Garnet Clinopyroxenite - Chlorite Eclogite Transition in a Xenolite from Moses Rock: Further Evidence for Metamorphosed Ophiolites Under the Colorado Plateau

  1. F.R. Boyd and
  2. Henry O.A. Meyer
  1. Herwart Helmstaedt and
  2. Daniel J. Schulze

Published Online: 19 MAR 2013

DOI: 10.1029/SP016p0357

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

How to Cite

Helmstaedt, H. and Schulze, D. J. (1979) Garnet Clinopyroxenite - Chlorite Eclogite Transition in a Xenolite from Moses Rock: Further Evidence for Metamorphosed Ophiolites Under the Colorado Plateau, 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/SP016p0357

Author Information

  1. Department of Geological Sciences, Queen's University, Kingston, Ontario, Canada K7L 3N6

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:

  • Eclogitic assemblage;
  • Garnet clinopyroxenites;
  • Moses rock;
  • Ultramafic xenotiths;
  • Upper mantle constraints

Summary

Pyrope and calcic clinopyroxene in a garnet clinopyroxenite from Moses Rock have reacted to stably coexisting magnesian chlorite, less pyropic garnet, and omphacite, the assemblage of a chlorite eclogite. The hydration reaction can be balanced, provided the system is open to sodium and oxygen. Retrogression may have occurred when garnet clinopyroxenite in the upper mantle came into contact with subducted, sodium-rich ocean floor rocks now represented by xenoliths of Group C eclogites and jadeite rocks. Iron-magnesium distribution coefficients of the secondary garnetomphacite pair and of garnet and clinopyroxene rims in Group C eclogite xenoliths are compatible with this interpretation and suggest that retrogressive metamorphism of the garnet clinopyroxenite and progressive metamorphism of the Group C eclogites took place at similar physical conditions prior to kimberlite eruption. The similarity of the ultramafic xenolith suite from the Colorado plateau kimberlites with rocks exposed in metamorphosed ophiolite complexes of high-pressure metamorphic belts leaves little doubt that a shallow slab of subducted oceanic lithosphere existed under the Colorado plateau at the time of kimberlite eruption.