Fast Production of Aerosols and Organic Compounds in Magmatic and Mud Volcanoes: Observations and Experimental Modelling

Vladimir A. Alekseev (a.getling@g23.relcom.ru)

Troitsk Institute for Innovation and Thermonuclear Research, Troitsk, Moscow Region, 142092, Russia

Aerosol and gas emanation in tectonic activity zones is an active natural process that carries away metals and organic compounds from the Earth into the atmosphere. The occurrence of these processes has been among decisive factors of the biospheric evolution. A major portion of aerosols is supplied by the eruption of magmatic and mud volcanoes and by earthquakes. The fine (submicron) fraction is especially enriched in different metals and organic compounds. We have studied volcanoes of the Kamchatka Peninsula and mud volcanoes of the Central Asia, the Caucasus and the Crimea. Great amounts of metals and organic compounds were observed in the fine fraction with particle sizes of less than one micrometer. The motion of aerosols results in the generation of strong electric fields. Melt aerosols are quenched at velocities as high as 10⁵­10⁷ deg/s. Under such conditions, the synthesis of organic compounds takes place. As an example, we consider some aromatic compounds. We experimentally simulated the processes of the production of organic compounds on aerosols in hot gas streams with the melting of particles and its subsequent rapid quenching. Experimental data on the degassing of aerosols are also presented.

OH Zoning in Diopside

Michael Andrut (a8601uaa@rs6000.univie.ac.at) & Anton Beran (anton.beran@.univie.ac.at)

Institut für Mineralogie und Kristallographie, Universität Wien - Geozentrum, Althanstr. 14, A-1090 Vienna, Austria

Pyroxenes are known to contain essential amounts of hydrogen. The hydrogen content ranges from about 100 to 1000 wt.ppm H₂O and vary as a function of the geological environment, with the greatest amounts occurring in mantle derived samples. FTIR micro-spectroscopy is an extremely sensitive method for detecting small amounts of hydrogen bonded to oxygen in the structure of nominally anhydrous minerals. Single crystal spectra show that the intensities of certain OH absorption bands are correlated with the composition, thus suggesting that crystal chemical or compositional factors control the OH incorporation in pyroxenes (Skogby et al., 1990). Kinetic studies by Ingrin et al. (1995) suggest an isotropic behaviour of hydrogen diffusion in diopside.

A gem-quality diopside single-crystal from Rotkopf, Tyrol, showing a colourless and a light-green part (due to about 2 wt.% FeO) was investigated by FTIR microscopy, using a circular measuring spot of 990 µm diameter. The light-green part of the crystal shows a "significant" diopside OH spectrum with bands centred at 3647, 3537, 3464 and 3359 cm^-1 which was described by Beran (1976), Ingrin et al. (1989), and Skogby et al. (1990). The intensities of the bands are varying within a limited range. The OH absorptions of the colourless crystal part reveal a completely different type of spectrum, characterised by absorption bands at 3725, 3649 and 3490 cm^-1 and by an additional "amphibole band" at 3677 cm^-1. The summed mean OH band intensities of the colourless crystal part are by a factor of about 70 weaker than those of the light-green crystal part. From these spectroscopic results it is concluded that different defined types of OH defects occurring within one crystal are strongly controlled by the minor element content.

Beran A, Tschermaks Min Petr Mitt, 23, 79-85, (1976).

Ingrin J, Latrous K, Doukhan J-C & Doukhan N, Eur J Mineral, 1, 327-341, (1989).

Ingrin J, Hercule S & Charton T, J Geophys Res 100, 15, 489-15,499, (1995).

Skogby H, Bell DR & Rossman GR, Am Mineral, 75, 764-774, (1990).

Anomalous Compression of Coesite

Ross J. Angel (ross.angel@uni-bayreuth.de)¹, Jed L. Mosenfelder (jed@gps.caltech.edu), Cliff S. J. Shaw (cliff.shaw@uni-bayreuth.de)¹ & Nancy L. Ross (n.ross@ucl.ac.uk)²

¹ Bayersiches Geoinstitut, Universitaet Bayreuth, D-95440 Bayreuth, Germany

² Dept. Geological Sciences, University College London, Gower St., London, WC1E 6BT, England

Existing literature data on the elasticity of coesite derived from Brillouin spectroscopy measurements and from isothermal compression measurements made by X-ray diffraction are inconsistent. We have therefore synthesised single-crystal samples of coesite at pressures from 3 to 7 GPa, and have undertaken new compression measurements by single-crystal X-ray diffraction in diamond-anvil cells with the aim of resolving this discrepancy.

All cell parameters evolve smoothly with pressure up to 9.6 GPa. Repeat measurements on different crystals synthesised at different conditions yield volume-pressure data that is identical within the small experimental uncertainties. However, despite the quality and the consistency of the data, no 3rd-order Equation of State fits the P-V data; fitting the data with a fourth-order EoS yields K_T0 = 102.5(1.0) GPa, K' = 2.0(3), and K'' = +0.65(5) GPa^-1. Normally, K" has an implied negative value in a 3rd-order EoS, representing a slowing-down in the rate at which a material becomes stiffer upon compression. By contrast, coesite stiffens more rapidly as pressure increases, at least up to 10 GPa. This behaviour is probably due to >60% of the volume compression being accommodated by the closing up of the feldspar-like crankshaft chains of SiO₄ tetrahedra within the structure. As compression continues, the resistance of the Si-O-Si linkages to continuing reduction in angle must increase, resulting in this anomalous compression. The same compression mechanism operates in feldspars, but does not result in anomalous behaviour. The reason appears to be that coesite, as a structure only stable at high pressures, is over-expanded at room pressure. Initial rapid compression occurs until pressures above 3.5 GPa when, with the structure compressed to a more "normal" configuration of Si-O-Si bonds, the compressional behaviour also becomes more "normal".