GEOCHEMICAL, PETROLOGICAL AND FIELD STUDY OF MOTTS GNEISS AND OTHER LINEATED GNEISSES IN THE UCHEE BELT OF WESTERN GEORGIA AND EASTERN ALABAMA: AN ATLANTA CONSORTIUM OF RESEARCH IN EARTH SCIENCES (ACRES) PROGRESS REPORT

Similar geochemistry, mineral content, texture and associated lithologies suggest correlation among the Motts gneiss (MG) in eastern Alabama and Flat Rock Park-type lineated gneiss (LG) in Columbus. These same features distinguish these rocks from other felsic rocks in the Uchee belt. Mylonitic gneiss (JCG) at Junction City, Georgia, shares some features with the MG and LG, but also contains features characteristic of other lithologies in the Uchee belt. MG and LG are mineralogically and geochemically granitoidal lineated orthogneiss. They contain deformed mafic xenoliths as well as aplitic, granitic, and pegmatoidal dikes. The MG and LG plot as granite on the IUGS diagrams and the Le Bas diagram. Similarity in incompatible trace element ratios (e.g., Zr/Nb) and highly evolved characteristics of aplite with respect to the host gneiss, indicate that there is probably a genetic link between the aplite and host gneiss in both the LG and MG and, furthermore, that the MG and LG are the same unit. Aplite is not found in other Uchee belt units. Furthermore, the MG and LG are more silicic, more alkalic and less mafic than other Uchee belt felsic gneiss. The JCG is similar to the MG and LG in that the JCG also contains aplitic dikes which are apparently discordant to the lineation in the adjacent mylonitic gneiss. However, parts of the JCG are more quartz dioritic than granitic. Additionally,tabular amphibolite bodies and calcsilicate pods, both present in Phenix City gneiss and in the North Columbus metamorphic complex, are found in the JCG but have not yet been recognized in the MG and LG. Further geochemical and petrologic study will test the distinctiveness of the MG and LG and the degree to which lithologies in the Junction City gneiss share characteristics with units in the Uchee belt. This study supported by NSF Grant EAR-9820701 to Thomas B. Hanley.