Seismic Profiling of the Lower Crust: Dixie Valley, Nevada
- Muawia Barazangi and
- Larry Brown
Published Online: 15 MAR 2013
Copyright 1986 by the American Geophysical Union.
Reflection Seismology: The Continental Crust
How to Cite
Okaya, D. A. (1986) Seismic Profiling of the Lower Crust: Dixie Valley, Nevada, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0269
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875905143
Online ISBN: 9781118670118
- Seismic reflection method—Congresses
Shallow industry reflection profiles may be used to image the lower crust provided (1) a Vibroseis (registered trademark of CONOCO, Inc.) source was used, (2) the source signal was an upsweep, composed from low to high frequencies, and (3) the original uncorrelated field gathers are available for extended correlation. Extended correlation increases Vibroseis gather lengths by using a correlation sweep shorter in time than the original field sweep. The correlation sweep may either contain a fixed frequency bandwidth or be a “self-truncating” sweep whose frequency content diminishes with time. Recorrelation of three seismic lines in Dixie Valley using a “self-truncating sweep” converts profile travel-time from 4 seconds to 12 seconds. Conventional CDP stacking of the recorrelated data reveals basin reflections and many short, sub-horizontal reflections present in the intermediate to deep crust. These reflections are present in adjacent recorrelated field gathers, suggesting they are not seismic artifacts. Reflections in the intermediate crust may be due to Mesozoic basinal shelf sediments or their metamorphic equivalent. Lower crustal reflections may be due to some combination of internally layered or extensionally elongated magmatic intrusions, banded or laminated schists or gneisses, or compositionally varied granulites derived from recrystallization of lower crustal mafic rocks. A zone of reflections at the base of the lower crust may be related to the Moho transition zone. Possibilities to account for such a thick or laminated zone of reflections include crystallized layering from multiple melt, layering of partial melt, mantle-derived intrusion, delamination of upper mantle material, cumulate layering, and metasedimentary layering. A sharp drop in the density of these reflections occurs below 10 seconds.