The Complexity of the Continental Lower Crust and Moho from Pmp Data: Results from Cocrust Experiments

  1. Robert F. Mereu,
  2. Stephan Mueller and
  3. David M. Fountain
  1. R. F. Mereu,
  2. J. Baerg and
  3. J. Wu

Published Online: 9 APR 2013

DOI: 10.1029/GM051p0103

Properties and Processes of Earth's Lower Crust

Properties and Processes of Earth's Lower Crust

How to Cite

Mereu, R. F., Baerg, J. and Wu, J. (1989) The Complexity of the Continental Lower Crust and Moho from Pmp Data: Results from Cocrust Experiments, in Properties and Processes of Earth's Lower Crust (eds R. F. Mereu, S. Mueller and D. M. Fountain), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM051p0103

Author Information

  1. Department of Geophysics, University of Western Ontario, London, Ontario, Canada N6a 5B7

Publication History

  1. Published Online: 9 APR 2013
  2. Published Print: 1 JAN 1989

ISBN Information

Print ISBN: 9780875904566

Online ISBN: 9781118666388

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Keywords:

  • Earth—Crust—Congresses;
  • Geophysics—Congresses

Summary

Over the past ten years a series of long range seismic refraction and wide-angle reflection experiments was conducted by a consortium of Canadian university and government crustal seismologists (COCRUST). the main tectonic features of interest were: the Vancouver Island Subduction Zone, the Peace River Arch, the Williston Basin, the Churchill-Superior Geological Boundary, the Kapuskasing Structural Zone, the Abitibi Greenstone Belt, the Grenville Front and the Ottawa- Bonnechere Graben. A comparison of the record sections from one area to another shows significant variations in the appearance of the ProP wide-angle reflected signals. To carry out a more detailed analysis of these phases, a normal moveout corrected intensity section which flattens out the PmP reflection hyperbola and emphasizes areas of large signal complexities was plotted in addition to the conventional record section. Data from this intensity section was then applied to obtain a quantitative measurement of a complexity parameter. These measurements were used to infer or compare differences which may exist in crustal heterogeneity from one region to another.

The results show, that in most areas of the regions studied, the Moho is a poorly defined transition zone. A few exceptional profiles were, however, observed in stable tectonic regions such as that of the Peace River Arch area of Alberta and the Central Gneiss Belt of the Grenville Province just south of the Grenville Front in Quebec. Many of the seismic traces from these areas showed well defined simple PmP pulses of relatively large amplitude. As the complexity of the lower crust increased, the amplitudes of PmP not only decreased but were embedded in a scattered wave field which originated from laterally heterogeneous structures just above the Moho. the most complex lower crusts and disrupted Mohos were found under the Ottawa-Bonnechere Graben, the Kapuskasing Uplift and the Vancouver Island Subduction Zone. the results indicate that once tectonic forces disturb the Moho, the period for the Moho to re-establish itself as a sharp first order discontinuity must be very long in geological time