Periodic formation of magma fractures and generation of layered gabbros in the lower crust beneath oceanic spreading ridges

Peter B. Kelemen, Einat Aharonov

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

143 Scopus citations

Abstract

There must be a transition from continuous porous flow to transient formation of melt-filled fractures in the region of magma transport below oceanic spreading centers. This transition may occur at permeability barriers that impede porous flow of melt, at the base of the oceanic crust and within the lower crust. We summarize evidence for formation of melt-filled lenses at the base of the crust in the Oman ophiolite, and evidence indicating that melt is very efficiently extracted from these lenses, probably in fractures. We also discuss the possible formation of melt lenses elsewhere in the oceanic lower crust. We then present a simple physical model for the periodic formation of melt-filled fractures originating in a melt lens beneath a permeability barrier. Finally, quantitative models show how modal layering in lower crustal gabbros can form as a result of the periodic pressure changes associated with fracture formation. An ancillary result of chemical modeling is the quantification of a thermal gradient in the lower crust of the Oman ophiolite during igneous accretion beneath a spreading center, from 1165 to 1195°C near the dike/gabbro transition to ~1240°C near the crust/mantle transition. This and other data for the Oman gabbros support models in which much of the lower crust forms by crystallization in sills at a variety of depths, from the dike/gabbro transition to the base of the crust.

Original languageAmerican English
Title of host publicationFaulting and Magmatism at Mid-Ocean Ridges, 1998
EditorsPaul T. Delaney, W. Roger Buck, Jeffrey A. Karson, Yves Lagabrielle
PublisherBlackwell Publishing Ltd.
Pages267-289
Number of pages23
ISBN (Electronic)9781118664506
ISBN (Print)9780875900896
DOIs
StatePublished - 1998
Externally publishedYes

Publication series

NameGeophysical Monograph Series
Volume106
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

Bibliographical note

Publisher Copyright:
© 1998 by the American Geophysical Union.

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