Eastern Granite-Rhyolite Province (Basement)

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This is an informal unit. A formal description has not been peer-reviewed or published.

Lithostratigraphy: Basement - Eastern Granite-Rhyolite Province
Chronostratigraphy: Precambrian Erathem

Primary source

Freiburg, J.T. et al., Petrology, geochronology, and geophysical characterization of Mesoproterozoic rocks in central Illinois, USA, Geoscience Frontiers, https://doi.org/10.1016/j.gsf.2019.07.004

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Stratigraphic relationships

Extent and thickness

The Precambrian basement of most of the Illinois Basin is referred to as the Eastern Granite-Rhyolite Province (EGRP), which occurs from western Ohio and Kentucky westward to Missouri, Kansas, and Oklahoma (Denison et al., 1987). Zircon U-Pb ages for the EGRP range from 1.35 Ga to 1.55 Ga (Hoppe et al., 1983; Bickford et al., 1986; Hoffman, 1989; Van Schmus et al., 1996). The EGRP belt stretches SW–NE across the southern and eastern parts of the United States and is interpreted as a juvenile terrane accreted to the margin of the Laurentian continent (Whitmeyer and Karlstrom, 2007). A proposed crustal terrane boundary has been identified by using Nd model ages with protolith ages older than 1.55 Ga on the northwestern side and younger than 1.55 Ga to the southeast (Van Schmus et al., 1996). This Nd boundary runs SW–NE through central Illinois, near the IBDP–ICCS site.


The EGRP is characterized by undeformed and mostly unmetamorphosed rhyolite to dacite with granite of extensional or intraplate (i.e., anorogenic) tectonic origin (Bickford et al., 1986). A-type granites were intruded within the EGRP between 1.48 Ga and 1.35 Ga and occur (Van Schmus et al., 1996) in older Paleo- and Mesoproterozoic crust to the north and west (Karlstrom and Humphreys, 1998; Van Schmus et al., 1996; Whitmeyer and Karlstrom, 2007). Juvenile EGRP volcanic and intrusive rocks crop out in southeastern Canada (Dickin and Higgins, 1992; Gower and Tucker, 1994; Rivers, 1997), the St. Francois Mountains of Missouri (Bowring et al., 1992; Van Schmus et al., 1996), northwestern Texas (Patchett, 1989; Mosher, 1998; Barnes et al., 1999), southern New Mexico (Barnes et al., 1999), and parts of northern Mexico (Patchett and Ruiz, 1989).




Well log characteristics


Age and correlation

The Proterozoic tectonic evolution of Laurentia is complicated and represents more than 800 million years of deformation, crustal forma-tion, southward growth, and metamorphism (Whitmeyer and Karlstrom, 2007). These Proterozoic orogenic belts extend thousands of kilometers from Arizona to Labrador. This southward growth began with two cycles of accretionary orogenesis, beginning with the Yavapai Orogeny ca. 1800–1700 Ma and concluding with the Mazatzal Orogeny from 1700 Ma to 1600 Ma (Karlstrom and Bowring, 1988; Bowring and Karlstrom, 1990; Whitmeyer and Karlstrom, 2007). These two belts are collectively as much as 1000 km (621 mi) wide and are composed largely of juvenile crust (Hill and Bickford, 2001; Whitmeyer and Karlstrom, 2007). The Yavapai and Mazatzal events were followed by widespread, obscure, and enigmatic felsic volcanism and granitic magmatism from 1480 Ma to 1360 Ma, which is collectively referred to as the Midcontinent Granite-Rhyolite (MCGR) province (Lidiak et al., 1966; Van Schmus et al., 1975, 1996; Hoppe et al., 1983; Bickford et al., 1986, 2015; Bowring et al., 1992; Dewane and Van Schmus, 2007). The development of the Laurentian basement culminated with the Grenville Orogeny and the assembly of Rodina from 1300 Ma to 1000 Ma (Dalziel, 1991; Moores, 1991; Craddock et al., 2017a).

Environments of deposition

Seismic reflection data reveal the EGRP as being structurally complex in Illinois (Pratt et al., 1989). Before the Paleozoic Illinois Basin formed, a similar structural depression, referred to as the proto-Illinois Basin, formed between 1.48 Ga and 500 Ma (Kolata and Nelson, 2010) and may be evidence of rifting in central Illinois (Marshak and Paulsen, 1996). Despite the lack of drill holes penetrating Precambrian rocks perceived to be part of the proto-Illinois Basin, evidence for the early basin is two-fold:

(1) A prominent layered sequence of subhorizontal seismic reflectors appears to sag into a depression that lies north of the Illinois Basin depocenter (McBride et al., 2003). This layered succession is referred to as the Centralia sequence (Pratt et al., 1989, 1992) and exhibits a geometry that strongly suggests a succession of layered rocks that have been postulated as sedimentary or volcanic in origin (McBride and Kolata, 1999).
(2) The Centralia sequence is overlain by the Mt. Simon Sandstone, which has a depocenter in east-central Illinois approximately 300km (186 mi) north of the post-Mt. Simon Paleozoic sediment depocenter (the Illinois Basin in southern Illinois; Freiburg et al., 2014). The thickness trends of the Mt. Simon roughly coincide with that of the underlying Centralia succession, suggesting a similar subsidence event that accommodates both units (McBride et al., 2003). Prominent pinch-out boundaries of the Centralia sequence are observed on seismic profiles in west-central and south-central Illinois (Pratt et al., 1989; McBride and Kolata, 1999; McBride et al., 2003) and may correspond to a rift bound-ary, as marked by the Nd line of Van Schmus et al. (1996) and McBride et al. (2016).

Economic importance


The Centralia sequence (as mentioned above), is defined by seismic reflection. It's lithology is not well defined.


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