Rocky Mountain (56th Annual) and Cordilleran (100th Annual) Joint Meeting (May 3–5, 2004)

Paper No. 1
Presentation Time: 8:00 AM


MCBRIDE, John H. and OKURE, Maxwell S., Department of Geology, Brigham Young Univ, P. O. Box 24606, Provo, UT 84602,

Reflectivity images of the uppermost mantle and lower crust beneath the Illinois basin have been derived from reprocessing of several hundred kilometers of industry seismic reflection data using extended vibroseis correlation. The recorrelation was based on extending an originally 4-s correlated record, acquired with a 16-s sweep from 14 to 126 Hz, to the absolute limit of the full 20 s (~70 km) listening travel time. This National Science Foundation-supported project demonstrates the value of procuring “old” seismic reflection records from the petroleum industry and reprocessing them using up-to-date techniques in order to obtain new information of research interest. The reprocessing results are highly successful--prominent dipping reflections continue to near the bottom of the records. Occasional Moho reflections are observed across the profiles, while reflectivity in the lower crust is marked by intermittent horizontal packages (“layering”?) and short, gently dipping reflections and diffraction segments. Sub-Moho mantle reflections, although rare in general on deep reflection profiles, occur frequently on the Illinois basin profiles and in one case can clearly be correlated across two intersecting profiles making possible the measurement of a true dip and strike. The presence of newly observed mantle reflectivity beneath the Illinois basin indicates significant upper mantle heterogeneity, relative to other parts of the USA studied using reflection methods. A possible interpretation for the dipping mantle reflectors is that they represent remnants (“scars”) of lithospheric delamination associated with mobilization of the asthenosphere and the consequent melting of Proterozoic crust that led to the intrusion/extrusion of the granite-rhyolite province that underlies much of the mid-continent USA. Toward the completion of this project, we will collaborate with secondary education students in order to “translate” our results for elementary and high-school students and teachers for presentation in their classrooms.