Petrology

, Volume 18, Issue 3, pp 263–277

Variolitic lavas in the axial rift of the Mid-Atlantic Ridge and their origin (Sierra Leone area, 6°18′N)

  • I. S. Krassivskaya
  • E. V. Sharkov
  • N. S. Bortnikov
  • A. V. Chistyakov
  • N. V. Trubkin
  • T. I. Golovanova
Article

Abstract

Altered variolites described for the first time in the axial zone of the Mid-Atlantic Ridge are represented by rounded globules of andesite (icelandite) composition with light trachyandesite rim embedded in a picrobasaltic matrix. The globules were transferred with picrobasaltic melt and then floated to the surface of lava flow, while formation of leucocratic rims was presumably related to thermodiffusion (Soret effect) in a cooling heterogeneous melt. This heterogeneous melt was formed by penetration of ascending column of picrobasaltic magma in already existing small intracructsal magmatic chamber filled with residual icelanditetype andesite melt and involvement of the latter into a general upward movement. The rapid ascent of the melts in the oceanic spreading zones by means of turbulent flowing caused dispersion of the extragenous melt into small drops in a jet of picrobasaltic magma, without their interaction. Variolites were formed during cooling of such heterogeneous lava flow. No signs of liquid immiscibility were found in the studied variolites.

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Copyright information

© Pleiades Publishing, Ltd. 2010

Authors and Affiliations

  • I. S. Krassivskaya
    • 1
  • E. V. Sharkov
    • 1
  • N. S. Bortnikov
    • 1
  • A. V. Chistyakov
    • 1
  • N. V. Trubkin
    • 1
  • T. I. Golovanova
    • 1
  1. 1.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and GeochemistryRussian Academy of SciencesMoscowRussia

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