The behavior of protons during wet olivine deformation under the conditions of the kimberlite process |
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Authors: | N R Khisina R Wirth |
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Institution: | (1) Institute of Applied Geosciences, Technical University Berlin, Ernst Reuter-Platz 1, 10623 Berlin, Germany;(2) Institute of Geochemistry, Mineralogy and Ore Formation, Ukrainian Academy of Sciences, Prospekt Palladina 34, 03142 Kyiv, Ukraine |
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Abstract: | This paper reports the results of optical and electron microscopic investigations of mantle olivine samples with H2O contents of tens-hundreds ppm weight. Samples were obtained from the xenoliths and xenocrysts of the Udachnaya pipe. At
the scale of optical microscope magnification, a peculiar banded microstructure was observed in thin sections prepared parallel
to the olivine (010) plane. It is formed by cross-hatched bands parallel to four crystallographic directions of the olivine
structure: 100], 001], 101], and −101]. At the scale of electron optical magnifications, the banded microstructure is
observed as nanometer-sized heterogeneities of various types which are related to olivine deformation: (a) planar defects
parallel to (100) and (001) corresponding to the (100)010] and (001)100] dislocation glide systems, respectively; they are
occasionally transformed into lamellae or decorated by nanoinclusions; and (b) nanometer-sized heterogeneities formed by nanoinclusion
arrays not related to planar defects and oriented along the same directions of the olivine structure as the optically visible
bands. The deformation structures are decorated by coupled point OH-bearing defects, which were initially present in the olivine.
The crystallographically oriented arrays of nanoinclusions of high-pressure hydrous silicates are considered as a result of
olivine deprotonization (elimination of OH-bearing defects from the olivine structure) in the zones of previous deformation
compression in the crystal. Light refraction effects on the nanoinclusions make these zones optically visible and produce
the banded microstructure, which is a consequence of previous deformation. |
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