A seismic cross section of the New England Appalachians: The Orogen Exposed

  1. Muawia Barazangi and
  2. Larry Brown
  1. Robert A. Phinney

Published Online: 15 MAR 2013

DOI: 10.1029/GD014p0157

Reflection Seismology: The Continental Crust

Reflection Seismology: The Continental Crust

How to Cite

Phinney, R. A. (1986) A seismic cross section of the New England Appalachians: The Orogen Exposed, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0157

Author Information

  1. Department of Geological and Geophysical Sciences, Princeton University, Princeton, NJ 08544

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



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


Several marine multichannel seismic reflection lines collected by the U.S. Geological Survey in its assessment of the Eastern U.S. continental margin for oil and gas are found to constitute a high quality deep reflection profile of the continental crust on the Long Island platform. In the time range 4–11 seconds (10–35 km), the CDP section shows nearly continuous, dense, well-correlated reflections. The systematic variation in local dip angle of these reflections defines large-scale tectonic packets which constitute the bulk of the crystalline crust in this area. Most conspicuous is a single large packet in the eastern end of the line which deps to the W at 25 degrees and extends from the sediment-basement boundary to the lower crustal boundary layer (Moho) at 25–30 km. This packet is interpreted as an accretionary structure formed and thickened to continental thickness during the late Paleozoic accretion of Avalonia and the Appalachian margin of North America. In the center and western portions of the line a low angle complex packet dipping east at depth is interpreted as the pre-Acadian margin of North America. A “keystone” packet lying between these two bodies, and forming most of the basement subcrop under the central portion of the line, appears to correlate with the high grade medial zone of south central New England, and appears to be the strongly compressed, thickened, and uplifted remains of the oceanic basin, volcanic islands, and marginal sedimentary wedges which separated Avalonia from North America before their collision. The lowest 1–2 seconds of the crust appears as a nearly horizontal layered complex, with at least two pronounced local structural breaks. I suggest that this “Moho” forms the lower carapace of a compressional orogen which was thickened to at least 45 km during Paleozoic collision(s). It is interpreted as the highly strained tectonic boundary layer established during the subduction of oceanic crust at an active continental margin.