The mean critical radius of spherical quartz inclusions in albite is 5 μm for the upper chlorite zone and garnet zone, 10 μm for the lower biotite zone, and 20 μm for the upper biotite zone in the Sambagawa metamorphic terrain. The mean values of the critical radii of spherical quartz inclusions in oligoclase of the Ryoke metamorphic rocks is about 5 μm for the chlorite zone and about 10–20 μm for the sillimanite zone.
Assuming temperatures of about 350°C for the upper chlorite and garnet zones, 400°C for the lower biotite zone, 550°C for the upper biotite zone, and 700°C for the sillimanite zone, the activation energy for the grain boundary diffusion of oxygen along the quartz/plagioclase interfase is estimated to be about 30 kcal/mol. 相似文献
Using a group of epidote-glaucophane schists from the Kotu area of the Sanbagawa metamor-phic belt in Shlkoku, Japan (isophysical compositional),univariant boundary lines were determined for the assemblages that, in addition to the ubiquitous quartz + albite + phengitic mica, contain hematite + chlorite, garnet + chlorite and actinolite + chlorite, respectively. The slopes of the univariant boundary lines obtained from petrographical data are in good agreement with those calculated in a model system.
The positions of isophysical univariant boundary lines on the amphibole compositional diagram serve to distinguish the grade of metamorphism among the rocks of the same mineral facies. The hematite-chlorite univariant boundary line can be used to divide the zone of epidote-glaucophane schists of the Sanbagawa metamorphic belt into three, and the garnet-chlorite-paragonite invariant equilibrium can be used to divide the epidote zone of New Caledonia into three. 相似文献
相似文献
13.
《Resource Geology》2018,68(1):83-92
Cu–Mo mineralization occurs in southern part of the Chatree Au–Ag deposit, central Thailand. Quartz veins of Cu–Mo mineralization are divided into five types: Types A, B, C, D and E. Quartz veins of Types A, B and C are hosted in altered granodiorite porphyry, and quartz veins of Types D and E occur in altered andesite lava. Mineral assemblages of Types A, B and C quartz veins are composed of qz–chl–ilt–mol–py–ccp, qz–chl–ilt–ccp–py and qz–chl–ilt–ccp–py–sp–po, respectively. Types D and E quartz veins consist of qz–chl–py–ccp–sp–po and qz–ep, respectively. Fluid inclusions of quartz veins are divided into liquid‐rich two‐phases fluid inclusion, vapor‐rich two‐phases fluid inclusion and multiphase solid‐bearing fluid inclusion. Coexistence of a halite‐bearing fluid inclusion having salinity of 37 equiv. wt.% NaCl and a vapor‐rich two‐phases fluid inclusion having salinity of 1 equiv. wt.% NaCl suggests that the Cu–Mo‐bearing quartz veins were formed at temperature of 450°C and pressure of 250 bars (depth of approximately 1.5 km from the paleosurface). Based on the formation temperature of 450°C of quartz veins and the δ18O values of quartz of the quartz veins, the δ18O value of fluid responsible for the Cu–Mo‐bearing quartz vein is estimated to be +9.9‰. The origin of fluid forming the Cu–Mo‐bearing quartz veins in the N prospect of the Chatree mining area would be magmatic water. Based on the characteristics of geology, age, mineral assemblage and the formation environment, Cu–Mo mineralization would be different from the epithermal Au–Ag mineralization of the Chatree mining area. 相似文献
14.
Jörn H. Kruhl 《International Journal of Earth Sciences》2001,90(1):104-117
The shape, pattern and crystallographic orientation of grain boundaries represent important characteristics of crystalline material and contain information about its deformation and annealing history. The present study includes measurements of grain boundaries from experimentally annealed analogue material as well as natural foam texture of quartz and plagioclase. The main subject is the relation between the development of a foam texture and the crystallographic orientation of its grain boundaries and their geometry. (1) During annealing, grain sizes stabilize at certain values. On a statistical basis, these values can be applied as a geothermometer. (2) On the light-microscope scale, the grain boundaries in foam textures commonly consist of two or several planar facets. They are preferentially oriented along specific crystallographic planes, namely in relation to both neighbouring crystals; for quartz they tend to be rhombohedral. (3) Even highly misoriented facets and dihedral angles largely deviating from the 'equilibrium angle' of 120° may be stable over long periods of annealing. (4) Parts of single boundaries may migrate, whereas other parts are stationary during annealing. The results of the present study suggest that the anisotropy of surface energy has a considerable influence on the development of foam textures and that modelling of texture development should include the influence of the crystallographic orientation of grain boundaries. 相似文献
15.
Mineral assemblages in pegmatite samples from Kolsva, Swedenand Marikov, Czechoslovakia show that chrysoberyl is alwaysaccompanied by quartz, and is a breakdown product of primarypegmatitic beryl. Textures and the mineral-forming process forthe Kolsva pegmatite are explained by the reactions beryl +K-feldspar + H+ = chrysoberyl + quartz + SiO2, aq + K+ + H2Oor alternatively beryl Kfeldspar + H2O = chrysoberyl+ quartz + melt. Mineral assemblages from mica-rich parts ofthe pegmatite include sillimaniteKfeldspar, muscoviteKfeldsparsillimanite,and annitemagnetitespinelsillimanitegarnet.Details about the composition and the textural relationshipsof these minerals are given; they indicate a post-pegmatiticmetamorphic event at PT conditions near to the anatecticregime. The samples from Marikov show textures, which are explainedby the reactions beryl + albite + H+ = chrysoberyl + quartz+ Na+ + H2O or alternatively beryl + albite + H2O = chrysoberyl+ quartz + melt. Breakdown of muscovite produces sillimaniteaccording to the reactions beryl + albite + muscovite + H+ =chrysoberyl + quartz + sillimanite + Na+ + K+ + H2O or alternativelyberyl + albite + muscovite + H2O = chrysoberyl + quartz + sillimanite+ melt. Similar reaction textures and mineral assemblages were foundin other chrysoberyl-bearing pegmatites (Maroankora, Madagascar;Helsinki, Finland; Haddam, Greenfield, Greenwood, U.S.A.). Hydrothermal experiments located the reaction beryl + alkalifeldspar + H2O = chrysoberyl + phenakite + melt at PTconditions between the KfeldsparquartzH2Osolidus and the Kfeldsparalbitequartz-H2Osolidus. It is concluded that the formation of Al-rich minerals likechrysoberyl and sillimanite in pegmatites is due to a post-pegmatiticevent at high PT conditions. The question as to whichof the alternative set of reactions is more likely, the ionicequilibria or the anatectic chrysoberyl formation, must be leftopen. The previous hypothesis of a desilification of a pegmatitewhich intruded into SiO2-poor country rocks, or of the assimilationof Al2O3-rich country rocks, cannot explain the mineral assemblagesof the two pegmatites. 相似文献
16.
The texture, distribution, and infiltration tendency of a quartz-albite melt in equilibrium with a synthetic, texturally-equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1,250° C and 8 kbar hydrostatic pressure. Wetting angle measurements from melt distribution experiments show a dihedral angle () of 60 degrees, implying a quartz/quartz interfacial energy approximately 1.7 times the quartz/melt value. Because of this specific relationship between interfacial energies, the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections, possibly forming some interconnected channels. Stability of melt in pockets and along grain edge intersections was observed in a fourteen-day, dispersed-melt experiment, yet melt pools failed to disperse into the quartzite during infiltration experiments. Comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement, and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically.While these experiments are not strictly applicable to real crustal systems, they do indicate that, at least in some felsic systems, the melt has no preference for uniform grainedge wetting relative to collection at grain corners or in large pools. This ambivalent behavior is attributable to the 60-degree wetting angle, which has been shown to separate systems in which melt tends to disperse in interconnected channels (<60°) from those in which melt tends to become isolated at grain corners (> 60°). 相似文献
17.
钠长石花岗岩中雪球结构形成机理的研究 总被引:5,自引:0,他引:5
在某些富锂、氟含稀有金属花岗岩的石英和钾长石斑晶中常见 (半 )雪球结构。雪球结构的产出特征、雪球体中钠长石的电子探针分析结果以及其他间接证据都说明 ,雪球结构是在岩浆结晶分异过程中形成的。对矿物结晶顺序、石英和钠长石的生长速率以及固相线温度的研究表明 ,富锂、氟、钠的花岗质残余岩浆完全具备形成雪球结构的条件。岩浆熔体中较高的Na2 O/K2 O比值和F、H2 O含量在雪球结构的形成过程中起着重要的作用 :F的高含量使岩浆固相线温度降低 ,岩浆得以充分分异演化 ,形成接近端员组分的钾长石和钠长石 ;Na2 O/K2 O比值较大使钠长石首先结晶 ;较高的F和H2 O含量使岩浆粘度降低 ,石英的生长速率相对加快并逐渐包裹钠长石形成雪球结构。 相似文献
18.
Marian B. Holness 《Contributions to Mineralogy and Petrology》1995,118(4):356-364
An investigation was made of the effect of trace amounts of feldspar (Na and/or K) on dihedral angles in the quartz-H2O-CO2 system at 4 kbar and 450–1050°C. Quartz-quartz-H2O dihedral angles in feldspar-bearing quartz aggregates are observed to be the same as those in pure quartz aggregates at
temperatures below 500°C. Above this temperature, they decrease with increasing temperature until the solidus. The final angle
at the inception of melting is about 65° for microcline-quartz-H2O and microcline-albite-quartz-H2O, and much less than 60° (the critical value for formation of grain-edge fluid channels in an isotropic system) for the albite-quartz-H2O system. CO2 was observed to produce a constant quartz-quartz-fluid dihedral angle of 97° in feldspar-bearing quartz aggregates at all
temperatures studied. Also examined were the dihedral angles for the two co-existing supersolidus fluids in quartz aggregates.
In all systems the quartz-volatile fluid angle is greater than 60°, whereas the quartz-melt angle is lower than 60°. Both
super-solidus angles decrease with increasing temperature. The transition from nonconnected to connected poro- sity with increasing
temperature observed in the quartz-albite-H2O system some tens of degrees below the solidus (termed a permeability transition), if a common feature of rocks near their
melting points, will play an important role in controlling the permeability of high-grade rocks to aqueous fluids.
Received: 27 October 1993 / Accepted: 11 July 1994 相似文献
19.
Marian B. Holness M. J. Bickle Colin M. Graham 《Contributions to Mineralogy and Petrology》1991,108(3):356-367
In the aureole of the Beinn an Dubhaich granite, Skye, the minimum observed median forsterite-calcite-calcite dihedral angle
varies from 110° at the olivinein isograd to about 165° (the equilibrium value) at the granite-limestone contact. Laboratory
experiments were performed to investigate the kinetics of this textural change. It was found that the rate of change of the
forsterite-calcite-calcite dihedral angle followed approximately first-order kinetics with an activation energy of 48±4 kJ
mol-1 for fluid-present conditions, and 90 ±4 kJ mol-1 for fluid-absent conditions. Scanning ion imaging demonstrated that, at least in the early stages of textural change, solution-reprecipitation
of the calcite was the rate determining step in the fluid-present runs. The latter result and the value of the activation
energy are both consistent with the activation energy found by previous authors for (albeit zeroth order) silicate-aqueous
solution solution-reprecipitation reactions. The value of activation energy for the dry data does not correspond to those
for either grain boundary or volume diffusion of oxygen or magnesium in forsterite. The mechanism for textural equilibration
in the fluid-absent runs is uncertain. Application of the experimentally-derived rate equation to the Beinn an Dubhaich marbles
gave activation energies higher than those obtained experimentally. It is concluded from consideration of grain growth effects
that activation energies derived from the Beinn an Dubhaich marbles probably reflect textural equilibration under predominantly
fluid-absent conditions. 相似文献
20.
Richard Wirth 《Contributions to Mineralogy and Petrology》1996,124(1):44-54
Olivine grain boundaries and phase boundaries in xenoliths from San Carlos have been investigated by high-resolution transmission
electron microscopy (HREM) and analytical electron microscopy (AEM). Thin amorphous intergranular layers with variable width
(1–2 nm) were detected along olivine grain boundaries. The Al2O3, TiO2 and CaO concentrations of the amorphous layers increase with increasing width of the layer. The composition of the amorphous
intergranular layers depends on the interface type – grain or phase boundary. Morphology, amorphous state and chemical composition
of the intergranular layer suggest the presence of a melt film at olivine grain boundaries. Since the composition of the amorphous
phase strongly depends on the type of interface, the melt must have been generated at the grain boundary. Also, the melt chemistry
is different from the composition of partial melts produced from possible hydrous phases, such as phlogopite or amphibole,
and from the host basanite. The mobility of very thin melt films is assumed to be very limited due to the strong interface
forces between the melt and the grain boundary. It is concluded that grain boundary melting occurred at the interfaces due
to decompression during uplift. The melt wetted olivine grain boundaries as well as olivine-opx phase boundaries. The thin
amorphous layers formed melt microsystems. Mixing of melts from different microsystems is suggested to occur in wider melt
films, melt veins or melt pockets thus creating a magmatic melt that could be extracted from its source.
Received: 6 November 1995 / Accepted: 24 January 1996 相似文献
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