Identifying paleoproterozoic and mesoproterozoic crustal domains within the Southern Granite and Rhyolite Province, midcontinent North America

The Southern Granite-Rhyolite (SGR) province, in the southern midcontinent of North America, represents a major pulse of crustal formation during the Mesoproterozoic. Basement rock units of this province are primarily restricted to the subsurface with the exception of exposures in the Arbuckle Mountains and in Mayes County, Oklahoma. Felsic igneous rocks characterize the SGR province with published U-Pb ages ranging from 14,00 to 1340 Ma. In addition to the crystallization ages, crustal residence ages of 1.98 to 1.49 Ga have been determined by previous Sm-Nd isotopic studies. The purpose of this study is to locate the southern boundary of Paleoproterozoic crust within the southern midcontinent region. New information presented in this study includes Sm Nd isotopic data for 71 whole-rock samples in and around the SGR province as well as U-Pb ages for each of the four Precambrian units in the Arbuckle Mountains. Single-grain analyses of U-Pb isotopes in zircon samples provided ages with lower errors than previously published data allowing a for detailed study of the age relationships between basement rock units in the Arbuckle Mountains. These refined crystallization ages include the Burch Granodiorite 1390 ± 7 Ma, Blue River Gneiss 1389 ± 10 Ma, Troy Granite 1368 ± 3 Ma and the Tishomingo Granite 1363 ± 8 Ma. Given these new crystallization ages, it is evident that there may have been two episodes of igneous activity represented by the Precambrian units of the Arbuckle Mountains. Whole-rock samples from drill cores, drill cuttings, and surface exposures were analyzed for Sm Nd isotopes to determine the crustal residence age with respect to the depleted mantle model curve (T_DM) and the ϵ_Nd(t) values. Values of ϵ_Nd(t) within the SGR province ranged from −1.2 to +4.5 with corresponding crustal residence ages of 1.95 to 1.34 Ga. This range of Sm-Nd data suggests variable contamination by the melting of older lithospheric material that was added to a presumably juvenile magma (epsilon = +4.5). Domains underlain by Paleoproterozoic crust related to the southern margin of pre-1.55 Ga Laurentia are defined by older crustal residence ages (1.95 to 1.55 Ga) and generally lower ϵ_Nd(t) values (−1.2 to 2.0). Conversely, domains underlain by Mesoproterozoic crust have younger crustal residence ages (1.54 to 1.34 Ga), which are close to the age of crystallization, and higher ϵ_Nd(t) values (2.0 to 4.5). Using these data, the southern limit of Paleoproterozoic crust at 1.37 Ga extends from northwest Arkansas to the southeast corner of New Mexico. Tectonic interpretations of previous and new isotopic data along with geochemical data within the province focus on the development of the southern margin of the continent. These interpretations suggest episodes of crustal growth along an Andean-type continental margin to the south followed by felsic igneous activity possibly in a back-arc extensional setting.