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Contributions to Mineralogy and Petrology

, Volume 100, Issue 4, pp 510–527 | Cite as

Metasomatised and veined upper-mantle xenoliths from Pello Hill, Tanzania: evidence for anomalously-light mantle beneath the Tanzanian sector of the East African Rift Valley

  • J. B. Dawson
  • J. V. Smith
Article

Abstract

Peridotite xenoliths from the Pello tuff cone in the Rift Valley of northern Tanzania, bear witness to upper mantle veining and metasomatism. Veins of katungite composition, with an asthenospheric signature, have imposed K, Fe, Ti, OH and REE metasomatism upon previously depleted peridotite. Chemical and mineralogical gradients are present in the peridotite wall rocks, and hydrous phases developed in the peridotite are generally lower in Ti and Fe, but higher in Mg and Cr, than those in the veins. The metasomatism has reduced the density of affected peridotite by up to 4.5%, supporting earlier geophysical models for low-density mantle beneath the Rift Valley. Age constraints for the metasomatically-induced density decrease permit correlation with Recent faulting in the Rift Valley, but not with the major upwarp of the Kenya Dome in the late Tertiary.

Keywords

Mineral Resource Wall Rock Rift Valley Density Decrease Hydrous Phasis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • J. B. Dawson
    • 1
  • J. V. Smith
    • 2
  1. 1.Department of GeologyUniversity of SheffieldSheffieldUK
  2. 2.Department of Geophysical SciencesUniversity of ChicagoIllinoisUSA

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