CAT SQUARE BASIN DEVELOPMENT: TECTONIC IMPLICATIONS OF WHOLE-ROCK AMPHIBOLITE GEOCHEMISTRY

The Cat Square terrane was first recognized from detrital zircon geochronology in North Carolina and subsequently interpreted to be the product of deposition of both Laurentian and periGondwanan derived sediments on ocean crust in a remnant ocean basin that closed during the Acadian/Neoacadian orogeny by obduction of the Carolina superterrane onto the Laurentian margin. Several recent studies have investigated the southwestern extent of the Cat Square terrane in central Georgia; the most recent has focused in part on characterizing the development of the Cat Square basin through whole-rock geochemical analyses of selected amphibolite samples. Mafic rocks, hypothesized to be remnants of ocean crust that once comprised the floor of the Cat Square basin, occur in the Cat Square terrane as amphibolite in boudinage layers within biotite gneiss, xenoliths in plutonic rocks, and less common map-scale bodies. Whole-rock geochemical analyses of samples from the central Georgia Cat Square terrane were made to determine the origin of these amphibolites and identify volcanic provenance to construct a viable tectonic model for Cat Square basin development. These data are compared with previous amphibolite geochemical analyses from the Cat Square terrane in North Carolina, and demonstrate that Cat Square basalts are not homogenous and represent at least two distinct compositions. Most central Georgia amphibolite samples exhibit normalized multi-element “spider” diagram patterns indicative of within-plate eruptive settings; samples from North Carolina and one sample from Georgia suggest basalts generated by mixing of two magmas, and demonstrate patterns similar to basalts erupted in continental arc settings. Various tectonic discriminant diagrams further confirm generation of basalt in these eruptive environments. Based on these data, a tectonic model is proposed where the Cat Square basin developed in a back-arc setting between Laurentia and the Carolina superterrane, providing a scenario that best accommodates presently available data.