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Chapter 15: Crustal structure of the continental interior

By
L. W. Braile
L. W. Braile
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Published:
January 01, 1989

Seismic refraction profiles and deep seismic reflection profiling data have been compiled for the continental interior of the United States and adjacent southern Canada. A total of 58 refraction profiles and 17 deep reflection profiling studies are available in the midcontinental area. Statistics derived from the refraction data indicate that the crust of the continental interior is characterized by a crustal thickness of about 43 km, an average crustal compressional seismic velocity of 6.5 km/sec, and a nearly uniform uppermost mantle compressional velocity (Pn) of 8.1 km/sec. The crust displays a generally layered character with compressional velocities near 6.1 km/sec for the upper 10 to 20 km and about 6.8 km/sec for the lower crust. In some areas, generally near the southern and western margins of the relatively undeformed craton, a high-velocity (approximately 7.0 to 7.4 km/sec) lower crustal layer 10 to 20 km thick is present just above the Moho. These areas also display higher than average mean crustal velocity and crustal thickness. Contour diagrams of crustal seismic data also identify a crustal structure anomaly consisting of higher average crustal velocity and crustal thickness associated with the Midcontinent Rift System. Seismic reflection profiling data, which are primarily available in areas of the midcontinent that are known to be anomalous, provide improved resolution of structural features of the continental crust, particularly in areas characterized by the presence of thick (5 to 20 km or more) basins filled with Proterozoic sedimentary or volcanic rocks. For other parts of the crystalline crust, seismic reflections are, in general, laterally discontinuous and commonly dip moderately, relative to shallow reflections and reflections from the underlying crust-mantle boundary.

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Contents

GSA Memoirs

Geophysical Framework of the Continental United States

L. C. Pakiser
L. C. Pakiser
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Walter D. Mooney
Walter D. Mooney
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Geological Society of America
Volume
172
ISBN print:
9780813711720
Publication date:
January 01, 1989

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