Mineralogical Studies of Samoan Ultramafic Xenoliths: Implications for Upper Mantle Processes

  1. Barbara H. Keating,
  2. Patricia Fryer,
  3. Rodey Batiza and
  4. George W. Boehlert
  1. Elizabeth Wright

Published Online: 18 MAR 2013

DOI: 10.1029/GM043p0221

Seamounts, Islands, and Atolls

Seamounts, Islands, and Atolls

How to Cite

Wright, E. (1987) Mineralogical Studies of Samoan Ultramafic Xenoliths: Implications for Upper Mantle Processes, in Seamounts, Islands, and Atolls (eds B. H. Keating, P. Fryer, R. Batiza and G. W. Boehlert), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM043p0221

Author Information

  1. Department of Geological Sciences, University of Illinois, Chicago, IL 60680

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1987

ISBN Information

Print ISBN: 9780875900681

Online ISBN: 9781118664209



  • Seamounts;
  • Coral reefs and islands


Two types of ultramafic xenoliths are included in Samoan post-erosional lavas: harzburgite-lherzolite (HL) nodules showing porphyroclastic and equigranular-mosaic textures, and dunite-wehrlites (DW) showing tectonized cumulate textures. Signs of reaction and equilibration with the host lavas include zonation within olivine and chromite grains in the xenolith and reaction of xenolith orthopyroxene in contact with undersaturated host liquids to form olivine+clinopyroxene+glass. Textures such as symplectic intergrowth of chromite with silicate phases and variable recrystallization indicate a history of vertical movement of mantle material prior to inclusion of that material in upward-migrating magmas. HL mineral compositions suggest that they sample infusible residue remaining after a melting episode which may have produced the Samoan shields, whereas the DW group may represent early cumulates from those lavas. The two groups may form the oceanic analogs to the division between Cr-diopside and Al-augite types of xenoliths observed in continental settings.