GEOCHEMICAL CHARACTERIZATION OF THE CAMBRIAN CHILHOWEE GROUP, ORDOVICIAN ROCKMART SLATE, AND PHYLLITE ASSOCIATED WITH THE EMERSON-TALLADEGA FAULT ZONE; FROM CARTERSVILLE, GA, TO BORDEN SPRINGS, AL

Shales of the Lower Cambrian Chilhowee Group, the Middle Ordovician Rockmart Slate, and phyllite of the Piedmont/Blue Ridge south of the Emerson-Talladega fault have a complex relationship. Published and unpublished maps by Kath and Crawford have shown these relationships in the Borden Springs, AL-GA, and Benedict, GA, 7.5-minute quadrangles. Lithologic similarities between these units have led to many different interpretations by previous workers in this area. In our earlier study on the mineralogy of these rock units by x-ray powder diffraction (XRD) we concluded that the Rockmart Slate can be distinguished from the other units based on the presence of carbonate minerals and lack of orthoclase. Even though field testing by application of HCl does not show the presence of carbonate, geochemical analysis by inductively coupled plasma–optical emission spectrometry (ICP-OES) shows that the Rockmart Slate is distinguishable from the other rock units by their elevated CaO, and lower K₂O and MgO.

Additionally, diamond drill core from Davis Mountain, south of Indian Mountain area in Alabama, and drill cuttings from Dobbins Mountain, near Cartersville, Georgia have also been analyzed by ICP-OES. The samples from Davis Mountain were mapped by previous workers to be Rockmart Slate, whereas the area of Dobbins Mountain was mapped as Chilhowee Group undifferentiated. Geochemically, the samples from Davis Mountain and Dobbins Mountain are indistinguishable and can be correlated with the Cambrian aged Chilhowee Group shale.

Phyllite samples taken from south of the Emerson-Talladega Fault zone were also analyzed and compared to the Chilhowee Group shale and Rockmart Slate. Based on geochemical signatures, the Chilhowee Group shale, rather than the Rockmart Slate is the most likely protolith for the Piedmont/Blue Ridge phyllite south of the Emerson-Talladega Fault zone in the study area.