PRELIMINARY GEOLOGIC MAP OF PART OF THE BLUE RIDGE IN NORTHERN GEORGIA: PART II, STRATIGRAPHY, TECTONOSTRATIGRAPHY, AND STRUCTURE

In the Preliminary Geologic Map of Part of the Blue Ridge in northern Georgia the oldest rocks are the ~1.1 Ga Corbin Metagranite basement in the Corbin massif. The basement rocks are overlain unconformably by metaconglomerate, quartzite, graphitic phyllite, and graphitic quartzite of the Pinelog Formation that is overlain by graphitic metapelite and lesser amounts of metaconglomerate of the Nantahala Formation, though the contact between the Pinelog and Nantahala is in many places a thrust with mylonites of the Padgett Falls Member of the Nantahala above it. The Holly Springs Formation, a turbidite flysch unit of interlayered metapelite and metagraywacke, has been placed upon the Pinelog and Nantahala Formations by the Talladega-Cartersville thrust, that trends around the Corbin massif to continue into Alabama. This sequence of Nantahala-Holly Springs is repeated to the east where the Jasper thrust has placed slivers of Pinelog Formation, and a thinner section of Padgett Falls and Holly Springs over the western outcrop belt of Holly Springs and Nantahala. Still farther east, in what has been called the “Murphy syncline,” marbles, mafic metavolcanic rocks, aluminous schist, and quartzose garnetiferous schist with quartzite lenses and layers crop out from beneath the Whitestone thrust. Study of cores shows that no unconformity intervenes between the marble and the mafic volcanics. Rather, there is a sedimentary mixture of marbles, hornblende-bearing marbles, calcium-rich amphibolite, and amphibolite at both contacts and in the center of the marble, though locally the amphibolite has been thrust upon the marble. Overlying the Whitestone thrust are rocks of the Great Smoky Group, including the Lay Dam/Emuckfaw Formation. All of these rocks belong to the Laurentian margin. In the southern part of the map and along the Dahlonega zone the Allatoona thrust has placed mafic metavolcanic rocks and related seafloor metasedimentary rocks in the Allatoona allochthon over the parautochthonous Laurentian margin rocks. These sequences continue to the northeast along the Dahlonega shear zone/fault zone/ gold belt. Later dextral strike-slip on the Etowah fault along the northwestern side of the Dahlonega zone has displaced the Allatoona fault by 40-50 km, from near Austell, Ga., to southwest of Dahlonega, Ga.