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Fine-scale structure of the Precambrian beneath the Illinois Basin

John H. McBride, Hannes E. Leetaru, R. William Keach and Eleanor I. McBride
Fine-scale structure of the Precambrian beneath the Illinois Basin
Geosphere (Boulder, CO) (April 2016) 12 (2): 585-606


Increasing our understanding of the heterogeneity of Precambrian crust continues to be a focus for deep seismic reflection studies. High-resolution two-dimensional (2D) seismic profiles and a high-resolution 3D seismic volume, all centered on Decatur (Illinois, USA), provide new insights on the structure and composition of Precambrian basement beneath the Illinois Basin of the central USA midcontinent. The new data reveal a pattern of strong and coherent reflections and associated diffractions deeply buried within the eastern Granite-Rhyolite Province. This pattern is dominated by a thick seismic stratigraphic sequence, which is wedge or bowl shaped in cross section and has an angular unconformity with the overlying Paleozoic section. Deeper intrabasement bowl-shaped sequences or series are also observed in the same area. We interpret these features to be a northward continuation of analogous basement sequences located 75 km to the south below the southern part of the Illinois Basin. This correlation indicates a vast Precambrian province with a north-south dimension of >200 km. Although multiple explanations are admissible for the Precambrian reflectivity, the most likely for our study area is igneous intrusion of broad mafic igneous (diabase?) sills possibly underlain by small plutons. The concentration of such mafic (or bimodal) igneous activity within or coeval with the eastern Granite-Rhyolite Province suggests an episode of Proterozoic crustal extension and rifting.

EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 12
Serial Issue: 2
Title: Fine-scale structure of the Precambrian beneath the Illinois Basin
Affiliation: Brigham Young University, Department of Geological Sciences, Provo, UT, United States
Pages: 585-606
Published: 201604
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 98
Accession Number: 2016-053867
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch maps
N39°36'00" - N40°04'00", W89°12'00" - W88°45'00"
Secondary Affiliation: Illinois State Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201626
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