EXPERIMENTAL STUDY OF THE LEAK-TIGHTNESS OF WATER-CONTAINING SILICATE MELT INCLUSIONS UNDER THE CONFINING PRESSURE OF D2O AT 650?C AND 3 kbar
S.Z. Smirnova, V.G. Tomasa, E.N. Sokolovab, and I.N. Kupriyanova
a Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Melt inclusions in minerals, thermometry, D2O, IR spectroscopy
Pages: 537-547
Abstract
The paper is devoted to the experimental study of the leak-tightness of water-containing melt inclusions heated in the autoclave at high temperature and under the pressure of D2O. Quartz-hosted silicate melt inclusions from the rhyolite tuffs of the Taupo volcanic zone (New Zealand) and a tourmaline-pegmatite vein from the southwestern Pamirs were heated at 650?C and 3 kbar. The penetration of heavy water into the inclusions was controlled by IR spectroscopy. The studies have demonstrated that inclusions can remain leak-tight under these conditions and not exchange water with the environment even if the confining pressure is 1.5-3 times above their internal pressure. The influence of water diffusion through the quartz lattice and dislocations on the leak-tightness of inclusions can be neglected in the thermometry of water-containing melt inclusions. The crucial factors determining water exchange between the inclusions and the environment in the experiments performed are mechanical defects (open and healed cracks). Using D2O as a pressurizing medium makes it possible to control the leak-tightness of the heated inclusions. To do this, it is recommended that melt inclusions be homogenized under the pressure of D2O above the expected entrapment pressure and studied by IR spectroscopy after the heating.
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