Peridotite Xenoliths and the Dynamics of Kimberlite Intrusion

  1. F.R. Boyd and
  2. Henry O.A. Meyer
  1. Jean-Claude C. Mercier

Published Online: 19 MAR 2013

DOI: 10.1029/SP016p0197

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

How to Cite

Mercier, J.-C. C. (1979) Peridotite Xenoliths and the Dynamics of Kimberlite Intrusion, in The Mantle Sample: Inclusion in Kimberlites and Other Volcanics (eds F.R. Boyd and H. O.A. Meyer), American Geophysical Union, Washington, D.C.. doi: 10.1029/SP016p0197

Author Information

  1. Department of Earth and Space Sciences, Suny - Stony Brook, Stony Brook, New York 11794

Publication History

  1. Published Online: 19 MAR 2013
  2. Published Print: 1 JAN 1979

ISBN Information

Print ISBN: 9780875902135

Online ISBN: 9781118664858

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Keywords:

  • Annealing-recrystallization;
  • Eruption-channel formation.;
  • Geopiezometers;
  • Kimberlite intrusion;
  • Peridotite xenoliths;
  • Sheared textures

Summary

The time for garnet-peridotite xenoliths in kimberlite to reach the surface (4–6 h) and the kimberlite average intrusion velocity (40–70 kin/h) are estimated from annealed olivine-tablet sizes in porphyroclastic peridotites and from the growth rate for annealing calculated on the basis of experimental data: during primary annealing re-crystallization, tablet-shaped olivine neoblasts grow at a constant rate prooortional to the annealing temperature and to the strain energy stored in the paleoblasts. This energy is proportional to the differential stress immediately prior to annealing, this stress being known through calibration of its effects on mean olivine-subgrain sizes and grain sizes resulting respectively from syntectonic recovery and recrystallization. In addition, experimentally determined flow laws for dry olivine are used to derive strain-rates from the stress and temperature data, hence the duration of the late deformation whenever strain can be estimated from internal deformation of olivine or recrvstallized enstatite laminae. As these estimates range from a few hours to a few tens of years, the deformation cannot be related to major tectonic phenomena such as the ascent of large diapirs or convection-related flow, a conclusion in accord with the unrealistic plate-velocity estimates (3 to 30 km/yr) implied by such models. These deformations are therefore ascribed to kimberlite-conduit formation, the longest times being regarded as artifacts possibly due to heterogeneous deformation. Stresses experienced just prior to sampling (.4–1.2 kbar) are combined with estimates of the diameter (10–50m) of the zone mechanically perturbed by the kimberlite ascent, to estimate the energy released through conduit formation (∼1014J, or 0.05 megaton).