GEOCHEMICAL ANALYSIS OF THE UPPERMOST GREAT SMOKY GROUP AND TALLADEGA BELT ROCKS IN GEORGIA: PROPOSED CORRELATION AND IMPLICATIONS FOR PROVENANCE

New whole rock and feldspar Pb isotope data from low-grade metasedimentary Murphy structure and Talladega Belt rocks in Georgia are presented. Based on lithologic similarities and evidence of continuous mappable units, it has been proposed that rocks of the Murphy Group and underlying Dean Formation of the uppermost Great Smoky Group correlate with rocks in parts of the Talladega Group. A Precambrian age has been suggested for the Dean Formation on the basis of a paucity of fossils and the possible correlation between the overlying Murphy Group and the Lower Cambrian Chilhowee Group. Locally exposed Grenville-aged basement rocks, such as the Allatoona Complex, have long been thought of as a potential source for the clastic units in the uppermost Great Smoky Group, Murphy and Talladega Belts.

Metaconglomerate and phyllite samples were collected at six locations along strike in the Murphy and Talladega Belts extending from the Ellijay Quadrangle, located in central north Georgia, to the Felton Quadrangle, located to the southwest near the Georgia-Alabama line. Pb isotope data were obtained by ICP mass spectrometry, with laser ablation of feldspars from clasts in the metaconglomerates, and from whole rock powder of the phyllites. The feldspar and whole rock Pb isotope data permit correlations between several Dean/Murphy/Talladega rock units and a shared provenance. However, the feldspar Pb isotopic compositions are significantly more radiogenic than the whole rock Pb isotopic compositions of locally exposed Grenville basement (data of Sinha et al. 1996), in the Corbin-Salem Church antiform. Therefore, the metaconglomerates and, by inference, the phyllite whole rock samples from the Murphy and Talladega Belts are not likely derived solely from this previously proposed basement source.