Modern Analogs for Some Midcrustal Reflections Observed Beneath Collisional Mountain Belts

  1. Muawia Barazangi and
  2. Larry Brown
  1. Robert J. Lillie1 and
  2. Mohammed Yousuf2

Published Online: 15 MAR 2013

DOI: 10.1029/GD014p0055

Reflection Seismology: The Continental Crust

Reflection Seismology: The Continental Crust

How to Cite

Lillie, R. J. and Yousuf, M. (1986) Modern Analogs for Some Midcrustal Reflections Observed Beneath Collisional Mountain Belts, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0055

Author Information

  1. 1

    Department of Geology, Oregon State University, Corvallis, Oregon, 97331

  2. 2

    Oil and Gas Development Corporation, Markaz F/7, Islamabad, Pakistan

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

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Keywords:

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

Summary

Seismic reflection data across collisional mountain belts often show prominent events at midcrustal levels. Through an example in the southern Appalachian mountains, three types of sequences are identified and compared to reflection data from modern compressional and extensional settings. Beneath foreland areas, dipping events which lie entirely beneath underthrusted shelf strata are interpreted as late–Precambrian rift graben fill, analogous to Mesozoic rift grabens observed on seismic profiles from the east coast of the United States. More typical features of the foreland, however, are small normal fault offsets of the underthrusted shelf strata. These normal faults commonly result in thrust ramping but apparently are not associated with continental rifting processes. Rather, the faults are similar to features contemporaneous with thrust faulting which have been observed on seismic profiles across areas of modern collisional deformation, such as the Himalayan foreland in Pakistan. The third type of reflection sequence consists of eastward dipping events which lie along the Appalachian gravity and magnetic gradients associated with the edge of precollisional continental basement. Although these dipping sequences may be a product of collisional deformation, it is possible that they represent original volcanic stratigraphy at the early Paleozoic continent/ocean boundary.