Physics
Scientific paper
Apr 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.304...71b&link_type=abstract
Earth and Planetary Science Letters, Volume 304, Issue 1-2, p. 71-84.
Physics
Scientific paper
The study presents microstructures and crystallographic preferred orientations (CPO) of minerals obtained by electron back-scattered diffraction (EBSD) in a suite of 23 fresh mantle xenoliths (20 peridotites, 2 eclogites and 1 pyroxenite) from the Udachnaya kimberlite in central Siberian craton. The suite includes coarse spinel- and garnet-facies peridotites equilibrated at 760-1000 °C from the upper part of the mantle lithosphere (45-160 km) and porphyroclastic garnet peridotites from the base of the lithosphere (160-210 km; 1200-1320 °C). The data indicate that dislocation creep is the main deformation mechanism in the peridotites and eclogites. The CPO patterns of olivine suggest a dominant activation of the (010) [100] slip system. Within this general pattern, coarse peridotites show a better alignment of [100]-olivine while porphyroclastic rocks have a better alignment of [010]-olivine. Recrystallization in the porphyroclastic peridotites reduces olivine grain size and facilitates the development of a mosaic matrix that leads to a decrease in the CPO strength. Orthopyroxene in peridotites slips parallel to (100) [001]; clinopyroxene shows a clear slip direction on [001] in both peridotites and eclogites. Seismic properties estimated from the CPO data and modal abundances of major minerals show significant differences between peridotites, eclogites and pyroxenites; some differences also exist between peridotite types. Importantly, coarse peridotites have much higher anisotropy than eclogites and may yield higher P-wave velocities in the fast direction (Vp ≥ 8.8 km/s). Thus, the extremely high sub-Moho velocities (Vp > 8.7 km/s) reported from some seismic profiles in the Siberian craton can be better explained by strong anisotropy of coarse peridotites in a horizontally foliated mantle rather than by the presence of abundant eclogites.
Ashchepkov Igor V.
Bascou Jérôme
Doucet Luc S.
Golovin Alexander V.
Ionov Dmitri A.
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