Proterozoic geology of the east-central Midcontinent basement

Abstract

The Precambrian basement beneath much of Illinois, Michigan, southwestern Ontario, Indiana, western Ohio, western Kentucky, and southeastern Missouri (including exposures in the S t Francois Mountains) is known as the eastern granite-rhyolite prov ince. This crust is characterized by undeformed and mostly unmetamorphosed highsilica rhyolite to dacite with epizonal granite of equivalent composition having zircon UPb ages of 1,470 ± 30 Ma. The Precambrian subcrop beneath parts of southwestern Mis souri, southern Kansas, northern Arkansas, most of Oklahoma (including small areas of outcrop), and the panhandle of Texas is known as the southern granite-rhyolite province. This crust is also characterized by undeformed and mostly unmetamorphosed high-silica rhyolite to dacite with epizonal granite, but zircon U-Pb ages from this province are about 100 m.y. younger, 1,370 ± 30 Ma. We have obtained additional zircon U-Pb ages and whole-rock Sm-Nd data for many drill-hole samples and a few outcrop samples from these provinces to (1) define their geographic limits more accurately, and (2) use them as a means of defining the age of the crust which presumably underlies these two provinces and from which the granite and rhyolite magmas were derived.These granite-rhyolite provinces were previously thought to have formed from anatectic melting of preexisting Paleoproterozoic crust, which is a southward and eastward extension of the 1,600 to 1,800 Ma Central Plains orogen. However, recent Sm-Nd stud ies, including additional data reported here, indicate that some of the rhyolite and gran ite from both the eastern granite-rhyolite province and the southern granite-rhyolite province have Nd crustal residence ages indicating magma derivation from juvenile, mantle-derived sources that are only slightly older than the granites and rhyolites them selves. As a result, a relatively sharp boundary can be defined that separates Mesoproterozoic granites and rhyolites (regardless of age) having Nd crustal residence ages indicative of Paleoproterozoic crustal sources (TDM > 1,550 Ma) from ones having younger crustal sources (TDM < 1,550 Ma). This boundary extends northeasterly from southeastern Oklahoma through southeastern Missouri, southern Illinois, central Indi ana, southeastern Michigan, and into southwestern Ontario; its southwestern extension is not defined, but it probably parallels, and may be close to, the northwestern boundary of the Llano province in Texas. The underlying crust northwest of boundary line is inferred to be Paleoproterozoic, whereas the underlying crust southeast of this bound- Van Schmus, W. R., Bickford, M. E., and Turek, A., 1996, Proterozoic geology of the east-central Midcontinent basement, in van der Pluijm, B. A., and Catacosinos, P. A., eds., Basement and Basins of Eastern North America: Boulder, Colorado, Geological Society of America Special Paper 308. 7 on May 15, 2015 specialpapers.gsapubs.org Downloaded from 8 W. R. Van Schmus and Othersary is inferred to be Mesoproterozoic. We interpret this boundary ...

Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA

“…It separates Nd-t DM >1.5 Ga crust from Nd-t DM <1.5 crust, which suggests a possible crustal boundary between >1.5 Ga Laurentia and juvenile crust accreting onto the southeastern margin of the Mazatzal Province (Laurentia). The Granite-Rhyolite Province and Palaeoproterozoic crust farther west were intruded by A-type granites between 1.48 Ga and 1.35 Ga Page 6 of 53 A c c e p t e d M a n u s c r i p t (Van Schmus et al, 1996). The older components within the Granite-Rhyolite Province have been correlated to parts of the Central Gneiss Belt in Canada (Easton, 1986;Slagstad et al, 2004;Slagstad et al, 2009).…”

“…More recent work on the evolution of exposed Grenvillian aged rocks have focused on zircon U-Pb and whole-rock Sm-Nd analyses (i.e. Daly & McLelland 1991;McLelland et al, 1993;Van Schmus et al, 1996;Rohs & Van Schmus, 2007;Fisher at al, 2010). The Adirondacks have Nd-model ages between 1.55 and 1.0 Ga (the majority between 1.4 and 1.3 Ga; Daly & McLelland 1991;McLelland et al, 1993;Fisher at al, 2010).…”

“…1.55-1.35 Ga) the Granite Rhyolite Province formed through anatectic melting and addition of juvenile melts to the southern margin of Laurentia (Van Schmus et al, 1996). Van Schmus et al (1996) outlined a crustal boundary across the mid-continent extending from Mexico to Ontario.…”

“…1.55-1.35 Ga) the Granite Rhyolite Province formed through anatectic melting and addition of juvenile melts to the southern margin of Laurentia (Van Schmus et al, 1996). Van Schmus et al (1996) outlined a crustal boundary across the mid-continent extending from Mexico to Ontario. It separates Nd-t DM >1.5 Ga crust from Nd-t DM <1.5 crust, which suggests a possible crustal boundary between >1.5 Ga Laurentia and juvenile crust accreting onto the southeastern margin of the Mazatzal Province (Laurentia).…”

“…Recent work on the evolution of rocks affected by Grenvillian orogenesis in the mid-continent have focused on zircon U-Pb and Sm-Nd analyses on the few available exposed outcrops (i.e. Daly & McLelland 1991;McLelland et al, 1993;Van Schmus et al, 1996;Rohs & Van Schmus, 2007;Fisher at al, 2010;Fig. 1).…”