Viscosity of Silicate Melts in the Join Ab-Di-H₂O-H₂ and the Basis Principles of a New Structure-chemical Model to Predict of the Viscosity of Magmatic Melts

Edward Persikov (persikov@iem.ac.ru) & Pavel Bukhtiyarov

Institute of Experimental Mineralogy RAS, 142432, Chernogolovka, Russia

In spite of a rather long history, up to now only the viscosity of silicate and magmatic melts from acidic to basic composition at the relatively low pressures, corresponding to the Earth crust is well studied. The highly essential investigations of the water- and hydrogen-bearing ultrabasic melts, as well as the study of the viscosity of magmatic melts under the mantle P-T parameters are rather limited. The problem of the development of physical-chemical model for the calculation and prediction of the magmatic melts viscosity also remains essential, particularly for the P-T parameters of the upper mantle. In this respect, the experimental investigations of rheological properties (viscosity, activation energy) of model silicate melts in the system albite-diopside-water- hydrogen have been studied at lithostatic pressures up to 50 kbars and fluid pressures up to 5 kbars in the temperature range 1100^o - 1850^oC. The viscosity of fluid-bearing melts has been determined using unique high gas pressure viscometer and the viscosity of volatiles free melts under super-high lithostatic pressures has been studied using "split-sphere" type apparatus. The results obtained indicate that the viscosity of all studied melts decreased with increasing temperature by exponentially, a new values of activation energies at high fluid and super-high lithostatic pressures were obtained. Viscosities and activation energies of all melts up to metasilicate compositions decreased with increasing both lithostatic, water and hydrogen pressures and in contrary, increased with pressure for more depolymerized ultrabasic melts. The pressure values which consists to the minimums of viscosities and activation energies decreased with increasing of melt basicity. The basis principles of a new structure-chemical model for calculation and prediction of magmatic melts viscosities in full composition range from acidic to ultrabasic at high and super-high pressures have been suggested. Using this model a general melt viscosity - pressure diagram has been constructed for the Earth's crust and upper mantle. The generalized dependencies of the viscosity and activation energy for near-liquidus magmas in the whole range of the depths of their existence in nature will have an extremal character. Thus, in the acidic-basic range of the compositions two minima and one maximum will take place, while for the ultrabasic melts only one maximum and minimum will be found.

Thermodynamic Conditions of Metamorphic-Metasomatic Formations Near Ore-bearing Complexes

Valentin Petrov (petrov@adm.kolasc.net.ru), Zinaida Voloshina (root@geo.kolasc.net.ru) & Vladimir Karzhavin (root@geo.kolasc.net.ru)

Geological Institute, Kola Science centre RAS, Apatity, 184200, Russia

In order to study the evolution of metamorphic processes and evaluate their thermodynamic parameters, late magmatic and superimposed metasomatic mineral assemblages were investigated near the contacts of ore-bearing metamorphic garnet-biotitå-amphibole rocks of the Fedorovo-Panskiy massif. The massif is located in the central part of the Kola peninsula and contains two stratified platinum-bearing layers horizon. On the basis of a detailed research of structures of coexisting minerals parageneses, three consequent stages of crystallization and mineral formation have been distinguished. The observed natural process of transformation of rocks in time from the initial crystallization of magmatic substance up the formation of mineral assemblages is justified by the carried out theoretical research, and the thermodynamic conditions are described by appropriate chemical reactions. On the basis of comparisons of phase interrelations and the obtained calculated material, some feature of the evolution of P-T parameters are established metamorphism for the regressive.

The conditions for the evaluation of the thermodynamic parameters obtained by using mineralogical geothermobarometers and by the date from the calculations serve as a basis for revealing of mineral facies of metamorphic and metasomatic processes of rocks of the investigated massif. The established orientation of metasomatism in near ore-bearing garnet-biotite rocks, reflected in P-T-t trends, a mineralogical of data modelling, testifies to local warming under corresponding rise of pressure in the natural system and a consequent drop of these parameters.

Thermomagnetic Analysis Based on Magnetic Susceptibility Measurements: A Sensitive Tool of Determining Magnetic Mineral Phases

Eduard Petrovsky (edp@ig.cas.cz)¹, Ales Kapicka (kapicka@ig.cas.cz)¹, Viktor Hoffmann (viktor.hoffmann@uni-tuebingen.de)², Erwin Appel (erwin.appel@uni-tuebingen.de)², Robert Scholger (scholger@grz08u.unileoben.ac.at)³ & Neli Jordanova (neli@ig.cas.cz)¹

¹ Geophysical Institute, Bocni II/1401, 141 31 Prague 4, Czech Republic

² University of Tuebingen, Sigwartstr. 10, 72076 Tuebingen, Germany

³ Montanuniversitaet Leoben, Paleomagnetic Laboratory Gams, 8130 Frohnleiten, Austria

Recent development of instruments and methods used in rock magnetism enables highly-sensitive determination of various magnetic mineral phases. In particular, temperature dependence of magnetic susceptibility, following the Curie-Weiss law, can be used in examining magnetic-transition temperatures, such as Curie (Tc) or Neel (Tn) temperatures in case of ferri- or anti-ferromagnetic minerals. In our contribution, we will demonstrate the method, using highly-sensitive automatic susceptibility bridge equipped with cryo-furnace attachment, enabling measurements in temperature range from -195°C to +700°C. Sensitivity of the instrument enables detection of very low concentrations of magnetic minerals, often beyond the sensitivity limit of "classical" X-ray analysis. In our contribution, typical behaviour of basic magnetic minerals, such as (titano)magnetite, maghemite, hematite, goethite and pyrrhotite will be shown. Effect of oxidation and temperature-induced transformation will be discussed. For example, the whole pathway of thermal decomposition of lepidocrocite to maghemite and hematite can be clearly observed. The other possibility is assessment of grain-size distribution of assembly of magnetite particles. Shape of susceptibility vs. temperature curve is different for ultra-fine superparamagnetic, stable single-domain and coarse multi domain particles. Finally, oxidation of magnetite can be reflected by e.g. sharpness of low-temperature Verwey transition.