PALEOPROTEROZOIC AND MESOPROTEROZOIC DOMAINS WITHIN THE SOUTHERN GRANITE-RHYOLITE PROVINCE IDENTIFIED USING SM-ND ISOTOPIC METHODS

In the midcontinent of North America, large areas of the Precambrian basement formed during the Proterozoic. This study presents new information about the temporal framework and tectonic processes indicated by rock samples associated with the Southern Granite-Rhyolite (SGR) province. The purpose of this research was to examine basement samples within the southern midcontinent in order to refine the limits and properties of individual crustal domains. Previous studies have shown that crustal residence ages, as determined by Sm-Nd isotopic analysis, typically decrease to the south and east. More than sixty whole-rock samples were analyzed for crustal residence ages as part of this study. These samples also indicated a trend in the crustal residence ages decreasing to the south and east. Four crustal domains have been identified in the SGR province using the new isotopic data along with previous isotopic data, rock descriptions, and geochemical data. Two of the domains, the Panhandle and Eastern Domains, have crustal residence ages >1.55 Ga indicating the presence of Paleoproterozoic crust below the SGR province. The other two domains, the Arbuckle and Crystalline Domains, have crustal residence ages <1.55 Ga and have been interpreted as underlain by Mesoproterozoic crust. The tectonic interpretation of this data focuses on the growth of the continent during the Proterozoic including accretion of arc terranes, crustal growth at the continental margin, and widespread extension.