A Mechanism of Formation of Oceanic Magma

  1. Gordon A. Macdonald and
  2. Hisashi Kuno
  1. Yu. M. Scheinmann

Published Online: 21 MAR 2013

DOI: 10.1029/GM006p0181

The Crust of the Pacific Basin

The Crust of the Pacific Basin

How to Cite

Scheinmann, Yu. M. (1962) A Mechanism of Formation of Oceanic Magma, in The Crust of the Pacific Basin (eds G. A. Macdonald and H. Kuno), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM006p0181

Author Information

  1. Institute of the Physics of the Earth, Academy of Sciences, USSR, Moscow, USSR

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1962

Book Series:

  1. Geophysical Monograph Series

Book Series Editors:

  1. Waldo E. Smith

ISBN Information

Print ISBN: 9780875900063

Online ISBN: 9781118669310



  • Alkali-rich ultrabasic magma;
  • Basalt melting;
  • Continental and ocean masses;
  • Formation of Oceanic Magma;
  • Gutenberg's layer


All oceanic magmas originate below the M discontinuity. Ultrabasic magmas are produced by melting of the entire material of the mantle, and the basaltic magma by its partial melting. Magma is generated by a specific tectonic mechanism—by deep fractures around which the pressure decreases and along which melts easily rise. At higher temperatures this mechanism generates alkaline ultrabasic magmas by melting of the entire material of the mantle. An increase in the abundance of fractures and lengthening of their life lead to the escape of the entire basaltic component. In the mantle a ‘barren' layer arises underlain by the mantle proper which retained the basaltic component. At their boundary and below it the velocities of earthquake waves decrease (the low-velocity layer of Gutenberg). The ‘barren' layer melts at a particularly high temperature and accordingly at maximum tectonic activity (as a rule, under geosynclines). In oceanic areas such magma is rarely found, or is entirely absent. Oceanic magmas thus originate mainly within Gutenberg's low-velocity layer and are directly connected with deep tectonic mechanisms.