GEOLOGIC MAP OF FORELAND-DIPPING DUPLEX STRUCTURES IN THE SOUTHWESTERN MOUNTAIN CITY WINDOW, CHESTOA QUADRANGLE, TENNESSEE APPALACHIANS

The Chestoa quadrangle in northeast Tennessee holds a classic example of a foreland-dipping duplex. This structure contains some of the deepest thrust slices in the Mountain City Window and the northeastern-most occurrence of the Ocoee Series. However, previous maps of this area are limited to a regional scale and have significant differences in fault branching and cutoff geometries. We present a new 1:24,000 bedrock geologic map in the northern part of the 7.5’ Chestoa quadrangle.

This map shows three northwest-dipping thrust faults repeating Cambrian and Precambrian stratigraphy. Mapped Cambrian units include the Rome Formation, the Shady Dolomite, and the clastic Chilhowee Group comprising the Erwin, Hampton, and Unicoi Formations. Underlying these, below an erosional unconformity, are the Sandsuck Shale and the Snowbird Formation of the Precambrian Ocoee Series. In the center of our map area, Snowbird through Rome stratigraphy dips northwest approximately 50 – 70° and is thrust over Snowbird through Shady stratigraphy dipping northwest approximately 60 – 80o. The central thrust fault between these two fault blocks strikes southwest on either side of the Nolichucky River and changes strike to south-southeast in the southern map area. Both hanging wall and footwall cutoffs are present against the central fault. In the northwest part of the map, a thrust fault striking southwest and dipping northwest thrusts the Unicoi Formation and Ocoee Series over the central fault blocks. In the northeast corner of the map, a thrust fault striking southwest and dipping northwest thrusts the Ocoee Series over the Unicoi formation, with a hanging wall cutoff present in the Ocoee Series. In the southern map area, Ocoee Series units change orientation to strike southeast and dip southwest approximately 20 – 30°. Precambrian crystalline basement (predominantly kspar-bearing gneiss) is thrust over the Ocoee Series at the southern edge of the map area near highway 19W.

Our mapping makes key changes to previous maps of the area, including reducing the number of thrust faults in the duplex, eliminating abrupt fault tips, and altering the location of the cutoff of the northeastern-most Ocoee Series. This mapping provides new information for studying both regional stratigraphy and structural kinematics in the Appalachians.