Crustal Reflections and Crustal Structure

  1. Muawia Barazangi and
  2. Larry Brown
  1. Scott B. Smithson,
  2. Roy A. Johnson and
  3. Charles A. Hurich

Published Online: 15 MAR 2013

DOI: 10.1029/GD014p0021

Reflection Seismology: The Continental Crust

Reflection Seismology: The Continental Crust

How to Cite

Smithson, S. B., Johnson, R. A. and Hurich, C. A. (1986) Crustal Reflections and Crustal Structure, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0021

Author Information

  1. Department of Geology and Geophysics, Program for Crustal Studies, University of Wyoming, P.O. Box 3006, Laramie, Wyoming 82071

Publication History

  1. Published Online: 15 MAR 2013
  2. Published Print: 1 JAN 1986

Book Series:

  1. Geodynamics Series

ISBN Information

Print ISBN: 9780875905143

Online ISBN: 9781118670118

SEARCH

Keywords:

  • Earth—Crust—Congresses;
  • Continents—Congresses;
  • Seismic reflection method—Congresses

Summary

The nature of crustal reflectors is still a major question, especially since typical structures in the crystalline crust are so complex that they would generate short, possibly arcuate events. Evidence starting with the Wind River thrust suggests that crustal fault zones (mylonites) may be good reflectors, and recent profiling over mylonites and accompanying detachment faults in the Kettle Dome and the Ruby Mountains, metamorphic core complexes, shows consistent subhorizontal reflections that can be correlated with the lithology of the mylonite zones. Reflections are so abundant within these sillimanite-grade mylonite zones as to resemble a sedimentary terrain. These specially designed reflection experiments conclusively demonstrate for the first time that mylonites are good reflectors. On the other hand, the flanking thrust fault on the Laramie Range only generates a minimal reflection in the relatively shallow zone where brittle deformation predominates. These results show that mylonite zones may be the best reflectors in the crust because of their layered, planar geometry that commonly includes low dip, and crustal scale deformation may thus be mapped seismically. This means that such major features as thrusting, crustal doubling and crustal extension may be recognized through crustal reflection profiling. Crustal-scale duplexes may exist and give the appearance of dipping sedimentary reflections generated from their numerous mylonite zones. The best crustal reflections in the U.S. seem to be related to crustal extension in the western U.S.