Mineralogies, Densities and Seismic Velocities of Garnet Lherzolites and their Geophysical Implications

  1. F.R. Boyd and
  2. Henry O.A. Meyer
  1. Thomas H. Jordan

Published Online: 19 MAR 2013

DOI: 10.1029/SP016p0001

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

How to Cite

Jordan, T. H. (1979) Mineralogies, Densities and Seismic Velocities of Garnet Lherzolites and their Geophysical Implications, 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/SP016p0001

Author Information

  1. Geological Reserach Division, Scripps Institution of Oceanography, La Jolla, California 92093

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:

  • Continental roots;
  • Densities;
  • Garnet lherzolites;
  • Geophysical implications;
  • Mantle compositions;
  • Mineralogies;
  • Oceanic lithospheric structure;
  • Seismic velocities

Summary

A simple algorithm for estimating the mineral composition, density and seismic velocities of a garnet lherzolite from its whole rock oxide composition has been devised and successfully tested against observations. The algorithm has been applied to 78 analyses of garnet lherzolite xenoliths from kimberlite pipes and to 9 model compositions for the oceanic upper mantle. Normative densities and velocities for these samples correlate well with Fe/Fe + Mg. Removal of a basaltic fraction from fertile garnet lherzolite lowers its normative density, in agreement with the conclusions of O'Hara [1975] and Boyd and McCallister [1976]. The average continental garnet lherzolite (ACGL) constructed from the xenoli[h compositions is significantly depleted in normative garnet and clinopyroxene relative to the range for oceanic upper mantle models, and its normatire density is significantly less (3.353 gm/cm3 vs. 3.397 gm/cm3 for pyrolite). The data support Jordan's [1975a] hypothesis that the large sub-lithospheric temperature gradients associated with deep continental root zones are dynamically stabilized by compositional gradients. It is suggested that substantial variations in lithospheric density and thickness are generated in regions of anomalous oceanic vulcanism (e.g. Hawaii and Iceland); these may contribute to observed gravity anomalies and residual depth anomalies, and may exert some dynamical control on the subduction process.