Science Letters:Discovery of ultrahigh-T spinel-garnet granulite with pure CO_2 fluid inclusions from the Altay erogenic belt, NW China

We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the or-thopyroxenes have high XMg and A12O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around -56.7℃, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3-23.8℃ translating into CO2 densities of the order of 0.86-0.88 g/cm3. Based on preliminary mineral paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions.

In situ Raman spectroscopic quantification of CH4–CO2 mixture: application to fluid inclusions hosted in quartz veins from the Longmaxi Formation shales in Sichuan Basin, southwestern China

We re-evaluate the Raman spectroscopic quantification of the molar ratio and pressure for CH4–CO2 mixtures.Firstly,the Raman quantification factors of CH4 and CO2 increase with rising pressure at room temperature,indicating that Raman quantification of CH4/CO2 molar ratio can be applied to those fluid inclusions(FIs)with high internal pressure(i.e.,>15 MPa).Secondly,the v1(CH4)peak position shifts to lower wavenumber with increasing pressure at constant temperature,confirming that the v1(CH4)peak position can be used to calculate the fluid pressure.However,this method should be carefully calibrated before applying to FI analyses because large discrepancies exist among the reported v1(CH4)-P curves,especially in the highpressure range.These calibrations are applied to CH4-rich FIs in quartz veins of the Silurian Longmaxi black shales in southern Sichuan Basin.The vapor phases of these FIs are mainly composed of CH4 and minor CO2,with CO2 molar fractions from4.4%to 7.4%.The pressure of single-phase gas FI ranges from 103.65 to 128.35 MPa at room temperature,which is higher than previously reported.Thermodynamic calculations supported the presence of extremely high-pressure CH4-saturated fluid(218.03–256.82 MPa at 200°C),which may be responsible for the expulsion of CH4 to adjacent reservoirs.

Determining Fluid Compositions in the H_2O-NaCl-CaCl_2 System with Cryogenic Raman Spectroscopy:Application to Natural Fluid Inclusions

Previous cryogenic Raman spectroscopic analysis of H_2O-NaCl-CaCl_2 solutions has identified the Raman peaks of various hydrates of NaCl and CaCl_2,and established a linear relationship between Raman band intensity of the hydrates and the composition of the solution（NaCl/（NaCl＋CaCl_2） molar ratio,or X_（NaC1）） using synthetic fluids,which created the opportunity to quantitatively determine the solute composition of aqueous fluid inclusions with cryogenic Raman spectroscopy.This paper aims to test the feasibility of this newly established method with natural fluid inclusions.Twenty-five fluid inclusions in quartz from various occurrences which show a high degree of freezing during the cooling processes were carefully chosen for cryogenic Raman analysis.X_（Na）Cl was calculated using their spectra and an equation established in a previous study.These inclusions were then analyzed with the thermal decrepitation-SEM-EDS method.The X_（NaCl） values estimated from the two methods show a 1：1 correlation,indicating that the new,non-destructive cryogenic Raman spectroscopic analysis method can indeed be used for fluid inclusion compositional study.

CO_2 Density-Raman Shift Relation Derived from Synthetic Inclusions in Fused Silica Capillaries and Applications

The density of CO2 inclusions in minerals is commonly used to determine the crystallizing conditions of the host minerals.However,the conventional microthermometry method is difficult to apply for inclusions that are small in size（【5-10μm） or low in density.Raman analysis is an alternative method for determining CO2 density,provided that

Methane-rich fluid inclusions and their hosting volcanic reservoir rocks of the Songliao Basin, NE China

Methane-rich fluids were recognized to be hosted in the reservoir volcanic rocks as primary inclusions. Samples were collected from core-drillings of volcanic gas reservoirs with reversed δ13C of alkane in the Xujiaweizi depression of the Songliao Basin. The volcanic rocks are rhyolite dominant being enriched in the more incompatible elements like Cs, Rb, Ba, Th, U and Th with relative high LREE, depleted HREE and negative anomalies of Ti and Nb, suggesting a melt involving both in mantle source and crustal assimilation. Primary fluids hosted in the volcanic rocks should have the same provenance with the magma. The authors concluded that the enclosed CH4 in the volcanics are mantle/magma-derived alkane and the reversed δ13C of alkane in the corresponding gas reservoirs is partly resulted from mixture between biogenic and abiogenic gases.

Discovery and Significance of High CH_4 Primary Fluid Inclusions in Reservoir Volcanic Rocks of the Songliao Basin,NE China

Comparing compositions of the fluid inclusions in volcanic rocks to the contents and isotopes of the gases in corresponding volcanic reservoirs using microthermometry, Raman microspectroscopy and mass spectrum analysis, we found that： （1） up to 82 mole% methane exists in the primary inclusions hosted in the reservoir volcanic rocks; （2） high CH4 inclusions recognized in the volcanic rocks correspond to CH4-bcaring CO2 reservoirs that are rich in helium and with a high ^3He/^4He ratio and which show reversed order of 813C in alkane; （3） in gas reservoirs of such abiotic methane （〉80%） and a mix of CH4 and CO2, the enclosed content of CH4 in the volcanic inclusions is usually below 42 mole%, and the reversed order of δ^13C in alkane is sometimes irregular in the corresponding gas pools; （4） a glassy inclusion with a homogeneous temperature over 900℃ also contains a small portion of CH4 although predominantly CO2. This affinity between gas pool and content of inclusion in the same volcanic reservoirs demonstrates that magma-originated gases, both CH4 and CO2, have contributed significantly to the corresponding gas pools and that the assumed hydrocarbon budget of the bulk earth might be much larger than conventionally supposed.

高温高压条件下单一CO_(2)体系的傅里叶红外光谱定量模型及天然包裹体应用

傅里叶红外光谱是可以用于定性识别天然流体包裹体组分的原位无损分析技术,目前针对于天然包裹体的温度—压强—组分的定量分析是激光谱学地质应用的重点和难点以及发展方向,傅里叶红外光谱对于天然流体包裹体的定量方法和模型尚未建立。通过高压毛细硅管封装技术结合傅里叶红外光谱仪,对单一CO_(2)体系2ν2+ν3和ν1+ν3伸缩振动双峰进行40~80℃,60~500 bar压强范围下红外光谱的采集和观测,获取了不同温度和压强范围下红外光谱参数,通过拟合和计算获取该体系下傅里叶红外光谱的峰面积和峰位移,建立了CO_(2)的2ν2+ν3和ν1+ν3伸缩振动双峰体系下傅里叶红外光谱流体的密度与峰面积,压强与峰面积的标定模型,并明确CO_(2)的2ν2+ν3和ν1+ν3伸缩振动双峰形态随温度压强的变化特征,讨论了峰位移随温度和压强的变化。通过单一CO_(2)组分傅里叶红外光谱定量技术,在40℃下,采集莺歌海盆地黄流组储层中石英裂隙内纯CO_(2)包裹体的伸缩振动双峰峰面积来计算的密度,同时在室温下,采集包裹体的拉曼光谱,对比利用两种不同原位分析测试方法所计算密度,验证了傅里叶红外光谱定量分析的可行性,傅里叶红外光谱定量分析相比于拉曼光谱定量分析具有不受实验仪器和环境限制的优点,其定量方法可以避免由于仪器所处不同实验室之间产生的误差。

Experimental and petrological constraints on local-scale interaction of biotite-amphibole gneiss with H_2O-CO_2-(K,Na) Cl fluids at middle-crustal conditions:Example from the Limpopo Complex,South Africa

Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.

Applications of the SW96 formulation in the thermodynamic calculation of fluid inclusions and mineral-fluid equilibria

The SW96 formulation explicit in Helmholtz free energy proposed by Span and Wagner(1996)is the most accurate multifunction equation of state of CO_2 fluid,from which all thermodynamic properties can be obtained over a wide temperature-pressure range from 216.592 to 1100 K and from 0 to 8000 bar with or close to experimental accuracy.This paper reports the applications of the SW96 formulation in fluid inclusions and mineral-fluid equilibria.A reliable and highly efficient algorithm is presented for the saturated properties of CO_2 so that the formulation can be conveniently applied in the study of fluid inclusions,such as calculation of homogenization pressures,homogenization densities(or molar volumes),volume fractions of vapor phase and isochores.Meanwhile,the univariant curves of some typical decarbonation reactions of minerals are calculated with the SW96 formulation and relevant thermodynamic models of minerals.The computer code of the SW96 formulation can be obtained from the corresponding author.

Evolution of Diagenetic Fluid of the Dawsonite-Bearing Sandstone in the Jiyang Depression,Eastern China

Based on the petrology,isotope geochemistry and fluid inclusions analysis,we established the evolutionary mode of the diagenetic fluid of dawsonite-bearing sandstone in the Jiyang Depression.Dawsonite-bearing sandstone is characterized by double injection of CO_(2)and oil-gas in the Jiyang Depression that have experienced a relatively complex diagenetic fluid evolution process.The diagenetic sequence of secondary minerals involves secondary enlargement of quartz,kaolinite,first-stage calcite,dawsonite,second-stage calcite,ferrocalcite,dolomite and ankerite.Hydrocarbon charging in the dawsonite-bearing sandstone occurred at around 2.6–0 Myr.The CO_(2)charging event occurred during Dongying tectonism,forming the Pingfangwang CO_(2)gas reservoir,which provided an abundant carbon source for dawsonite precipitation.Carbon and oxygen isotopic compositions of dawsonite demonstrate that CO_(2)forming the dawsonite was of an inorganic origin derived from the mantle,and that water mediating the proc-ess during dawsonite precipitation was sequestered brine with a fluid temperature of 82℃.The evolutionary sequence of the diagenetic fluid in the dawsonite-bearing sandstone was:alkaline syngenetic fluids,weak alkaline fluids during organic acid forma-tion,acidic fluids in the early stage of CO_(2)injection,alkaline fluids in the late stage of CO_(2)injection,and weak alkaline fluids during oil and gas charging.The mode indicates an increase in-HCO_(3)because of the CO_(2)injection,and the loss of Ca^(2+)and Mg^(2+)due to the precipitation of carbonate minerals.Therefore,the evolutionary mode of diagenetic fluids is in good agreement with high HCO_(3)^(-),low Ca^(2+)and low Mg^(2+)composition of the present formation water in the dawsonite-bearing sandstone.

Research on Fluid Inclusions of the Yinshan Polymetallic Deposit, Jiangxi Province, China

In this paper some new advances in the study of fluid inclusions of the Yinshan deposit in Jiangxi Province, China, are presented. The fluid inclusions of the deposit can be divided into four types: 1) gas rich inclusions; 2) liquid rich inclusions; 3) salt saturated H 2O inclusions; and 4) single phase or multiphase CO 2 rich inclusions. Homogenization temperatures of the fluid inclusions range from 100 to 520℃, mainly in the range 120-400℃. The daughter crystal bearing multiphase inclusions present in quartz porphyries (including Nos. 13 and 4 dikes) have been observed. In ore veins, some daughter crystal bearing multiphase inclusions have been observed, too. On the basis of the results of fluid inclusion research, the authors suggest that the ore forming fluid must have a close genetic relation to magmatic hydrothermal solution. The ore forming fluid was dominantly originated from the depth and the mixing of magmatic solution with meteoric water was enhanced during ascending of the fluid, accompanying immiscibility and boiling of fluid. There may be a concealed igneous body at the depth of the Yinshan deposit, which furnishes the scientific basis for metallogenic prognosis at the depth of the Yinshan deposit.

滇西北兰坪铅锌银铜矿田含烃富CO_2成矿流体及其地质意义

在流体包裹体显微冷热台系统观测基础上,通过显微激光拉曼探针揭示出兰坪中—新生代盆地内金顶及外围矿床成矿主阶段原生流体包裹体含烃富CO_2,成分变化大。流体成分的耦合关系研究,并配合O、C同位素分析认为成矿流体中部分CO_2来自地幔,部分是沉积地层中碳酸盐岩和有机质分解成因,H_2O和烃主要起源于大气成因盆地卤水和地层有机质。地幔源CO_2对贱金属元素的搬运可能贡献突出,而烃类对金属元素的沉淀意义重大。成矿流体成分具有幔源(富CO_2和金属元素)和壳源(盆地流体富烃类和H_2O)两种流体混合的特征,暗示不同性质流体的混合可能是成矿作用基本方式。

小秦岭地区花岗岩体中CO_2-H_2O包裹体的找矿意义

小秦岭地区与金矿成因有关的燕山期文峪花岗岩及其派生石英脉中发育了非常丰富的ＣＯ２－Ｈ２Ｏ包裹体，其流体为富含ＣＯ２的低盐度（＜１０％ＮａＣｌ）流体，这与含金石英脉内的包裹体类型及金矿成矿流体性质上十分相似。与金矿成因无关的华山岩体内包裹体类型则为水溶液包裹体，流体性质为贫ＣＯ２的低盐度流体。与金矿有关，但其周围矿化很差的娘娘山岩体内ＣＯ２－Ｈ２Ｏ包裹体数量很少。因此，ＣＯ２－Ｈ２Ｏ包裹体可以作为与金矿成因有关的花岗岩体关联程度的判别标志。

用均匀设计CO_2超临界混合萃取当归、川芎、香附中挥发性成分及提取物β-CD包合的研究

目的 考察超临界流体CO2 萃取当归、川芎和香附中挥发性成分及所得混合挥发油的 β 环糊精包合物的制备工艺。方法 均匀设计方法 ,正交实验法。结果 萃取条件是 :萃取压力 30Pa ,萃取温度 6 0℃ ,解析温度Ⅰ 6 0℃ ,解析温度Π30℃ ,萃取时间 4 .0h。β CD包合物的制备最佳工艺条件是 :水 ,油与 β CD之比为 1∶10 (mL) ,研磨法 ,时间 6 0min。结论 确定了CO2 超临界混合萃取方法及挥发油的 β

A New Method for Determining Fluid Compositions in the H_2O-NaClCaCl_2 System with Cryogenic Raman Spectroscopy

Raman peaks of various hydrates in the H20-NaCl-CaCl2 system have been previously identified, but a quantitative relationship between the Raman peaks and XNaCl （i.e.,NaCl/ （NaCl＋CaCl2）） has not been established, mainly due to the difficulty to freeze the solutions. This problem was solved by adding alumina powder to the solutions to facilitate nucleation of crystals. Cryogenic （-185℃） Raman spectroscopic studies of alumina-spiced solutions indicate that XNaCl is linearly correlated with the total peak area fraction of hydrohalite. Capsules of solutions made from silica capillary were prepared to simulate fluid inclusions. Most of these artificial fluid inclusions could not be totally frozen even at temperatures as low as -185℃, and the total peak area fraction of hydrohalite is not correlated linearly with XNaCI. However, the degree of deviation （△XNaCl） from the linear correlation established earlier is related to the amount of residual solution, which is reflected by the ratio （r） of the baseline ＂bump＂ area, resulting from the interstitial unfrozen brine near 3435 cm^-1, and the total hydrate peak area between 3350 and 3600 cm^-1. A linear correlation between △XNaCl and r is established to estimate XNaCl from cryogenic Raman spectroscopic analysis for fluid inclusions.

Experimental Study on Water-rock Reactions with CO2 Fluid in a Deep Sandstone Formation under High Temperature and Pressure

Qiongdongnan Basin has a tectonic geological background of high temperature and high pressure in a deep reservoir setting,with mantle-derived CO2.A water-rock reaction device was used under high temperature and high pressure conditions,in conjunction with scanning electron microscope(SEM)observations,to carry out an experimental study of the diagenetic reaction between sandstone at depth and CO2-rich fluid,which is of great significance for revealing the dissolution of deep clastic rock reservoirs and the developmental mechanism of secondary pores,promoting deep oil and gas exploration.In this study,the experimental scheme of the water-rock reaction system was designed according to the parameters of the diagenetic background of the deep sandstone reservoir in the Qiongdongnan Basin.Three groups of single mineral samples were prepared in this experiment,including K-feldspar samples,albite samples and calcite samples.Using CO2 as a reaction solution,a series of diagenetic reaction simulation experiments were carried out in a semi-closed high temperature and high pressure simulation system.A field emission scanning electron microscope(SEM)was used to observe the microscopic appearance of the mineral samples after the water-rock reaction,the characteristics of dissolution under high temperature and high pressure,as well as the development of secondary pores.The experimental results showed that the CO2-rich fluid has an obvious dissolution effect on K-feldspar,albite and calcite under high temperature and high pressure.For the three minerals,the main temperature and pressure window for dissolution ranged from 150℃to 300℃and 45 MPa to 60 MPa.Scanning electron microscope observations revealed that the dissolution effect of K-feldspar is most obvious under conditions of 150℃and 45 MPa,in contrast to conditions of200℃and 50 MPa for albite and calcite.Through the comparative analysis of experimental conditions and procedures,a coupling effect occurred between the temperature and pressure change and the dissolution strength and calcite.Under high temperature and high pressure,pressure changed the solubility of CO2,furthermore,the dissolution effect and strength of the sandstone components were also affected.The experiment revealed that high temperature and high pressure conditions with CO2-rich fluid has a significant dissolution effect on aluminosilicate minerals and is conducive to the formation of secondary pores and effective reservoirs.Going forward with the above understanding has important implications for the promotion of deep oil and gas exploration.

High-precision analysis of carbon isotopic composition for individual CO_(2)inclusions via Raman spectroscopy to reveal the multiple-stages evolution of CO_(2)-bearing fluids and melts

The carbon isotopic composition of CO_(2)inclusions trapped in minerals reflects the origin and evolution of CO_(2)-bearing fluids and melts,and records the multiple-stages carbon geodynamic cycle,as CO_(2)took part in various geological processes widely.However,the practical method for determination isotope composition of individual CO_(2)inclusion is still lacking.Developing a microanalytical technique with spatial resolution in micrometers to precisely determinate theδ^(13)C value of individual CO_(2)inclusion,will make it possible to analyze a tiny portion of a zoning mineral crystal,distinguish the differences in micro-scale,and possible to find many useful information that could not be obtained with the bulk extraction and analysis techniques.In this study,we systematically collected Raman spectra of CO_(2)standards with different d13C values(34.9‰to 3.58‰)at 32.0℃and from 7.0 MPa to 120.0 MPa,and developed a new procedure to precisely determinate theδ^(13)C value of individual CO_(2)inclusion.We investigated the relationship among the Raman peak intensity ratio,d13C value,and CO_(2)density,and established a calibration model with high accuracy(0.5‰1.5‰),sufficient for geological application to distinguish different source of CO_(2)with varyingδ^(13)CO_(2).As a demonstration,we measured theδ^(13)C values and the density of CO_(2)inclusions in the growth zones of alkali basalt-hosted corundum megacrysts from Changle,Shandong Province.We found the significant differences of density and d13C between the CO_(2)inclusions in the core of corundum and those inclusions in the outer growth zones,the d13C value decreases from core to rim with decreasing density:δ^(13)C values are from7.5‰to9.2‰for the inclusions in the core,indicating the corundum core was crystallized from mantle-derived magmas;from13.5‰to18.5‰for CO_(2)inclusions in zone 1 and from16.5‰to–22.0‰for inclusions in zone 2,indicating the outer zones of corundum grew in a lowδ^(13)C value environment,resulted from an infilling of low d13C value fluid and/or degassing of the ascending basaltic magma.

CO_2-Hydrocarbon fluids of the Jade hydrothermal field in the Okinawa trough: fluid inclusion evidence

The Okinawa trough is a spreading back-arc basin featuring emitting hydrothermal solutions (black chimney type) and modern sulfide precipitation on the sea floor. The study of fluid inclusions in water-rock interaction products in the Jade hydrothermal field indicates that the deep hydrothermal system beneath the sea floor is fairly rich in gas and there are two independent and coexisting fluids-CO 2-hydrocarbon fluid and salt aqueous fluid. On the whole, the composition of CO 2-hydrocarbon fluid inclusions is similar to that of the fluid inclusions in natural gas fields. The dominant composition of the inclusions in aqueous fluid is H 2O with CO 2 and CH 4 being oversaturated. The salt aqueous fluid of the Jade hydrothermal system might be emitted through a black chimney, whereas CO 2-rich fluids discharge CO 2 bubbles and CO 2 hydrate through fissures. Hydrocarbons in gas phase or in fluid might be enclosed somewhere under the sea. Large storage of CO 2-CH 4-H 2S gas or fluid and reaction of this gas or fluid with salt water will lead to commercial sulfide deposits.

Gas contents and CO_2 isotope studies on fluid inclusion in ultra-high pressure metamorphic rock from Shuanghe area,Dabie Mountain

Step heating experiments on ultra-high pressure (UHP) rocks from the Dabie Mountain shows a majority of CO2 in fluid inclusion (excluding H2O) ; CO is also a significant component, with a small content of N2 and CH4 Carbon isotopic composition of CO2 in fluid of metamorphic climax stage ( - 25‰- - 30‰) is different from that of mantle carbon, indicating that UHP rocks did not experience obvious transformation by mantle fluids despite their subduction depth. CO2 was derived from carbon matter in the protoliths of UHP rocks in a relatively confined system, showing that the UHP rocks subsided quickly and uplifted quickly from the mantle.

库车克拉2气田多期油气充注的古流体证据

对库车前陆盆地克拉2气田储集层进行流体包裹体分析、荧光光谱分析、场发射扫描电镜观察、岩心显微CT扫描及油气地球化学分析,从古流体证据的角度综合研究克拉2气田多阶段油气充注过程。克拉2气田经历了中新世早中期(N1)原油充注、上新世库车组沉积期(N2)高成熟油气充注与破坏、第四系(Q1以来)高—过成熟煤成气充注的3期成藏过程。储集层中广泛分布的残余干沥青、较发育的气液两相烃包裹体、纳米孔中的残余油、现今气层和水层中较高的颗粒(抽提物)荧光指数、储集层岩石较大的热解值等均是早期原油充注的证据;残余干沥青、含沥青的3相烃包裹体、凝析油轻质正构烷烃大量损失、石蜡质和芳烃等重组分含量相对较高、金刚烷含量异常高等均是早期原油遭受气洗发生脱沥青作用的有力证据。