东准噶尔蒙西斑岩铜钼矿床脉体特征及其形成机制

蒙西斑岩铜钼矿床位于东准噶尔伊吾县琼河坝花岗岩北侧,以发育细脉、网脉状矿化为特征。脉体类型多样,包括石英脉、石英硫化物脉和硫化物脉等。根据脉体力学成因机制,其又可划分为水压破裂充填脉和构造破裂充填脉。构造破裂充填脉体按破裂形成的位错特征有正断与逆断两种。地表石英脉产状陡立,明显受断裂控制。脉体体积分数统计结果显示流体富集区呈向北缓倾的带状分布于深100～400m范围内,并与矿化富集带有较好的对应关系。脉体富集带内,脉体以共轭形式存在,一组为倾角较小的逆断破裂充填脉,另一组为倾角较大的正断破裂充填脉,他们可能为缓倾逆冲剪切带的次级破裂与充填脉,即富矿带内脉体是沿矿区低角度逆冲断裂次级破裂面充填的。矿区地表及深部(400m以下)脉体以陡立为主,矿化较弱。矿区流体的运移具先沿水压直立破裂往上运移,进入剪切带后沿剪切带次级破裂侧向和向上运移,并在剪切带中富集成矿。低温矿物组合脉体穿切高温矿物组合脉体的特征说明脉体形成过程矿区处于隆升构造环境,这对斑岩铜矿成矿有利。     

Dehydration veins in diagenetic and very-low-grade metamorphic rocks: features of the crustal seismogenic zone and their significance to mineral facies

Abstract Declining temperatures during decay of a hydrothermal system, or during uplift and erosion, tend to result in veins involving progressive hydration reactions, e.g. veins with laumontite cutting prehnitepumpellyite facies rocks, and stilbite veins cutting laumontite veins. In contrast, examples are described of analcime replacement of heulandite along fractures in heulanditized vitric tuff, of replacement of analcime by albite along fractures in quartz-analcime rock, of joint-controlled replacement of heulandite in tuff by laumontite + quartz + (Na, K)-feldspars, of replacement of laumontite by prehnite + quartz along fractures in alumontitized vitric tuff, and of laumontitebearing feldspathic sandstones cut by vein assemblages of quartz and prehnite ° Calcite. The vein mineral assemblage, sometimes with pumpellyite and/or epidote in the prehnite-bearing veins, tends to spread as a zone of dehydration into the adjacent country rock. Except perhaps for albite replacement of analcime, and for laumontite replacement of heulandite, these open-system reactions involve cation activity ratios in the fluid. All involve dehydration. They are favoured by an increase in temperature, and except under certain situations where P-T equilibrium curves have negative slopes, are favoured by a fall in P_H2O. Evidence indicates that in at least some cases the triggering mechanism was a drop in P_H2O; this may be a widespread phenomenon associated with brittle fracture in the seismogenic upper crust. This may cause fluid pressure to drop from values approaching lithostatic to nearer hydrostatic, and equilibrium may be displaced to yield a less hydrous assemblage that appears as a dehydration vein and vein verge. The dehydration vein assemblage may be diagnostic of a higher grade mineral facies and adds to the mineral complexity attributable to varying permeabilities and fluid pressures in upper crustal strata. Mineral facies are likely to be more uniformly distributed in higher grade rocks from below the brittle-ductile transition zone. Reactions involving complex solid solutions are inappropriate as facies boundaries.     

Mass transfer and porosity evolution during low temperature water–rock interaction in gneisses of the simano nappe: Arvigo,Val Calanca,Swiss Alps

Late Alpine fissures and fractures in amphibolite-facies basement gneisses at Arvigo (Val Calanca, Swiss Alps) show distinct cm-sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high-grade gneiss assemblages. The process of selvage or reaction-vein formation occurred in the brittle deformation regime and at temperatures characteristic of, first the prehnite-pumpellyite facies and then later of the zeolite facies. The vein formation occurred during uplift and cooling at very late stages of the Alpine orogeny. The reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space. The central zone of the Arvigo veins contains an early assemblage with epidote, prehnite and chlorite and a late succession sequence of various species of zeolite. The veins of the Arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate Ca–zeolite. This is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of Ca–zeolite species. Vein formation during late uplift and cooling of the Alps occurred at continuously decreasing T and at hydrostatic pressure: (1) coexisting prehnite/epidote records temperatures of 330–380°C, (2) chlorite formation at temperature of 333 ± 32°C and (3) formation of zeolites <250°C. In the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss. In addition to albitisation, chloritisation of biotite is the second important reaction in the alteration process. The reactions release components for the formation of Ca–Al silicates. The water–rock interaction is associated with a depletion of Al, Si, Ca, Fe and K in the altered wall rock. The overall reaction is associated with an increase in porosity of up to 14.2 ± 2.2% in the selvage zone (altered wall rock), caused by the volume decrease during albitisation and the removal of biotite. The propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution-reprecipitation mechanism. Zeolite formation is tied to the plagioclase alteration reaction in the rock matrix, which releases components for zeolite formation to a CO₂-poor aqueous liquid.     

Synmetamorphic veining: origin of andalusite-bearing veins in the Vedrette di Ries contact aureole, Eastern Alps, Italy

Discordant andalusite-biotite-quartz-bearing veins occur in the contact aureole of the Vedrette di Ries pluton (Italian Eastern Alps), never outside the area of contact metamorphic andalusite development. Andalusite veins are found only within andalusite-bearing hornfelses, and vein biotite occurs wherever host-rock garnet is partially replaced by biotite. Veins formed during contact metamorphism, synchronously with the crystallization of andalusite and biotite within host rocks. Their pegmatitic structure and their orientation suggest that vein parageneses crystallized within fluid-filled cavities that opened by hydraulic fracturing. A mechanism of synmetamorphic veining is proposed to explain rock failure and subsequent mineral deposition within veins. During hydrofracturing induced by dehydration reactions in response to heating in the aureole, fissures were immediately filled with locally derived fluids. The lack of large-scale flux, together with high fluid pressures required by hydrofracturing, suggest fluid in the cavities was a virtually stagnant, passive medium, and that mass-transport toward fractures was driven by intergranular diffusion. Because temperature and P_f values within veins are similar to those in the host rock, vein assemblages are interpreted as the stable, high-T side of reactions taking place within pelitic schists, at the time when fractures opened. Once nucleation of product phases occurred, chemical components released by dissolution of reactant minerals were driven to precipitation sites by chemical potential gradients. Since nucleation was favoured at the strained grains of vein walls, andalusite and biotite simultaneously grew in vein and host rock. The proposed genetic model contrasts with generally adopted metasomatic mechanisms for the genesis of Al₂SiO₅-bearing veins, in not requiring large fluid/rock ratios or a highly ‘aggressive’ fluid composition. The mechanism of synmetamorphic veining may be particularly useful in the interpretation of vein occurrences in medium- and deep-crustal rocks which have undergone extensive devolatilization.     

湖北郧县王家庄绿色纤维状石英-云母脉特征及成因--对板块构造几个问题的思考

湖北郧县王家庄有两期脉体 ,早期为纤维状石英脉 ,总体呈北北东向分布 ,平行脉壁有一中间面使其对称分布 ,显示张性裂隙持续发育过程 ;与之垂直的横向压性裂隙将它“错开”。形貌上酷似板块构造的大洋中脊和转换断层。晚期云母脉叠置在上述两组裂隙之上 ,并使原来裂隙性质发生变化。这些特征与区域应力场分布 ,特别是与两郧断裂的演化息息相关。根据分形理论 ,将王家庄石英云母脉与板块构造进行对比 ,一方面从微观的角度证实了板块构造一些基本观点的合理性。同时从微观信息得到深入研究板块构造的一些新启示 :对板块形成机制不要局限于软流圈对流 ,而应从更深层次研究地幔物质运动规律 ;要将大陆和大洋作为一个整体研究全球应力场分布规律与构造演化历史 ,其中转换断层是联系大陆和大洋的纽带 ;加强RRR型三联点研究 ,它是研究深部 (地幔 )物质运动和上部 (地壳、岩石圈 )构造应力场相互关系的重要窗口     

渤海湾盆地海域片麻岩潜山风化壳型储层特征及发育模式

渤海湾盆地海域太古代-古元古代片麻岩潜山分布面积巨大,已发现多个油气田,有重要勘探价值。本文综合应用岩心、铸体薄片、X衍射、扫描电镜、常规物性、锆石测年、矿物溶蚀模拟等实验手段及统计分析方法落实了渤海片麻岩风化壳型储层地质特征、成因机理及发育模式。研究表明,片麻岩中长英质矿物含量大于70%有利于形成潜山裂缝型优质储层;大气水风化淋滤作用对长石类矿物的溶蚀,形成大量次生孔隙和沿裂缝的溶蚀扩大孔隙,极大改善了片麻岩潜山的储层物性;构造作用产生的断裂和节理不仅可以直接提供储集空间,还可以作为渗流通道加大风化淋滤作用的影响深度和范围,促进深部岩石的溶蚀改造,加速风化过程。上述主控因素指导下建立自上往下发育粘土带、砂化带、砂化砾石带、裂缝带和基岩带的片麻岩风化壳型潜山储层发育模式。     

A review of the formation of tectonic veins and their microstructures

Veins are common features in rocks and extremely useful structures to determine stress, strain, pressure, temperature, fluid composition and fluid origin during their formation. Here we provide an overview of the origin and terminology of veins. Contrary to the classical tripartite division of veins into syntaxial (inward growth), antitaxial (outward growth) and stretching veins (no consistent growth direction), we emphasise a continuum between syntaxial and stretching veins that form from the crack-seal process, as opposed to antitaxial veins that grow without the presence of an open fracture during growth. Through an overview of geochemical methods that can be applied to veins we also address the potential, but so far little-investigated link between microstructure and geochemistry. There are basically four mechanisms with increasing transport rates and concomitant decreasing fluid–rock interaction: (1) diffusion of dissolved matter through stagnant pore fluid; (2) flow of fluid with dissolved matter through pores; (3) flow of fluid with dissolved matter through fractures and (4) movement of fractures together with the contained fluid and dissolved matter (mobile hydrofractures). A vein system is rarely the product of a single transport and mineral precipitation mechanism, as these vary strongly both in space and time within a single system.     

Use of fracture filling mineral assemblages for characterizing water-rock interactions during exhumation of an accretionary complex: An example from the Shimanto Belt,southern Kyushu Japan

Various fracture filling minerals and secondary minerals in fracture walls were formed by fluid-rock interaction during the exhumation of the Palaeogene Shimanto Belt of Kyushu, Japan, which is located in an accretionary complex. Each mineral formed under favourable geological conditions and can be used to estimate the conditions of accretion and formation of the related rock sequences. Petrographic observations, mineralogical and geochemical analyses were made on fracture filling minerals and secondary minerals from boreholes of ca. 140 m depth, drilled in the Shimanto Belt. Results reveal that the secondary minerals were formed in three major stages distinguished by the sequential textural relationships of the minerals and the interpreted environment of mineral formation. Filling mineral assemblages show that the studied rock formation has been subducted to a depth of several km and the temperature reached was ca. 200–300 °C. After the subduction, the rock formation was uplifted and surface acidic water penetrated up to 80 m beneath the present ground surface. The acid water dissolved calcite fracture filling minerals to form the present groundwater flow-paths, which allowed recent wall rock alteration to occur. The results shown here imply that filling mineral assemblages can be an effective tool to evaluate the environmental changes during exhumation of an accretionary complex.     

Passive kimberlite intrusion into actively dilating dyke–fracture arrays: evidence from fibrous calcite veins and extensional fracture cleavage

Calcite veins are invariably associated with en-echelon kimberlite dyke–fracture arrays. A detailed microstructural study of veining indicates four vein types. Type I stretched or ataxial veins are defined by high aspect ratio calcite fibers that are crystallographically continuous with calcite of the kimberlite matrix wall rock, by elongated phenocrystic phlogopite with sharp crystal terminations centered on contacts between adjacent calcite fibers and by phenocrystic phlogopite that grows or extends across these veins. Type I vein mineralogy indicates syn-dilational crystallization of vein minerals in local tensional areas within the kimberlite. Vein Types II (stretched to syntaxial elongate-blocky) and III (antitaxial) indicate late crystallization vein mineral growth during subsequent or repeated dilation. Calcite fibers in Type I to Type III veins are orthogonal to the contacts of their host dykes regardless of the orientation of vein margins. Type IV calcite veins, with blocky or mosaic/polycrystalline textures, are attributed to minor post-intrusion extension, which was potentially accompanied by repeated kimberlite intrusion within a given dyke array. Syn-crystallization/syn-intrusion Type I veins and an ubiquitous dyke-parallel fracture cleavage, in a zone up to 4 m on either side of dyke contacts, suggest that en-echelon kimberlite dyke–fracture arrays occupied the approximate center of zones of active dilation within the brittle carapace of the upper crust. Type II and III veins indicate that extension or dilation continued, independently of an occupying kimberlite fluid phase, after initial intrusion. Arrested mobile hydrofracturing, under low differential stress within the upper brittle or seismic carapace of the continental crust, followed by repeated dilation of the dyke–fracture system, is proposed as a mechanism for producing the features observed in this study. The conditions constrained in this study indicate passive dyke intrusion into dilating fracture arrays during crustal extension.     

Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction–collision system,Bergen Arcs,Norway

Rb–Sr multimineral isochron data for metamorphic veins allow to date separate increments of the mineral reaction history of polymetamorphic terranes. Granulite facies rocks of the Lindås nappe, Bergen Arcs, Norway, were subducted and exhumed during the Caledonian orogeny. The rocks show petrographic evidence for two distinct events of local fluid infiltration and vein formation, along fractures and shear zones. The first occurred at eclogite facies (15–21 kbar, 650–750°C) and a later one at amphibolite facies conditions (8–10 kbar, 600°C). The presence of fluids enabled local metamorphic equilibration only near fluid pathways. In fluid-absent domains, preexisting assemblages were metastably preserved. This resulted in a heterogeneity of metamorphic signatures on meter to μm-scales. Well-preserved granulite facies rocks preserve their Proterozoic Rb–Sr mineral ages, as does the U–Pb system of zircon in most lithologies. Six Rb/Sr multimineral isochron ages for eclogite facies veins and their immediate wallrocks date the fluid-induced eclogitization at 429.9 ± 3.5 Ma (2σ, weighted average, MSWD = 0.39). An eclogite facies vein has yielded metamorphic zircon with concordant U–Pb ages of 429 ± 3 Ma, identical to the U–Pb age of 427.4 ± 0.9 Ma for zircon xenocrysts in an amphibolite facies vein. Seven Rb/Sr mineral isochron ages date amphibolite-facies fluid infiltration at 414.2 ± 2.8 Ma (MSWD = 1.5), an age value testifying to residence of the rocks in the deep orogenic crust at temperatures >600°C for nearly 15 Ma. The new data show that Rb–Sr mineral isochron ages effectively date fluid-induced (re)crystallization events rather than stages of cooling. The direct link between isotopic ages and distinct petrographic equilibrium assemblages aids to constrain the evolution of rocks in the P–T-reaction-time space, which is essential for understanding exhumation histories and the internal dynamics of orogens in general.     

Hydrothermal mineralization in the fields of temperature and pressure gradients

In this paper, we consider numerical simulation of mineral deposition from hydrothermal solutions under variable temperature and pressure conditions. The influence of solution source temperature depth, composition, and degree of oxidation on the composition of the products of mineral formation was evaluated. Conditions and reasons for the development of solution supersaturation/undersaturation with respect to major vein minerals were analyzed. Coupled variations in the degrees of dissociation of acids and complexes of major elements play the leading role in the formation of particular mineral assemblages. Chemical composition and degree of oxidation of the source of solutions modify vein mineralization but do not fundamentally change its character. The cooling, heating, and decompression of solutions result in the formation of distinctive mineral assemblages. This allows the use of data on the qualitative and quantitative composition of veins for the estimation of the conditions of solution evolution and its source.     

陕甘宁盆地川口油田低渗透油藏长6油层裂缝特征

通过对野外野头观测，岩心观察，薄片鉴定、地层倾角测井解释等方法，对川口油田长6油层裂缝进行了研究，川口油田长6油层主层裂缝方向为近EW向，天然显裂缝规模小且不发育，裂缝在原始地层条件下多为闭合状态，只有在人工激发后才会表现出明显的裂缝特征，川口油田储层类型为孔隙型储集层，该区油层埋深500－700m，垂向应力为最小主应力，压裂后理论上应产生水平缝，但受到天然垂直（闭合）缝的影响，在裂缝发育区可能会形成垂直压裂缝，在目前注水条件下，注水实验区储层裂缝的作用还未表现出来。     

准噶尔盆地克-百断裂带火山岩储层特征研究

为深入剖析准噶尔盆地克-百断裂带石炭系火山岩风化壳储层特殊性,寻找优质储层,对该区火山岩岩芯样品、普通薄片、铸体薄片、荧光薄片、成像测井等资料进行分析,探索火山岩风化壳孔缝基本特征和成因。研究结果认为:该火山岩储层孔缝类型和特征多样化,以次生溶孔、裂缝为主,为低孔特低渗储层;熔岩脆性大,构造裂缝较发育,熔岩层旋回顶部原生气孔发育;近断裂和风化壳顶面更易形成次生孔缝带。储集空间组合方式复杂,主要划分为裂缝-气孔、裂缝-颗粒间孔、裂缝-斑晶溶孔、裂缝-基质溶孔4种类型。后期的风化淋滤作用、构造破裂作用和溶蚀作用使风化壳的储集性能得到改善,而热液蚀变充填作用和胶结充填作用则对储层产生了破坏。油气聚集受断裂和不整合面的控制,可形成断裂控制的断阶式断块油气藏和不整合面控制的大型地层油气藏。     

黄陵背斜南翼牛蹄塘组二段页岩岩心裂缝脉体成岩环境演化与页岩气保存

岩心观察鄂西黄陵背斜南翼下寒武统牛蹄塘组二段黑色页岩中发育构造挤压成因的高角度裂缝和顺层裂缝.选取不同产状的典型裂缝脉体样品,薄片镜下观察发现高角度裂缝中充填方解石脉,顺层裂缝中充填方解石-白云石复合脉.通过阴极发光、流体包裹体分析以及微区原位元素测定,开展了裂缝脉体成岩环境演化研究,分析了不同产状裂缝对页岩气层局部封闭性的影响.阴极发光结果表明,高角度方解石脉和顺层方解石-白云石复合脉均为2期流体活动形成.根据流体包裹体分析,高角度方解石脉早期成脉流体主要为变质较深的地层卤水,晚期成脉流体混入了低矿化度流体,而顺层方解石-白云石复合脉2期成脉流体均未受低矿化度流体的改造.利用不同阴极发光的裂缝脉体碳酸盐矿物的微区原位微量元素测定结果,对铁锰含量、稀土元素（REE）和氧化还原判别参数分析显示,高角度方解石脉成岩环境经历了由还原环境向氧化环境转化,而顺层方解石-白云石复合脉的成岩环境长期保持了较为还原的环境.因此认为,高角度裂缝对页岩气层的局部封闭条件可能产生破坏作用,从而造成页岩气一定程度的散失,而顺层裂缝对局部封闭条件的破坏作用相对有限,裂缝发育特征及其经历的成岩演化过程研究可为页岩气层自封闭和页岩气微观保存条件的评价提供依据.      

加拿大Abitibi 绿岩带Donalda金矿近水平含金石英脉的显微构造分析及其对成矿流体动力学的指示

位于加拿大Abitibi 绿岩带南部的Donalda 金矿床主要由近水平的、与剪切带近垂直的含金石英脉组成,矿脉厚度0.3~0.5 m,含大量与脉壁平行的条带,指示多期次裂隙扩张和矿物沉淀。原生石英 c轴方位测量显示石英生长方向垂直于脉壁,指示断裂属张性,矿物沉淀属空间充填。显微裂隙、细脉及流体包裹体面 (FIPs) 的方位测量指示原生矿物受到了近直立的最大主压应力(σ1) 作用,与区域性的、近水平的南北向挤压应力不符。这一矛盾现象可用流体压力在超静岩和静水压力之间周期性变化及近水平断裂的周期性张开与闭合来解释。当流体压力大于静岩压力时,断裂张开,原生矿物沉淀,而当流体压力减小时,断裂上盘往下垮,两盘突出的矿物碰撞、碾压形成与脉壁平行的变形条带。由于断裂两盘岩石不是沿整条断裂都互相接触,两盘相顶部分承受的垂直应力大于水平方向的挤压应力, 这就解释了为什么显微构造指示近直立的最大主压应力(σ1)。这个流体构造模式支持断层阀模式,并且无须改变区域应力场就可解释脉体内局部主压应力的变化。     

脉体充填的力学机制

我们把脉体充填的断裂构造的发生发展过程分为三个阶段:生成阶段、发展阶段和破坏阶段。第一阶段主要地是在水平的挤压应力作用下发生的,一般在(水)平面上形成两组剪性断裂和一组横向张性断裂,而在横剖面上则出现两组纵向压性断裂,有时还见一组张裂。这种立体空间形变特点反映在平面上构成“米”字型。此外,还有其他一些断裂。     

Fractures,hydrothermal alterations and permeability in the Soultz Enhanced Geothermal System

Borehole studies of the Soultz-sous-Forêts granite are dedicated to deep geothermics. The hydraulic properties of the reservoir are mainly controlled by the occurrence of some altered cataclastic shear zones showing a low natural permeability characterized by the occurrence of brines. Those zones show a fracture cluster organisation with sealed fractures of various types (post-filled joints, sheared fractures, veins). The main hydrothermal deposits observed within the permeable zones are geodic quartz, carbonates, illite and more locally sulphides. The fracture wall–rocks are intensely transformed: dissolution of igneous minerals, crystallization of new minerals, porosity and permeability increase. It is important to characterize the newly-formed minerals in order to choose the reagents used to improve the permeability of the exchanger by chemical stimulations. This article represents a synthesis of the studies completed by the authors between 1990 and 2008 on the fracture networks, hydrothermal alterations and mineral crystallizations they induced and data about the flow pathways in the exchanger.     

Diagenesis in porosity evolution of opening-mode fractures, Middle Triassic to Lower Jurassic La Boca Formation, NE Mexico

Opening-mode fractures (joints) in Middle Triassic to Lower Jurassic La Boca Formation sandstones, northeastern Mexico, have patterns of fracture porosity, mineral-fill structures, and size distributions not previously described from outcrop. Patterns match those found in cores from many basins. We used aperture measurements along lines of observation (scanlines), fracture-trace maps, petrography, high-resolution scanning-electron-microscope-(SEM)-based cathodoluminescence, and fluid inclusions to characterize fracture populations. Open fractures are lined by quartz that precipitated while fractures were opening, whereas sealed fractures additionally contain calcite deposited after fractures ceased opening. Large fractures and arrays of contemporaneous microfractures have consistent power-law aperture-size scaling over approximately three orders of magnitude. Our results imply that open fractures and fracture sizes depend on diagenetic state. The interplay of fracture mechanics and diagenetic history is a determinant on effective porosity within fractures and, thus, open fracture persistence, connectivity, and fluid flow.     

柴达木盆地东坪地区基岩风化壳特征

柴达木盆地阿尔金山前斜坡带发现了规模分布的东坪基岩气田,其基岩风化壳的作用成为关注的问题。依据元素分析、X-射线衍射分析、岩心薄片观察,常规测井响应和成像测井响应特征,识别出东坪地区基岩风化壳发育不同结构层,且不同结构层的储集特征有很大差异。研究表明,基岩风化壳结构可划分为土壤层、完全风化层和半风化层,而半风化层又可进一步分为溶蚀带和崩解带;其中土壤层厚度0~2 m,完全风化层厚度4~15 m,溶蚀带厚度365~164 m,崩解带厚度300~1 000 m。基岩半风化层是储层发育带,其中溶蚀带储集物性好于崩解带,溶蚀带发育较多的溶蚀孔洞和溶蚀加宽的网状裂缝,孔隙度范围2%~16%;而崩解带发育弱溶蚀构造缝和节理缝,孔隙度范围2%~8%。东坪地区大规模发育基岩风化壳为柴达木盆地远离烃源岩灶的斜坡地区寻找油气提供了借鉴依据。     

超临界流体的快速泄出:来自霓辉石英脉的证据

河南外方山地区熊耳群火山岩中新发现了一种霓辉石英脉群,脉表现出独特的矿物组合及晶体特征,如霓辉石英脉具有复杂的矿物组成,表现出强烈的不平衡特点;霓辉石英脉具明显的对称分带特征,各分带中矿物组成及特征显著不同;存在具熔蚀边结构的钾长石-霓辉石集合体团块;霓辉石具在明显核幔结构,内核化学成分与幔边部存在较大差异;钾长石晶体元素分布存在似"文象"结构,表现出Fe元素的熔体分离特征;脉中矿物普遍发育环带结构;霓辉石英脉交代致密火山岩围岩形成蚀变带,新生大量榍石、霓辉石等矿物且含量随着与脉壁距离的增加急剧减少,显示出强烈的流体/气体扩散交代作用.霓辉石英脉独特的矿物组合及晶体特征反映了其成因的复杂性以及生长环境的变化.根据霓辉石英脉矿物的特点,推测其源于流体、熔体和晶体的混合物,并经历了快速侵位、快速冷却的过程,因而能够保存流体演化各阶段的结晶信息,保留不同成因的晶体群.外方山霓辉石英脉矿物可划分为捕虏晶亚群、熔体晶体群、超临界流体亚群、热液晶体亚群和凝聚晶体亚群等.外方山霓辉石英脉矿物晶体群的深入研究可能有助于揭示岩浆熔体向流体转换的机制及侵位机制,进而可揭示岩浆-流体成矿作用.