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Equilibria Modelling (equilibrium + modelling)
Selected AbstractsMetastable persistence of pelitic metamorphic assemblages at the root of a Cretaceous magmatic arc , Fiordland, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009N. R. DACZKO Abstract Four aluminosilicate-bearing, amphibolite facies pelitic schists sampled from the root of the long-lived eastern Gondwana continental magmatic arc now exposed in southwest Fiordland, New Zealand, record remarkably different P,T,t histories. The four samples were collected from within 20 km of each other within the Fanny Bay Group and Deep Cove Gneiss near Dusky Sound. Integrated petrography, mineral chemistry, mineral equilibria modelling and in situ electron microprobe chemical dating of monazite shows that the sample of the Fanny Bay Group south of the Dusky Fault records a Carboniferous history with peak conditions of 4,4.5 kbar at 570,590 °C, while one sample of the Deep Cove Gneiss from Long Island records a Cretaceous history with apparent peak conditions of 7.5 kbar at 650 °C. Two other samples of the Deep Cove Gneiss from Resolution Island record mixed Carboniferous and Cretaceous histories with apparent peak conditions of 7 kbar at 650 °C and 3,7 kbar at 640,720 °C. The metapelitic schists on Resolution Island were intruded by arc magmas including the voluminous high- P Western Fiordland Orthogneiss, yet they lack mineralogical evidence of the Cretaceous high- P (>12 kbar) event. Analysis of water isopleths in a model system shows that the amount of water accommodated in the rock mineral assemblage increases with pressure. With the exhaustion of all free water, and without the addition of external water, these rocks persisted metastably within the deep arc during the high- P event. The emplacement of large volumes of diorite (i.e. the Western Fiordland Orthogneiss) into the root of the Early Cretaceous continental magmatic arc did not lead to regional granulite facies metamorphism of the country rock schists, as large volumes of amphibolite facies rock metamorphosed under medium- P conditions persisted metastably in the deep arc crust. [source] Phase equilibria modelling of kyanite-bearing anatectic paragneisses from the central Grenville ProvinceJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2008A. INDARES Abstract Kyanite-bearing paragneisses from the Manicouagan Imbricate Zone and its footwall (high- P belt of the central Grenville Province) preserve evidence of partial melting with development of metamorphic textures involving biotite,garnet ± kyanite ± plagioclase ± K-feldspar,quartz. Garnet in these rocks displays a variety of zoning patterns with respect to Ca. Pseudosection modelling in the Na2O,CaO,K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,O (NCKFMASHTO) system using measured bulk rock compositions accounts for the textural evolution of two aluminous and two sub-aluminous samples from the presumed thermal peak to conditions at which retained melt solidified. The prograde features are best explained by pseudosections calculated with compositions to account for melt loss. The intersection of isopleths of grossular content and Fe/(Fe + Mg) relating to large porphyroblasts of garnet provide constraints on the P,T conditions of the metamorphic peak. These P,T estimates are considered to be minima because of the potential for diffusional modification of the composition of garnet at high- T and during the early stages of cooling. However, they are consistent with textural observations and pseudosection topology, with peak assemblages best preserved in rocks for which the calculated pseudosections predict only small changes in mineral proportions in the P,T interval, in which retrograde reactions are inferred to have occurred between the thermal peak and the solidus. Maximum P,T conditions (14.5,15.5 kbar and 840,890 °C) and steep retrograde P,T paths inferred for rocks from the Manicouagan Imbricate Zone are comparable with those determined for mafic rocks from the same area. In contrast, maximum P,T conditions of 12.5,13 kbar and 815,830 °C and flatter P,T paths are inferred for the rocks of the footwall to the Manicouagan Imbricate Zone. The general consistency between textures, mineral compositions and the topologies of the calculated pseudosections suggests that the pseudosection approach is an appropriate tool for inferring the P,T evolution of high- P anatectic quartzo-feldspathic rocks. [source] On the roles of deformation and fluid during rejuvenation of a polymetamorphic terrane: inferences on the geodynamic evolution of the Ruker Province, East AntarcticaJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2007G. PHILLIPS Abstract Evaluating pressure,temperature (P,T) conditions through mineral equilibria modelling within an amphibolite facies polymetamorphic terrane requires knowledge of the fluid content of the rocks. The Archean-Palaeoproterozoic basement rocks of the Ruker Province, East Antarctica, preserve evidence of three metamorphic events (M1,M3). Of particular interest is the M3 event, which is constrained to the early Palaeozoic (c. 550,480 Ma). Evaluation of the tectonic setting during this time is important because the Ruker Province is located within a critical region with respect to models of Gondwana assembly. Structural evidence of the early Palaeozoic event is preserved as large (up to ,500 m wide) high strain zones that cut the orthogneiss-metasedimentary basement (Tingey Complex) of the Ruker Province. Rocks within these zones have been thoroughly recrystallized and preserve a dominant shear fabric and M3 mineral assemblages that formed at P,T conditions of 4.0,5.2 kbar and 565,640 °C. Distal to these zones, rocks preserve more complex petrographic relationships with S1 and S2 foliations, being incompletely overgrown by M3 retrograde assemblages. We show that the mineral assemblages preserved during the M3 event are highly dependent on the availability of fluid H2O, which is strongly influenced by the structural setting (i.e. proximity to the high-strain zones). P,T structural and fluid flow constraints support a model of basin inversion during early Palaeozoic crustal rejuvenation in the Ruker Province. [source] The lawsonite paradox: a comparison of field evidence and mineral equilibria modellingJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2006G. L. CLARKE Abstract Lawsonite equilibria are predicted to occur over a broad P,T spectrum developed during subduction, yet lawsonite-bearing assemblages are rare. In the context of mafic mineral equilibria modelled for the range of common crustal metamorphism (4,23 kbar, 400,750 °C) using the system Na2O-CaO-K2O-FeO-MgO-Al2O3 -SiO2 -H2O and the software thermocalc, unusually high water contents are demanded by lawsonite assemblages. As a consequence, lawsonite assemblages are predicted to have difficulty forming and lawsonite equilibria to be uncommon. Metabasalt undergoing cooler subduction may experience substantial periods involving the metastable persistence of mineral assemblages because of water under-saturation with non-occurrence of recrystallization. If formed, lawsonite-bearing assemblages are observed to be highly unstable; their preservation requires that exhumation be accompanied by substantial cooling. The amount of structurally bound H2O in minerals plays a critical role in the formation and preservation of mineral assemblages, controlling key changes in rocks undergoing subduction. [source] Contact metamorphic P,T,t paths from Sm,Nd garnet ages, phase equilibria modelling and thermobarometry: Garnet Ledge, south-eastern Alaska, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2001H. H. Stowell Abstract Sm,Nd garnet-whole rock geochronology, phase equilibria, and thermobarometry results from Garnet Ledge, south-eastern Alaska, provide the first precisely constrained P,T,t path for garnet zone contact metamorphism. Garnet cores from two crystals and associated whole rocks yield a four point isochron age for initial garnet growth of 89.9 ± 3.6 Ma. Garnet rims and matrix minerals from the same samples yield a five point isochron age for final garnet growth of 89 ± 1 Ma. Six size fractions of zircon from the adjacent pluton yield a concordant U,Pb age of 91.6 ± 0.5 Ma. The garnet core and rim, and zircon ages are compatible with single-stage garnet growth during and/or after pluton emplacement. All garnet core,whole rock and garnet rim-matrix data from the two samples constrain garnet growth duration to ,5.5 my. A garnet mid-point and the associated matrix from one of the two garnet crystals yield an age of 90.0 ± 1.0 Ma. This mid-point result is logically younger than the 90.7 ± 5.6 Ma core,whole rock age and older than the 88.4 ± 2.5 Ma rim-matrix age for this sample. A MnNaCaKFMASH phase diagram (P,T pseudosection) and the garnet core composition are used to predict that cores of garnet crystals grew at 610 ± 20 °C and 5 ± 1 kbar. This exceeds the temperature of the garnet-in reaction by c. 50 °C and is compatible with overstepping of the garnet growth reaction during contact metamorphism. Intersection of three reactions involving garnet-biotite-sillimanite-plagioclase-quartz calculated by THERMOCALC in average P,T mode, and exchange thermobarometry were used to estimate peak metamorphic conditions of 678 ± 58 °C at 6.1 ± 0.9 kbar and 685 ± 50 °C at 6.3 ± 1 kbar, respectively. Integration of pressure, temperature, and age estimates yields a pressure-temperature-time path compatible with near isobaric garnet growth over an interval of c. 70 °C and c. 2.3 my. [source] Comments on the Productivity Commission's Modelling of the Economy-Wide Effects of Future Automotive Assistance,ECONOMIC PAPERS: A JOURNAL OF APPLIED ECONOMICS AND POLICY, Issue 1 2009Peter B. Dixon C68; F13 The Productivity Commission claims on the basis of computable general equilibrium modelling that a seemingly small reduction in assistance to the Australian Automotive industry (a cut in tariffs from 10 per cent to 5 per cent and elimination of the ACIS scheme) would generate an annual welfare benefit of about $500 million. I explain that this implausible result rests on an implicit manna-from-heaven assumption. Using results published by the Commission, I rework their welfare calculations. With parameter values favoured by them, the corrected annual welfare gain is $66 million. With what I consider more realistic parameter values, the welfare effect is negative. [source] Formation of copper complexes in landfill leachate and their toxicity to zebrafish embryosENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2000Jonathon K. Fraser Abstract Toxic metal organic complexeshavenot been found in natural waters, although someorganicacids form bioavailable lipophilic and metabolite-type metal complexes. Landfill leachates usually contain organic acids and in the urban environment these leachates, when mixed with storm waters containing Cu, could be a source of toxic Cu organic complexes in streams and estuaries. We investigated the formation of Cu complexes in the leachate from an active urban landfill and found that some of the complexes formed were toxic to zebrafish embryos. High and low nominal molecular weight (NMWT) fractions; >5,000 Da and <700 Da, of leachate both formed Cu complexes with almost identical Cu complexing characteristics but the toxicity was due solely to the low NMWT complexes formed in the <700 Da fraction. Chemical equilibrium modelling with MINTEQA2 and H and Cu complex conditional association constants and ligand concentrations obtained from pH and Cu titrations with a Cu ion-selective electrode and van den Berg,Ruzic analyses of the titration data was used to calculate the copper speciation in the embryo test solutions. This calculated speciation, which was confirmed by measurements of Cu2+ in the test solutions, enabled the toxicity due to the free Cu ion and to the Cu complexes to be distinguished. [source] A regional impact assessment of climate and land-use change on alpine vegetationJOURNAL OF BIOGEOGRAPHY, Issue 3 2003Thomas Dirnböck Abstract Aim, Assessing potential response of alpine plant species distribution to different future climatic and land-use scenarios. Location, Four mountain ranges totalling 150 km2 in the north-eastern Calcareous Alps of Austria. Methods, Ordinal regression models of eighty-five alpine plant species based on environmental constraints and land use determining their abundance. Site conditions are simulated spatially using a GIS, a Digital Terrain Model, meteorological station data and existing maps. Additionally, historical records were investigated to derive data on time spans since pastures were abandoned. This was then used to assess land-use impacts on vegetation patterns in combination with climatic changes. Results, A regionalized GCM scenario for 2050 (+ 0.65 °C, ,30 mm August precipitation) will only lead to local loss of potential habitat for alpine plant species. More profound changes (+ 2 °C, ,30 mm August precipitation; + 2 °C, ,60 mm August precipitation) however, will bring about a severe contraction of the alpine, non-forest zone, because of range expansion of the treeline conifer Pinus mugo Turra and many alpine species will loose major parts of their habitat. Precipitation change significantly influences predicted future habitat patterns, mostly by enhancing the general trend. Maintenance of summer pastures facilitates the persistence of alpine plant species by providing refuges, but existing pastures are too small in the area to effectively prevent the regional extinction risk of alpine plant species. Main conclusions, The results support earlier hypotheses that alpine plant species on mountain ranges with restricted habitat availability above the treeline will experience severe fragmentation and habitat loss, but only if the mean annual temperature increases by 2 °C or more. Even in temperate alpine regions it is important to consider precipitation in addition to temperature when climate impacts are to be assessed. The maintenance of large summer farms may contribute to preventing the expected loss of non-forest habitats for alpine plant species. Conceptual and technical shortcomings of static equilibrium modelling limit the mechanistic understanding of the processes involved. [source] Removal of anionic pollutants from groundwaters using Alamine 336: chemical equilibrium modellingJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2006Eugenio Bringas Abstract This work reports the study of the chemical equilibrium of the extraction of chromium(VI) anions from groundwaters where other anionic species are present, mainly sulfate and chloride anions, using Alamine 336 as extractant. The analysis was performed working with two different systems: (i) a binary system (sulfate and chloride anions) and, (ii) a tertiary system (chromium, sulfate and chloride anions) with a composition of 9.6,15.4 mol Cr6+ m,3, 5.2,16.7 mol SO42, m,3 and 4.2,13.5 mol Cl, m,3 respectively. A careful experimental design was performed and the data were correlated to the mathematical models obtaining the equilibrium parameters of the extraction reactions in both systems. Copyright © 2006 Society of Chemical Industry [source] | ||||||||||