Mobility and H2O loss from fluid inclusions in natural quartz crystals |
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Authors: | Andreas Audétat Detlef Günther |
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Institution: | Institute for Isotope Geology, ETH Zentrum/NO, CH-8092 Zürich, Switzerland e-mail: audetat@erdw.ethz.ch, Tel.:+41-1-6326082, Fax:+41-1-6321179, CH Laboratory of Inorganic Chemistry, ETHZ, Universit?tsstrasse 6, CH-8092 Zürich, Switzerland e-mail: guenther@inorg.chem.ethz.ch, Tel.:+41-6324687, Fax:+41-1-6321090, CH
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Abstract: | Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the
mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary
trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed
inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up
to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged
ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice
during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not
only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated
internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads
to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other
samples.
Received: 17 November 1998 / Accepted: 16 April 1999 |
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