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Geoscience Frontiers


Eastern granite-rhyolite province, Mesoproterozoic, Carbon storage, Reflection seismology, Zircon U-Pb geochronology, Illinois


The Precambrian basement rocks of the Eastern Granite-Rhyolite Province (EGRP) in central Illinois (midcontinent region of North America) exhibit a complex history of early volcanism, granite emplacement, and intrusion of mafic rocks. A comprehensive suite of dedicated petrographic analyses, geophysical logs, and drill core from four basement-penetrating wells, two-dimensional and three-dimensional seismic reflection data, and U-Pb age data from the Illinois Basin–Decatur Project (IBDP) and Illinois Carbon Capture Storage (ICCS) Project site provide new constraints for interpreting the Precambrian basement of the Illinois Basin. These new data reveal the basement to be compositionally and structurally complex, having typical EGRP felsic volcanic rocks intruded by the first reported gabbro in the Precambrian basement in Illinois. Zircons (n ¼ 29) from rhyolite give a U-Pb weighted mean average age of 1467 9 Ma. Zircons (n ¼ 3) from a gabbro dike that intrudes the rhyolite yield a concordia age of 1073 12 Ma, which corresponds to Grenville-age extension and represents the first Grenville-age rock in Illinois and in the EGRP. A high-resolution three-dimensional seismic reflection volume, coincident with the four wells, provides a context for interpreting the petrological data and implies a high degree of heterogeneity for basement rocks at the IBDP–ICCS site, as also shown by the drill cores. The occurrence of Grenville-age gabbro is related to a prominent bowl-like structure observed on local two-dimensional seismic reflection profiles and the three-dimensional volume that is interpreted as a deep-seated mafic sill complex. Furthermore, heterogeneities such as the brecciated EGRP rhyolite and later gabbro intrusion observed in the basement lithology at the IBDP–ICCS may reflect previously unknown distal elements of the 1.1 Ga Midcontinent Rift in the EGRP and more likely Grenville-age extension.

Funding Source

This research was supported by the Midwest Geological Sequestration Consortium (MGSC), which is funded by the U.S. Department of Energy through the National Energy Technology Laboratory (NETL) via the Regional Carbon Sequestration Partnership Program (contract number DE-FC26-05NT42588) and by a cost share agreement with the Illinois Department of Commerce and Economic Opportunity, Office of Coal Development through the Illinois Clean Coal Institute.



This article was originally published in Geoscience Frontiers, vol. 11, issue 2, March 2020;

This is an open access article under the CC BY-NC-ND license (

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