COSMOGENIC 26AL-10BE BURIAL DATING OF TENNESSEE AND LITTLE TENNESSEE RIVER TERRACE DEPOSITS IN THE EASTERN TENNESSEE SEISMIC ZONE

The eastern Tennessee seismic zone (ETSZ) trends 045 through Vonore, Tennessee (located ~48 km SW of Knoxville, TN). The greatest concentration of historic earthquakes in the ETSZ occur near Vonore. Both normal and thrust faults that displace Quaternary sediments 1-2 m have been identified in this area suggesting one or more Mw >6 earthquakes. These faults have NE-striking, SE-dipping orientations, contain characteristic red sandy clay-filled fault gouge, and are a part of 060 deformation zone.

As many as nine terraces (T₁-T₉) have been identified above the modern floodplain (T₀) along the Tellico Reservoir on the Little Tennessee River near Vonore. Only the ages of lower terraces were previously delimited by 14C. T₁ has a 14C age of 10-12 ka and T₂ has a 14C of ~25 ka. The highest elevation terraces (T₈, T₉) were sampled for cosmogenic 26Al-10Be burial dating to delimit the ages of previously identified faults, and possibly locate evidence of faults that may displace the terraces. Samples were collected from four locations (5 samples in each location, 20 samples total) on both the north and south sides of the reservoir near previously identified faults. Additional samples were collected ~80 m above the modern floodplain from a Tennessee River terrace deposit exposed near Rocky Hill (in Knoxville), TN. Quartz rich pebbles were collected from these high river terraces and processed using standard Al-26 and Be-10 sample preparation procedures, where they were then analyzed using the Accelerator Mass Spectrometer (AMS) at PRIME Lab at Purdue University. Tentative burial age calculations for two of the sample locations near Vonore on the south side of the reservoir yield ages of ~204 ka and 2.21 Ma (38 and 33 m above T₀, respectively). The additional two sample locations on the north side of the reservoir have burial ages of ~773 ka and ~807 ka (31 and 20 m above T₀, respectively). The Rocky Hill deposit has a much younger age of ~154 ka despite its elevation above T₀. Additionally, previously delimited ages of French Broad River terrace deposits on Douglas Lake (E of Knoxville) using optically stimulated luminescence reveal ages of ~73 ka and ~203 ka.