GEOLOGIC MAP OF THE NORTHEASTERN UNICOI AND NORTHWESTERN IRON MOUNTAIN GAP QUADRANGLES, TENNESSEE APPALACHIANS

This geologic map shows the NE quarter of the 7.5’ Unicoi Quadrangle and the adjacent NW quarter of the 7.5’ Iron Mountain Gap Quadrangle at a scale of 1:24,000. This map area in the Appalachians in NE Tennessee contains a foreland dipping duplex. We were drawn to this area because of discrepancies in fault patterns in previous maps, and in our mapping we resolve these inconsistencies in fault termination and branching patterns, as well as reduce the number of faults and subdivide previously undifferentiated basement units.

The exposed units mapped in this area are Ordovician through Precambrian in age. The O-Ꞓ Knox Group is limestone in this area. The Cambrian units include the clastic Conasauga Formation, the Honaker Dolomite, the clastic Rome Formation, the Shady Dolomite, and the Chilhowee Group containing the clastic Erwin, Hampton, and Unicoi Formations. Also mapped are PꞒ crystalline basement units of granite, quartz monzonite, and gabbro, as well as gneisses with these protoliths.

The eastern part of the map contains three thrust slices of Cambrian and Ordovician clastic and carbonate units dipping NW. The northwestern package contains Knox Group through Unicoi Formation, the middle package contains the Rome Formation through the crystalline basement, and the southeastern package exposes the Erwin Formation through the basement. The Knox Group in the NW sheet is folded by the Shady Valley syncline which strikes NE-SW. We found evidence in the form of mylonitic textures to extend one of the thrust faults farther east than in previous mapping into the basement to separate granite and quartz monzonite. The NE corner of the Limestone Cove Window is also seen in the south of our map area, exposing the Rome Formation and Shady Dolomite. We reduce the number of faults in the map area and resolve discrepancies in fault patterns.

We also differentiate the crystalline basement units underlying the Chilhowee Group. It is mostly composed of granite and biotite quartz monzonite, as well as smaller gabbro bodies. The contacts between igneous units are of both intrusive and faulting natures. Metamorphic textures, present as gneissic banding and mylonitic foliation, help support areas of deformation within the basement. This differentiation is helpful in understanding the magmatic and deformation history in the basement.