ISOTOPIC CONNECTIONS BETWEEN BASEMENT ROCKS EXPOSED IN THE ST. FRANCOIS MOUNTAINS AND THE ARBUCKLE MOUNTAINS, SOUTHERN MID-CONTINENT, NORTH AMERICA

Abstract

Two distinct crustal provinces have been identified in the southern mid-continent based on U–Pb crystallization ages. Both contain large volumes of undeformed granite and rhyolite, with minor amounts of metamorphic rock and mafic intrusions. The Eastern Granite-Rhyolite province is characterized by felsic rocks with crystallization ages of 1,470±30Ma and exposures are restricted to the St. Francois Mountains in southeastern Missouri. Similarly, the Southern Granite-Rhyolite (SGR) province is characterized by felsic units with ages of 1,370±30Ma with primary exposures in the eastern Arbuckle Mountains of southern Oklahoma. Within the SGR province three magmatic pulses can be identified starting at 1,400, 1,370, and 1,340Ma. Although the crystallization ages are different, the Sm–Nd isotopic signatures are similar for the units exposed in these areas as well as the buried basement in between. Depleted mantle model ages for rocks within the Arbuckle Mountains range from 1,530 to 1,430Ma with ɛNd(t) values of +3.2 to +4.1 while units of the St. Francois Mountains range from 1,550 to 1,430Ma and +4.5 to +4.7. Comparison of Sm–Nd isotopic data also indicate similarities between the 147Sm/144Nd and 143Nd/144Nd ratios for the rock units in these areas suggesting a common source.