Obiettivo The co-ordinator is Dr J. R. Ashworth (University of Birmingham, U.K.) and the other three member groups are (1) Dr V. S. Sheplev and V. A. Ananyev (Russian Academy of Sciences, Novosibirsk), (2) Professor I. K. Karpov (Russian Academy of Sciences, Irkutsk), and (3) Prof S. S. Augustithis and two colleagues (Athens, Greece).The project is an extension of previous collaborative work by Ashworth and Sheplev on coronas. A corona is a small scale (< 1 cm) layered structure, formed between two reactant mineral grains under metamorphic conditions deep in the Earth's crust. Unusually for a metamorphic reaction, the incomplete consumption of the product mineral grains enables the chemical reaction to be reconstructed quite accurately. The arrangement of the product minerals in a layered structure indicates that the reaction was diffusion-controlled. Previous work, modelling the reactions at layer boundaries and the diffusive fluxes between them, has shown that Al and Si are elements that commonly show limited diffusion and strongly influence the distribution of minerals among layers. In our recent work (Ashworth & Sheplev, 1997; Ashworth et al., 1998), we have been able to estimate the affinity, that is the driving force of the reaction which is a measure of departure from equilibrium.We now propose to generalise our approach to produce a new method of geothermobarometry, that is, of estimating the temperature (T) and pressure (P) at which metamorphic reaction occurred. For corona reactions, existing methods of P-T estimation cannot make use of minerals situated in different parts of the layer structure (e.g. not in direct contact), because they were not at mutual equilibrium during the reaction. However, we can now estimate the chemical-potential gradients across the corona that measures this disequilibrium. We can introduce a correction for the effect into the geothermobarometric method, following the thorough mathematical formulation of the corona-forming system by Ashworth & Sheplev (1997).We shall incorporate, in suitably modified form, Karpov's method of finding the mineral assemblage which represents the minimum free energy for a given system under stipulated P and T. This will be used to predict the mineral assemblage produced by a corona reaction, as a function of variable P and T. Thus the restriction in previous work, that only the observed product minerals could be used in diffusive reaction models, will be removed. We hope to recognise coronas which grew during changing P-T conditions, by finding that they contain different minerals predicted to form in different P-T ranges.Karpov will provide the expertise on the free-energy minimisation method, and the database of thermodynamic properties of minerals (including solid solutions of variable composition) which is necessary for its use. Sheplev's group will write the theoretical model of the corona reactions, and may possibly also obtain new data from new rock samples; Augustithis will advise on suitable rocks for interpretation and possible new quantitative analysis. Ashworth will apply the theory to specific petrological examples, and will appraise the practical difficulties that arise; eventually, Ashworth will write up for publication. The results should include P-T estimates for specific rocks, and discussion of likely remaining errors in the new geobarometric method.The project is planned to last three years. Sheplev is to visit Ashworth in Birmingham twice for one month each time: near the end of the first year, and again near the end of the second year. Sheplev is also to visit Augustithis in Athens for approximately one week, near the end of the first year. Programma(i) IC-INTAS - International Association for the promotion of cooperation with scientists from the independent states of the former Soviet Union (INTAS), 1993- Argomento(i) 5 - Earth Sciences, Environment, Energy INTAS - INTAS Invito a presentare proposte Data not available Meccanismo di finanziamento Data not available Coordinatore University of Birmingham Contributo UE Nessun dato Indirizzo B15 2TT Birmingham Regno Unito Mostra sulla mappa Costo totale Nessun dato Partecipanti (4) Classifica in ordine alfabetico Classifica per Contributo UE Espandi tutto Riduci tutto Laboratory of Textural Analysis Grecia Contributo UE Nessun dato Indirizzo Hymettou 89, Pangrati 11633 Athens Mostra sulla mappa Costo totale Nessun dato Siberian Branch of Russian Academy of Sciences Russia Contributo UE Nessun dato Indirizzo Favorskogo Str. 1a 664033 Irkutsk Mostra sulla mappa Costo totale Nessun dato Siberian Branch of Russian Academy of Sciences Russia Contributo UE Nessun dato Indirizzo Prospect akademica Koptuga 630090 Novosibirsk Mostra sulla mappa Costo totale Nessun dato Siberian Branch of Russian Academy of Sciences Russia Contributo UE Nessun dato Indirizzo Prospect akademica Koptuga 630090 Novosibirsk Mostra sulla mappa Costo totale Nessun dato
