Geochemistry of gneisses and amphibolites in the Uchee Belt of western Georgia and eastern Alabama; an ACRES progress report

Undergraduate students, high school teachers, and university faculty representing ACRES (Atlanta Consortium for Research in Earth Sciences) studied lineated gneiss (LG) exposed at Flat Rock Park (FRP) and vicinity in Columbus, GA, and Motts gneiss (MG) in eastern Alabama. The LG and MG are mineralogically and geochemically granitoidal lineated orthogneisses. They contain deformed mafic xenoliths, as well as aplitic, granitic and pegmatoidal dikes that cut the dominant lineation. Based on chemical analyses, the LG from FRP and the MG 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 gneisses, indicate there is probably a genetic link between the MG and the FRP LG. These rocks are chemically distinct from other nearby felsic gneiss. Phenix City gneiss amphibolites from Lindsey Creek and North Highland Mills dam in Columbus were also analyzed for major and trace elements. These amphibolites are low K tholeiitic rocks with an island arc affinity and are similar to rocks from the area that have already been analyzed. The amphibolites show a wide range of fractionation (41 to 62 percent SiO (sub 2) ). Consistency in incompatible element ratios over a wide range of fractionation of some of the samples show a probable genetic relationship among the various amphibolites of Lindsey Creek. Future work should involve more extensive collecting and analysis of both felsic rocks and amphibolites in the Uchee belt. More time should also be spent describing the thin sections of the existing collection and comparing the REE patterns for the FRP, MG and other felsic rocks in the Uchee belt.