Model for large strain consolidation with compressible pore fluid     

Patrick J. Fox  Tong Qiu 《国际地质力学数值与分析法杂志》2004,28(11):1167-1188

A numerical model, called CCPF1 (C onsolidation with C ompressible P ore F luid 1 ), is presented for one‐dimensional large strain consolidation of a saturated porous medium with compressible pore fluid. The algorithm includes all the capabilities of a previous large strain consolidation code, CS2, written for incompressible pore fluid. In addition, fluid density and fluid viscosity are functions of fluid pressure in CCPF1. Generalization of the numerical approach to accommodate these functions requires several modifications to the CS2 method, including phase relationships, intrinsic permeability, pore pressure, fluid potential, and mass flux. Inertial forces are neglected and isothermal conditions are assumed. The development of CCPF1 is first presented, followed by an example that illustrates the effects of pore fluid compressibility on the mechanics of consolidation of saturated porous media. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Fluid inclusion evidence for basement decompression during Permo-Triassic extension, SE New England, USA     

K. O'HARA 《Journal of Metamorphic Geology》1991,9(5):567-579

Abstract CO₂-bearing fluid inclusions in strongly lineated but weakly foliated late Precambrian gneisses within the Hope Valley Shear zone of Connecticut and Rhode Island are of mixed composition ( X _co2± 0.1; 7 wt% NaCl equivalent) and variable density (0.59–0.86 g/ml) and occur mainly as isolated inclusions. Also present are dilute (3 wt% NaCl equivalent) aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism. Isochores for dense isolated CO₂-bearing inclusions indicate pressures of 7.5–9 kbar at 500–600° C, the estimated temperature conditions of peak metamorphism. Published ⁴⁰Ar/³⁹Ar hornblende plateau age spectra indicate cooling through about 500° C at 265 ± 5 Ma. Isochores for low-density CO₂-bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism (325–400° C) and indicate pressures of 3–4 kbar. Published ⁴⁰Ar/³⁹Ar biotite plateau ages indicate cooling through about 300° C at 250 ± 5 Ma. These data define a P–T uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0.4 and 3.3 mm/year in Permian time. Exhumation of basement gneisses was coeval with normal (west-down) motion along the regional basement–cover contact (Honey Hill–Lake Char–Willimantic fault system), and is interpreted as due to post-orogenic extensional collapse of the Alleghanian orogeny.  相似文献   

Endogreisen, brecciation and fluid activity at the Mount Bischoff Sn-deposit, north-west Tasmania, Australia     

J.H. WRIGHT  T.A.P. KWAK 《Journal of Metamorphic Geology》1988,6(6):629-650

Abstract Endogreisens which replace K-feld-spar-quartz dykes in a Devonian (360 Ma) tin deposit at Mt Bischoff, north-west Tasmania, formed from the interaction of unusual solutions, probably derived from an underlying leucogranite pluton, porphyry dykes and limited quantities of local dolomitic country rock components. The intensity of greisenization and pH of the solutions increase inward to the greisenized dykes'cores and downward. The following types of greisen assemblages indicate increasing degrees of greisenization: 'sericite'muscovite + quartz ± tourmaline ± fluorite, topaz + quartz ± tourmaline ± fluorite, weberite, prosopite, ralstonite, Ca-ralstonite; and quartz ± topaz ± fluorite. Where the solutions interacted with dolomite, exogreisens consisting of topaz- or tourmaline-bearing assemblages were formed. The greisens were subsequently overprinted to varying degrees by siderite, sulphides and hydrous silicates (talc, serpentine, chlorite, micas).
The temperature during greisenization ranged from 180 to 414°C, based on fluid inclusions in topaz, quartz, fluorite, sellaite and cassiterite. The main greisen-forming event occurred at temperatures of 360±20°C. The fluids boiled intermittently. Their salinities ranged from 31.5 to 38.9 wt% total dissolved salts, consisting of Ca–K–Na–Fe–Cl±hydrocarbon species. Fluid inclusion data indicate that only 0.5–1.5 km of cover were present above this deposit at the time of formation.
The greisenized dykes were intruded by and intrude different stages of breccias. The breccias consist mainly of country rock and greisenized dyke fragments, with rock-flour and later tourmaline alteration. The Mt Bischoff greisen system is possibly part of a 'porphyry tin'style deposit formed at near-surface conditions (0.5–1.0 km).  相似文献   

Metagabbro and associated eclogites in the Lubrin area, Nevado-Filabride Complex, Spain     

L. MORTEN  G. M. BARGOSSI  J. M. MARTINEZ MARTINEZ  E. PUGA  A. DIAZ de  FEDERICO 《Journal of Metamorphic Geology》1987,5(2):155-174

Abstract Several small bodies of metabasite (maximum dimensions of 1000 m x 500 m) are included in the metamorphic rocks of the Nevado-Filabride Complex in the Betic Cordilleras (Almeria Region). The body of 400 m x 100 m, located 200 m due west of the Lubrin village, contains troctolitic gabbro with well-preserved igneous textures and mineral compositions, wholly amphibolitized gabbro, garnet-bearing metagabbro eclogite. Along with the textural and mineral changes, sensible and regular geochemical variations can be observed, where the content of MgO decreases from 24% to 11%, while that of CaO and Na₂O increases from 7% to 11% and from 2% to 3%, respectively. In addition, the content of some minor elements such as Sr, Y, Nb, Zr and Sc increases while that of Ni and Cr decreases from troctolitic gabbro to the eclogite. The amphibolitized gabbro shows values scattered around those of the troctolitic gabbro. These geochemical variations are ascribed to inherited differences in the pre-metamorphic protolith, i.e. a fractionated gabbro which varies from olivine-rich to clinopyroxene-rich gabbro. Nevertheless, some metasomatism affected the Lubrin body without changing the main chemical trends, as documented by the significantly different ⁸⁷Sr/⁸⁶Sr ratios of each rock-type. This points to a metasomatism which involved the introduction of crustal radiogenic strontium. The petrographical and mineral chemical features are interpreted to be the result of syn-metamorphic fluid circulation possibly combined with deformation by shearing. The igneous texture and mineral chemistry have been retained wherever both fluid circulation and shearing were ineffective. On the contrary, where both events were effective, the formation of eclogite occurred. Later, the entire body underwent a retrogressive amphi-bolitic stage under greenschist facies conditions, which was probably responsible for the formation of the amphibolitized gabbro portion and for the retrogression of the eclogite.  相似文献   

A New Interpretation of Centimetre-scale Variations in the Progress of Infiltration-driven Metamorphic Reactions: Case Study of Carbonated Metaperidotite, Val d'Efra, Central Alps, Switzerland   总被引：1，自引：0，他引：1  

FERRY  JOHN M.; RUMBLE  DOUGLAS  III; WING  BOSWELL A.; PENNISTON-DORLAND  SARAH C. 《Journal of Petrology》2005,46(8):1725-1746

Progress () of the infiltration-driven reaction, 4olivine +5CO₂ + H₂O = talc + 5magnesite, that occurred during Barrovianregional metamorphism, varies at the cm-scale by a factor of3·5 within an 3 m³ volume of rock. Mineral and stableisotope compositions record that X_CO2, ¹⁸O_fluid, and ¹³C_fluidwere uniform within error of measurement in the same rock volume.The conventional interpretation of small-scale variations in in terms of channelized fluid flow cannot explain the uniformityin fluid composition. Small-scale variations in resulted insteadbecause (a) reactant olivine was a solid solution, (b) initiallythere were small-scale variations in the amount and compositionof olivine, and (c) fluid composition was completely homogenizedover the same scale by diffusion–dispersion during infiltrationand subsequent reaction. Assuming isochemical reaction, spatialvariations in image variations in the (Mg + Fe)/Si of the parentrock rather than the geometry of metamorphic fluid flow. Ifinfiltration-driven reactions involve minerals fixed in composition,on the other hand, spatial variations in do directly imagefluid flow paths. The geometry of fluid flow can never be determinedfrom geochemical tracers over a distance smaller than the oneover which fluid composition is completely homogenized by diffusion–dispersion. KEY WORDS: Alpine Barrovian metamorphism; diffusion; metamorphic fluid composition; metamorphic fluid flow; reaction progress  相似文献   

P–T–fluid evolution in the Mahalapye Complex, Limpopo high-grade terrane, eastern Botswana     

K. HISADA  L. L. PERCHUK  T. V. GERYA  D. D. VAN REENEN  B. K. PAYA 《Journal of Metamorphic Geology》2005,23(5):313-334

Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high‐grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well‐developed textures inferred to record metasomatic reactions, such as Bt ? And + Qtz + (K₂O) and Bt ± Qtz ? Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO₂ and H₂O ( = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low‐pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga.  相似文献   

Some Homogeneous Bianchi type IX Viscous Fluid Cosmological Models with a Varying Λ     

Anirudh?PradhanEmail author  Sudhir?Kumar?Srivastav  Mahesh?Kumar?Yadav 《Astrophysics and Space Science》2005,298(3):419-432

Some Bianchi type IX viscous fluid cosmological models are investigated. To get a solution, a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density, whereas the coefficient of shear viscosity is considered as proportional to scale of expansion in the model. The cosmological constant Λ is found to be positive and is a decreasing function of time, which is supported by results from recent supernovae observations. Some physical and geometric properties of the models are also discussed.  相似文献   

Reporting Bias as a Result of Core Loss at Las Cruces: A Case Study     

S.?HenleyEmail author  M.?Doyle 《Natural Resources Research》2005,14(1):19-30

The most important copper minerals of the Las Cruces deposit in the pyrite belt of southern Spain are supergene enrichment zone sulphides of which chalcocite is the most significant. The deposit is overlain by 140 metres of barren marls and has been explored only by drilling. Drill cores have been split and assayed, but it became clear that there was a substantial problem related to core recovery which affects, in particular, some of the higher grade material. Much of the chalcocite is present in a friable and unconsolidated form and its progressive loss is evident visually in many core samples. The result of this loss of chalcocite is that there is a systematic downward bias on copper assays, leading directly to under-reporting of the copper resource. Studies of the assay data indicate the likely degree of under-reporting, but there is no simple way in which the reported resource estimates can validly be corrected.  相似文献   

On the origin of CO₂-rich fluid inclusions in migmatites     

L.S. HOLLISTER 《Journal of Metamorphic Geology》1988,6(4):467-474

Abstract Nearly pure CO₂ fluid inclusions are abundant in migmatites although H₂O-rich fluids are predicted from the phase equilibria. Processes which may play a role in this observation include (1) the effects of decompression on melt, (2) generation of a CO₂-bearing volatile phase by the reaction graphite + quartz + biotite + plagioclase = melt + orthopyroxene + CO₂-rich vapour, (3) selective leakage of H₂O from CO₂+ H₂O inclusions when the pressure in the inclusion exceeds the confining pressure during decompression, and (4) enrichment of grain-boundary vapour in CO₂ by subsolidus retrograde hydration reactions.  相似文献   

Dehydration melting, fluid buffering and decompressional P–T path in a granulite complex from the Eastern Ghats, India     

S. DASGUPTA  P. SENGUPTA  M. FUKUOKA  S. CHAKRABORTI 《Journal of Metamorphic Geology》1992,10(6):777-788

A suite of metapelites, charnockites, calc-silicate rocks, quartzo-feldspathic gneisses and mafic granulites is exposed at Garbham, a part of the Eastern Ghats granulite belt of India. Reaction textures and mineral compositional data have been used to determine the P–T–X evolutionary history of the granulites. In metapelites and charnockites, dehydration melting reactions involving biotite produced quartzofeldspathic segregations during peak metamorphism. However, migration of melt from the site of generation was limited. Subsequent to peak metamorphism at c . 860° C and 8 kbar, the complex evolved through nearly isothermal decompression to 530–650° C and 4–5 kbar. During this phase, coronal garnet grew in the calc-silicates, while garnet in the presence of quartz broke down in charnockite and mafic granulite. Fluid activities during metamorphism were internally buffered in different lithologies in the presence of a melt phase. The P–T path of the granulites at Garbham contrasts sharply with the other parts of the Eastern Ghats granulite belt where the rocks show dominantly near-isobaric cooling subsequent to peak metamorphism.  相似文献