19. An Age-Dependent, Two-Layer Model for Marine Magnetic Anomalies

  1. George H. Sutton,
  2. Murli H. Manghnani,
  3. Ralph Moberly and
  4. Ethel U. Mcafee
  1. Richard J. Blakely

Published Online: 17 MAR 2013

DOI: 10.1029/GM019p0227

The Geophysics of the Pacific Ocean Basin and Its Margin

The Geophysics of the Pacific Ocean Basin and Its Margin

How to Cite

Blakely, R. J. (1976) An Age-Dependent, Two-Layer Model for Marine Magnetic Anomalies, in The Geophysics of the Pacific Ocean Basin and Its Margin (eds G. H. Sutton, M. H. Manghnani, R. Moberly and E. U. Mcafee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM019p0227

Author Information

  1. School of Oceanography, Oregon State University, Corvallis, Oregon 97331

Publication History

  1. Published Online: 17 MAR 2013
  2. Published Print: 1 JAN 1976

ISBN Information

Print ISBN: 9780875900193

Online ISBN: 9781118663592



  • Geophysics—Pacific area—Congress;
  • Woollard, George Prior, 1908


Marine magnetic anomalies of the North Pacific Ocean are analyzed to determine the recording fidelity of the oceanic crust as a function of crustal age. The parameter describing fidelity is the width W of the transition from crust of predominantly normal polarity to crust of predominantly reversed polarity. The width of the transition zone is related to the distance ΔX between the zeros of the first derivative of the total-field anomaly. Average values of ΔX are found for specific crustal ages, using profiles from the North Pacific, and then converted to transition widths by comparing with computer-generated profiles. Transition width increases monotonically with age throughout the Cenozoic, starting at 2 km and increasing to 20 km, assuming a layer thickness of 0.5 km. Increasing transition width is considered to be a manifestation of a more complicated crustal source consisting of two discrete layers. In this model, an upper layer corresponds to pillow basalt with a high initial magnetization and a narrow transition zone. A thicker, underlying layer corresponds to basaltic dikes with lower magnetization and wider transition zone. It is suggested that the wide transition zone of the second layer is the result of a Curie-point isotherm which slopes gently away from the spreading center. As the crust ages, the upper layer loses its high intensity of magnetization because of progressive, low-temperature oxidation of titanomagnetite in the pillow basalts. Consequently, surface anomalies over old crust are more representative of deeper magnetic sources. Such a model predicts a general deterioration of the recording fidelity of the ocean crust and may partially explain the general lack of very short polarity intervals retained by older crust.