti and A1, low- temperature re-equilibrated quartz typically shows reduced trace element concentrations. The result- ing microstructures in CL can be basically distinguished in diffusion patterns （along microfractures and grain boundaries）, and secondary quartz formed by dissolution-reprecipitation. Most of these textures are formed during retrograde fluid-controlled processes between ca. 220 and 500 ℃, i.e. the range of semi-brittle deformation （greenschist-facies） and can be correlated with the fluid inclusions. In this way modified and re-trapped fluids can be identified, even when there are no optical features observed under the microscope.  相似文献   

2.
大陆碰撞过程中熔/流体的组成和演化是研究大陆深俯冲动力学的重要内容,而超高压岩石记录了大陆俯冲和折返过程中的熔/流体-岩石相互作用,因而是研究大陆碰撞过程中熔/流体组成和演化的天然实验室。大陆俯冲带高压/超高压变质矿物中多相固体包裹体作为熔/流体活动的直接记录,为我们提供了揭示超高压变质过程中熔/流体演化的重要制约。近年来,围绕超高压岩石中多相固体包裹体的形成时间、演化过程及其所反映的俯冲带超高压变质熔/流体的组成和性质,进行了大量的研究工作。超高压岩石中多相固体包裹体的发现,为理解峰期超高压变质流体的组成和演化提供了重要制约,同时也为研究俯冲板片-地幔楔界面的熔/流体交代作用提供了新的途径。本文从多相固体包裹体形成机制、结构形态特征、矿物化学成分及其地质地球化学意义等方面,对于超高压变质岩中多相固体包裹体的研究现状和存在的问题进行系统地总结和探讨,以期促进多相固体包裹体的岩石学和地球化学研究。  相似文献   

3.
The Chinese Continental Scientific Drilling (CCSD) main drill hole (0–3000 m) in Donghai, southern Sulu orogen, consists of eclogite, paragneiss, orthogneiss, schist and garnet peridotite. Detailed investigations of Raman, cathodoluminescence, and microprobe analyses show that zircons from most eclogites, gneisses and schists have oscillatory zoned magmatic cores with low-pressure mineral inclusions of Qtz, Pl, Kf and Ap, and a metamorphic rim with relatively uniform luminescence and eclogite-facies mineral inclusions of Grt, Omp, Phn, Coe and Rt. The chemical compositions of the UHP metamorphic mineral inclusions in zircon are similar to those from the matrix of the host rocks. Similar UHP metamorphic P–T conditions of about 770 °C and 32 kbar were estimated from coexisting minerals in zircon and in the matrix. These observations suggest that all investigated lithologies experienced a joint in situ UHP metamorphism during continental deep subduction. In rare cases, magmatic cores of zircon contain coesite and omphacite inclusions and show patchy and irregular luminescence, implying that the cores have been largely altered possibly by fluid–mineral interaction during UHP metamorphism.

Abundant H2O–CO2, H2O- or CO2-dominated fluid inclusions with low to medium salinities occur isolated or clustered in the magmatic cores of some zircons, coexisting with low-P mineral inclusions. These fluid inclusions should have been trapped during magmatic crystallization and thus as primary. Only few H2O- and/or CO2-dominated fluid inclusions were found to occur together with UHP mineral inclusions in zircons of metamorphic origin, indicating that UHP metamorphism occurred under relatively dry conditions. The diversity in fluid inclusion populations in UHP rocks from different depths suggests a closed fluid system, without large-scale fluid migration during subduction and exhumation.  相似文献   


4.
Fluid inclusions and clay mineralogy of the Permo-Triassic rocks from the Espina and Espadà Ranges (SE Iberian Chain, Spain) have been investigated to establish their relationship with hydrothermal fluid circulation during the Alpine Orogeny. Primary fluid inclusions in quartz-filled tension gashes in Permo-Triassic sandstones reveal maximum temperatures around 230 °C and very constant salinities of 8.5% wt. eq. NaCl. Secondary fluid inclusions found in quartz from the Santonian Ba–Cu–Hg deposits show similar compositional and thermodynamic characteristics, denoting an Alpine recrystallization. Clay mineral composition of Permo-Triassic mudrocks is characterized by pyrophyillite, indicating low-grade metamorphic conditions. Field observations and experimental data suggest that the crystallization of quartz in tension gashes, the formation of secondary fluid inclusions and the development of the metamorphism are contemporaneous and related to fluid circulation during the Alpine compression. Fluid flow took place along the Hercynian fault system that was reactivated during the Mesozoic rift stage and inverted during the Alpine deformation.  相似文献   

5.
The Whitestone Anorthosite (WSA), located in southern Ontario, underwent granulite facies metamorphism during the Grenville orogeny at 1.16 Ga. During the waning stages of metamorphism fluids infiltrated the outer portions of the anorthosite and promoted the formation of an envelope comprised of upper amphibolite facies mineral assemblages. Also, this envelope corresponds to portions of the anorthosite that underwent deformation related to movement along a high-grade ductile shear zone. Samples from this portion of the anorthosite (the margin) contain CO2-rich inclusions in plagioclase porphyroclasts (relict igneous phenocrysts), matrix plagioclase and garnet. These inclusions have features which normally are interpreted as indicating that they are texturally primary, but they have relatively low CO2 densities (0.61–0.95 g cm-3). Plagioclase from the anorthosite interior contains texturally secondary inclusions with relatively high CO2 densities (generally from 0.99 to 1.10 g cm-3). The high CO2 densities suggest that the inclusions in the plagioclase of the anorthosite core formed prior to inclusions in porphyroclast minerals of the outer portions of the anorthosite, an interpretation that is apparently inconsistent with inclusion textures. This apparent paradox indicates that most fluid inclusions from the anorthosite margin were formed during, or were modified by, the dynamic recrystallization that affected this portion of the WSA. In either case, late formation or modification, the texturally primary fluid inclusions do not contain pristine samples of the peak metamorphic fluid. Furthermore, because shear-related deformation is apparently associated with entrapment of the lowest fluid densities, some strain localization persisted to relatively low temperatures (e.g. less than approximately 500° C). These results constrain a part of the retrograde P–T path for this portion of the Grenville Orogen to temperatures of approximately 400–500° C at pressures of approximately 1–2 kbar.  相似文献   

6.
Non-aqueous CO2 and CO2-rich fluid inclusions are found in the vein quartz hosting mesothermal gold-sulphide mineralization at Bin Yauri, northwestern Nigeria. Although mineralizing fluids responsible for gold mineralization are thought to be CO2-rich, the occurrence of predominantly pure to nearly pure CO2 inclusions is nevertheless unusual for a hydrothermal fluid system. Many studies of similar CO2-rich fluid inclusions, mainly in metamorphic rocks, proposed preferential loss (leakage) of H2O from H2O-CO2 inclusions after entrapment. In this study however, it is proposed that phase separation (fluid immiscibility) of low salinity CO2-rich hydrothermal fluids during deposition of the gold mineralization led to the loss of the H2O phase and selective entrapment of the CO2. The loss of H2O to the wallrocks resulted in increasing oxidizing effects. There is evidence to suggest that the original CO2-rich fluid was intrinsically oxidized, or perhaps in equilibrium with oxidizing conditions in the source rocks. The source of the implicated fluid is thought to be subducted metasediments, subjected to dehydration and devolatilization reactions along a transcurrent Anka fault/shear system, which has been described as a Pan-African (450–750 Ma) crustal suture.  相似文献   

7.
Fluid inclusions in quartz veins within Proterozoic metamorphic rocks in the Black Hills, South Dakota, were examined by microthermometry and Raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic-rich shales and late-orogenic magmatism, both of which were related to the collision of the Wyoming and Superior crustal blocks. Fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet-grade conditions, and in veins within the aureole of the Harney Peak Granite (HPG), where temperatures reached second-sillimanite grade conditions. Early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early CH4 or CO2 and N2-dominated inclusions. These fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase. They are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fO2 conditions. Most inclusions in the quartz veins are, however, secondary CO2-bearing. They imply a transition to higher fO2 conditions with increasing temperature of regional metamorphism. The fO2 conditions may have been controlled by the mineral assemblage in the host metapelites. The prevalence of bimodal distributions of trapped CO2-N2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism.In the aureole of the HPG, graphite was evidently consumed by influx of magmatic fluids. CO2-H2O fluid inclusions dominate, but they have significantly less N2 than inclusions at lower metamorphic grades. All inclusions define secondary trails in mostly unstrained quartz. The bimodality of inclusion compositions is not as well defined as at lower grades, with many inclusions containing intermediate CO2-H2O compositions. This suggests that a single fluid phase existed at the high temperatures in the granite aureole, but then unmixed during cooling. A set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains CH4-bearing inclusions with little N2. The existence of CH4 in these inclusions is attributed to complexing of magmatic B with hydroxyl anions taken from the CO2-H2O fluid phase, effectively causing reduction in fO2 and promoting precipitation of graphite.  相似文献   

8.
In this paper the first fluid-inclusion data are presented from Late Archaean Scourian granulites of the Lewisian complex of mainland northwest Scotland. Pure CO2 or CO2-dominated fluid inclusions are moderately abundant in pristine granulites. These inclusions show homogenization temperatures ranging from − 54 to + 10 °C with a very prominent histogram peak at − 16 to − 32 °C. Isochores corresponding to this main histogram peak agree with P-T estimates for granulite-facies recrystallization during the Badcallian (750–800 °C, 7–8 kbar) as well as with Inverian P-T conditions (550–600 °C, 5 kbar). The maximum densities encountered could correspond to fluids trapped during an early, higher P-T phase of the Badcallian metamorphism (900–1000 °C, 11–12 kbar). Homogenization temperatures substantially higher than the main histogram peak may represent Laxfordian reworking (≤ 500 °C, < 4 kbar). In the pristine granulites, aqueous fluid inclusions are of very subordinate importance and occur only along late secondary healed fractures. In rocks which have been retrograded to amphibolite facies from Inverian and/or Laxfordian shear zones, CO2 inclusions are conspicuously absent; only secondary aqueous inclusions are present, presumably related to post-granulite hydration processes. These data illustrate the importance of CO2-rich fluids for the petrogenesis of Late Archaean granulites, and demonstrate that early fluid inclusions may survive subsequent metamorphic processes as long as no new fluid is introduced into the system.  相似文献   

9.
An investigation has been made of the relationships between tectonic processes and fluid inclusions in quartz from variably deformed and syntectonically recrystallized granitic rocks from the Lachlan Fold Belt, eastern Australia. The quartz contains many fluid inclusions which decorate healed fractures introduced as a result of late-stage brittle deformation. The majority of small inclusions however, are associated with deformation band boundaries and deformation lamellae showing that they have been introduced during or subsequent to ductile deformation. Fluid inclusions disappear from the cores of sub-grains during recovery and before recrystallization, and new inclusions which form along sub-grain boundaries coalesce into stringers. Inclusions are eliminated from both sides of low angle boundaries showing that inclusions leak their contents either through the system of dislocations which accompanies grain interior slip, or by a dissolution-condensation process whereby inclusion contents move by lattice diffusion and condense on the boundaries.  相似文献   

10.
矿物或流体包体可以有效保存寄主矿物生长过程中的化学环境、温度、压力等信息。在高压变质过程中,石榴子石中石英包体的分子振动与环境压力之间具有良好的相关性。根据这一特性,前人提出了石英包体拉曼偏移压力计,其原理是利用显微激光拉曼光谱仪分析石英包体在室温常压下保留的残余压力,再结合石英与寄主矿物的弹性物理特性,恢复石英包体被捕获时的压力,属于矿物物理光谱学压力计,本文介绍了利用石英包体的拉曼位移计算变质压力的基本原理和方法,并对不同方法的适用条件和使用局限做了简要分析。石英包体拉曼偏移压力计是恢复变质岩石形成温度和压力条件的有效方法,具有广泛的应用前景。  相似文献   

11.
Larryn W. Diamond   《Lithos》2001,55(1-4):69-99
Aqueous solutions that contain volatile (gas) components are one of the most important types of fluid in the Earth's crust. The record that such fluids have left in the form of fluid inclusions in minerals provides a wealth of insight into the geochemical and petrologic processes in which the fluids participated. This article reviews the systematics of CO2–H2O fluid inclusions as a starting point for interpreting the chemically more complex systems. The phase relations of the binary are described with respect to a qualitative P–T–X model, and isoplethic–isochoric paths through this model are used to explain the equilibrium and non-equilibrium behaviour of fluid inclusions during microthermometric heating and cooling. The P–T–X framework is then used to discuss the various modes of fluid inclusion entrapment, and how the resulting assemblage textures can be used to interpret the P–T conditions, phase states, and evolution paths of the parent solutions. Finally, quantitative methods are reviewed by which bulk molar volume and composition of CO2–H2O fluid inclusions can be determined from microthermometric observations of phase transitions.  相似文献   

12.
ABSTRACT P-T conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations. These observations suggest that inclusions formed during early stages of regional metamorphism continue to re-equilibrate during burial and subsequent uplift in response to differential pressure. P-T conditions accompanying burial and uplift were experimentally simulated by initially forming pure H2O inclusions in quartz at elevated temperatures and pressures, and then re-equilibrating the inclusions in the presence of a 20 wt% NaCl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re-equilibration. In all samples re-equilibrated at confining pressures below the internal pressure, some inclusions were formed that had compositions of 20 wt% NaCl and densities in accord with the final P-T conditions. Additionally, some inclusions were observed to contain fluids of intermediate salinities (between 0 and 20 wt% NaCl). Densities of these inclusions were also consistent with formation at the re-equilibration P-T conditions. The remainder of the fluid inclusions observed in these samples contained pure H2O and their homogenization temperatures corresponded to densities intermediate between the initial and final P-T conditions. In short-term experiments (7 days) where the initial internal overpressure exceeded 1 kbar, no inclusions were found that contained the original density and none were found to have totally re-equilibrated. Instead, most H2O inclusions re-equilibrated until their internal pressures were between ∼750 and 1500 bars above the confining pressure, regardless of the initial pressure differential. In a long-term experiment (52 days), inclusions re-equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar (i.e. total re-equilibration) and 1.2 kbar above the confining pressure. In experiments where the confining pressure during re-equilibration exceeded the initial internal pressure, densities of pure H2O inclusions increased to values intermediate between the initial and final P-T conditions. Additionally, these inclusions were generally surrounded by a three-dimensional halo of smaller inclusions, also of intermediate density, resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure. In extreme cases where confining pressures were 4–5 kbar above the initial pressure, the parent inclusion almost completely closed leaving only the three-dimensional array of small (5 μm) inclusions, the outline of which may be several times the volume of the original inclusion. Groups of such inclusions closely resemble textures commonly observed in medium- to high-grade metamorphic rocks. Inclusions containing 10 and 42 wt% NaCl solutions trapped at 600 °c and 3 kbar were re-equilibrated at 600 °c and 1 kbar for 5 days in dry argon to evaluate the importance of H2O diffusion as a mechanism of lowering the inclusion bulk density. Salinities of re-equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved. Density changes similar to those previously described were noted in these experiments, in inclusions showing no visible microfractures. Therefore, density variations observed in inclusions in this study, re-equilibrated under rapid deformation conditions, are considered to result from a change in the inclusion volume, without significant loss of contents by diffusion or leakage.  相似文献   

13.
The ultrahigh-temperature (UHT) metamorphism of the Napier Complex is characterized by the presence of dry mineral assemblages, the stability of which requires anhydrous conditions. Typically, the presence of the index mineral orthopyroxene in more than one lithology indicates that H2O activities were substantially low. In this study, we investigate a suite of UHT rocks comprising quartzo-feldspathic garnet gneiss, sapphirine granulite, garnet-orthopyroxene gneiss, and magnetite-quartz gneiss from Tonagh Island. High Al contents in orthopyroxene from sapphirine granulite, the presence of an equilibrium sapphirine-quartz assemblage, mesoperthite in quartzo-feldspathic garnet gneiss, and an inverted pigeonite-augite assemblage in magnetite-quartz gneiss indicate that the peak temperature conditions were higher than 1,000 °C. Petrology, mineral phase equilibria, and pressure-temperature computations presented in this study indicate that the Tonagh Island granulites experienced maximum P-T conditions of up to 9 kbar and 1,100 °C, which are comparable with previous P-T estimates for Tonagh and East Tonagh Islands. The textures and mineral reactions preserved by these UHT rocks are consistent with an isobaric cooling (IBC) history probably following an counterclockwise P-T path. We document the occurrence of very high-density CO2-rich fluid inclusions in the UHT rocks from Tonagh Island and characterize their nature, composition, and density from systematic petrographic and microthermometric studies. Our study shows the common presence of carbonic fluid inclusions entrapped within sapphirine, quartz, garnet and orthopyroxene. Analysed fluid inclusions in sapphirine, and some in garnet and quartz, were trapped during mineral growth at UHT conditions as 'primary' inclusions. The melting temperatures of fluids in most cases lie in the range of -56.3 to -57.2 °C, close to the triple point for pure CO2 (-56.6 °C). The only exceptions are fluid inclusions in magnetite-quartz gneiss, which show slight depression in their melting temperatures (-56.7 to -57.8 °C) suggesting traces of additional fluid species such as N2 in the dominantly CO2-rich fluid. Homogenization of pure CO2 inclusions in the quartzo-feldspathic garnet gneiss, sapphirine granulite, and garnet-orthopyroxene gneiss occurs into the liquid phase at temperatures in the range of -34.9 to +4.2 °C. This translates into very high CO2 densities in the range of 0.95-1.07 g/cm3. In the garnet-orthopyroxene gneiss, the composition and density of inclusions in the different minerals show systematic variation, with highest homogenization temperatures (lowest density) yielded by inclusions in garnet, as against inclusions with lowest homogenization (high density) in quartz. This could be a reflection of continued recrystallization of quartz with entrapment of late fluids along the IBC path. Very high-density CO2 inclusions in sapphirine associated with quartz in the Tonagh Island rocks provide potential evidence for the involvement of CO2-rich fluids during extreme crustal temperatures associated with UHT metamorphism. The estimated CO2 isochores for sapphirine granulite intersect the counterclockwise P-T trajectory of Tonagh Island rocks at around 6-9 kbar at 1,100 °C, which corresponds to the peak metamorphic conditions of this terrane derived from mineral phase equilibria, and the stability field of sapphirine + quartz. Therefore, we infer that CO2 was the dominant fluid species present during the peak metamorphism in Tonagh Island, and interpret that the fluid inclusions preserve traces of the synmetamorphic fluid from the UHT event. The stability of anhydrous minerals, such as orthopyroxene, in the study area might have been achieved by the lowering of H2O activity through the influx of CO2 at peak metamorphic conditions (>1,100 °C). Our microthermometric data support a counterclockwise P-T path for the Napier Complex.  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.
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   

16.
Three successive metamorphic stages M1, M2 and M3 have been distinguished in polymetamorphic granulite facies quartz-feldspathic gneisses from the Seiland Igneous Province, Caledonides of northern Norway. An early period of contact metamorphism (M1; 750–950°C, ca. 5 kbar) was followed by cooling, accompanied by strong shearing and recrystallization at intermediate-P granulite facies conditions (M2; 700–750°C, 5–6kbar). High-P granulite facies (M3; ca. 700°C, 7–8 kbar) is related to recrystallization in narrow ductile shear zones and secondary growth on M2 minerals. On the basis of composition, fluid inclusions in cordierite, quartz and garnet can be divided into three major types: (1) CO2 inclusions; (2) mixed CO2–N2 inclusions; (3) N2 inclusions. Fluid chronology and mineral assemblages suggest that the earliest inclusions consist of pure CO2 and were trapped at the M1 contact metamorphic episode. A carbonic fluid was also present during the intermediate-P granulite facies M2 metamorphism. The CO2-rich inclusions in M2 garnet can be divided into two generations, an early lower-density and a late higher-density, with isochores crosscutting the P-T box of M2 and M3, respectively. The nitrogen-rich fluids were introduced at a late stage in the fluid evolution during the high-P M3 event. The mixed CO2–N2 inclusions, with density characteristics compatible with M3 conditions, are probably produced from intersection between pre-existing pure CO2 inclusions and N2 fluids introduced during M3. The fluid inclusion data agree with the P-T evolution established from mineral assemblages and mineral chemistry.  相似文献   

17.
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   

18.
Minerals in eclogites from different localities in the Western Gneiss Region of the Norwegian Caledonides (age 425 Ma) contain a variety of fluid inclusions. The earliest inclusions recognized are contained in undeformed quartz grains, protected by garnet, and consist of H2O+N2 (with ). The reconstructed P-V-T-X properties of these fluid inclusions are compatible with peak or early-retrograde metamorphic conditions. Matrix minerals (quartz, garnet, apatite, plagioclase) contain a complex pattern of mostly truly secondary inclusions, dominated by CO2 and N2. The textural patterns and P-V-T-X properties of these inclusions are incompatible with the high pressures of the eclogite-forming metamorphic event, but suggest that they were formed during uplift, by a combination of remobilization of preexisting inclusions and influx of external fluids. The fluid introduced at a late stage was dominated by CO2, and did not contain N2. The present data agree with theoretical predictions of eclogite fluids from mineral equilibria, and highlight the differences between granulite (CO2) and eclogite (H2O+N2) fluid regimes. The provenance of the nitrogen in the eclogite fluid inclusions represents an important, but unsolved question in the petrology of high-pressure metamorphic rocks.Contribution no. 68 to the Norwegian programme of the International Lithosphere Project  相似文献   

19.
《Applied Geochemistry》2000,15(1):13-25
The carboxylate (formate, acetate, propionate and oxalate) and common inorganic anions (F−, Cl− and SO2−4) compositions for aqueous fluid inclusion leachates from 17 mineral samples collected from various deposits have been determined using ion chromatography in conjunction with microthermometric measurements on the fluid inclusions of their host minerals. The minerals, quartz, fluorite, barite, beryl and a few `ore' minerals (wolframite, pyrite and galena), came from hydrothermal vein-type deposits in felsic igneous rocks or Archean metamorphic rocks. The results indicate that short-chain carboxylates are common components in hydrothermal fluids and can be present in considerable amounts. Formic acid (as formate) is the dominant species over other carboxylic acids. The present study raises new questions about the origin and geochemical significance of carboxylates in hydrothermal ore-forming processes.  相似文献   

20.
CO2–CH4 fluid inclusions are present in anatectic layer-parallel leucosomes from graphite-bearing metasedimentary rocks in the Skagit migmatite complex, North Cascades, Washington. Petrological evidence and additional fluid inclusion observations indicate, however, that the Skagit Gneiss was infiltrated by a water-rich fluid during high-temperature metamorphism and migmatization. CO2-rich fluid inclusions have not been observed in Skagit metasedimentary mesosomes or melanosomes, meta-igneous migmatites, or unmigmatized rocks, and are absent from subsolidus leucosomes in metasedimentary migmatites. The observation that CO2-rich inclusions are present only in leucosomes interpreted to be anatectic based on independent mineralogical and chemical criteria suggests that their formation is related to migmatization by partial melting. Although some post-entrapment modification of fluid inclusion composition may have occurred during decompression and deformation, the generation of the CO2-rich fluid is attributed to water-saturated partial melting of graphitic metasedimentary rocks by a reaction such as biotite + plagioclase + quartz + graphite ± Al2SiO5+ water-rich fluid = garnet + melt + CO2–CH4. The presence of CO2-rich fluid inclusions in leucosomes may therefore be an indication that these leucosomes formed by anatexis. Based on the inferences that (1) an influx of fluid triggered partial melting, and (2) some episodes of fluid inclusion trapping are related to migmatization by anatexis, it is concluded that a free fluid was present at some time during high-temperature metamorphism. The infiltrating fluid was a water-rich fluid that may have been derived from nearby crystallizing plutons. Because partial melting took place at pressures of at least 5 kbar, abundant free fluid may have been present in the crust during orogenesis at depths of at least 15 km.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号