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 ​= ​29) from rhyolite give a U-Pb weighted mean average age of 1467 ​± ​9 ​Ma. Zircons (n ​= ​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.

伊利诺伊州中部（北美中部大陆地区）东部花岗岩-流纹岩省（EGRP）的前寒武纪基底岩具有复杂的早期火山作用，花岗岩沉积和镁铁质岩侵入的历史。一整套综合的专门的岩石学分析，地球物理测井和来自四个地下穿透井的岩心，二维和三维地震反射数据以及伊利诺伊盆地迪凯特项目（IBDP）和伊利诺伊州的U-Pb年龄数据碳捕集封存（ICCS）项目站点为解释伊利诺伊盆地前寒武纪基底提供了新的限制。这些新数据揭示了地下室的成分和结构复杂，在伊利诺伊州的前寒武纪地下室中，首次被报道的长辉岩侵入了典型的EGRP长英质火山岩。锆石（n  = 29）由流纹岩给出的U-Pb加权平均年龄为1467±9 Ma。锆石（ñ = 3）侵入流纹岩的辉长岩堤坝产生的共生年龄为1073±12 Ma，对应于格林维尔时代的延伸，代表了伊利诺伊州和EGRP中的第一批格林维尔时代的岩石。与四个井相吻合的高分辨率三维地震反射体，为解释岩石学数据提供了背景，并暗示了IBDP-ICCS现场基底岩的高度异质性，这也由钻芯显示。格林维尔时代辉长岩的发生与在局部二维地震反射剖面上观察到的碗状结构突出以及三维体积（被解释为深基性镁铁基岩复合体）有关。此外，