Dislocation deformation mechanisms in peridotite xenoliths in kimberlites |
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| Authors: | J N Boland J M A Buiskool Toxopeus |
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| Institution: | (1) Research School of Earth Sciences, The Australian National University, P.O. Box 4, 2600 Canberra, A.C.T., Australia;(2) Geologisch en Mineralogisch Instituut der Rijksuniversiteit, Garenmarkt 1B, Leiden, The Netherlands |
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| Abstract: | The dislocation substructures in olivine from coarse-grained peridotite xenoliths in kimberlites from the Lesotho region have been determined. The 100] dislocations may be located in simple (100) tilt boundaries while the density of free or individual 100] dislocations is 106/cm2 or less. The 001] dislocations form (010) twist arrays or more complex (100) subboundaries with the 100] dislocations; the density of free 001] dislocations increases to 8 × 108/cm2 in those grains in which tangles are observed. The simple (100) subboundaries are considered to result from a high temperature, slow strain-rate deformation (creep-like process) while the more complex subboundaries composed of 100] and 001] dislocations, as well as the high density of 001] dislocations, indicate faster strain rates and/or lower deformation temperatures than the creep deformation. These two broad phases of deformation have been interpreted as an early stage of mantle-type flow followed by deformation during or subsequent to the emplacement of the kimberlite. |
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